Dual Motor AWD Electric Bikes – Case Study: Fat Trail and Hill Climber

Built to conquer the weakness of twin hubs in hills – and eliminate the damage a mid drive does to an ebike’s drivetrain. The bike I call 2Fat did all that.

AWD Ebikes Menu
AWD. OMG. WTF!
Case Study – Flatland Fat Bike Commuter. Hub+Hub
Case Study – Alpine Road & Trail. Hub+Mid Drive (you are here)
Case Study – Low-Power Cargo Beast. Hub+Mid Drive

So, my Gen 1, 1.5 and 3 bike layouts are all twin geared hub designs. What was Gen 2?

2Fat

  • 750w, 35a geared Bafang G060 front hub motor
  • 30a BBSHD mid drive
  • 52v, 12.5ah rear motor battery in triangle
  • 52v, 12.5ah front motor battery on rack top
  • Batteries connected in parallel to form a single ‘virtual’ 25ah power source to both motors
  • KT and Bafang displays
  • 160Nm rear… 80 Nm front (do the math on that one!)

I live part-time in two towns: The first, an extended work visa, is in Fresno California, smack in the middle of California’s San Joaquin Valley and flat as a table. I built The Colonel, The Purple Thing and The Great Pumpkin for commuting in Fresno.

While I most often take pics of it in a wooded area, 2Fat is just as happy on paved, hilly roads. Shown here with front panniers, its 4-bag carry capacity makes it a quasi-cargo bike.

After a fashion, I finally was able to get a big enough bike rack on the back of my SUV to bring the Colonel to my actual home in Pacific Grove, California. My house is at the top of the hill there. Unlike in Fresno, nothing in or around the area is flat. You are either going up a steep hill, or down one, or both.

My intention was to be able to use the Colonel like I did in Fresno, as local errand transport and a light duty cargo-shopper. Unfortunately, I found out the first day about the limitations of hub drives: They suck in hills.

Hubs are Single Speed

Hub drives power an ebike via the axle. They don’t – and they can’t – use the gears of the bike. Forcing a single speed hub motor up a hill makes it just as miserable as a human stuck with no gears. So even though I have very powerful hubs, and they were geared hubs that put down the most torque of any on the market… they still struggled. Even with two of them. I could hear the gears groaning inside the motor casings and I could tell that, while I could get up the hills, my motors were not happy about it. I did not want to lug them into an early grave. I had already gone to a lot of trouble to make the bike bulletproof and had no desire to ignore the problem and inevitably kill it.

These twin 80Nm hub motor wheels were on The Colonel at the time of my first hill country ride (above). Now they are on the Great Pumpkin.

The solution?

I Need To Build a New Bike

Everybody knows mid drives are the solution to the hill problem for an ebike. A hub motor is single speed and at least relatively weak on torque, but a mid drive uses the gears in the drivetrain, plus it has double or more the torque output of a hub, and thats before you factor in the multiplier of the gears. Wonderful right? Except mid drive motors – especially DIY builds – are notorious for putting drivetrains into an early grave. Why? Well because they pour a LOT more power through the chainring, chain, rear cluster and cassette body (i.e. “the drivetrain”) than a bicycle was ever meant to withstand.

  • A normal cyclist can pump out maybe 300 watts for a minute or so, but typically normal sustained – strong – output is about 100 watts.
  • A professional sprinter/mutant is capable of pumping out almost 1000 watts, but only for about a minute or two. Thats not enough power to make a slice of toast.
  • EU-market electric motors must peak at 250w of output to stay legal (pssst… they don’t).
  • A 25-amp BBS02 on a 48v system puts out in excess of 1250 watts peak
  • Your garden variety 30-amp BBSHD running under a 52v battery is peaking – and can sustain – about 1750 watts of output.
My rear rack trunk battery. The capped red wire is for charging. The black wire on the rack stay is power output to the front motor. This is the original dual-separate-battery config

That gives some perspective on how much abuse is heaped upon a drivetrain with a mid drive. Coming off the successful builds of The Colonel (v1.0) and the Purple Thing (v1.5), I knew AWD reduced load on the individual motors dramatically when they work together as a team.

Given that, I thought about how I could use a front hub to reduce or eliminate the shock that a mid-drive puts onto the ebike’s drivetrain. Not only would I gain the traction benefits of AWD, and the benefit of reduced load from the team effort – things I already knew were a big positive – the front hub would also, if used in a slightly different way, provide an important added benefit: eliminating all the extra wear and tear that goes with having a mid drive.

If it worked, it would give me a bike with all the original AWD performance benefits, plus the ability to effortlessly climb walls, without tearing the bike up.

SPOILER ALERT: It worked unbelievably well.

New steel on the right, used alloy (1000 miles of use) on the left. And this was WITH AWD to reduce the wear and tear. Ordinary single-motor systems with this mileage would be dramatically worse. Substituting the steel body eliminates all wear.

In fact this bike is a showcase on how AWD can almost eliminate mid-drive wear and tear. Making a bike that climbs hills and bombs trails really well is almost an afterthought.

So that is what I am going to focus on here in this article. What was built and how was it used?

The Build

Briefly, this bike is the Great Pumpkin on the front wheel, and a typical mid-drive installation on the back. In between is the usual extra wiring scattered all over the place to deal with powering two motors, set up dual PAS etc..

The Front Motor

2Fat has another Bafang G060 80Nm front fat motor installed – this time its inside of a custom-built 100mm double-wall Weinmann (branded as an Origin8) rim. Go fat or go home. Attached are the same two torque arms as seen on the Pumpkin’s installation, and once again the controller is sitting in a grommeted handlebar bag that doubles as a wallet/keys/phone holder. It also serves to disguise the uncut steering tube I used to give me a more upright – but not too upright – riding position.

Another big, fat, 80Nm front hub motor. This time laced into a 100mm rim. Because fat bike.

Different from the Pumpkin is the battery setup. This bike was built before the v3.0 Pumpkin came onto this Earth (The Purple Thing had just been born). So, lacking the wherewithal to commission a big custom battery for the triangle, I used two packs, one for each motor. The front motor’s 12ah 52v battery was located in the rack trunk at the back of the bike. I had already learned I did not want to put a battery on the front rack as it made the steering too heavy. The rear motor’s 17.5ah pack was in the triangle.

It could be worse: Tucked in between the panniers in the rack trunk is one of two batteries. The second pack is in the triangle. Whats on the front rack? A weatherproof, adjustable 5a charger.

Additionally, due to the very low standover of 2Fat’s Large sized frame thanks to its top tube (it is a titanium, USA-made Chumba Ursa Major) there is not enough room to plug in a properly big battery in the triangle to handle both motors. So I had to do two batteries and live with the awful choice of putting one on the back rack.

After running the two dissimilar, separate batteries from its initial build in 2017 to March 2021, I switched to two identical, now-parallel’d-together packs in the same locations. Each is 12.5ah (14S6P) with Samsung 25R cells. Each has a 50a continuous BMS. As such, the system has a single 25ah power supply with a BMS capable of handling 100 continuous amps. Considering I can never peak past 65, I’m in great shape. I purchased the packs from Bicycle Motorworks, who builds their packs in the USA and constructs them at time of order.

Sidebar:  
Running battery packs in parallel should only be done by those who have done the research and know exactly what they are getting into.  In this case, both packs are identical, being manufactured to-order together, and have the same charge cycle count.  Their voltages were matched before they were joined and there is some additional babysitting that will be necessary for charging and balancing.  If you can avoid running packs in parallel and use just one battery: Do that instead.  

Using two entirely separate batteries is a kludge and your last resort. Not only will you have to charge them separately, you will also draw down the two batteries separately at different rates which will result in uneven remaining power, lesser range and more frequent recharges.

The Rear Motor

This is pretty much your garden-variety 52v BBSHD installation. It has a couple of nice spiffs in the form of a 42T Lekkie Bling Ring, and Lekkie Buzz Bars, but neither of those things are a requirement of the AWD approach we’re discussing here.

The rear wheel is another matching Weinmann 100mm rim, again with DT Champion 2.0 spokes and 16mm brass nipples. The rear hub is a DT 350 Big Ride, which has sealed cartridge bearings and has been upgraded to a steel cassette body. Additionally a 9-speed Shimano HG400 cluster gives me steel cogs literally welded together into a single cluster, that spreads the enormous torque of the BBSHD across the entire steel cassette body. The DT350’s ratchet engagement mechanism is one of the few known bombproof rear hub mechanisms when faced with the power of the Dark Side 30a BBSHD motor.

A solid rear wheel build with extra strength parts throughout is crucial to a successful mid drive ebike.

205mm front and rear rotors with Magura MT5e brakes

The Special Bits

There is a bit more that went into making these motors work together. The complete integration possible on the Pumpkin thanks to the use of identical motors and controllers wouldn’t work here.

Brake Cutoffs

Trying to share cutoff signals between the motors again – using adapters for the red-to-yellow connections found on the BBSHD – resulted in bricking both motors. I tried everything to share the signals. It can’t be done unless you are willing to install a second, independent set of hydraulic magnet style cutoffs, zip tied to the integrated MT5e cutoffs and connected via a ‘y’ further down the line. That would work but it would look like crap, for very little benefit over what I ended up doing: I set up the front brake to engage the front motor cutoff, and the rear – with a red-to-yellow HIGO adapter – to cut off the rear motor. Since I always use both levers to do my braking I get an effective result.

Pedal Assist

PAS for the BBSHD is built into its motor casing, so it just works. PAS for the front motor was another matter entirely. Ordinarily the assist disc and sensor runs on the right-hand, drive side of the bike and hides behind the front chainring. This is not possible with the BBSHD’s secondary gear housing being there instead. So PAS had to be made to work on the left hand side. The KT controller has left-hand PAS sensor installation settings.

What was needed then was a left-hand install. This was quite a bit trickier, since the 120mm motor running in front of 5″ tire-compatible chainstays had zero extra spindle length to mount the disk. Lacking a bottom bracket cup to mount the PAS sensor ring, I set it behind a second inner lockring – I used two inner lock rings stacked like jam nuts rather than the usual inner+outer ring. These doubled inner rings had the secondary benefit of being a more aggressive, solid mounting for the motor.

With the sensor mounted, next I had the sensor ring to deal with. As noted above… there was no length available period for the sensor disk as the crankarms mounted pretty much flush to the bottom bracket.

The eventual solution involved hogging out the center of the PAS sensor disc so it could sit on the inner flange of the Lekkie crankarm instead of the spindle. I prepped the crankarm with… thin strips of thick duct tape so the disk would sit tightly on the flange. It was a bodge but it worked, and with just one improvement since installation in 2017 it has held perfectly. That improvement is a zip tie to help hold the disk steady in position (of course I used a zip tie. We have duct tape in the mix; all thats missing is a zip tie).

Worth noting: I used this identical PAS ring mounting when I built the Lizzard King AWD cargo bike in 2021. Not only did I have enough extra spindle so I did not have to do this surgery on the ring, I also realized I could unscrew and reverse the sensor in its mounting ring. This eliminated the need to use the reverse settings in the display/controller. Since the inset ring was reversed, it was outset now… and that held the sensor closer to the magnets (they work fine inset as seen here, but closer is better).

The Cockpit

Here’s where the eagle-eyed may spot a preview of how I ride this bike to soften up the mid drive.

Those are Jones SG bars with ESI XL Extra Chunky grips, wrapped in silicone tape

On the right, we have the grip, then the brake lever, followed by the 9-speed shifter. Here again we see a v2.0 feature that v3.0 fixed: A SRAM drivetrain gives us a SRAM, not Shimano shifter. The Shimano shifter needs so much real estate on the grip it is impossible to put a throttle on that side of the handlebars. Look at the cockpit of The Great Pumpkin and the Lizzard King to see how a SRAM shifter solves this and lets me do one throttle per thumb.

Being unable to do that at the time – and believe me I tried EVERY possible combination of throttles. I still have most of them in a box in my garage. I settled on two styles of thumb throttle, side by side on the left, with the innermost throttle being for the hub/front and the outermost for the BBSHD/rear. As for the eagle-eyed part: The front throttle is cocked higher so between that and its longer throw, it is engaged first and when at 100% it follows the natural curve of my thumb. Both throttles can then be at 100% and my hand stays comfortable at WFO.

How To Ride It

At last we get to the point!

I already let the cat out of the bag earlier: The biggest deal associated with this bike is not that it can climb really well (REALLY well). Nor is its ability to handle trails and rotten conditions its star quality.

2Fat was made to get dirty

No, the real point of having a mid drive teamed with a front hub motor is to use that hub motor to take the shock off the drivetrain that mid drives deliver. Do that and you also take away the excess wear and tear on the parts (if we are being fair, a lot of this comes from doofus riders who don’t know what they are doing).

When starting, start with the hub

This is most of the deal right here. Don’t make the mid drive haul the bike up from a dead stop. Its got the torque to do it. But everything takes a beating in the process. The nylon gears inside of the mid drive. The chainring. The poor chain. The suffering cogs. The cassette body being dug into by the cogs. The pawls inside of the cassette body that are straining against the hub. Your ebike hates you for doing this to it.

By using a mid-drive-strong chain, a steel cluster and a steel cassette body with a ratchet engagement mechanism, we harden the drivetrain to be very tolerant of this abuse. Between that and learning how to use a mid drive, wear and tear really isn’t bad at all. Maybe no worse than a quality analog bike used hard. But still… even with the hardened drivetrain it sure would be nice to take things easier.

By using a hub motor to get the bike rolling – even by just a few mph – we accomplish this mission. Using my pedaling-friendly BBSHD programming or something like it, the BBSHD will not kick in on pedaling until the bike crosses about 5 mph. So from a stop, you hit the front throttle for about one full second. That throttle is cocked up a bit higher on 2Fat to make that a natural move. The bike starts up from its dead stop without any strain on the drivetrain since the BBSHD is not even running. Simultaneously, you also start pedaling. This engages the cassette mechanism.

When speed crosses 5 mph, the BBSHD’s pedal assist now kicks in on a drivetrain that is already engaged. There is no longer a risk of having the motor jerk the chain and smash the cluster into engagement. And with this gentle engagement, the motor starts working on a bike that is already moving. So you get the doubled benefit of a lighter effort against all components to get your fat bike off its fat ass. Instead, you get smooth – and strong – acceleration. The lack of lugging the motor has the further benefit of not generating anywhere near as much heat since the motor is no longer running at low rpms for anywhere near as long. And those nylon gears inside the motor are writing you a nice thank-you card.

Or…

Rather than using the throttle, you could also just start pedaling. I have set the KT controller to engage PAS as quickly as possible. Combine that with the BBSHD’s controller being told to hang back for the initial startup, and you have a completely thumbs-off solution that implements at a nice gentle pace.

So… It just works.

Or you can force it! Remember with this setup you have two throttles. There’s no law that says if you need it, you can’t jump the gun and either hit the rear throttle early, or hit it so the motor engages harder than it would have in your designated PAS mode. So if you need a little extra push thanks to an XL load of groceries, or a steep hill, you have options at your disposal.

Downshift? Schmownshift!

One of the mantras associated with smart mid drive riding is that you always Always ALWAYS freaking downshift the bike when you come to a stop. The LAST thing you want is to lug the motor up from a dead stop because of all the brutality it visits on your chain, your cogs blah blah blah. So that means you remember to downshift one or two… maybe even three times before you come to a stop. When the light turns green you upshift in sequence one gear at a time as you get back up to speed again. Thus as we all understand: you row thru the gears.

Another rule mid drive mavens repeat ad nauseum is – if you have an 11T small rear cog… stay the hell off of it. Its too small to use on a mid drive. It bogs the bejesus out of the motor from a stop, its too small to be able to get up to speed before the sun sets and if thats not bad enough, the teeny cog on even the steel Shimano clusters is alloy and it is not attached like all the others are. Its an individual. So not only do they dig into the cassette body harder, they die fast. Like Really Fast. As in a few hundred miles tops.

Well, on AWD mid drives like 2Fat, you can forget about all that. Because of the powered front hub doing its part (either thru a quick dab of throttle or just letting PAS start the bike), there is no longer a need to shift at a light. You can forget about the whole process. Just leave it and it’ll be fine as if it was a hub motor! In fact the front motor allows the bike to increase its speed so it gets up and goes fast just like a hub motor does.

I found this out within a day of building the bike, and since then learned from experience the 11T cog will last about 1500 miles before it typically cracks (two so far). Thats not so bad for a readily available US$7 part. And if I wanted it to live longer, well it wouldn’t kill me to go up a gear at a light once in a while.

At the office, outside my e-garage. There is a trail network along my commute route that 2Fat lets me take

Wrapping It All Up

2Fat itself is not the ideal example of how to execute this concept. It is a product of when it was built and my knowledge level at that time. In the present day, I for sure would not want to build a bike with two batteries, and if I did I would NEVER put one on the back rack. But thats partly the limits of the frame I used. I came within a hair of using a Salsa Blackborow frame kit for this bike until, at the last minute, this titanium beauty fell into my lap for a song… but thats another story.

Next, I wouldn’t use Shimano components thanks to the real estate problems introduced by the shifter. Instead I’d use SRAM components so I could do one throttle per thumb.

Really the Great Pumpkin with its XL size and XL triangle, plus its SRAM shifters – would be ideal here. But them’s the breaks. This is what I’ve got. Boo hoo.

With that said… I did learn as I went along, and in 2021 I returned to dual motor bikes with the Lizzard King, a bike meant to prove a different kind of AWD could be awesome: You don’t need the 80Nm, 35a punch of the Pumpkin’s or 2Fat’s front hub to gain the benefits of AWD. A low power implementation, done a little differently, should be very effective and appeal to a much broader range of everyday, low-speed, low-drama ebike use. And…

SPOILER ALERT: It worked unbelievably well.

Dual Motor AWD Electric Bikes – Case Study: Twin Geared Hub Commuter

A big bruiser geared specifically to be pedaled hard at 32-34 mph, this is my commuter workout-workhorse. Don’t want to sweat? Just relax and pedal easy… at 28 mph.

AWD Ebikes Menu
AWD. OMG. WTF!
Case Study – Flatland Fat Bike Commuter. Hub+Hub (you are here)
Case Study – Alpine Road & Trail. Hub+Mid Drive
Case Study – Low-Power Cargo Beast. Hub+Mid Drive

The Great Pumpkin

  • 2 x 750w 80Nm geared Bafang G060 hubs
  • 1 x 52v, 30ah battery with Samsung 30Q cells, 90a continuous BMS
  • 2 x 35a KT brand controllers
  • 2 x KT brand displays
  • 160 Nm total power

The Great Pumpkin remains my fast commuter workhorse. This bike is meant for transportation to and from a destination, not sightseeing. As such it is designed to travel as close to the safe, legal speed limit as possible. Here in California the assist limit is 28 mph, I stay on the street (no shared-use bike paths allowed) and this bike’s gears are made to let me power it up past that 28 mph limit to about 34 mph – if I am strong enough to pull it off.


A note on speeds and our local roads here, and how they influence the design and capabilities of this ebike:  in California the law limits ebikes to 28 mph (45 km/h) of assist.  Thats an assist limit, not a speed limit.   The maximum lawful speed is the posted motor vehicle speed limit, adjusted downward if necessary to maintain safety.  So if you can pedal the bike faster than 28, thats fine so long as doing that is "safe for conditions".  

These speeds seem like a lot to readers in some parts of the world.  But remember here in the USA we've got open roads that are nothing like you see in many urban centers in, for example, the EU.  The two pictures above come from two different places along my 15-mile commute route.  The speed limit signs are in mph not km/h.  Bear in mind drivers regularly exceed these limits by a significant margin so in rush hour traffic a 30 mph bike is by far the slowest thing on the tarmac, with no pedestrian issues to speak of.  So, on streets like this, if I can pedal to 34 mph - and oftentimes I can - thats perfectly legal.  In fact I have been paced and radar'd by police cruisers and motorcycle traffic enforcement many times without incident.

So the secondary purpose of this bike is to enable me to work hard while still transporting me to Point B at a practical speed. You’ve heard how ebikes let you arrive at your destination without getting all sweaty? Well, this one lets you arrive all sweaty on purpose if you like.

The geared hub motors let it accelerate fast in traffic, and despite its necessary lack of suspension, the fat tires (and the suspension seatpost) let it ride well on lousy pavement. It has over 7000 miles on it at present (March 2021), and benefits from all of the learning I got the hard way building its predecessors. In fact, I am using the same set of wheels I had built for my very first AWD ebike: The Colonel. This is a testament to finding a good wheelbuilder at the Local Bike Shop of your choice and have them build you a quality wheel with quality components.

Fresh from the wheel builder in March of 2017. DT Champion 2.0 spokes, 16mm brass nipples, double-wall Weinmann 80mm rims. Still going strong today, three bike builds later.

Motor Choice

The Pumpkin is a flat-country bike. Dual geared hubs are powerful, but hub motors – since they power thru the axle and cannot use gears – are just single-speed. Despite their power and ability to handle lots of current, they can get the bike up steep hillside streets, but they struggle doing it. Riding this bike in the Carmel/Pacific Grove portion of the Monterey Bay Area, where nothing is flat, I found it could climb anything but it lugged its motors mightily doing so, to the point I feared for their long life. But if you live on flat land (and this bike’s permanent home is in the table-flat San Joaquin Valley), this is the design that will gobble up pavement for lunch. It will get you where you need to be safely and quickly as an ebike can legally travel.

Why didn’t I choose maintenance-free direct drive hubs? Because they lack torque, and that means slow acceleration unless I load the bike down with bigger, higher voltage batteries and motors with much more unsprung mass.

Battery

Having done it the wrong way before out of necessity (translation: too expensive) I put in a single big battery on this bike. It has the biggest battery I could fit into the triangle of this XL-sized frame (A Chumba Ursa Major made with chromoly tubing). A 14S9p (52v) pack that uses Samsung 30Q cells to give me about 30ah. That means it takes awhile to charge. But it also takes awhile to drain, and this single battery is placed down in the triangle where it does not reduce the carry capacity of the bike, or screw up its performance with schlocky placement of a battery on the rear rack.

But doing an AWD bike with a single battery means you have to address more than just size. The Battery Management System (BMS) has to be able to handle the amp draw of two motors simultaneously. Looking for batteries out in the wild that can do this… you’ll find almost none that are capable of it.

Initial battery fitment prior to connecting the power and charging cables. The bag hides a multitude of cable-routing sins.

How do you calculate the sort of battery you need? You take the peak output of both of your motors and add them together. Your BMS’ “continuous” power rating has to be more than that peak to ensure your motors never trip the BMS’ limits. If they do, to reset the battery you have to hook it up to a charger, which is unlikely to be handy on the side of any road you’re traveling on.

So, with a 35a rear controller and a 35a front controller, I need a battery with a 70a continuous (or more) BMS, and thats a special order item. In my case, the BMS can handle 80a continuous current.

Controllers and Wiring

The 35 amp KT brand rear motor controller is sitting under the saddle, zip-tied neatly with small clear, low-visibility ties to the seatpost mounting arms of the rear rack. This puts the controller in open air to keep its heat down. It will reach temperatures of 135 degrees fahrenheit if stored enclosed. A home-made fender comprising of an extended commercial mudguard and cut-to-size flexible cutting board provides complete coverage from water coming up off the rear tire.

The front motor controller is an identical 35 amp KT, housed in the handlebar bag. This bag has had reinforced brass grommet holes placed strategically inside and out so cables can pass thru its inside compartments to the outside of the bag, without creating issues of splashing water (here again extended fenders help). The top of the bag is left zipped open and this keeps heat from becoming a problem. The front motor cable travels directly up and into this bag, while cables for pedal assist, brake cutoffs, display and throttle exit out either a grommeted side entry or out the open top of the bag. The bag itself essentially hides all of the front motor cabling rats’ nest, both by housing excess wire inside itself and via natural camouflage, providing a black backdrop to black cables running along and woven into its MOLLE exterior. Cables exiting and entering are carefully bundled together for neatness.

Is that a controller mounted to the front rack? Nope its a 5 amp weatherproof charger, with the cables housed in the dump pouch, just behind it.

The center triangle bag is stuffed mostly full with the custom-sized triangle battery. Like any triangle bag on an ebike, it also serves to hide excess wiring, and given the dual custom splitters for brake cutoff signals and pedal assist (one sensor signal is split off to both motors for simultaneous PAS power) there is plenty of wiring that thankfully remains invisible thanks to this bag, which seldom needs to be opened. The bag has forward and rear-facing cable holes that don’t suffer from water ingestion, again thanks to the fender setup. A capped XT60 charger plug is coming out the front of the bag just behind (and shielded by) the head tube, and this cap is removed and a charger is plugged in here to recharge the battery.

Display/Controls

Ergonomically, the cockpit is very well designed and reflects this being my third or fourth try at doing the job. There is one throttle for each thumb in easy reach, and both throttles are clocked so when fully engaged, the paddle is pointing straight down. If you hit a pothole your thumb doesn’t push thru and break the throttle. It slips off instead. The PAS panel is also one-per-side, and also within thumb reach without losing your grip on the bars. SRAM 9-speed shifters are in use, because a SRAM shifter gives you enough real estate on a handgrip (vs. Shimano) to stack multiple hand controls and still be able to easily reach everything.

Cockpit view. Notice the max speed reading on the top display. I used the gears and got a workout on the ride into the office that day.

Despite the duplicated motors and controllers, the displays are mismatched simply because I am re-using parts from older bikes no longer on the front line (in this case parts came off The Purple Thing). For this build I needed a new display and the KT model LCD8H was available, so I grabbed one. It is the same display as the KT model LCD3 above it, used for the front motor. The LCD8H is just in color and easier to configure.

And in case you noticed… yes this is a bike with Class 3/Speed Pedelec performance that has throttles. Reality is, though, the bike is designed specifically as a pedelec. Pedaling acceleration via PAS is plenty fast and is in fact (thanks to controller settings) a little faster than using the throttles. They are only put into use typically for a split second on take-off from a standing start while I regain my balance on the bike and settle in to pedaling. If I am crossing a 4-lane street, I am off the throttles before I get past the first lane while crossing and won’t touch them again until the next stop at the next intersection.

Power (too hot)

These two 80Nm motors have controllers feeding 35a to each axle provide giggle-inducing acceleration. So much so I found performance needs to be turned down for multiple reasons:

#1 (Safety). Come to a stop at an intersection. Acceleration is so strong from a stop, you leap forward so fast you are always the first vehicle that gets to the other side, and you’d better be hanging on. Thats fine if you meant to do that. If on the other hand you accidentally engaged pedal assist, you could be throwing yourself – literally – into the path of a car.

#2 – (Safety). Come to a stop at an intersection. Put your feet down, release the bars and take a drink or something. If you engage again (pedal assist or throttle) and forget to put your handlebars straight, your front wheel will shoot off in the direction its pointed in. Typically a bad thing.

#3 – (Fork survival). With this much torque pulling on the front fork, things start to happen that a bicycle was never stressed or designed for. A front fork was never designed to be pulled on hard, for extended periods or in sudden jerks. Especially not day after day for days and weeks stretching into years.

#4 – (Frame survival). This one was unexpected: Even though I am using a highly durable hand-made-in-USA frame, I still found it was straining under the repeated daily stress of stoplight-to-stoplight acceleration from the rear motor. Specifically I started to hear creaks from the rear triangle and dropouts. eek.

#5 – (Safety again for crying out loud!). I use fat street-smoothie tires in summer. Doing that with the motors unrestrained makes for about a half rotation of front wheel spin on full throttle, and maybe a 1/4 spin on pedal assist… and a goodly chirp out of the back, at the least (lots more if the ground is not clean, dry pavement). Thats fun for an afternoon showing off but more than that and its just plain dangerous.

Power (just right)

To slow down the bike so it accelerates at a safe rate on city streets, and doesn’t wear itself out from all the extra stress of doing this day in and day out, I utilize a setting in each of the two KT brand controllers that sets the power curve to ‘slow start’: C5=00 is undocumented on all but the newest KT display manuals. Where it is documented, it is listed as the most restricted of the three ‘slow start’ modes.

What this does is create an acceleration curve slope that is shallow at tip-in but increasingly steep as it continues forward. Here’s the crazy-cool part: Even dialed way down on both motors this bike is still typically faster than anything else crossing the intersection from a standing start. So you aren’t missing out on much in the way of fun if you want to pour on the amps. Its just safe, sane and controllable when its put on a leash.

Torque Arms (!)

I’m not going to get too deep into the specifics of this topic, but I will say if you use hub motors you have to use torque arms. Gotta do it. Thats for any motor that has ‘flats’ on its axle to allow their use (which is almost all of them). It is true many motors do not need torque arms because they are of such low power. I will say having suffered the consequences of not using one, its WAY better to be safe than sorry and just go ahead and install them regardless of motor power.

What could happen? If you don’t use a torque arm, the force of the motor will overwhelm your bicycle’s dropouts and the motor will “spin out”. That means your steel dropouts will not be able to contain the motor’s axle, which will spin (instead of the motor casing spinning) and when that happens the dropouts spread. Your frame or fork is effectively destroyed and unsalvageable at that point. These 750w, 80Nm motors are right on the edge of demanding two torque arms. For sure they need one. I have used two on the front motor and one on the rear, where the stronger rear dropouts are much less likely to have an issue.

Gearing

Last but not least… take a look at the pictures on this page and you will see the biggest front chainring ever on a fat bike. Look to the back axle and you may be looking at the smallest cluster. And the derailleur is a mid-length cage, to boot. Fact is, this bike was geared to be pedaled fast on the street, not overland on trails as is the norm for fat bikes.

The front chainring is a 50T ring, while the rear cluster has an 11T small cog. Frankly I forget the size of the biggest cog because I never use it. Its 28T… Maybe 30. And since the hubs on this bike are the motors, powering the bike thru the axle, not the drivetrain, gearing is largely useless unless I want to pedal faster while going slow. This almost never happens because this bike should not be taken on pedestrian paths or similar where such slow travel is necessary.

Redundancy

For a daily driver bike that is transportation, not recreation, you need to address many areas to ensure reliable, day-in, day-out operation. There are many issues addressed on that topic with this bike, but I’ll only touch on the AWD-specific ones here. In a word: Redundancy. If you do a general overview of this bike’s propulsion systems, you will see almost everything but the battery is a separate, independent system. None of this is accidental or done because I was forced to do so (you can buy controller solutions that reach out to two motors at once, for instance). Its done this way because its better. Dual throttles are better. Setting PAS independently per wheel is better than combining the two. Even two different displays let you focus on different bits of each (although that one I could do without if push came to shove).

Redundancy on a dual motor bike can be a big benefit. I’ve had one unfortunate lesson in this: I went over the handlebars and slammed straight down on the pavement, cracking some ribs. I also bent my front fork (just a little) and smashed my rear throttle, among other things. That broken throttle disabled the rear motor despite all other components being in working order. I was able to limp the bike home without pedaling, which I really needed given the cracked ribs and various and sundry other minor injuries.

This is one more reason by the way, why I want throttles on the bike. If I am physically unable to pedal I want to be able to get me and the bike home, or to the emergency room as the case may be.

Gallery

And THAT is my rain or shine daily driver.

Dual Motor AWD Electric Bikes (the good and bad)

I like to build top-quality-component ebikes from the frame up. Quite a few of them are dual motor or AWD or 2WD or whatever you want to call them. Why would you build an AWD ebike?

AWD Ebikes Menu
AWD. OMG. WTF! (you are here)
Case Study – Flatland Fat Bike Commuter. Hub+Hub
Case Study – Alpine Road & Trail. Hub+Mid Drive
Case Study – Low-Power Cargo Beast. Hub+Mid Drive

In the Beginning…

Well, I could spell ‘ebike’ and that was about it. I had a solid background as a lifelong cyclist, but I went over to the Dark Side and started riding ebikes. I had been working on my own bikes for most of my life and I was pretty good at that part.

So, as an experienced cyclist but a newbie ebike owner I came across a bike built by my (now) friend Houshmand Moarefi, who is the head honcho over at Ebikes USA in Denver. He took the same model of rear-hub-motor ebike I had, upgraded the rear motor, then added a front motor, controller and surrounding bits to make a badass AWD e-fatbike. He posted his creation on the Interwebs.

Figure 1: Houshmand Moarefi’s 2wd Sondors Original. Want to know what dual-motor is good for on an ebike? Just look here. He still rides this bike and you can see it on display at Ebikes USA in Denver.

After seeing the bike online – and peppering Houshmand with questions – I did what everyone on the internet does: shamelessly copied his idea. It is pictured in Figure 2 below. This was taken the night I completed it, moments before I opened that garage door and took my first ride.

Figure 2: AWD by Matt… Version 1.0000. a.k.a. The Colonel (“Colonel Sondors”). How much did I have to learn about doing AWD right? I’ll have to make a list.

Its a good thing I took the picture, as 15 minutes later I broke it. I got it fixed and it gave me years of service, but thats another story entirely. Suffice it to say in that pictured moment, we see triumph and despair occurring almost simultaneously.

What are we in for, building one of these things?

First… “Whhyyy?”

Why put two motors on an ebike? Well… “because we can” works. But lets do better than that.

Is it even possible?

Not so long ago, internet experts in the DIY ebike crafting community would tell you all about how a powered awd ebike could not even function in the first place.

  1. The powered wheels would fight for supremacy between each other.
  2. It is essential to match the power to both wheels but impossible to do so.
  3. Even slight differences in wheel circumference between the two would make terrible things happen.
  4. blah blah blah

So, I was being told it could not be done after having put thousands of successful miles on a bike that could not exist. A lesson on the value of internet experts. Only value the advice of those who have done the work and actually know things.

I don’t want to get too deep into a litany of refutation on common mistakes, but I do want to clear up a couple that come up the most often. All three, really, are more or less re-statements of the same misconception:

Matching Power (current) to the Wheels

This is a common worry, but not a real one as you will discover moments into your first ride. The concern is dissimilar power levels cause problems. They don’t. Tailoring power front to back as conditions change is a major benefit to AWD. In simple clean/dry conditions, all that will happen is the wheel that gets less power doesn’t work as hard.

The easiest way to understand how this is: Geared hubs freewheel forward. So the same thing happens if you have no motor on the back and you are, say, going down a hill with a front motor. The watt output of the front motor decreases as gravity ‘powers’ the speed increase (or you pedal your little heart out on flat ground). Likewise, differences in circumference are a non issue. This is true in bikes with slightly different tire sizes, but is most visibly proven with the in-service bike pictured below.

Figure 3: Different types of motors with perpetually different outputs… and totally different wheel sizes. It still works great.
Contention

Here again, one ride will lay this concern to rest. Two motors will not fight for supremacy with each other despite differing power levels. Partly because of the geared hub’s ability to freewheel. You should take it for granted you will have different power levels on each axle. I commonly keep low power on my front wheel (I will expand on why further on) but for my hub+hub commuter I often just go full blast on each motor and pedal up over top of it. In that instance, with two big motors giving it their all I only very rarely feel a bit of a shift in pull vs. push and it is very minor. Another technique on that bike: 5 levels of PAS on the rear wheel plus 5 on the front means that – in good conditions where I do not vary the power for safety – I have PAS with 5+5=10 levels. As I want more I ratchet up the rear a notch, then the front, then the rear and so on never giving all PAS power to just one wheel.

One Throttle/Two Motors

You don’t want this. You can have it but you are selling yourself and the platform short if you go to the extra amount of trouble to make it happen. I will get into some real world specifics of why this is later on. The short version is if you unify the throttles or even work harder to unify PAS power levels to the two wheels you will be introducing problems with traction and control. You want to keep your control granular. It won’t be confusing or difficult!

What About Two Direct Drive Hubs With Regen?

What I said above doesn’t apply. If you expect to use regen on a twin-DD-hub AWD bike then you are talking about a whole different animal in terms of two hub motors coexisting. I know its been done, but I have never done it personally. I will let some other pioneer on the trail take the arrows in the back on that one (I suspect: regen can be used on the rear but not on the front… or just don’t do regen at all with DD hubs).

A final point: Years into having AWD bikes in service, there are now numerous commercially-produced examples in plain sight. The arguments that it cannot be done have melted away now that so many have obviously done it.

Figure 4: The Purple Thing. Built after the death of The Colonel (cracked frame not related to AWD)

So YES you can do AWD. The question is are you doing it right? Well, thats a whole ‘nother thing.

Whats the Up Side?

Take a look at Figure 1 for the most obvious example: All Wheel Drive on a bicycle is every bit as good of an idea on a bike for the reasons it is a good idea on a car, truck or ATV. On other vehicles, just putting more power to your back wheels is not anywhere near as good of a solution as putting power down to all wheels. It is the same on a bicycle, but so few have done it, the result is not considered to be the obvious no-brainer it is on other platforms.

If conditions are sub-optimal, as in rain, snow, mud, riverbed rocks, hillsides and whatnot… AWD on a bike gets you through it easier, across the board. If conditions are ridiculously bad, AWD can get you thru things you thought were impossible to ride. Oftentimes so easily you stop, look back and wonder how the hell you just did that.

The range of things that you can ride through just got a lot wider.

If on the other hand conditions are just dandy – say, a smooth, flat, dry paved street – having both wheels deliver power to the ground is again an improvement for all the same reasons it is better on a performance exotic car. Powered traction is distributed across twice as much rubber to the ground. Everything just works better.

And since the improvement makes for a qualitative, but drama-free result, its really hard to describe other than to say ‘everything just works better” or “this is how it was meant to be” … which do not help much when explaining AWD to skeptics. Nonetheless… the nebulous, big-brush-stroke description is accurate.

In terms of acceleration, doing it with AWD vs. RWD is a very different rider experience. You aren’t being pinned to your seat, nor is your body wanting to slide off the back while you hold onto the handlebars for dear life. Instead you get an amazing rate of acceleration, but it is smooth and – again – without drama. The feeling is of it being effortless for the bike to do what its doing.

Mechanically there are benefits as well. If you are keeping tabs on the amount of heat your motor generates, you’ll find gunning one motor around will get so hot you may not be able to touch it for awhile. Not so good for longevity, especially if it has nylon gears inside. But: Run two geared hub motors as a team to achieve the same performance and by some miracle the two don’t even get a fraction as hot as did the one. All of a sudden a motor that was working itself to death isn’t even breaking a sweat, and you’re going at least as fast and as hard.

How is this possible? In May of 2020 Grin Technologies did a detailed technical analysis of multi-motor ebikes. They explain how this is possible, complete with the technical details on why it happens. Its well worth a watch if you are interested in taking a deep technical dive on your AWD ebike options. I have queue’d up the video in the link below to the exact spot where he explains the heat reduction.

Another issue not generally considered is redundancy. With two motors, if something bad happens on your ride and you lose a motor, you still have another and can limp home on it. I learned this the hard way once when I went over the handlebars on my twin-hub Great Pumpkin. I smashed one of the throttles and disabled the rear motor completely. I managed to roll home on the front motor without needing to pedal. With freshly cracked ribs that was exactly what I needed.

Whats the Down Side?

AWD is not all sunshine and roses. There are down sides. Most of them only affect the bike builder. But a few do affect the rider, so we’ll look at the negatives from both perspectives.

For The Builder…

Put simply, AWD on an ebike is one hell of a lot more work. There is so much more you have to keep track of. So many more wires that have to be hidden.

Fig. 5: Custom brake cutoff splitters and extensions for sending signals to 2 controllers

You have to address the issue of brake cutoffs going to two separate motors simultaneously. Pedal-assist to two motors at once is a beautiful thing. But only for the person riding the bike. For the builder it typically means customized controller settings and maybe even a little fabrication to get a sensor signal to two motors at once.

Fig. 6: PAS splitter cable (one sensor –> 2 controllers)

Battery power? You’re going to need a big battery, and it needs to deliver more power than pretty much any regular ebike battery available on the open market. So you either have a single custom pack made or kludge together off-the-shelf packs and suffer through the weight and space issues that go with them.

Fig. 7: Cutout sized, marked and photo sent to the battery builder. All thats left is to drain my bank account.

What does a front motor need in terms of structural support? You’d better think that one through. NEVER use a suspension fork in an AWD build. Your motor can literally pull the thing apart. Whoever designed a bicycle fork never expected a powerful motor would be pulling on it for extended periods, or in sudden jerks. Thats tough on a chromoly fork but they can handle it. Its typically too much for an alloy fork (aluminum is nice and light but doesn’t bend: it breaks) and it is definitely too much for a suspension fork that has 2-piece blades that can be literally pulled apart.

Not to mention fork dropouts. A hub motor must have torque arms attached that prevent the motor from ‘spinning out’ (That is how I broke the Colonel on its maiden voyage; destroying its fork dropouts). You generally cannot use quality torque arms on a suspension fork due to its physical construction. If so, the dropouts have to endure 100% of the punishment and… newsflash … they may survive today but they won’t have the kind of long life they would have had without a motor axle trying to tear thru them.. Internet discussion groups are chock full of pictures of DIY builds where someone used a front hub motor and their suspension fork’s dropouts snapped clean apart. Even with a torque arm.

We’re not done with the front fork yet. Regardless of construction, that pulling on it can loosen your headset at an alarmingly fast rate depending on your power and acceleration levels. If its a problem you have, you will want to think of ways to keep that headset in place (psssst… use two star nuts) and while you are at it, make sure you use a superduty headset with steel races. And a serious mtb stem that clamps the crap out of your steering tube.

You can google “broken ebike fork” or just follow this link (one of many) on Endless Sphere to see more electric motor + fork carnage.

So… How do you get away with using a front suspension fork, then? You see people do it with front-motor bikes. Assuming they thought the job through and are not just future emergency-room visitors, its simple: use a very low power motor. Or neuter a powerful motor and trust the buyer won’t know any better because hey… nobody has any actual experience with these things so you can give them just a little power and they will still be thrilled.

So… to build or sell an AWD bike its a whole lot of work for the same result (a single finished bike). Its no wonder AWD bikes are not common, and when they are up for sale, the seller wants a high price. Assuming they did their job right (never assume), a lot of work went into that bike.

Fig. 8: Wires everywhere. I have to figure out a way to hide all this…

For The Rider…

Fortunately, the downsides of AWD are minimal if all you have to do is ride the bike. But they do exist. All of the negatives can be eliminated if you just realize this bike is a new kind of animal and take it easy when starting out. So… learn how to handle the increased traction, power, and the subtly different behavior.

Dual Throttle

If your bike builder did the job right (I’ve said that two times so far and not by accident), you have two throttles – one for each thumb – to let you apply power granularly to each motor as the needs of the moment come up. Thats a new feature you will need a bit of time to learn how to take best advantage of. The basics of this will be learned by the time you have traveled about one city block. The finer points will take some experience – not a lot – to figure out.

  1. Holding down the front throttle in a turn has the end result of elongating your turn radius (this is about how you naturally ride, not how the bike handles… but it still happens). You cannot take a turn as sharply if applying front throttle, and could wind up smashing into the center median in a right turn in traffic, or the curb in a left turn thru an intersection. There is an easy solution: stop pedaling, release front throttle, turn in, re-engage front throttle just at turn-in so the slight delay will engage the motor right about at the moment of corner exit. Leave rear throttle engaged throughout the turn if you can safely get away with it). That turn procedure all takes place in the space of about two seconds. It will become second nature in short order. But it has to be learned. Now… thats how you hot rod your way thru a turn. You won’t want to do that all the time, and mostly you will go thru a turn no differently than you do on any ebike.
  2. On singletrack/trails, less power to the front wheel is more. Rip down a trail, hit a root and the front wheel bounces up. If it comes down pointed in a different direction than you are headed, your now-powered front wheel will shoot off in that new direction if its going full blast. Keep front motor pedal assist power low – much lower than what you have set for the rear. Then when the inevitable happens its easy to deal with. I’ve found pedal assist dialed down in the 200-250w range is best. If you decide you want more front wheel power at any point, a dab of throttle will do ya. You know you are overdoing it if you get any level of wheel spin in the front.
  3. You are no longer the slowest thing accelerating from a stop at an intersection. So if you are not the first vehicle in the left turn lane, Your instinctive use of full throttles to both motors will rocket you right into the rear bumper of the car in front of you. This is an easy fix. In a left-turn-lane situation, initially use only rear throttle, then add the front when the car in front of you starts to pick up speed. Dial it back again as that car completes their turn and lifts on their own throttle before straightening out. Or you can just hit the front throttle for a split second to get yourself rolling from a stop, then drop it and let PAS manage the rest.

Clearly from these examples, manual AWD acceleration (separate from pedal assist) is a learning process. A dual throttle is a big part of getting this down pat without needing to dumb down the bike’s performance.

You can run an AWD bike with a single shared throttle, but doing so means you will be lifting more frequently and when you do its all-on or all-off. You will lose the ability to decide for yourself what happens. The result is more jerky and less refined.

Battery

If your bike builder did the job right (there it is again), its got a single big battery with a high capacity Battery Management System (BMS) capable of handling the peak and continuous loads of both motors running together. For the rider who has such a setup, the only thing necessary is to set aside enough quality time on a charger to get this bike up to snuff to carry the day’s ride.

Fig. 9: The Purple Thing was … Gen 1.5. Rear motor battery in triangle, front motor battery in the rear rack pack. Front controller in the handlebar bag. Rear controller is in open air under the seat on the rack stays (best for cooling).

For the rider not lucky enough to get a proper battery, that means – at the least – putting up with dual batteries in positions that reduce carry capacity. The rear rack typically gets the duty for one battery in a dual-pack system, so whatever your rack’s capacity was, take off 10 lbs and only use the sides. You may also have to deal with charging the two batteries separately, which is a big drag on convenience and turnaround. You *will* have days where you forget to go and switch the charger to the other battery. Speaking personally: Been there, done that.

Fig. 10: One of my Gen 1.0 iterations with the front motor battery in the bag under the handlebars. Don’t ever do this (but the dual kickstand worked *great*).
Maintenance

Two motors = two sets of service intervals. In practice this should not be a big deal, but fair is fair – we have to count this as double the effort on motor maintenance. This is the part where the direct drive hub people all jump up and remind you for the 100th time their hubs need no maintenance. You will also get slightly increased wear on the front tire, now that its powered.

Commercial Feasibility

I’ve made it pretty clear what I think a proper feature set is for these sorts of bikes, based on the fact I started doing it a while ago, and I’ve had the opportunity to work thru a variety of designs and iterations to find out what works best.

  • Dual throttle
  • Single hi-current battery low and centered
  • Redundant, dual controllers and displays
  • NO front suspension
  • Shared signals from sensors

All you have to do is look at what is out there commercially to see none of them do this. When I look, I see the sort of features – and mistakes – from when I first started kludging AWD bikes together. The reality is, from a commercial perspective we are unlikely to make much headway forward in the near term. Why?

Money… thats why. What I describe is maximum-cost given its redundancy. Its also darned expensive to build an XL battery with a high capacity BMS, and in addition to that, there is the issue of minimum order quantities from component/battery manufacturers. I don’t see a proper AWD bike coming from a commercial vendor unless one goes on a mission to sell a great bike and not take such a high profit margin.

More likely to happen: Development of a suspension fork strong enough to withstand the pull of a front motor over the long haul. It remains to be seen if ANY of those in use now on commercial AWD bikes is going to last. We’ll have to see if product liability issues (and injuries) ensue from whats in use now, or whether the sellers have de-tuned the front motors sufficiently to let those forks survive. But down the road, this is definitely something that could successfully evolve.

Something that came on stage right about the time I published this article is the Eunorau Defender-S on Indiegogo. That is a full-suspension bike, so there’s the front-suspension concern. Given its late-2021 delivery date (plenty of time to figure stuff out), the fact this vendor is going nowhere near any obviously phony claims, and reliable people who know the company are giving it a serious look, this AWD bike may be something of a landmark for the species both in price and thoughtful use of components.

I would be remiss if I did not mention the AWD motorcycles, bikes and ebikes developed by Christini, where they have created a unique, robust, mature – and patented – system to share the power from one motor (rider or electric) to two wheels via mechanical linkage. Lets say that a different way so its clear what they have accomplished: They tap into the power of a single motor (either the rider or a BBSHD) and use that to successfully, reliably power two wheels. Its pretty neat stuff.

What does all this mean for the DIY ebiker? Well, the tools and components are out there for you to build your own, and do it considerably better or less expensively (or both) than anything available in the commercial marketplace.

Fat chance you’ll see a tree-climber like this in stores near you anytime soon.

Wrapping It All Up

The best way to see what good can come from an AWD bike is to look at some representative examples. I have chosen three that work very well for me, and do so in very different ways. Because we’ve gotten to a good place to pause with this post, I’ll do so and point you to the individual case studies that should be linked together in the menu up top.

A Lightweight Electric Emergency Bike Pump

Got an ebike? Use the big battery you are already lugging around to power a small portable pump.

Me personally, I like to ride around on ebikes with fat tires, and I have several of them. The most recent addition to The Pacific Fleet is my Surly Big Fat Dummy. Its a monstrous cargo bike that, for me, doubles as a commuter. A few nights ago, on my way home from work – in the dark – I picked up a piece of twisted metal in my back tire. Part of the reinflation process (I use Flatout tire sealant so you need air in the tires as they spin around and seal the hole) requires air in the tires.

Because I wasn’t paying close enough attention, by the time I got the bike pulled over and the metal removed, my 26×4.3″ tire was flat as a pancake. Fortunately, I had a painless solution in my panniers and that solution is the subject of this post.

Now, when it comes to bicycle commuting this ain’t my first rodeo. I have always carried a Lezyne portable fat bike pump and it makes pumping fat bike tires tolerable. But its still far from ideal. Life sucks while you are putting in those 250+ pump strokes. And it ain’t quick by any stretch. If your tire is leaking air while you are pumping, the pump may not be a workable solution. As a backup I used to carry 25g co2 cartridges. Two of those monsters would blast a fat tire up far enough, fast enough, to be able to jump back on the bike and roll a half block or so to let the tire sealant do its job. Followed by another 250 pumps to get the now sealed but mostly-flat-again tire back up to rideable pressure.

But… you can only carry so many single-use co2 cartridges, and they are very pricey at that large size. Some time ago I came across a better way to deal with this issue.

The Portable Pump Solution

Wouldn’t it be nice if you could just connect a hose to a small portable compressor, flick a switch and pump up your tire? And the compressor pumped fast enough to outpace even nail-sized holes in your tube or tire? Well, portable pumps like that have been around for quite a while. Small automotive ones connect to your cigarette lighter plug in your car (I have this one in mine). Unfortunately they run on 12v DC. Your ebike is running at least 36v DC and likely more. So you can’t use those. There are plenty of pumps available that have their own internal battery… but batteries are heavy and so are those pumps. Besides. You already have a great big battery on the bike. Why can’t you use it?

Well, you can but you need a pump that can run on 48v. Fortunately they do exist but you have to look for them. Here is the one I use, purchased from Amazon.

Yeah yeah. I know. China. If you can find a USA-made portable pump that runs directly on a 48v power source, feel free to drop me a line and I’ll add it in here. As it stands, there are only a very few such pumps readily visible on the market and they are all from the Far East. I have used them a half dozen times without incident. Will they last forever? Good question. I do still carry my hand pump just in case.

DIY a Battery Plug

As you may have noticed from the pictures, the pump has an odd plug on it. What you want to do is plug straight into your main battery. To do that you are going to have to get your hands dirty. From here on, I’ll give a step-by-step on how to make this happen.

Step 1: Snip off the plug

View of the cut off plug and spread pump wires

This one is pretty simple. Take a pair of scissors and snip off the plug.

Step 2: spread and strip the wire ends

You can see the wire strippers I used in the picture above. I used the 18ga hole, and I left about twice as much bare wire as I ordinarily need for a crimp connector. These wires are so thin I want to fold it back so the butt-end connector I will use has more material to grab onto.

Step 3: Determine which wire is hot

Yeah thats right. The plug gives us no indication which is the hot wire, so we have to figure that out for ourselves. What I do is bring out a bike battery and connect a bare XT90 pigtail to its output cord. This in turn gives me a bare, hot lead that I had sure better be careful with, and so must you.

View of the bare hot wire setup
Those are bare live wires on the end of that pigtail! Be careful.

So the next move is to bring the bare, stripped pump wires up to the bare battery wires and – after turning on the pump, touch the wires together to see which combination fires up the pump. Getting it wrong will not hurt anything. Just try the other combination if your first try doesn’t work.

View of the marked hot wire next to the live bare wires
When you know which wire is hot, mark it. I used a bit of red heatshrink pushed over the wire end.

As soon as you have marked your hot wire, disconnect the pigtail so you don’t have bare hot wires waiting to say hi to the cat.

Step 4: Make the connection

My choice for this job is a combination of the following:
1. Marine adhesive butt-end connectors
2. Adhesive heatshrink over the individual wires on each side
3. Adhesive Heatshrink over the butt-end connectors

I’m looking to make a reinforced and solid connection since the wires on the Chinese side are pretty flimsy. Here’s what it looks like after I have crimped the wires together, but before I have done the final heatshrink of first the connectors, and then the sheathing over them.

overall view of the connection prior to heatshrink activation

Notice the different colored rings on each side of the connections?

Closeup view of the wire connectors

I used ‘step down’ connectors because the pump side wire was so much thinner. 18 gauge if we are being generous and probably 20 gauge if we are being accurate. This is why I folded the pump wires over to double them up. Which will only give more material to the crimp itself. The true strength of the connection comes mostly from the connector ends, plus the adhesive sheathing over top of that.

Step 5: Activate the Heatshrink (last step)

Finally, heat shrink the connectors first, then the individual wire sheaths, and finally the connector sheaths that also go over top of the individual small wires. BE CAREFUL on the pump side as the pump wire is very intolerant of heat and will happily melt on you even with mild heat. I use a heat gun set to low. You could get away with a hair dryer. I wouldn’t want to use an open flame due to the fragility of the pump wires.

View of finished plug
The layered heatshrink is not particularly flexible but it greatly strengthens and stabilizes the connection.

Epilogue

View of finished pump
I have added a Presta adapter to the end of the pump hose. Because I opted for a strong rather than a flexible connection, the battery plug no longer folds into the cubby on the pump.

At this point we just toss our pump into a bag to protect it from everyday rummaging, and that bag into our panniers. We’ll all hope we never have to use it, but we will of course.

View of pump inside carry bag