Big And Cheap: DIY Cargo Bike Bags

There is another post that shows later improvements to these bags.  Here is another one that covers a hole I left in this article below.
Great Big Bags 2.0 uses a better attachment method.

I have a Mongoose Envoy that I turned into a project bike.  I essentially took a very inexpensive bike with low end components (but a fantastic frame, with a good fork and wheels) and rebuilt it into a high power, heavy duty cargo bike with better components than I’d get if I paid for one from a major manufacturer.

The Envoy comes with two almost-38L-each panniers (24″ long x 16″ tall x 6″ deep).  Thats one hell of a lot for a bag on a normal bike.  But on a mid tail cargo bike frame, they’re smaller than what they could be.

The stock bags look skinny, and are no thicker than a normal pannier.  But I’ve had them loaded with a complete Costco grocery run where the bike ended up well past its 140-lb rated cargo capacity.  Using an elastic bungee net to make sure everything stayed tight to the bike, all I had to do was lumber home without killing myself.

img_20191111_112329
Figure 1.  A light shopping run – not using front bags.  The bags we’ll make here are about the same size as the ones shown, but more than double the width.  Note the cargo net used here as insurance that those bags stay put.

So… the bags work great and are essentially free.  But I’d like something that better suits the capacity that the mid-tail cargo frame can handle.

I managed to score a brand new set of Surly Dummy bags for a great price.  I found they were great bikepacking bags not suited to bulk grocery hauling.  Whats needed is a giant hole you can dump stuff into and zip closed.

It looked to me like the Yuba Go-Getter bag ($300 plus shipping for the pair) was the closest fit to this idea, and to my frame (It is meant to fit their popular Yuba Mundo cargo mid tail)  I contacted Yuba about the exact size of the bags, and that they would be going on a non-Yuba bike.  They promptly got back to me with this:

  • Length – 29″ / 74 cm
  • Depth – 10″ / 25cm
  • Height – 17″ / 43cm
  • Volume comes to about 84 quarts or 79.5 liters.
  • It is important to note that we designed the Go-Getter to be specifically compatible with our Yuba Mundos and we cannot guarantee its compatibility with non-Yuba bikes.
Go-Getter-Angle_600x600
Figure 2: A single Yuba Go-Getter bag mounted on a Yuba Mundo cargo bike.

Thats pretty awesome in terms of capacity.  However, those dimensions are just enough to worry me on my bike.  The Envoy’s bags are 24″ long.  29″ might end up pushing into my heel clearance.  The height of 17″ is for sure an issue.  Envoy bags are 16″ tall, and its already a problem that those bags essentially sit directly on the lower rack.  While the bike frame is rated for 90 lbs, the lower rack is only rated for 20 per side, or 40 lbs total.  Now, they can handle much more than that in real life, and I have reinforced the lower rack’s attachment to the frame (Supplementing the factory’s four connections with an additional six that are each stronger than the simple factory bolt), but still a bag that basically sits its weight on that lower rack is not ideal.

What would be better would be a bag that is a little shorter, that bows downward under load, putting strain primarily on its hanging hooks, so only partial weight is borne by the lower rack.  Add in a couple straps to help take the load off those 4 hooks and its better still.

I think my solution accomplishes that.  Bear in mind everything I did here was done specific to this bike.  You can take these ideas and make adjustments so this basic concept fits to yours.

The Budget

Lets call the number I am trying to beat the cost of the Yuba Go-Getter bags, which were my benchmark for capacity:  $300.  So I wanted this project to come in as far under this number as possible and still get a quality bag.  As you can see from the build sheet below, I came in well under the commercial product’s price point.

Build Sheet ($111.50, or $55.75 each)

Rothco Parachute Bag (2)             Amazon   45.98
3"x30"velcro cinch straps (8)        Amazon   21.54
C.S. Osborne #6 13/16" grommets (8)  Amazon   11.36
Stainless 0.3"/0.78" S hooks (8)     Amazon    2.67 
Therm-a-Rest Classic Foam Pad        Amazon   29.95

The Bags

I want something more durable than the fabled, dirt cheap Ikea bag.  But really those bags got dropped as candidates because the zippered version is so short at 11″ that it would be putting the load unnecessarily high.  Also its 28″ length is again just enough to worry me.  And how sturdy is it?  The zipper in particular?

I had a candidate already in my hands in the form of a Rothco Parachute Bag.  These are simple, cheap $23 bags made of reasonably thick canvas and strong, smooth zippers with a snapped storm flap.  Dimensions are 24″ long (identical to the Mongoose stock size), 15″ tall (1″ shorter than stock, so addresses my height/weight concerns) and 13″ deep.  Work out those measurements to cubic inches (4680) and convert to liters and you have a 76.7L pannier bag.

Since I already had one of these bags in my closet, I was able to toss in some full size pillows (it ate 3 of them and still wasn’t quite full) and sized it to the bike.  Looked like a perfect fit.  So I bought two more for testing.

Attachment

After a fair bit of fussing around, trying to figure out exactly how I wanted to attach the bags to the bike (it actually took a few weeks), I settled on primary support being grommet holes in the bags, which will connect to simple S hooks mounted to the frame.  These will be further supported by straps.

I used the C.S. Osborne #6 grommet, which has a 13/16″ hole.  Why this brand and size?  Well, there are drapery grommets, shower curtain grommets and outdoor tarp grommets.  The grommets for curtains are nowhere near strong enough to work on a tarp… or a pannier.  I knew from experience the Osborne grommets are solid and will distribute the forces involved as well as possible.

I chose a 13/16″ size because… I had the grommets and the grommet tool already.

20170218_143537Sidebar:  The #6 grommet size is the smallest size commonly available that will let you fit an XT90 connector thru the hole.  Thats why I have the grommets and tools in my garage – from building battery bags for my custom ebikes.  I grommet the pass-thru holes in the bags.  And since I have been using them for years, I know they hold up.  The bag on the right was made in early 2017 and is still in use today.  This $12 Amazon bag with reinforced holes is way cheaper than a custom ebike bag.

  • You can see in the first pic below, three of the four grommets’ upper edges match the seam of the bag, while the forward-most grommet is lower.  Oops.  My second bag had them all even and all in the lower orientation.  Despite the different mounting, you can’t tell the difference in how they sit on the bike.
  • The single brass grommet was deliberate as I wanted a quick visual cue to help me orient the bag.  Brass = rear for both bags.

Straps

Not wanting to rely totally on the hooks, there are two dedicated three-inch velcro cinch straps.  These are actually made up of two 30-inch straps combined to make one longer strap.  I had to do this as there does not appear to be a 3″ wide velcro cinch strap in a 60″+ size on the market.  If you wanted to save some money and use a narrower strap, 2″ cinch straps are widely available.  In fact, the pics below show an early test fitment where I was using 2″ x 72″ straps, which worked OK but were so long they were a bit unwieldy.  Shorter straps were more convenient and the wider 3″ version provided more support.

The right way to use the straps:  Loop over the rack at top, and the very bottom, directly underneath.  But do NOT loop under the lower rack and then go up over the bag.  Instead, from the bottom of the bike frame, loop the strap directly under the bag and then back up to the top.  The top loop over the rack helps support the bag’s weight.  The bottom loop onto the lower portion of the frame (or rack depending on your bike) helps hold the bag close to the frame so it won’t flop around.  And the remainder of the strap, directly up against the bag and not under the lower rack, holds up the bottom of the bag, preventing – along with the padding – the bag from sagging.

Hooks

These are pretty straightforward.  I wanted an S hook with beveled edges that allows quick attach/detach, but at the same time is shaped in such a way that the bag will not easily come undone from it as I bounce from pothole to pothole.  I searched for months for such a hook for a cargo net and fell into the ones I am specifying in the build sheet.  Originally meant for my cargo net, they are also perfect for this project as well.  I have the painted black versions but I am spec’ing the unpainted stainless versions.  For your own personal bike, you may need something different.  Follow the link above and note the seller offers three sizes.

More Options

  • Most of the reason I used pre-made cinch straps rather than buying webbing and fastex-style buckles is that hook/loop strapping is much easier to adjust.  This makes it easy to cinch up the straps when the bags are empty, and fold the bags up quite nicely.  There is even a deep, wide pocket formed by this process that is a decent candidate for stuffing in whatever fits.
  • During testing of the bag when fully loaded, I ran a 15″ x 30″ cargo net from my top rack, over the bag and underneath to the bottom rack.  It provided great support to keep the bag from sagging, and held it firmly, close to the frame.  For really heavy loads this looks like a smart thing to have available; especially since it can lay flat in the bottom of the bag and take up no extra space.
  • I have a 24″ x 36″ cargo net (see it in action in Figure 1 above) that I can use to stretch over my entire cargo area.  Up over a side bag, the loaded upper deck and back down over the other side.  For big, heavy loads, a net like this can put a gentle, compressing and enveloping grip over the entire load in the rear.

Where Do You Go From Here?

Unless you have a Mongoose Envoy then your bags will need to be tailored to whatever your bike fittings are.  Expect to put the grommets in different places.  Maybe use a different size of S hook.  Don’t expect my project to work perfectly for your bike although the parts I am using should be mighty close to universal once you space things out per your bike’s needs.

In the photo above: I had so much room in the new bags after loading up my shopping cart, I never even used the 36″ x 12″ duffel that sits atop my 40″ rear deck.  There is almost 154 liters of pannier space in those bags, and after dumping that whole shopping cart into them (the front bags helped too)… they still aren’t full!

Mongoose – Chapter 9 (Low Cost Builds)

So in Chapter 8, I put up a Build Sheet.  If you do all the math, you will find my $750 bike turned into a $3600 bike (some bits, like the battery, I already owned and just plugged in so cashwise I am not out the full parts total).  Given how expensive quality cargo bikes are, and the level of quality I have now, I am very happy with that cost vs. benefit.  I have a really solid frame and top quality components, and a bike that is probably the best all-around transportation/auto replacement bike I have ever owned.

But what of all of this was actually necessary?  I build bikes as projects.  Generally, I am more concerned with making the bike the best it can be.  I don’t pay as much attention to final cost as most people would.  Especially since I oftentimes upgrade in bits and pieces, which is less of a shock to the budget.

Based on my experience with the stock Mongoose bike – seeing first hand what worked, what didn’t and what I changed because I had more money than brains – I can see a different way to go that might be of a lot more interest to people who just want a good bike that doesn’t break the bank.  For the record, I’m of the opinion that the Mongoose Envoy represents a significant break from current cargo bike offerings in that it can be built into a first class solution for a lot less, thanks to its bargain basement starting price.

So… lets build a few different configurations using my kitchen-sink, spaghetti-against-the-wall build.  In the end, I replaced everything but the frame, headset and fork.

All prices are in US Dollars.  The last two builds are non-electrified.

Build #1:  Just The Very Basics+Assist ($1,807.48)

This is a low-cost build that changes only the things that I think must be replaced.

Right off the bat, you can see I left on the Magura 4-piston MT5 brakes, and the great big (but relatively inexpensive) thick rotors.  These brakes work so smoothly and so well when I have had this bike fully loaded.  I think you’d be insane not to take any and all uncertainty completely out of your braking equation.  These brakes are not overly powerful when you consider the duty cycle they will have to put up with.  Safety first, but this choice also guarantees trouble-free ease of use.

This build uses the BBS02 because it is lower-cost and still does a spot-on job.  You can see from my motor choice post that if I did not already have other BBSHD bikes in my stable, I would have chosen the ’02 for this build as it is ideally suited for the cargo bike job.  The cost below does upgrade to the mini color display; adding $40.  Knowing the different displays as I do, this is well worth that minor upcharge.

Note I changed the shifter… that has to happen thanks to the change in brakes.  The stock brake levers are combined with shifters (cheaper that way, I bet) and if one goes, so must the other.

Mongoose Envoy Bike               Amazon               731.49
Magura MT5 disk brake set         bike-discount.de     137.00
ISH-203 203mm rear disk adapter   bike-discount.de       6.86
QM5 203mm front disk adapter      bike-discount.de       6.86
Tektro 203-17 downhill rotors (2) ebay (hi-powercyles)  42.40
MicroSHIFT TS70-9 shifter         Amazon                22.88
BBSO2 motor kit                   Luna Cycle           490.00
   68-73mm standard motor
   mounting hardware
   wiring harness
   speed sensor
   basic crankarms
   Luna 500C mini color display
   Universal thumb throttle
Battery Solution
   52v 12.5ah battery pack, basic Bicycle Motorworks   369.99
   pack construction, 50a BMS and
   Samsung 25R cells

Build #2: Change Out The Drivetrain ($1,933.00)

Includes everything above, plus the following, which adds $144.61 to the build price.

Everything From Build #1 plus...
KMC X9.93 chain (7 feet/more links)  Luna Cycle   57.75
Shimano HG400-9 12-36T cluster       Amazon       25.99
Shimano RD-M591 9spd derailleur      Amazon       41.78

This takes out the frankly bottom-end Shimano drivetrain and in its place substitutes a smooth-as-glass 9-speed click-shift setup.  Yes the chain is expensive but if you want to do a mid drive right, you have to pay attention to the chain and the rear cluster, which in this case is a durable, steel, welded-together unit that will give longevity and will not tear into your cassette body.

You can get a strong steel cluster with an 11T small rear cog, and I suggest you resist the temptation.  11T cogs are always problematic on mid drives in the first place.  On a cargo bike the problem is worse.  The speed you can achieve dropping that one tooth is likely unattainable anyway.  Especially when you factor in the weight and the motor-bogging that will occur under load.  Don’t do it.  Get the 12T.

Worth noting:  The stock Mongoose 8-speed cluster is also a welded steel unit so its just as survivable.  Also the Mongoose chain is an 8-speed KMC, so its likely just as durable.  The weak links – no pun intended – are the rear derailleur and shifters.  Mine worked poorly although I intended to replace it with a 9-speed from the get-go, so I didn’t try to adjust it into compliance.

At this point, we have a really first class electrified cargo bike that stops easily, shifts smoothly, will survive over the long term thanks to the components we plugged into the drivetrain… and we’re still under 2 grand.

Build #3: Add a Front Rack ($1,988.48)

Yikes we’re still under 2 grand here!

Everything From Build #2 plus...
Front Rack 
   Axiom Streamliner Front Rack  Amazon       46.99 
   Delta AxelRodz skewers        Amazon        8.49

Adding the front rack greatly increases your versatility.  For mine, I use waterproof RockBros 27L panniers similar to Ortlieb rolltops: They are big, carry a lot and mount about 2″ low on the rack.

Note my discussion of the installation of this rack in the Odds and Ends post.  You’ll need to spring for about 20 stainless 5/32″ fender washers to fit the rear AxelRodz skewer onto your front axle.  This sounds crazy but really, it works very well.

Build #4: Beef Up The Drivetrain ($2,187.43)

We’re adding almost $200 with just these next two parts.

At this point, since we are building with a BBS02, we’ll want to address its weak links a little differently than I did with my BBSHD.

The Lekkie chainring gives you some offset to bring your chain line back into alignment, provides a tooth profile that eliminates any chain drops and lasts, essentially, forever provided you do your part as described in the mid-drive section of the motor musings chapter.

Everything From Build #3 plus...
   Lekkie Buzz Bars (crankarms)  California-ebike    99.00
   Lekkie BBS02 46T chainring    California-ebike    99.95

As for the crankarms, those are self-extracting, quality bits of forged alloy, versus the low-end Chinesium alloy used on the stock arms.  Those square-taper arms are often replaced, and the fact they only cost about $15 each makes said replacement relatively painless… but never having to replace them in the first place is an idea that has some merit.

You can consider the crankarms an optional option and see if you pedal hard eough to make them fail, which you might not, in which case you’ll save yourself a hundred bucks.

Build #5: No E-Assist, Proper Parts ($1,081.69)

What about just treating the Envoy as a ‘donor’ to make an analog bike?  Take advantage of the great frame and replace the iffy components to make yourself something really good for really cheap?

I did not throw on the hand built uber-wheels, or change the tires.  Both of those components work well on the stock bike.  Sure I think custom wheels and upgraded tires are a good idea, but they are icing on a cake and, particularly with the wheels, spike the build price up considerably.

I focused on turning the bike into a silky-smooth-running, safely-stopping hauler.

  • The drivetrain – excepting the front crankset – was replaced with a great Shimano 9-speed long cage derailleur
  • The chain may seem expensive, but you’ll have to buy two 9-speed chains to make one long enough to fit this bike, or just buy the super-strong one I did that is in one piece already with no potential mid-chain weak spots where the two chains would otherwise be attached together.
Mongoose Envoy Bike                Amazon            731.49
Magura MT5 disk brake set          bike-discount.de  137.00
ISH-203 203mm rear disk adapter    bike-discount.de    6.86
QM5 203mm front disk adapter       bike-discount.de    6.86
Tektro 203-17 downhill rotors (2)  ebay               42.40
MicroSHIFT TS70-9 shifter          Amazon             22.88
Shimano HG400-9 12-36T cluster     Amazon             25.99 
Shimano RD-M591 9spd derailleur    Amazon             41.78
Shimano FD-M591 derailleur (front) Amazon             29.95
KMC X9.93 (two of them)            Amazon             36.48

Build #6: No Electrics, Fully Loaded ($1,566.41)

This one has almost everything but the kitchen sink thrown in for max comfort and quality.  Here again though, I left off the hand built wheels.

  • The Thudbuster LT is pricey but its such a big change to the comfort of the bike, a top build has to have it.
  • $90 for a kickstand is hard to choke down, but if the bike falls over once at the store with 100 lbs of groceries in the bags… it doesn’t seem quite so expensive.
  • Those Jones bars are just too comfortable.  Nothing wrong with the stock bars… but if we are throwing on stuff to feel good, these have to be on the list.
  • I use the RockBros panniers with my own front Axiom rack and decided to include them here.  They are big, waterproof and inexpensive.  While you do not want to overload your front rack, these can carry jumbo bags o’ tortilla chips without squishing any.  So as usual, size does matter.
Everything from Build #5 plus...
Thudbuster LT 27.2 XL            Amazon      119.99
Ursus Jumbo Superduty kickstand  Amazon       79.99 
Jones H-Bar SG Loop Handlebars   Jones Bikes  79.00 
Jones 205mm Kraton Soft Grips    Jones Bikes  20.00
Front Rack 
   Axiom Streamliner Front Rack  Amazon       46.99   
   Delta AxelRodz skewers        Amazon        8.49
   RockBros 27L Panniers         Amazon      108.99

Wrapping it all up…

The first four builds above address all of the functional weaknesses of the $730 Mongoose Envoy.  Do these things and you have

  • upgraded an analog bike into a solid electric performer
  • addressed every functional weakness in the original bike

The last two builds take a look at the same thing, but go in the direction of making the bike the best it can be without a motor.

One functional item I am leaving off here is a heavy duty wheel build.  While I have one in progress, and its on the build sheet, the fact is I have not yet killed the stock wheels.  Nor have I ding’d them.  They are still nicely true, and my desire for a 30mm internal, survive-the-apocalypse set of wheels can be argued as me overdoing it… again.

There are a lot of other line items on my personal build sheet that are not discussed on the electric builds.  Stuff like the Thudbuster seatpost, or the Jones bars.  These address personal comfort issues that don’t need to be there.  Those are items you can spring for individually over time… or not.  You know how the bike upgrade thing goes…

So have at it!