Here’s The Problem
If you shift under power with a BBS02 or BBSHD, you will do so using a LOT more power than your ebike’s drivetrain (chainring, cogs and chain) was ever designed to handle. Shifting while under even a moderate amount of power is a great way to snap your chain and take the Walk Of Shame home. Worse: you can crack or even taco a cog.
Here’s The Solution
Use a gear sensor. Thats not so tough, right? First of all, what is a gear sensor? Its a little box, with a little wheel inside. You run your shift cable thru the little box, in one side and out the other (which means you need to cut and re-section your shift cable housing), with the cable running across the little wheel. When the wheel senses any motion, it sends a signal to your motor that cuts the power for a split second and takes the pain away from your drivetrain when a shift occurs.
Whats Wrong With That?
Nothing, so long as it works. The little wheel inside is mechanical and crud-sensitive. Lots of folks have issues with them not working after rain storms or mud baths. You can solve that by wrapping it somehow to keep the grit out.
Its also not the ONLY way to do the job. Like I said, I had my first BBSHD without one. I learned to shift without needing a gear sensor. By the time I built my second bike, I had that method down pat. So yeah sure the sensor is nice but I have already learned another way, and I have found – even though I have bought sensors and have had them right in front of me during a new build – I don’t feel a need for them.
But I sure as hell have a need for the job they do. Everyone does. So don’t let anyone tell you the problem is not real. Its probably the #1 way to snap a chain on a mid drive bike.
Gear Sensor Alternatives
So there are a number of different ways to do this job. I’ll list the one I use last
Use the brake cutoff as a clutch
Its simple: Squeeze the brake handle just a little bit to engage the brake cutoff. That cuts power to the motor and gets you the same thing a gear sensor does. The trick is to not engage the brakes to any noticeable degree and lose any of that hard-won momentum. Interestingly, Magura MT5e ebike brake levers have a special little hinge in the middle of the lever. It lets you do this more easily without engaging the actual brakes.
Thats nice, assuming everything works. If you are a little jumpy, or the bike is bouncing along a trail or something, then that delicate caress on the brake lever might be a little more than you figured and … well, you get it. We live in an imperfect world. But this method still works pretty good.
Use a cutoff button on the handlebars
This is definitely not a common solution, but it does work, and is what I used on BBSHD Bike #1 until I gave up on it and perfected the method I describe next.
What is it? Its just a dead-man switch on the bars. Press it and for as long as you hold it, the motor is cut off. Release it and the motor re-engages. Its a brake cutoff that has no brake pads. The other end of the switch has a yellow Higo/Julet that connects directly to the BBSHD’s motor cutoff plug.
In practice, I found it took too much thinking to reach for the button just prior to a shift. It felt forced and I didn’t take to it. Maybe you will and if so its a dirt cheap and simple method to try that doesn’t involve screwing around with your shift cables.
Adapt your pedal cadence
This is the method I settled on, and even after buying and successfully using a gear sensor, I have never felt a need to install another one. This method is just a natural part of my riding style now and is trained into muscle memory… so I do it naturally and automatically on any bike no matter what. Here’s what I do, in order. These steps occur in very rapid succession so making a shift happen occurs in about one to 1 1/2 seconds.
- Step 1: Stop pedaling.
- Step 2: Click the shift (just one gear).
- Step 3: Start pedaling. Muscle power completes the shift before the motor kicks in
Thats it. Do it fast and its just a quick stutter in your cadence. Changing your BBSxx settings so they are friendly to pedaling helps. The linked settings will cut the motor off fast and start it back up soft. Perfect for completing a shift.
When you get good at this, you will be able to click your shift a hair before the motor stops the rotation of the chainring. My more recent builds use SRAM 11 speed drivetrains that need only about 1/4 of a cog revolution to complete a shift. So if I do it right, I click while there is still a ghost of rotation left that makes the shift, so when I start pedaling again I’m already working with a shifted gearset.
Don’t try and get fancy right out of the gate. Just keep it simple and get the shift done. The high speed fancy stuff will come naturally as you gain experience.
Remember, there is nothing wrong with a gear sensor. They do their job. I just learned how to do without one. Having done that, I don’t feel a need to make the effort to install the sensors anymore.
In an ideal world, you do both. Truth be told I screw up every now and then. With the cadence technique and the sensor backing it up, you are pretty much guaranteed to never snap a chain thanks to shifting like a fathead.