Answered – Why Is My Bike Slipping?

In one of my previous posts, Peloton Bicycle Calibration, I had mentioned that there is actually an additional adjustment that can be performed on the bike which could have an impact, although extremely minor, in how much force is required to move the crank in circular motion. To be clear, this is not about proper calibration – but it is about addressing an issue you may have experienced on your bike – especially when riding hard.

The issue is known as “crank slippage” – I know, but let me explain. In the simplest terms, crank slippage is when you are engaged on your bike, usually with a high resistance setting and often when out of saddle. During this period of aggressive engagement, you are exerting a tremendous amount of force on the crank as you move the pedal from the top to it’s path toward the ground.

During this period of excessive force, you may feel what can be described as “slippage”; where the crank seems to instantly lose connection with the bike, the crank quickly falls forward feeling as though you are slipping forward – only to quickly feel as though the crank re-engages with the bike towards the bottom of the arc. Below you can see where this issue usually arises; it will happen on both sides and usually while moving from #1 to #2.

I personally had this issue for months and it was very frustrating as I could not push as hard as I wanted to. Peloton had informed me that the issue was more than likely caused by a non-calibrated bike. However, after calibrating the bicycle the issue remained.

After examining the bike in more detail I was able to trouble shoot the problem myself. As it turned out, it was the belt; for whatever reason, age, bike usage or a combination of both, the belt was somehow losing tracking at the crank or the flywheel.

What I was able to find out is that there is a way to adjust the tension of the belt by removing a small black cover on the front of left side of the bike; when looking at it from the front of the bike.

The box is attached to the bike with a phillips screw on top and a plastic plug on the bottom. When removed it will look like the photo below; notice the single HEX bolt in the picture.

Adjusting the tension on the belt is very easy, you can only turn the bolt two ways. However, you want to take your time to adjust the tension as there is no way to really measure how much you need to adjust the tension except to adjust minimally; test riding the bike, adjust again, test, etc, etc. The good news is you can ride the bike with the cover off without any issue. In essence you test out the situation where you are feeling the slip, hop off the bike and adjust, hop on the bike and test, hop off and adjust – you get the picture. There are some key points when adjusting; it’s a little counterintuitive.

Below is the same picture of the HEX bolt but with a HEX Wrench inserted into the bolt. Too add tension you push the wrench down, towards floor. Too remove tension you would lift the wrench up, towards the ceiling.

Remember, you do not want to add more tension than what is required for your belt to no longer slip – any more tension added than what is needed only serves to make the crank harder to turn.

I noticed the issue when doing out of saddle work, resistance in the 80’s. Hence, to adjust the bike, I would test out that scenario, then make a slight adjustment, test the scenario again, make an adjustment – and eventually I would land with just enough of an adjustment so that I no longer had the crank slipping on me.