I get a weird sensation on the left pedal when I'm riding one of my bikes, as if the pedal was not perpendicular to the crank arm. It feels like the pedal is moving under my foot, although there is no play anywhere, and nothing is loose. Through the pedalling motion, at one point I feel slightly more pressure on the outside of the shoe, then as the crank arm rotates the pressure shifts to the inside of the shoe.
It is a subtle feeling, nothing crazy, but I notice it and it annoys me. It's most noticeable when I change bikes. After I ride another ("non buggy") bike for a while, and then switch to this "buggy" one, I notice immediately the weird sensation in the left pedal (right one too, but less pronounced). Then I forget about it after 5 minutes of riding. I get used to the "buggy" bike. Or maybe both bikes are "buggy", just in slightly different ways.
I wonder if I can measure somehow, with decent precision, the alignment of the pedal in relation to the bottom bracket. The pedals' spindles should be parallel to the bottom bracket axle.
I have tried to do a measurement like this:
- have the bike fixed on the hometrainer
- place a spirit level along the pedal axle
- keep the spirit level on top of the pedal (like your shoe when riding)
- see if the bubble stays in the same place as the crank rotates
If the bubble stays in the same place then the pedal is parallel to the bottom bracket (right?).
Here is my result showing the maximum range of bubble movement as I rotate the crank:
I am not sure what conclusion to draw from this measurement. If I understand it right, it shows that the two rotating things (1. crank, 2. pedal) have rotation axes that are not parallel to each other. If they were parallel, then the bubble should have stayed in the same place (not necessarily in the middle, but same place). Is that correct? What other measurements can I do to check this?
Fun fact: none of my four bikes pass this test. Each one has some bubble movement, but the "buggy" one has a bit more bubble movement. Are these just normal manufacturing tolerances? Are all my bikes just misaligned? Is my test flawed?