There are two common mistakes people do when they purchase a triathlon bike and don’t get assistance with their bike fit/position. One is having the seat post too high and second is to just ride whatever crankset the bike comes equipped with, regardless of its size and the rider’s height.
Most bike companies try to match a correct or advisable size to the frameset size, but obviously we are all different and it’s not as simple as one size fits all. Actually, from my experience as a triathlete and as a coach, cranksets are usually by default a size too lrage for each frameset.
So how do you know if you are indeed riding the correct crank size? Here’s a simple test you can do on your own:
- Place your bike on the trainer and ride warm up for about 10 minutes. This test can also be performed outdoors but it’s safer and easier to do it on the trainer.
- Imagine that an entire pedal stroke is a clock so the top is the noon or 12 o’clock and the bottom is 6 o’clock. On the aero position, stop your right pedal stroke at around 3pm and unclick the other side. This is the initial position.
- Using just the force from the right leg, pedal VERY slowly backwards. The goal is to replicate your normal pedal stroke but backwards, so use your quads to pull the leg up and back.
- The final position is with your pedal at around 10 or 10 o’clock, so a little past backwards the noon/top positon.
- During this movement and as you pass the top/noon position of the pedal stroke, that’s the point where your hip angle is the most closed and where if it’s too closed, you are adding tightness to your hip flexors that may prevent you from running well. That top position is also where you would feel some resistance from your soft tissue if your crank arm is too long. If you feel any resistance, that’s something you must overcome every single time you pedal normally.
- Repeat this a couple of times with the right and then with the left.
Conclusions: If there’s any resistance on the top of your pedal stroke, you may consider a shorter crankarm. The other way around may also be true, if there’s no resistance at the top phase you may either be riding a crankarm that is your size or you may even investigate if there’s a possibility of extending it a little bit for further leverage when you pedal.