Changing chainring size when shortening cranks


Thanks for the RideLogic bike setup consultation. Two rides in with the new bar and I’m definitely adjusting, but it’s a way different feel than it used to be. Really liking it, and a lot of moves feel easier (as long as my legs are up for it). I’ve obviously taken a deep dive here, so why not dive all the way.

My next thing I’m looking at is crank length. You talk about switching from 30 to 28 teeth for a switch from 175 to 165. I’m considering going to 155. I currently have a 32 tooth and 170, I believe. How many teeth would I need for a 155mm crank?



Hi Ben,

175mm / 30t = 5.83kfu*
170mm / 5.83kfu = 29.2t
165mm / 5.83kfu = 28.3t
160mm / 5.83kfu = 27.4t
155mm / 5.83kfu = 26.6t
You won’t be buying a 26.6t chainring, so you’ll need to round down to 26t or up to 28t. If there are companies that offer odd-numbered rings, someone please comment down below.
Modern gearing is so low, I don’t think this is a critical change.
Does that help?
*kung fu units
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