Today we have a question about upgrading to a new crankset and getting the correct size…

I have a Fisher ARC Super, the crankset is a 130 mm. I wanted to upgrade and the smallest size on the upgrade is 165mm, can I do this?

Cranky Carl

Hi Carl,

Upgrading your road bike is fun, but it can bring it’s own share of headaches, as you have run into with the crankset sizing.

I’ve never seen a common road bike come with a 130mm crank arm length. I’m guessing that if you are seeing “130mm” that it is written on a chainring. In that case, it stands for 130mm bolt circle diameter (BCD), which is the measurement you would need for new replacement chainrings. (130mm BCD is common.)

Years ago, I never saw BCD printed on chainrings. You had to measure to figure it out. Nowadays it seems they are printing BCD on the chainring, which is extremely helpful, but could be confusing if you’re not already familiar with the numbers.

And just to make sure I cover everything, you’ll also see the number of teeth on the chainring printed on it. The outer chainring will most likely be a 50 or 53. (Here’s more info on chainring sizes, if you need it.)

For your crank arm length, look for some writing or a stamp on the back of the crank arm, near the pedal insert. I’m betting it’s 170mm or 175mm. That would be the size of crankset you are looking for.

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