Gear Combo Guru
Join Date: May 2007
Bikes: Spec' Tarmac (road), Ridley Fenix (commuter & fast tourer), Salsa Mamasita (MTB), CoMo Speedster (tandem), Surly Big Dummy (cargo), Airnimal (folder)
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I had a similar issue. I run 170mm on all my bikes. The dealer told me that our tandem would come with 170mm front and rear FSA Gossamer cranks, but I was wary of this because I couldn't find such a combination available anywhere else. When it arrived, it was 172.5mm at the front. I can certainly tell the difference, and spent several rides playing around with my seat height without improving things much, and was expeciting it to be something that would always bug me.
After one year and several thousand kms on the bike, I've decided that it the slightly longer front cranks aren't too much of a problem. They do have one advantage: I like to spin the pedals a bit faster than my stoker, and the longer cranks makes my cadence feel a bit higher than it really is, so this makes a happy compromise in cadence easier to achieve.
I therefore recommend putting a decent amount of mileage into the bike with the 172.5's before deciding whether changing them would be worth the hassle.