4iiii power meter - Different size left and right cranks

I’m looking at getting a 4iii power meter installed on one of my left side cranks. I’ve got two bikes that I use the most. One has a ultegra 172.5mm and the other a 105 175mm. If I get the power meter on the ultegra, could I use it on the bike with the right 105 crank? The length difference is minimal but just wondering if anyone has done similar in past.

Yes, you could do this.

I recommend you swap over your left cranks before you purchase a 4iiii and a do a couple of test rides to see if you notice the difference in left and right crank left and that you don’t get any muscular issues.

The 2.5mm is a small difference, I’ve known people do bigger differences when they have legs longer than the other etc.

I personally mentally would believe there was an issue, have a nag in my mind. However if you put on a bike with 2.5mm difference in crank length and didn’t tell me I doubt I’d notice.

Other option would be just purchase matching right crank arm for the 105. Sure you can get one used on eBay for cheapish.

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I would not recommend having different length cranks on a bike. It may affect knees or other joints and just wont feel right. Choose which bike is the most suitable to have the power cranks , its not advisable to swap them around as the bolts and splines will get worn and may eventually cause a problem futher down the line.

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Get a 4iiii that matches your ultegra and save up for a 172.5 105 crankset. I would NOT combine different length cranks.

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Your body wants symmetry and joint issues can develop from less difference than 2.5mm. I’d put the PM on your Ultegra and buy a matching length for the 105.

Maybe, maybe not. As a OCD engineer-type, I crave symmetry more than most. But as a trained fitter with 5 years of experience, I have seen some really questionable setups that “work” for people. We incorrectly assume that our bodies are symmetrical, and sometimes are, but more often have plenty of differences that exist and we naturally accommodate each and every day. I have swapped crank length on some riders on one side who have not even noticed the difference.

Point being that it might, or might not, make any functional difference to the rider. You won’t know without trying. It’s too difficult to predict what changes like that will or won’t do because we are all different.


Thanks everyone for your feedback. I think I’ll take the advice and put it on the ultegra and either save for another one or getting a matching length.
Appreciate it.

…another option you can look at is selling/swapping cranksets. It’s probably cheaper than a second power meter. I’ve done this for years (175 shimano cranks on all my bikes).

Now that Assimo (Sp?) have the cheaper pedal based power meter, I would consider going that direction as with swapping crank arms, I’m always locked into bikes with shimano BB’s, cranks, etc. Whereas Assimo’s you can swap all over the board.

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