I'd like to try a different crank arm length. I'm currently running a 175 on my Trek 5200 which has an Ultegra triple. I'd like to go to a 172.5, or a 170. I assume that I need only replace the right and left crank arms to accomplish this?? If this is the case, how do I do it? Do I need to torque the bolts? Locktight?

ThanX!!!!

to remove the crank arms, you will need to use a crank puller, (park tools makes a real nice one) specific to your bottom bracket (square, splined...) when you put the new cranks on you just need to tighten the bolts down (probably will be specific ft lbs in the instructions with the cranks), I have never used locktight....

as a final note, getting a new matching bottom bracket may not be a bad idea, as the splines could be different.

Sorry to be so simple, but what is the reason for changing the crank arm length?

I'm more of a spinner than a masher. From what I've read, a shorter crank arm length is more beneficial to my type of pedal cadence than a longer one. Also, I've done some calculations, and most authorities on the subject recommend a smaller length crank arm for my size.

FYI, I am 5' 8" with a 31" inseam (not pant size inseam, but a measured inseam). I am currently running a 175, but would like to try a 170 to see if I like it better. I can always sell my 175s if I like the new set-up better, and mitigate the expense.

It's either that, or I have entirely too much time on my hands to think about such things!!!!

Bac,

You will not need a crank puller for the Ultegra crank arms. Here is Shimano's diagram of your setup; https://bike.shimano.com/product_imag...FC_6503_EV.pdf
All you need to do is back the crank arm fixing bolt out with the crank arm cap in place and it acts as it's own crank puller. As long as you use Ultegra crank arms you will not have to replace the bottom bracket.

You will want to remove the crank arm cap before putting the setup back on so that you can see inside to make sure you have the splines lined up properly before tightening the crank arm bolt down with your wrench.

I am considering doing the same thing with my bikes. I am also 5'8" although my inseam measures about 32.6 inches. The Fit Kit recommends that I have 170 mm cranks. On my road bike I have 172.5 and on my mountain bike I have 175. When I get on my mountain bike after riding my road bike I notice a really big difference. I just haven't decided if I want to go to a 172.5 on the MTB and keep them the same or switch them both to 170.

Let us know how it works if you try it.

Most wheel pullers will do the job as well. I don't how how specific the park tool is or how expensive it is, but BigLots (discount everything store in Cleveland area) has wheel pullers for less than 10 bucks. Leather strapping or plastic cushions can be used so you don't mare the surfaces.

Hope this helps.

WOW Great topic. Was just looking into this myself. I'm 171cm tall thats what around 5'7" with a 31" measured inseam and it seems that the 172.5 is the correct crank length for my inseam measurement.

I've opted to switch my MTB over to 172.5 cranks as well. Tried 170mmpreviously and they were too short - d=cadence rose noticably with little power. with the 172.5 I seem more comfortable and able to produce power without to much mashing of the pedals.

My LBS also recommended that I have all my bikes with thesame crank length to help prevent injury.

Some good advise, I'm taking it.

Great link and info! Now, do I have the confidence to start turning the wrench? That is the real question!