Downsizing crank arms: Anyone done this?

[Dave]

I haven't experienced any problems with my replaced knees. I started with my normal 172.5 cranks arms, switched to 170 when I bought some new cranks and then to 175, just as an experiment. 175 is just under 21% of my cycling inseam. It took a little adjusting, but the 175s are working OK.

I have one leg that's maybe 6mm shorter than the other, so I went back to adding some shim under the cleat on the short leg, with the longer arms.

[Alistair]

Originally Posted by verbs4us

...But he suspected something was amiss with my hip. One doc and one X-ray series later and we uncovered a malformation of the r. femoral head, resulting in bone-on-bone in the flexed position.

My wife has a similar problem, and the resolution was the same - some saddle tweaks and shorter cranks, all with the goal of opening the hip angle as much as possible. She runs 160 or 165, but could probably go shorter. The only difference was she knew the problem existed, so the jump to shorter cranks was more obvious.

It took her a month or so to adjust, but the reduction in pain more than made up for it.

I recently went with 165 on my road bike as an experiment, mostly to see if it would allow a slightly more aero position. I haven't had any adverse effects, but also haven't done any real testing. The saddle-bar drop is a bit more than previously, FTP is steady, and I'm comfortable, so I guess it worked?

[Plum Hill]

Originally Posted by smead

I'm certainly no fit expert, but it seems odd to me to move the saddle fore/aft to compensate for different crank lengths as opposed to just raising/lowering the saddle. I set my saddle height measuring from the pedal spindle instead of the BB, that way the stroke is the same regardless of different crank lengths.

Saddle was moved up to compensate for the shorter crankarms. However, to keep KOP the saddle still had to go back some. Saddle does go back when raised but not in a 1:1 ratio. Theoretical, but in reality, probably picking nits.

[verbs4us]

Originally Posted by Plum Hill

How do you like the TA crank?
I have Campy 9 and 10 cranks to change out. The TA silver would look much better on my bikes than 4 arm Campy carbon, but much more costly. TA would require new BB. While I have Campy 102mm square taper BBs laying around, the TA requires 107mm. Campy crank cost $368 (using existing UT BB) vs $540 for complete TA setup.
Frugalness trumps vanity.

Phil Wood makes some bottom brackets that fit ISO (TA's spec). They are heavy but blast-proof and very stiff. TA's BB is made, I think, by SKF to their specs. There is a TA BB version with double adjustable sides, which is nice to enable fine-tuning of chain line. I run a Phil on one bike and TA on the other. Can't say I feel much difference; the Phil might be a smidge stiffer. The cranks are nearly the same weight as 1980s vintage Campy NR and seem to be stiffer. Their rings are very well made; although for my 11-speed I needed Stronglight. Yes, they are pricey but three things made it worth it to me: (1) a very low Q; (2) enormous range of ring sizes for 110 BDC and (3) quality materials and mfgr.

[dbanned]

I switched to shorter cranks not at the advice of a bike fitter but just to try them. Went from 175 to 165 and I felt like I had to ride in easier gears but spinning was easier.

[Waldo62]

After a crash with a deer resulted in a knee injury, I'm going down from 185s to 177.5s. 180s feel pretty good on the knee, but 177.5s, though somewhat awkward, make the knee feel better. I still ride the bike with the 185s occasionally, and though pedaling feels awesomely powerful and efficient, the knee doesn't love it.

[Ken Robb]

You might want to search the archives because we have had discussions about different crank lengths in the past.

[carpediemracing]

I've tried to go to shorter arms multiple times in the last 13 years. No real success.

I last tried 2020-2021, committing to 170s in early 2020. I'm still on them but have not had a lot of outdoors racing to test, but it was very hard doing races on the 170s.

I'm on 175s normally. And I don't have long legs. My BB-saddle is 675mm, give or take; my inseam is under 28" to give you an idea. 30" inseam jeans hit the ground by the heel, and my pant waist is not around around my thighs.

Early on I used 167.5s, then 170s. Only went to 175s in 2003, when I was super unfit and could basically go faster on 175s (31mph in a heavy cross/headwind on a beach side road, on the mountain bike, with 2" knobby tires and front suspension) than on 170s (tailwind one way 3 lane road, on a Giant TCR road bike). I had a great sprint with the 167.5s but couldn't stay on when stuff got hard in crits. With 175s I could stay in the group better but lost a bit in the sprint.

[Plum Hill]

https://www.pinkbike.com/news/why-sh...9a42-119570700

[tomato coupe]

Originally Posted by Plum Hill

https://www.pinkbike.com/news/why-sh...9a42-119570700

For those that don't have time to read the article:

"The main takeaway here is that sprint power output varied very little, especially across the middle three sizes (145, 170 and 195 mm) which is a much wider range of crank lengths than typically used."