Downsizing crank arms: Anyone done this?

[verbs4us]

After a routine fitting, my fitter suggested sliding the saddle 2 cm aft to improve the efficiency of my stroke. Severe pain, which felt like hip flexor strain, ensured, so he said to move it forward 1 cm, and the pain went away. 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.

From what? Could have chosen the wrong parents or it might have been from crashes in a mis-spent USCF youth. Either way, he recommended going with shorter crank arms. So we want from 170s, which I have ridden since Moses was boy, to 155s. Fifteen millimeters doesn’t seem like much but, boy, have to retain whole new muscle groups and the hills just feel steeper. Has anyone else made this kind of change, and for what reason and with what result? It’s kind of remarkable when you think about it: we tweak saddle position to within microns, as well as handlebar height, stem angles and cleat position. But we seem to more or less leave the crank length alone.

[EB]

I used to ride 175s at fitters advice, but now am on 170s for mountain bikes and 172.5 for road/gravel. I’ve never noticed a difference after adjusting saddle height, other than reduced pedal strikes in the case of mountain biking.

I’m fairly sure I could go to 165 and also not notice anything. For me at least, this fit parameter doesn’t seem to matter much relative to others.

As I recall most of the research on this shows that it doesn’t matter at all from an efficiency standpoint.

One reason the hills might feel steeper is that shorter cranks have less leverage (literally). You might try sizing down your chainrings if possible to offset the change in crank length.

[verbs4us]

Thanks Eli. Yep, thinking about going to a 110 spider instead of the 130 that's on there now, which has 38t as the smallest inner ring size. That's one good thing about TA cranks--a gazillion options.

[John H.]

I have gone from 175 to 170 over time.
Forward thinking fitters say that crank length is a fit parameter more than power/leverage (unless you are trying to win a stage race like the vuelta that has super steep climbing finishes).

[Hellgate]

After 35 years on 175s I'm moving to 172.5 with the new bike and eventually 170s. In ultra events I get past 5 to 7 hours and my hip flexors are cramping. I'm also moving my whole position forward 3mm. It doesn't sound like much but I'm hoping provides what I'm looking for.

For what it's worth my CX bikes were 170s. I could move from warming up on the road bike to the CX bike and not notice a thing. However, I suspect I'd notice 155s.

Good luck with the changes.

[Turkle]

I personally am moving from 175-172.5 because the shorter cranks allow me to ride down in the drops without my knees bouncing on my chest. I have short arms, long torso, average legs so my fit is a little weird but the couple millimeter difference pays big dividends when I'm putting the hammer down.

I was actually shocked when I was getting my fit and he made the cranks a little shorter. The difference was immediately noticeable and made a huge difference in the drops.

[bqdillon]

I have had a range of crank sizes from 155 to 175 and prefer 160-165 because of my height/ leg length (5’1 with a 29” inseam) I’ve never been x-rayed for damage but I’ve noticed less pain and a less awkward cadence with the shorter cranks. The 175s were terrible and felt like my whole leg movement was rocking my body and overextending my knee. I’ve adjusted my saddle height appropriately for all these changes as well.

The 155 is sort of a test to see how short I can go and if it’s beneficial but my cadence has to be so much higher and, like you said, it feels like I’m engaging different muscles. Not sure how long I’ll keep them and will probably swap them out for a 160.

[dgauthier]

Originally Posted by verbs4us

(...) 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 (...)

Wow, it sounds like that fitter really knows his stuff! Would you care to share his name?

[smead]

I rotate through a stable of 8-10 bikes with cranks ranging from 165-175, most 172.5. Over the years I've liked the 165s more and more to where I wish they were all that size, 170 tops. I'm no sprinter, like the revy fast spin feel of shorter cranks, can't say I notice any penalty on climbs, and I'm sure my old knees appreciate the smaller circles.

[Peter P.]

If you didn't have pain in your original position, why didn't you just return the original position and save the money on new, shorter cranks?
You know; if it ain't broke, don't fix it.

[verbs4us]

Originally Posted by dgauthier

Wow, it sounds like that fitter really knows his stuff! Would you care to share his name?

You can see from the banner, he's been doing this for a while:
https://www.happyfreedman.com/

[verbs4us]

Originally Posted by Peter P.

If you didn't have pain in your original position, why didn't you just return the original position and save the money on new, shorter cranks?
You know; if it ain't broke, don't fix it.

Didn't bother you with the whole story. Had a morton's neuroma and sometimes lateral knee pain. All the change was more preventive than anything.

[Plum Hill]

I’ve been having trouble with knee replacements. Fitter recommend 165 crankarms instead of the 172.5 and 175 I had been riding. Wow. What a difference. Very easy to spin; makes pedaling a joy.
I have noticed less power on hills, but I had lost that after the surgeries.
Between shorter cranks and long legs, I’m out of aft adjustment on the saddle. Clamp is getting close to rail bend.

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.

[smead]

Originally Posted by Plum Hill

I’ve been having trouble with knee replacements. Fitter recommend 165 crankarms instead of the 172.5 and 175 I had been riding. Wow. What a difference. Very easy to spin; makes pedaling a joy.
I have noticed less power on hills, but I had lost that after the surgeries.
Between shorter cranks and long legs, I’m out of aft adjustment on the saddle. Clamp is getting close to rail bend.

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.

[cmg]

So did the change improve the pedaling efficiency and elevate pain?