switching to shorter cranks?

[cuda]

I'm currently ridding a 175mm Easton on a compact that I got for a song. I switched from a 172.5. In both instances i'm riding a 50/34 and 80%/20% road / off road on a Pivot Vault (CX)

I now have about 700 miles on the crank. I like the added torque and the (seems like) ease of pushing a bigger gear for longer periods once I wind it up. I also like how it climbs.

Lately, i've been experiencing a little bit tightness in the top of my right knee and wondering if its due to running cranks that maybe are not "optimal."

Of course, maybe its just age (60)history and the "usual" tendonitis that seems to be an inseparable part of all my favorite activities.


I did some reading last night and found mention of riders mentioning going from 175mm to 170mm and seeing nagging knee problems alleviated.

Anyone here switched to smaller cranks? What has been your experience?

sorry if this should be in "bike fit" but i would rather get experience vs opinions and "science-type" answers.

thanks
cuda

[notsew]

I generally didn't buy into the crank/knee thing, but years ago I had some knee pain and happened to get a deal on a 170...poof, pain gone.

A few months ago I wanted to go compact and got a screaming deal on a 175, within a week the knee pain came back. So from my experience it makes a real difference, YMMV obviously.

Btw, anybody want to trade me a 170 for a 175 Chorus 11 Compact? :banana:

[eddief]

and lots of them have suggested it works in general and especially for lessening stress on the knees. recumbent riders do this almost 100% of the time due to the stress of having a fixed back position and the amount of extra stress that puts on the knee joints.

i never rode 175s but mostly 172.5. when i experimented with bents i went down to 165s. when i came back to upright bikes i settled on 170s. just recently i rode with 172.5 cuz that's what the bike came with. sold that crank and installed 170s and all was as it should be.

you can't know until you try it.

[mhespenheide]

I'm 6'4" and went from 175's up to 180's about 10 years ago. It took a couple years before I was fully comfortable with them and spinning back at normal cadences. Then, a few years ago I put a set of 177.5's on a new bike build and liked them almost immediately. Now that's all I'm riding. I suppose I should try out some 175's again, but since I'm not having any knee issues, I'll probably stick with the 177.5mm length for now.

[ChainNoise]

Started with 172.5, went to 175 rode that for a year. Had severe knee pain after a while and switched to 170s on a whim. Pain gone, can now ride all day with zero issues. I kinda wanna try 165s just for the hell of it.

[bcroslin]

I recently switched back to 170's from 172.5 so that I can get a tiny bit more hip rotation and I've noticed I'm so much more comfortable. I still have 172.5's on my gravel bike and I can feel the difference but it's not a deal breaker.

[Moyboy]

Switched from 172.5 to 165 due to by hip not being open enough to the top of the pedal stroke. I eventually went back to 170 and have stayed there. One benefit was a faster "normal" cadence by about 2 - 3 rpm.

[stien]

I've been on 165s on my road bike recently. It does increase your gearing a slight amount and I've found myself really slogging up local hills vs my wife with similar gearing.

I might end my 165 experiment and head back to 170 or 172.5 if someone wants to trade locally. 6800.

[cuda]

thanks for all the response, sounds like its worth giving it a try.

[Jef58]

I switched from 170 to 165 cranks. Sharing a single speed that has a 165/48 tooth crank, it felt 'better' when I rode it, so I tried it with the road bike. Ended up going with a Praxis sub-compact 48/32 in 165. I would love to have a Campy 165, but so far the Praxis is pretty darn good. All in all, I'm pretty happy with the change.

[sfscott]

I run 170s on road bikes.

My MTB has 175, which was kind of the default size available. I am having a lot of issues with pedal strikes, particularly on abrupt inclines after declines (rollers.)

I have added a fair bit of air to my rear shock, which should lift the BB up some, and a tech at the LBS suggested riding with the rear shock in "trail" setting.

Wondering if a move to 170s would help the pedal strikes--and what I reallywould be losing in leverage.

[thirdcog]

Certainly enough replies here from experience, but I'll add one more. I've only been cycling for about 5-6 years, so take this with a grain of salt; however, I recently made this jump to shorter cranks...almost on a complete whim.

Over the last few years I've bought and sold several bikes (some built with components I've acquired here...so thanks!), and in doing so learned a lot about fit and generally what works or doesn't for my odd proportions.

I never really gave much thought to my constant hip pain and lower back pains being related at all to crank arm length. I went through tons of saddles and bike set ups and so forth.....sometimes finding a workable set up.

Fast forward to a recent bike purchase, the factory crankset was one of those Shimano 510 non-level-specific cranks. Heavy, but decent enough. I knew I wanted to swap it out with something lighter, like an ultegra crank or similar. The bikes I've had all have had 172.5 length arms (54cm-56cm framesets).

So, I ran across an r8000 crank with the gearing that I perfer, except with 165 length arms. I had always been told that making a drastic jump like that would be ridiculous (laughs all around) and jokes would follow.

The deal on the crank was so good that it would have been stupid to pass up. I did some quick internet research for threads just like this one and kept finding experiences that all paralleled (at least for road bike applications). Seemed the shorter crank arms resulted for most in less pain in some weak areas, better cadences, HR, on and on.

I still doubted it, but jumped on the deal and thought it would be easy enough to try out and re-sell if needed. So I did exactly that.

172.5 to 165 seemed to make sense looking at my fit/proportions/current bike geo, etc. Most everyone in person in my orbit all said "no way, that's insane...you're going to hate that and lose all leverage/speed"

Long story short, I popped the crank on the bike easily, re-measured things and adjusted saddle height and position accordingly, and went for a test spin.

Immediately, I noticed that I felt "right" on the bike, and it SEEMED like I had more power. My pedal stroke felt different....no more dead spots. I have hills in my hood, and ramped up those. It actually felt more controlled, and LESS difficult. Out of the saddle didn't feel drastically different, although I did notice an extra jump in gears in terms of shifting for those efforts. Everything felt more connected.

It has been several weeks with this set up and I've found that I am less fatigued (relatively), I can breathe better, my hip no longer hurts, my lower back pains seem to have evaporated. I can also stay in the drops longer and more comfortably because of that hip angle change.

It doesn't feel like driving a clown car (which is what a fellow cyclist said here) or bizarrely ridiculous. It feels like what I imagined a good fitted bike would feel like, where it is part of me, not this thing I'm wrestling over the miles.

I won't say this is the experience for most, or anyone else, but I can say that for me, it was a massively positive move. I would joke about "now if my engine was just stronger" but honestly, it has gotten stronger over the last few weeks just from what seems to be a much more efficient expenditure of energy on the bike. Maybe it's all just placebo effect. But I'll take it.

It was a risk that has paid off greatly, and I'm glad I looked at my own proportions, did the numbers and looked at the possibilities.....and took the chance.

Hope it works out for any who try it. Everybody's body is different, of course.

[John H.]

I rode 175 cranks from the early 90's until 2005- As shoes and pedals evolved my saddle height seemed to get lower and lower.
I moved to 172.5 cranks right before Redlands classic in 2005. No issues. In fact I rode great there. Stayed on 172.5
I also used some 172.5 cranks on the mtb when Shimano used to produce XTR cranks in 172.5. They were somewhat hard to come by- But worth tracking down.
When everything went double and single chainring I had no choice but to go back to 175- I figured 170 was too short for me.

Fast forward to 2019- I have an aero road bike with an SRM Origin crankset on it. With this crank you can move the pedal inserts to use the crank as a 170, 172.5 or 175.
I had been using Shimano SPD SL pedals. I decided that I would try Speedplay Zero again (that is another story). The Speedplays have less stack- about 2.5mm. So instead of changing my saddle height, I decided I would change the crank to the 170 orientation.
To my surprise it felt really good. Power did not drop off, ability to stay in the aero position was great, out of saddle accelerating was good- also, it felt like I had really good control of the pedals.
I am going to keep running the 170's for a bit-