Going from 172.5mm to 170mm cranks

[Soloist604]

Hi all,

So a crankset that I recently bought only comes in 165mm, 170mm, and 175mm sizing. I've generally been running a 172.5mm on my bikes for years. I ended up buying the new crankset in the 170mm size and did a test ride yesterday.

Didn't think I'd notice a difference but when out on the test ride everything just felt "right". I couldn't have imagined that a 2.5mm change would make that much difference, but something just felt better. The q-factor on the new cranks is also about 5mm wider so this could also have contributed.

Thoughts from those with a bit more experience appreciated.

[ducati2]

What do you need to know if it felt “right”

[fignon's barber]

Different crank length also slightly changes your bb-saddle height feel as well.

[Ken Robb]

Check the archives for MANY opinions on this subject.

[shinomaster]

I started out in 170's and rode them for years, then I switched to 172.5's for cycocross and have them on 4 bikes. I've thought about switching back as it them helped me spin better but I don't think I can easily replace all my campy cranks.

[skouri1]

You have to make some adjustments in my experience but they are not prohibitive. Rode 172.5 for many years. Think I like the 170 better. Slightly higher saddle. Kept the same setback as that feels like the appropriate balance point . I would err towards shorter

[eddief]

If it makes you happy it can't be that bad.

[fourflys]

Originally Posted by Soloist604

Hi all,

So a crankset that I recently bought only comes in 165mm, 170mm, and 175mm sizing. I've generally been running a 172.5mm on my bikes for years. I ended up buying the new crankset in the 170mm size and did a test ride yesterday.

Didn't think I'd notice a difference but when out on the test ride everything just felt "right". I couldn't have imagined that a 2.5mm change would make that much difference, but something just felt better. The q-factor on the new cranks is also about 5mm wider so this could also have contributed.

Thoughts from those with a bit more experience appreciated.

cue all the "subject matter experts" chiming in that you really don't feel a difference, the feel is from something else, some long engineering thesis on crank length, etc..

Glad it made your ride better, that's all that matters! If it works for you, it works period..

Ride on!

[wooger]

Originally Posted by Soloist604

Hi all,

So a crankset that I recently bought only comes in 165mm, 170mm, and 175mm sizing. I've generally been running a 172.5mm on my bikes for years. I ended up buying the new crankset in the 170mm size and did a test ride yesterday.

Didn't think I'd notice a difference but when out on the test ride everything just felt "right". I couldn't have imagined that a 2.5mm change would make that much difference, but something just felt better. The q-factor on the new cranks is also about 5mm wider so this could also have contributed.

Thoughts from those with a bit more experience appreciated.

5mm extra q factor is probably as big an effect on feel than the crank length.

[oldpotatoe]

Originally Posted by Soloist604

Hi all,

So a crankset that I recently bought only comes in 165mm, 170mm, and 175mm sizing. I've generally been running a 172.5mm on my bikes for years. I ended up buying the new crankset in the 170mm size and did a test ride yesterday.

Didn't think I'd notice a difference but when out on the test ride everything just felt "right". I couldn't have imagined that a 2.5mm change would make that much difference, but something just felt better. The q-factor on the new cranks is also about 5mm wider so this could also have contributed.

Thoughts from those with a bit more experience appreciated.

Really doubt, on a test ride on a completely different bike, that 2.5mm had anything to do with it 'feeling right'...IMHO.

BITD we did an overhaul on a lady's really sweet pink DeRosa..On taking the cranks off(SuperRecord, old school), we noticed one crank was 170mm, the other 172.5mm. Customer had no idea..bought the bike used..was very happy with it...

[kppolich]

Going to shorter crank arms is mostly a Tri/TT thing due to the hip angle. Sure, a few mm's could help on a crit or something where cornering and pedal strikes could happen too.

Bike fit should be the first step in this process.

[Soloist604]

Thanks for all the replies. I'm also of the same opinion in that I don't necessarily think I'm a "good enough" cyclist to notice the 2.5mm shorter length. I'm assuming the q-factor may have had more to do with the "right" feeling. Was thinking about moving a bunch of bikes over to 170mm but looks like I'll save the $$$ instead

[fourflys]

Originally Posted by Soloist604

Thanks for all the replies. I'm also of the same opinion in that I don't necessarily think I'm a "good enough" cyclist to notice the 2.5mm shorter length. I'm assuming the q-factor may have had more to do with the "right" feeling. Was thinking about moving a bunch of bikes over to 170mm but looks like I'll save the $$$ instead

I agree, not sure I'd spend much to replace my 172.5 cranks with 170.. but, going forward, that will certainly be a consideration for me..

[fourflys]

Originally Posted by kppolich

Going to shorter crank arms is mostly a Tri/TT thing due to the hip angle. Sure, a few mm's could help on a crit or something where cornering and pedal strikes could happen too.

Bike fit should be the first step in this process.

agree on the bike fit, but the rest of this is bike fit thinking from 20+ years ago.. there seems to be a LOT of research done that shows most of us are riding cranks that are too long (at least if we are trying to optimize).. and not just 2.5-5mm too long.. I don't know if it makes that big of a difference, but folks who a lot smarter than me on bike fitting seem to think so..

[Mark McM]

Originally Posted by kppolich

Going to shorter crank arms is mostly a Tri/TT thing due to the hip angle. Sure, a few mm's could help on a crit or something where cornering and pedal strikes could happen too.

Bike fit should be the first step in this process.

There are other factors that may favor shorter cranks. This includes hip angle impingement, and knee issues (longer cranks increase knee angle, and more acute knee angles increase stresses in the knee). In any case, the one-size-fits-all approach to crank length may not work with all people*.


Although cranks are available in a few lengths, the range of common crank lengths has been quite narrow - a range of 170mm to 175mm is a difference of less than 3%. The range of human heights and leg lengths vary more widely than this (just the difference in average heights between males and females is about 9%, and variations within each sex is larger than this). The range of common crank lengths is so narrow that it is effectively one-size-fits-all.