I’m not normally one to get too bothered about crank length – over the three bikes I have I have three different crank lengths and can’t really notice a difference when I jump from one bike to the other, but they are all different bikes – 175 on my MTB, 172.5 on my road bike, 170 on my commuter/gravel/muck about with the kids hack. But I’m gathering parts for a new MTB build and on a whim bought a 165mm crank set. This was primarily off the back of a few test rides of the latest crop of Long Low and Slack bikes where I notices a significant increase in the frequency of pedal strikes, and quite hard pedal strikes compared to my current bike, so thinking 165mm cranks might help with that. But now wondering how it might affect overall gearing in the lowest gear and if I need to get a 2-tooth smaller chainring to compensate.

if you’ve already bought it, shove it on your existing bike & go for a ride ?

(my mtb has 165s on it; haven’t noticed anything in particular)

Try it but you probably do need a slightly smaller chainring. It’s easier to spin with 165s so no loss of top speed.

My Grrravel bike has 165 Zees on it (it’s that Grrr). I wanted to see if it helped my knees on long rides. I think it does. Check the effect on the gearing on Sheldon’s calculator if you want to check. You can read his thoughts on short cranks while you’re there.

My thoughts are similar to his. You notice for the first few pedal strokes, then you stop noticing. The gearing is the gearing: it’s a combination of wheel size, tyre size, sprockets and crank length. With sprockets changed to offset the change in crank length, there should be no difference to effort, but it will be easier to spin, and will be slightly easier on your knees, and you’ll smack your pedals into the ground slightly less often.

I run 165 cranks on my Bandit with thin pedals to help reduce pedal strikes.

I run 165mm on all my bikes. Find it better for my knees.

It’s 6% change in length vs 175mm, therefore 6% difference in torque.

Assume you normal cadence is 70RPM you’d need to bump up to 74 RPM to maintain the same power output.

Basically the change is insignificant in terms of output, but in terms of helping out your body, can be quite dramatic.

I also feel more stable, brings my feet more into under your COG when cranks are level. What’s more stable, standing feet under shoulders or feet in front of one another?

I’d say +1 on giving it a go.

I’ve only ridden one ride on 165 and I usually use 170 (but 175’s do my knees and hips after a hour or so)

I’d just got the cranks (some Zee 165’s) to cut down for the kids bike so figured I’d try before I took a saw and drill to them.

Didn’t notice any REAL difference… perhaps slightly higher cadence.

if I need to get a 2-tooth smaller chainring to compensate

If anything the reverse…. possibly depends what you’re riding though and if you’re a masher or prefer staying seated ….

If you’re riding what might otherwise be a push-up out of the saddle you MIGHT notice the difference in leverage … if you’re riding a marginal hill you might find you actually just stay seated more

165mm cause I’m a short arse – no issue with pedal strikes on my suppressor. there is a difference between the 175 I had before.

After a large amount of pedal strikes I swapped from 175 to 165, find it a lot easier on the old joints, will be swapping my other set to 165 when they need replacing.

The whole torque thing is absolutely correct, BUT, unless you are at the peak of physical fitness and technical prowess, you probably not going to notice any difference.
Off to measure my VO2 max rating.

just checked Sheldon’s gear calculator.

Gain ratio is 3.5 for 175mm cranks, nominal 27in wheel, 32/18
Gain ratio is 3.5 for 165mm cranks, nominal 27in wheel, 30/18

So your 2 teeth should be bob on for an adjustment.

165mm cranks here (another shortarse)- no problems at all. Switched from 175s that knackered my knees and didn’t notice any effect on gearing. Everything was just better.

165mm cranks here (another shortarse)- no problems at all. Switched from 175s that knackered my knees and didn’t notice any effect on gearing. Everything was just better.

From experience and reading, there is a sort of cut-off band at the bottom but sharp cut-off at the top…

I know 175’s knacker my knees and hips and 170’s don’t… so 175 to 170 or 175 to 165 is “everything is much better) but perhaps if I tried 160 I’d start to notice???? Never tried 172.5 but that extra 10mm (5×2) is enough to be night and day for me whereas 170-165 I just have a slightly higher cadence.

I actually tried 152 mm the other day for 30 mins … (although on kids bike and saddle way to low and on a bike park so not really a straight comparison ) and that did seem to affect pedalling on the way up…

I’ve used 140’s quite a bit on the trainer… because its actually easier just sticking a long seatpost into the kids bike than all the messing about

That really affects Cadence! I find myself spinning at 120 rpm

At 175cm tall, I found 155mm cranks noticeably bad and abandoned the experiment quickly.

🙂

From experience and reading, there is a sort of cut-off band at the bottom but sharp cut-off at the top…

I’d agree with that^

Currently seeing if I can live with 170mm on my new bike.

5′ 4″ 165mm. cranks mtb, 160mm. road bike. Once you get the hang of spinning a little quicker hills become a lot easier. I’ve been using short cranks for 15 years……before it became fashionable!

Thanks

if you’ve already bought it, shove it on your existing bike & go for a ride ?

That is of course the correct answer, but I’m still waiting for the new frame as I don’t want to sully them on my current bike! I want to wait for a nice fresh bike build. Silly I know.

I am a bit of a spinner anyway – on the flat my natural comfortable cadence is around 90 – 100 rpm, obviously less when things go steep, so shorter cranks might be more beneficial.

Gain ratio is 3.5 for 175mm cranks, nominal 27in wheel, 32/18
Gain ratio is 3.5 for 165mm cranks, nominal 27in wheel, 30/18

I did use the Sheldon Brown calculator but didn’t go the additional step to equate to chainring size equivalence, I worked it on some overall gear ratio number, so got two numbers, but I can’t really equate that to real life, but the equivalence to chainring size is useful – thanks.

Will be interesting experiment to see if I do really notice a difference on the same type of bike.

the difference between 175 and 165 is only 5%, not really enough to call them ‘long’ or ‘short’

wobliscott – gear ratios/inches go on sprocket size to sprocket size. If you’re playing with anything else, like wheel size, tyre size, crank length, you need to look at gain ratio.

What’s more stable, standing feet under shoulders or feet in front of one another?

Err, feet in front of one another slightly apart? Unless I’ve missed something?

Feet further apart is definitely more stable. Feet closer together allows more pumping power to be generated. I’m still not sure whether I prefer 165 or 170mm but they’re certainly better than 175mm and I have pretty long legs.