Crank length.

So, 175 or 170 douse 5mm really make a difference?

Help me understand.

No science to help you understand but I accidentally bought a pair of 165mm cranks and they felt weird. Would stick with what you know or try out first…

Those who have no issue with crank length will tell you it makes no difference. However, I’ve recently swiched all my bikes from 175 to 170 and my knees are thanking me. So much so that I’m planning on swapping the 172.5 that come standard on most road bikes my size with 170 before I’ve even ridden it. Maybe 2.5mm won’t make a difference but I don’t fancy finding out the hard way.

If all riders had the same length legs, all using the same length cranks would be reasonable. We don’t, it isn’t. Over-long cranks are likely to be more a problem than too short – if your cranks are too long your knees bend too much at the top of the stroke. I suspect the main reason people put up with ‘standard’ length is that shorter cranks are hard to find. I use 180 and my wife uses 155. The downside of shorter cranks is less leverage, so you may need lower gears.

175 on the cross bike and mountain bike and 172.5 on the road bike.

I bought a new road bike earlier in the year and spec’d 175 mm cranks something felt wrong and it wasn’t until I’d done a few rides I found they’d fitted 172.5’s. Once my LBS changed them to the 175 everything felt right. I wouldn’t have believed you could notice 2.5 mm.

What Greybeard said!

I use 170mm cranks and 175mm cranks just feel awkward. Longer cranks require a greater range of motion in the knee and I guess the reason you can feel the difference is because the differences in hip and ankle range of motion to accommodate a longer crank have quite a large knock on effect to knee ROM.

Just speculating but I’d say you could notice a 5mm crank length difference.

Been thinking about this a bit myself. getting bad knee pain on the Road Bike but not on the Hybrid. Difference is crank lengths, they are shorter on the hybrid. Just ordered a set of 170mm’s to replace the 175mm’s on there.

Maybe just part of getting older…

I have longish legs and use 175 on the road and mtb, when at newport the cranks were 165? and the difference was very obvious! Much much easier to spin.

I always had 165’s due to bikes with low BB’s. Recently I’ve had 2 new bikes, both with 175’s.

I can’t tell any difference. I’m 6’2″.

The general rule is the bigger you are the bigger cranks you use as stated above about the knee bend.

The best thing to do is just ride it and see how you get on.

Shorter cranks can also to help your cadence.

Its a bit of a read but interesting…

http://www.powercranks.com/cld.html?gclid=CJHK3PXW0bsCFROhwgodCHMAUQ

I have gone with 165 from 175 and am pleased I did. I tried 180mm as a cheaper unpopular size from ebay and had knee pain before I read the article.

SRAM needs to make 165mm XO1/XX1 and ditch the 175mm crap.

I once bought a bike where they had fitted a 172.5 on the left & a 175 on the right. Didn’t realise what they had done for 3 years….

The general rule is the bigger you are the bigger cranks you use as stated above about the knee bend.

No, not bigger but having a longer leg length.

http://www.machinehead-software.co.uk/bike/cranks/cyclist_crank_length_calculator.html

Although Sheldon reckons you short-arses should just deal with longer cranks, as per stairs and the like 🙂

http://sheldonbrown.com/cranks.html

I’ve used 175mm and 170mm with no issues. New CX bike has 170mm mainly to help in reducing toe overlap.

as a confirmed stumpist I like short cranks, currently have 165s on all my mtbs. I should be 152mm ish.

Shorter is better – 165s on all my bikes.

But then I am a short ar$e.

I’ve only just realised (after about 5 years) that the crank arms on my road bike are 170mm and the arms on my MTB are 175mm.

throw me in the “it doesn’t matter” bin.

175 on mtb and 172.5 on road and CX works for me. My track bike has 165 which was awkward on my dodgy knees first few times.

I think I can tell the difference but it makes no difference to me.

So, 175 or 170 douse 5mm really make a difference?

Help me understand.

Help us to help you.

How tall are you? Stumpy legs? What bike?

170 all round for me. Apart from 165 on my DH bike…

Of course its not 5mm its the combined total =10mm for the pair, I reckon I notice and appreciate the difference in describing a slightly smaller circle with my legs and having my feet a wee bit closer together when the cranks are levelled… YMMV

It works out as 10mm as you’ve got 5mm difference in each crank arm. If you moved your cleats 10mm back or forward it would feel hugely different.

I’m 5’10” with 175 on the HT and beater road bike, 172.5 on the nice road bike. I find it more stable a base to have a wider stance for landings/pumping etc. For spinning I find it feels better to have a tighter circle as your upper knee is less bent when pedalling at the top of the stroke. I briefly tried out track with 165mm cranks and it felt odd but good when flat out.

I reckon more XC style riding would suit a shorter crank for spinning and hill climbing, more trailsy/jumpy/DH riding would suit longer for stability.

When herself had a couple of road frames built for her in the late 90s they were both designed for use with 155 cranks so had low bottom bracket heights and short front centres.
I’ve read recently that Mike Burrough’s current plan for taking over the world involves that exact same approach.

Still waiting for the guy to turn up on this thread, who can tell the stiffness difference between 175 and 172.5….

Was a classic STW post.

Good point Chakaping.
(Wish I could work out how to do the quote thing)

I got a 840mm inside leg.
1690 tall(or short really)
45 years old.
And I always put a short stem on.

I’ve not got a road bike. (Yet)
29er trek hard tail
06 Spc fsr
Soon a Fuji Outland RC29 frame 17″

When I rode and did all the type of racing, time trial road race track and mtb, 25 years ago I damaged my knee with having the spd release too tight. So now I’m back on the bike after a long brake I’m now using non clip less pedals. Just in case. I used clip less for 6 months, very loose release set up but felt a twinge so did not want to risk it.

Stoddys – you are shorter than me, with longer inside leg. I think you’ll be fine on 172.5 or 175. You might find 170 a little short but would probs not notice after a few rides. I suggest the key is to have similar on all bikes.

I do have 175 on all my bikes at the moment.
I might try 170 just to see if it feels better. I was not sure you could notice it. Hence the question.
Thanks all.

I’m 2in shorter inside leg than you and my preferred option is 175mm if BB height allows it.

I have 6 different crank length on my cycles. Can definitely tell the difference between the longest and the shortest, and even between the shortest and next shortest, but given I’m standard male height of 5’9″ and happily use 125 cranks suggests the idea that you have to use longer cranks because you’re taller is a bit of a myth. Oh and I’m not totally sure I could tell the difference between 170 and 175 I have on a couple of different bikes -let alone between either of those and the 172.5 I have on several others!

I’m standard male height of 5’9″

Maybe in Asia 😉

Although Sheldon reckons you short-arses should just deal with longer cranks, as per stairs and the like

He says a lot more than that, most of it in favour of shorter cranks for shorter legs. The stairs argument is incorrect (not that I usually dare to disagree with Sheldon!) – when you’re climbing stairs, the height difference between your feet is one step, typically about 190. That’s the equivalent of 95 cranks, or even less because your higher foot is further forward so has less knee bend.

I’m standard male height of 5’9″ and happily use 125 cranks suggests the idea that you have to use longer cranks because you’re taller is a bit of a myth

Agreed, you don’t need longer cranks if you’re taller (or have longer legs), but you can cope with them. But if you have short legs, you do need shorter cranks, unless you want to wreck your knees.