Does the 5mm make such a difference? Maybe I should ask the wife!! 😀
I usually use 175mm cranks but I`ve seen some 170mm that I like, is it just a case of pulling the seatpost out a bit further to compensate? Or are they just designed for people with short legs?

crank lengths iirc are determined by the length of the rider’s femur?
used more religiously with road bikers.
noticed smaller mountain bikes are using 170mm cranks as standard these days.
whether you’d notice the difference between 170 and 175 – i couldn’t say.
i certainly don’t.

I have one of each on my bike. Can’t tell unless I concentrate when riding on flat tarmac

I have a set of 175mm’s on my SS and 170mm’s on my full sus. I can’t really feel any difference when riding, but psychologically I wouldn’t want anything shorter that 175mm for the SS… leverage?

How tall are you? Are you long legged or short legged for your height?

Most bike are fitted with 175’s as standard, though a lot of riders “should” be riding 170’s if the correct crank length is used as worked out (there’s a formula somewhere, can’t remember exactly what it is though).

I personally prefer 170’s anyway, they make my knees hurt less and allow me to spin a bit faster, and that’s despite being “average” height at 5ft 10-11″.

I notice quite a difference, many don’t. You won’t know if they are better for you unless you try them. You could get some 170mms and ride them until the chainrings wear out. I doubt you’ll notice enough of a difference to really hate it for a season and if you do, you can sell them on. One advantage, other than being quicker to spin, is that you get more pedal clearance.

ok im a woman and only 5ft small ! my bike frame size is soo tiny …(13 inch) and my cranks are 170mm.,,, i was after upgrading mine and saw some race face cranks (second hand in the lbs but they were 165mm so even smaller than my own ? i didnt get them ….. so is 170mm correect for a 5ft woman then ? its what came with the specialized bike anyway…

so is 170mm correect for a 5ft woman then ?

no, 165 or even 160, but one of our smaller women riders ( ~ 5′) tried 165s and didn’t like them – I think she said they hurt her calves or thighs. Perhaps it’s just what you’re used to.

Im 6ft so I dont know if im too tall for 170mm. However its for a spec enduro, so the extra pedal clearance would be good :D. I might take a chance and try em.

so simon are you saying the bike shop has put the wrong size cranks on my bike ? is 170mm too big for a 13 inch frame bike ??? im actually quite used to them now, but wen you look at the bike from a distance- i have always said the cranks look too long for the frame, yet there still is plenty of clearance …

I went from 175mm to 170mm and can’t tell the difference apart from the fact that I don’t clonk things quite so often.

so simon are you saying the bike shop has put the wrong size cranks on my bike ? is 170mm too big for a 13 inch frame bike ???

It seems the length is not critical. You might find a shorter crank more comfortable, but a research paper I found said that tests showed it doesn’t much affect pedalling efficiency

i went for 170mm on my pace for added clearance, but cant say i notice the difference to any others.

i’ve got 170’s on my full suss and i can’t stand them. can definately tell the difference.

road bikes the 170’s and 172.5’s feel right and can’t tell the difference!

I have done A LOT of research in this area! I’m a woman and 5’4″ and I have slightly dodgy knees – hence looking into all of this.

I used to use 175s and now have 165s. My knees used to really ache after riding with the 175s and now with the 165s they don’t. I also noticed I’m able to spin much faster with the shorter cranks and that they feel generally more comfortable.

I wouldn’t consider going back to 175s now (although owing to money saving I am using 170s on my ss bike, but will change them if I ride it enough and my knees start hurting)

Elaine-anne: you probably should have gone for the 165s as I think you’d notice you’d be able to spin quicker and they’d probably be more comfortable. But don’t stress too much, as long as knees aren’t hurting the 170s will be fine.

Plus, it has nothing to do with the bike size really (well only in it’s relation to the rider) I think you’d be hard-pressed to notice 165 cranks looking any shorter from a distance!

Anyway, Sheldon Brown bascially says that having crank arms that are too long for you may well put strain on your knees/hips, but that having ones that are too short for you shouldn’t have any negative effects. (Have a look at his website for more details. Being short – 165s are technically still too long for me, but short of getting some custom made they’re the best solution and really have made a huge difference for me.)

Hope that helps!

I always rode 175s but got given a set of 165 steel cranks for my all-round full sus (since transferred to my trials bike) and I didnt notice much change, but when I converted back to 175 the difference was very noticable. Not sure how much difference only 5mm would make, feeling-wise.

i went round the houses on this subject a few summers back when i needed a new chainset, always rode 175 but the best deal i could find was on a 170mm chainset.

after extensive googling and forum posting, the consensus weighed to the side that i would’nt notice the difference. the reality, however, was that i did’nt get on with them. they spinned up to fast for me, i like a slow winching cadence. sold them after the summer and ride 175 on all my bikes now.

mountain monkey :::: its funny you should mention that if cranks are too long for you then it could put strain on your knees and hips…. cos ive had a hurting hip now for 6 or 7 months , but it doesnt hurt when i ride, only normal walking can i feel the hip (dull ache….
so would i be able to feel any difference if i went from 170mm down to 165mm or even 160mm ? if i went shorter would i have to pedal any harder ? im not much good with crank sizing so any more sound advice wud be great …. cheers

i asked this qustion last week. i bought the 170 over 175 could not tell the difference

Elaine anne – bless you a sore hip for 6 months doesn’t sound great. Do you notice it hurting more after riding? My knees didn’t hurt when riding – just after.

In term of feel, I don’t know how much difference you’d notice (its subjective so hard to say), but it might be worth a shot to see if it helps. As you’ve got gears (presumably?!) you shouldn’t have to pedal any harder/easier – but shorter cranks allow you to be able to spin faster (which I think’s a good thing as you can gain momentum approaching something technical without changing gear).

Although you won’t necessarily find it ‘easier’, in theory you should need to use your easier gears more because you’ll have less leverage. I have to admit though, I’ve personally not really noticed this (I still don’t use my first 3 granny gears).

Like I said, it might be worth going down crank sizes just to see if it helps your hip. Thing is though, there isn’t a lot of choice. Only Shimano XT and XTR seem to do 165mm cranks and I haven’t found anyone mainstream doing 160mm.

Although crank length might help – it’s also worth considering your saddle position, as this can also cause issues.

Hope that helps! If you have anymore questions please feel free to ask!

so would i be able to feel any difference if i went from 170mm down to 165mm or even 160mm ? if i went shorter would i have to pedal any harder ? im not much good with crank sizing so any more sound advice wud be great …. cheers

It really does depend on the person. Are you the kind of person to notice small changes in setup or not? Personally for me the switch between 175s and 170s was like night and day, but that’s mainly cos my knees used to hurt after a ride, and they no longer do now I’ve switched! Plenty of people I know though wouldn’t be able to tell you how long their cranks were, or indeed tell the difference between one length and another.

Can be a ballache when it comes to bike spec, cos 99% of the time any bike, new or used, in my size (Medium, or 18″ roughly usually) will have 175mm cranks fitted to it!

Elaine anne – bless you a sore hip for 6 months doesn’t sound great. Do you notice it hurting more after riding? My knees didn’t hurt when riding – just after.

I used to get CHRONIC pain in my knees after a couple of hours on the bike, to the point where on a couple of rides I ended up getting pulled along by mates for the last drag home!

It’s worth saying that I also changed pedal type from Shimano SPD’s to Crank Bros Mallets/Candys/Eggbeaters which did help a bit too. But the biggest single change to help ease the pain in my knees was the crank length.

But again, as has also been mentioned, you may not notice the slightest bit of difference! Some do, some don’t.

Until recently, i had 4 bikes, with 4 different crank lengths – 165/170/175 and 180! What a mess! But you can really feel the difference. The 165s span up very quickly, so quick aceleration, whereas the 180s had lots of torque and leverage. My inside leg’s 32″ and 180 was really too long , but useful for singlespeed. My advise to people with even remotely dodgy knees is don’t ride singlespeed (Mountain Monkey!) and keep to cranks on the shorter side of safe. I’ve settled on 175 for mtb and 170 for road and all is good.
Going back to the original post, i’d say 170mm would be fine if you’re leg is 33″ or below

I have singlespeeded my road bike 2 weeks ago. And I have discover that the crank I though was a 175mm was in reality 170.

Bike is 11 years old, and if it wasn’t for reading it on the crank I would have never noticed it

Reluctant, I hear you and do actually agree. However, my road bike is singlespeed (170 cranks) and I never get sore knees after riding – but then admittedly I’m not trying to drag it up mountains. I keep my cadence relatively fast and so there’s rarely any additional strain on my kness, in fact I think I strain them less because I can’t change in to a gear that’s too hard, instead I spin along like a crazy thing!

Offroad though, I’m inclined to agree, BUT I’m taking it on relatively flat stuff (I’ll leave the trail centres for my geared bike) I’m also about to go down to a 32-18 ratio, which should be a lot more spiny than my current 32-16. I have also bought some cheap 170 cranks for it replacing the 175s.

So, I’ll see how I go – I’m really not planning on using tons of leverage to slowly grind up hills. I’ll just be whipping along the flats like a fool! 😀

Cheers for the advice though – if my kness do start suffering, I promise to stop! 🙁

Like mboy and moountain monkey I went short and have less knee pain. I also have fewer pedal strikes – big plus. Got 170mm on all my bikes. I’m 6ft

If you mash, then it makes sense to go long. If you spin – go short. Some are more efficient at low cadence so prefer to mash. I don’t.

FWIW there is no evidence at all behind the algorithm that femur length determines crank length. Not to say there isn’t proof, but it hasn’t been demonstrated yet.

if your knees are okay and you are on a geared bike then it makes **** all difference….just changes the gearing slightly….but you have gears so who cares