I’ve always ridden with 175mm cranks on mountain bikes. It seems to be the manufacturer’s standard size. Was wondering what other people use? Are any benefits using 170mm cranks apart from slightly better pedal clearance and a help for dodgy knees? Are shorter cranks more suitable for the smaller rider?

It seems to me that the shorter lever arm of a 170mm crank either means you need to more grunt to push the pedals, or you need to run to shift into a larger cog at the rear. If the latter, it either means you need to increase your cadence to maintain a given speed, or go slower for you normal cadence. Not sure what either feels like in real life. Other disadvantage is that you would run out of gears on the steep inclines sooner (I currently struggle on some climbs with 30T fr and 42 rear).

Having said all of the above 170mm seems to be more normal in the road bike world.

Ran 175s on everything for years, recently swapped the FS bike over to 165mm for extra pedal clearance, my HT was still on 175, the difference when swapping between them was just about noticeable but not enough to bother me. Have sold the HT now and bought a CX bike which came with 172.5mm cranks, feels fine to me.

What’s your femur length?

(170mm here btw, 5’7″ small).

I’ve got 175’s on the road bike (i think), 170’s on the HT and 165’s on the FS.

5’9″ with 31″ inside leg.

165 on all bikes but I’m a short arse

172.5 works for me.

I read somewhere that a 170mm crank is the same length as a 175mm crank, it’s just the hole that is moved 5mm. Not sure, can anyone confirm this?

andy4d – Member
I read somewhere that a 170mm crank is the same length as a 175mm crank, it’s just the hole that is moved 5mm. Not sure, can anyone confirm this?

Depends on the brand.

I bought some 170s cos they were cheap years ago and now all my bikes are on 170. There’s just something about them that feels like it spins a bit better/more evenly and the extra ground clearance, though it might seem tiny, makes a difference.

edit: I’m 5’9″ with 32″ inseam if that makes any kind of difference.

170mm on my road bike, 172.5mm on my cross bike and 175mm on my mtb, it’s what they came with.

FWIW Wiggo rides with 170mm cranks and he’s certainly not a short arse with short femurs

170’s on the MTB. Road bike – no idea.

170 on the Spitfire (fairly low BB), 165 on the Zero AM (low BB). Legs are somewhere around 33-34″.

I think most riders are using longer cranks than ideal, especially those under 5’9″ with average proportions.

170 for me. TBH I don’t feel the difference when riding but it’s more ground clearance which can only be good. (I’m a pretty average shaped 5’10). (I used to have a 175 and 170 version of the same crank on 2 different bikes, I couldn’t tell you which version which was on which bike)

Did have some 165s on the dh bike and that actually felt weirdly short- not on pedalling or anything but my stance on the pedals was different. Felt like much more of a difference than 5mm ought to really.

andy4d – Member

I read somewhere that a 170mm crank is the same length as a 175mm crank, it’s just the hole that is moved 5mm. Not sure, can anyone confirm this?

Sometimes. Usually on cheaper models- it’s like that on my Aeffects frinstance but not on the Nexts I had. I think all the named Shimanos do it with different length arms. Not ideal really but it’s usually pedals you hit rather than crank arms ime

170 and 165mm on my dartmoor hornet and transition suppressor respectively

I went for 170 yesterday on an order as my PRocess 153 comes with 170mm due to lower BB. So thought it made sense when i ordered a set for the Parkwood that i’d order the same length so i’ve got the same on both bikes.

the difference between 175 and 165 and less than 5%, or, to put it another way, it’s a bit less than the difference between a 19″ frame, and an 18″ frame.

ie. it’s not really as big a range as we’re led to believe.

i’ve got a selection of 175/172.5/170/165, my 5foot(1) wife has 140’s.

I had this at the w/end, I borrowed a whuye901 demo bike from my lbs to try it out. I thought it felt a bit odd when riding it back from the shop. Got home and measured the cranks to find it had 170mm fitted. Jumped on one of my other bikes with 175mm and noticed the difference straight away, a much better pedaling stroke. people say you can barely tell the difference but I didn’t like 170mm at all. I’m 5’4″ with 30in leg btw.

If you like to spin at high RPM (I do as ride either fixed or singlespeed) a shorter crank makes that easier.

How much is debatable as the difference is small (in available crank options) but I would imagine comparing a 150mm crank to a 200mm crank would demonstrate it well.
You also have to use lower gears when using shorter arms as will be spinning more for same speed.

Keva – Member
I had this at the w/end, I borrowed a whuye901 demo bike from my lbs to try it out. I thought it felt a bit odd when riding it back from the shop. Got home and measured the cranks to find it had 170mm fitted. Jumped on one of my other bikes with 175mm and noticed the difference straight away, a much better pedaling stroke. people say you can barely tell the difference but I didn’t like 170mm at all. I’m 5’4″ with 30in leg btw.

You are comparing 2 different bikes..
Which probably have different geometry, reach, bb height etc..

I bought the 165’s purely for a bit of extra clearance. I bought the bike off a mate and it he had 175’s on it. When I first started riding it, although the shock was not set up properly for me, i had a few pedal strikes, I wanted new cranks anyway so bought some shorter ones. I think it pedals better now but i have stiffened up the shock now as well so it’s probably more to do with that…..

165mm on the road bikes <- anything longer and it aggravates my dodgy knee on longer spins, I can also spin better on the short cranks, gear down by a couple of teeth and it all evens out to the same speed.

170mm on geared MTBs <- enough moving around on the bike that I avoid those issues ^

175mm on SS MTBs <- spent mostly standing pedalling or coasting so dont get the knee issues of sat down spinning unless on a longer ride, and the extra leverage is nice 🙂

5’7, 29in inside leg FWIW

the difference between 175 and 165 and less than 5%, or, to put it another way, it’s a bit less than the difference between a 19″ frame, and an 18″ frame.

ie. it’s not really as big a range as we’re led to believe.

While that is mathematically true, the difference it can have on the dynamic system which is your legs spinning in circles, with all the complex muscle and joint interactions that entails can be noticeable.

Also, don’t forget 10mm off the crank length is 20mm off the diameter of the circle you have to push the pedals around. On the road that can have a big impact on your position. Cranks 10mm shorter > saddle 10mm higher gains you 20mm of clearance for the pedal at the top of the stroke, which means you can either get lower or put your hips/knees through less extreme range of motion.

For some people a few mm here and there can be the difference between crippling pain after 30mins and a 7hr pain free ride, especially when looked at as a whole system with other adjustments rather than in isolation, although for some people it will have an effect even in isolation!

Different people are sensitive to it in different ways, and even though it may only be 5% in actual numbers it can be much more significant in real life. Human bodies are funny things and they all respond in different ways.

It can also be magnified or minimised by the geometry of the bike and your riding position on it, on some bikes/positions its more noticeable than others.

Different people are sensitive to it in different ways, and even though it may only be 5% in actual numbers it can be much more significant in real life.

oh absolutely. I couldn’t agree more.

it’s just that we’re presented with a ‘choice’ of 165-175*, as if that’s a full range to suit the buying public.

we can easily buy bikes in sizes from 13″, upto 22″; to suit riders less than 5foot, to those well on the way to 7foot. More or less all of these bikes will be fitted with 175mm cranks. which is clearly daft.

(*some choice exists outside this range, but not much, and not by much)

I like 165’s im 5 11 in height – dropping from 175’s cleared up a hotspot I’d developed on my knee ..

oh absolutely. I couldn’t agree more.

it’s just that we’re presented with a ‘choice’ of 165-175*, as if that’s a full range to suit the buying public. when it clearly isn’t.

(*some choice exists outside this range, but not much, and not by much)

gotcha, in my haste I misread your post and thought you were in the “it’s only 5% so it’s irrelevant” camp, sorry!

Indeed, a common moan, the main players are very poor at offering cranks outside that narrow range.

As you say there are other options but they are more limited, although if you’re willing to look at un-tredny square taper it’s not difficult to find options from 145mm to 180mm at least, and a lot of them are quite cheap.

It’s one of those ‘good for the average’ cases isn’t it. Not worth putting money into the fringe cases so they dont bother, not to mention that historically, especially in MTB crank lenght has been pretty much ignored and not really discussed, definitely not in mainstream media so a lot of people don’t even think about it, they’ll quite happily deliberate over the massive difference between 740mm bars or 760s, 10mm on a stem, or .5deg on a head angle, but never give their cranks a second thought…

Thanks guys! I’ve just got that idea which will make me a millionaire soon!!!

Expect a NEXT BIG THING that will revolutionise cycling: be it MTB or road.

Reverb-like cranks… You can reduce the lengths down to 40mm – this allows you to ride in the middle of the ruts that were previously rideable only in a “balance-bike style”, or extend it to 250mm to ride up the vertical walls!!!

Kickstarter link to follow! 😀

One thing that may confuse many riders switching to shorter cranks, is that you have to raise your saddle at the same time. If you don’t you won’t be able to use your leg strength fully. Get your hips in the right place vs the cranks and you’ll generate just as much power, and often more through increased cadence.

What may seem like the right height with 165 cranks will actually be too low if you’ve been riding 175 for years – it takes time to adapt.

@medoramas ^ Check out Geoff App’s/Haworth swing pedals.

eccentric/offset platform, so you get the effects of a longer lever in the powery bit, and then a shorter lever as it comes back round. There are other reasons for the design too but the effective leverage bit is what I noticed most when riding a Cleland.

150 usually, though I also have 125 and 140

150 usually, though I also have 125 and 140

‘bent?

It seems to me that the shorter lever arm of a 170mm crank either means you need to more grunt to push the pedals, or you need to run to shift into a larger cog at the rear

I’m convinced of this. It’s got to be harder to push a shorter crank. Science innit.

I’ve always used 175’s on everything but the dh bike. Any bike I’ve tried with shorter seems harder to pedal I reckon.

Pedal strikes can be an issue, not sure if 5-10mm makes too much real world difference, but I think you adjust technique to lessen the chances of that happening.

How dare you bring my sexuality into it!

The riding position is in fact far more upright than what most people are riding…

I’m convinced of this. It’s got to be harder to push a shorter crank. Science innit.

Read more, get unconvinced (kind of), yes it IS harder top push a shorter lever in the same gear, but that’s why we have gears!

With shorter cranks you adjust the gear appropriately, but spin a higher cadence* to compensate and it all comes out in the wash.

All longer cranks are doing is allowing you to push a bigger gear, but you can’t push it as quickly, there’s no point in having a massive gear if you don’t have time to get on top of it. swings and roundabouts and all that…

What works for you and your riding is what matters though, some people are natural grinders and may appreciate the longer lever and harder gear, others are spinners and will prefer the shorter cranks, and it changes between discipline too. Seated accelerations I find much easier and I’m much quicker on shorter cranks, for standy-uppy sprints to get going the longer ones might work better, but then you get the trade off once you’re up to speed of having to keep it spinning, so it is all very personal and situation dependant!

Have a look at how it works on the track, how they gear their bikes and the subtle difference between gearing for top speed, early acceleration, and mid-range acceleration.

You don’t really lose/gain power with different length cranks, there’s a lot of studies out there on this, some of them even suggest shorter ones can be better in some cases.

* cadence =/= foot speed

1 RPM of small circle means your foot is travelling less distance and slower than 1RPM on the bigger circle.

So either cadence goes up if you keep foot speed roughly the same on an easier gear, you’re not really pedalling faster as such, you’re just doing more RPM in a lower gear but going the same overall distance at the same power.

185mm on all my bikes. Not sure what I’ll do if/when they wear out or break. All other sports have always emphasised using a full range of movement, don’t see why cycling should be so different.

Mine was a silly comment, but in a way my use of those crank lengths on a gearing limited device does illustrate how crank length makes a difference to your effective gearing. Not that I’m convinced that there is a significant, or possibly even a noticeable difference between 170 and 175 (I’m all fancy pants and have 172.5 on my road bikes!) – that is less than a 3% difference, which is below the standard threshold for human perception, and certainly less than any advantage being attributed to them. However I can certainly tell the difference between 150 and 125 and it makes a real difference to how fast I can spin, and hence to my speed.

Name me one? All of those I can think of use a similarly limited range.

I’ve just changed from 175mm to 165mm on my mk2 Dialled Alpine due to suffering from quite a few pedal strikes. Just got back from Bike Park Wales and Forest of Dean and can’t feel any difference in pedalling but I definitely had less pedal strikes. I’m 6’2 with a 32″ inside leg and the frame is 18″.

i’m 5’8″ and all my cranks have always been 175mm
but more recently i’ve been considering switching to 170mm to see if it would make any difference for me…but for the time being im sticking to 175mm until i can find the right crank at 170mm

All other sports have always emphasised using a full range of movement, don’t see why cycling should be so different.

Because your limbs/joints/levers are not equally effective in all parts of that range.

It makes sense to use the most effective range of motion, if that happens to be all of it then fair enough, but legs certainly don’t work like that, they are decidedly more crap at pushing in certain configurations than others and the loads on some joints can be excessive too.

It’s also very personal and one of those cases where someone doing it differently doesn’t mean they’re necessarily doing it wrong.

Do we need to have a ‘Pick a crank size and be a dick about it’ thing like we do for wheels? 😉

All other sports have always emphasised using a full range of movement, don’t see why cycling should be so different.

in that case, you’d be happy if the steps in your house were each half a metre high…?

after all, you’d be climbing the stairs with more joint movement…

Wazoo has 175 mm, all my previous had 172.

But given I have tiny legs for someone 5’10” (30″ legs), my ideal size is probably closer to 160.

I’m convinced of this. It’s got to be harder to push a shorter crank. Science innit.

Yep. But your legs can spin smaller circles more quickly. Go down 10mm on crank length, go down two teeth on your chainring, comfortable cadence range will increase by at least 5%. I just measured and I’m a 34″ inside leg, riding 165 and 170mm cranks on my main MTBs, 170mm on my toddler XC bike and 170mm on my Brompton.

Science! 😉