[Closed] crank arm length 170mm or 175mm

At 5mm difference i dont think you would notice either way.

I would stick with 175mm as that is the most common size.

I have no idea of the crank length on my 5 bikes. I guess they are all between 170 and 175mm.

you can definitely feel 5mm.

I'm 5'7, 5'8 on a good day and run 175 normally, but have fitted 170s to a couple of bikes with low BBs, the extra 5mm can make all the difference and you get used to it very quickly.

fitting guides seem to put me on 170mm for MTB, and 167.5 on Road bike but a lot of it is personal pref too.

I feel more comfortable spinning with 170, but I'm down here at 5'7" and take 29" inside leg.

cool, thanks for the relpy, 175 is what I've always ran and been ok with. Was just wondering if it would benifit me with the shorter ones.

Ahh those other replys came in quick! Amedias- you think 170mm for me then??

I've used 165/170 & 175 & can't tell the difference, other than I clout my pedals less.

5'6", always use 170.

175 make my knees ache.
Bothers some but not others.

Had a bike once with different length cranks, took me ages to work out why I hated it

Yep, agree that you definitely notice 5mm. I feel like I'm twiddling on 170 or 172.5 but I've got long shanks. Not sure what's best for you, but it does make a difference to the leverage.

6'ft tall, I have 170 on my hardtail and 175 on my FS. Never noticed the difference

I felt a larger than expected difference between 170 and 175. Both in leverage and in the input it takes to ratchet between fast corners and body position. Both my bikes run 170s and I am 5'10. I feel I am giving a little away in power but enjoy the ease of movement more.

Ahh those other replys came in quick! Amedias- you think 170mm for me then??

depends, if you're happy with 175s then might as well stick with them. Hard to say which you'll prefer if you've only ever tried one length!

I'm 5ft11 (well just under) and have a 33" inseam, yet can't use 175's happily cos they aggravate my knees. Always use 170's cos my knees prefer them, and also cos it helped me learn a better spinning technique in the first place.

There's a lot of science behind optimum crank lengths on Sheldon Brown's website, but he does also then go on to say that largely and probably most importantly, it's about personal preference.

At 5ft9 with a 30" inseam though, see if you can get a go on a bike with 170's first to see if you like it. If you were 6ft6 and had 38" legs, you'd do well to run 180's!

Yeah amedias I see your point, might just stick with 175mm then.

Another vote for 170's here. 5'8 with 29" inseam but short thighs!
Got them on all bikes now, easier to spin and for me just feel nicer.
Originally swapped due to knee problems which shorter ones helped but now feel that I actually have more power on 170s although with small loss in leverage. Just seem to feel like I'm using the "correct" muscles or in a more efficient way.
Took some time to convince myself at first to swap from the "Norm".
Still a "personal" choice in that I think some people feel a difference and some not so much.
Hope this maybe of some help. Personally I think thigh length has more importance as to whether its worth trying.
Cheers

its not about the lenght its what you do with it that counts.

170mm for me, but I am ashort arse.

Also check frame specs & Q factor etc

Yep 170s here too and I'm just over 6' tall. I ride a lot of fixed and SS so need to spin fast, but they feel "right" compared with 175s for me. Don't forget to raise your saddle a little if trying shorter cranks!

yeah, sounds like 170 maybe the way to go then. I've got mild cerebral palsy and my left leg is 2 inch shorter than my right so might give 170's a shot.

imho you will definitely notice 5mm.

170s seem stiffer - not so much in a rotational direction but they seem to resist flexing in-and-out when you weight the pedals - and have a bit more ground clearance.

On the other hand they're harder to crank compared to 175s

For long days in the saddle I would go for 175s but for a couple of hours ragging around the local loop I would choose 170s.

At 5mm difference i dont think you would notice either way

<pedant> theres two cranks so the difference is really 10mm </pedant>

that said I've no idea what length the cranks are on any of my bikes, but then I've always used flats so my foot position is pretty random. If you're clipped in perhaps 10mm will be noticeable

rocketman - Member

imho you will definitely notice 5mm.

170s seem stiffer - not so much in a rotational direction but they seem to resist flexing in-and-out when you weight the pedals - and have a bit more ground clearance.

On the other hand they're harder to crank compared to 175s

For long days in the saddle I would go for 175s but for a couple of hours ragging around the local loop I would choose 170s.

Oh my word, post of the week for me. Made me chuckle.

5'7", 29" in-seam, 170mm cranks

On my 2 main bikes, one crank is 170 and one is 175. Not sure which is which tbh! Certainly can't feel any difference.

On the DH bike I had to fit 165s as it's a stubby wee thing and I was sometimes kneeing the crowns while climbing hard! (*) And they do feel a little different, though it's never really been a problem.

(* yes I know you're not supposed to do this. But I go for bike rides, not walks)

Just measured mine. I'm 5'11" with a 32" inside leg. I have a sets of 160, 165, 170 and 175 on my bikes at the moment and have never really noticed any difference.

I run 170s - 6'1" with 32" inside leg

Like em becuase:
I like bikes with low bbs
they feel like they allow you to spin easier/better
I have short legs 😉

The guys behind Bikefit have done some proper scientific research into this on road bikes and found that unless you are jumping from 165 to 180 not only will you not notice there will be no increase in power or speed. So just go 170.

I read an article from one of the pro road teams saying that they've also done testing and came to the conclusion that their team could run whatever they wanted crank length wise without much worry. I think I read it from a link on here earlier in the year, but can't be arsed to look it up.

At one time i had four bikes, running 165mm (road bike), 170s, 175s and 180s on my singlespeed. My knees didn't know if they were coming or going and over time, i've changed all to 175mm. It's better when switching between bikes now. If you're used to 175s i'd stick with them for continuity.

I'm 5'10 and like 175. More leverage and a wider base feels better on the MTB and road bike. I've had 170 and 172.5 on each respectively and 165 when I was briefly into track which felt a bit odd.

Another variable is your pedal thickness, 175 and thin pedals will be quite different to 170 and thick ones.

What do you dislike about 175, or have you just been pondering? 170 is probably a smidge lighter 😉

as you can see from all the answers here,you'll never know if you don't try it yourself.
because there is no answer.
it's quite a personal thing,a lot has been written about it,I've tried 165-170-172.5 and 175.
settled on 175 for mtb,170 for road 172.5 for cx-oddly enough,it's the middle one that feels the most strange.no issues changing between them though.165s are ace for rollers.
^pedal thickness doesn't have anything to do with it.the circle you're pedalling is higher or lower,not larger or smaller.
I'm 5'11",fwiw

rocketman = comedy genius!

If only GW were here 🙁

I'd always run 175's but as I'm just under 5'8 tried 170's on my last build, you can notice it, whether it makes any real performance difference is another matter, but they just didn't feel right and I ended up replacing them pretty quickly.

It might well be psychological but I feel a bit energy sapped on 170s.

Probably bugger all difference on a power metre of course!

My experience was that I had an old worn set of 170mm xt cranks and managed to score a good set of cheap 175mm xtr cranks. I had wanted the xtr cranks for years and really wanted to like then. 5 rides on them and I gave up as they did feel different to me. Sold them on here and was gutted I never got on with them. Still using the worn xts. Some people are more sensitive to change than others. I am not making any claims that this is linked to skill, just sensitivity.

Sod 5mm I can't ride 172.5 let alone 170. 175 or bust for me.

If, as is suggested previously, its been proven to make no difference, difinately go shorter. It can only have advantages in ground clearance and cadence. FWIW I'm 5'7" with 29" inside leg and run 165s on all my bikes and would go shorter on the DH bike if I could.