I like the idea of some 180mm cranks on my very large (near 22″ frame) 29er singlespeed.

My questions are:

1) does the extra 5mm length give that much more leverage compared to stnadard 175mm?

2) Does the extra length have a detrimental effect, in that, for a given cadence, your legs actually have to travel faster because the diameter of the cicle has increased? I am thinking of when you really spin out on a singlespeed here >100 rpm.

thanks

1) you would never really notice it.

2) i’m not a physics genius but i’d say that was a fairly daft question.

Sounds like you are tall so longer cranks would suit anyhow.

🙂

I think you would notice the difference, especially singlespeed. You’ll also bash your pedals on rocks and stuff if you’re not careful.

Theoretically it’s supposed to wreck your knees having longer cranks but probably not if you’re tall with long legs.

1) a few %

2 – because you have that few % increased leverage you could increase the gearing by that & thus your feet would be moving at the same speed but the RPM would be lower.

I think

If you really are tall I would have thought longer cranks would be a good idea

You’ll also bash your pedals on rocks and stuff if you’re not careful

i’m assuming a 29er has a higher BB so not necesarily any worse than a 26″ wheel bike with 175s

it makes sense as 29ers only make sense (to me) for taller people so scaling up the cranks as well could work

Just my experience on my original inbred 29er with Truvativ Stylo 180 cranks. They didn’t last long, sadly, and it was a shame to go back down to 175s

It was very noticable racing bmx with 180s when i should have been using 175s.
Ive also just moved onto cranks on the geared mtb that are 5mm longer and its noticable but not to the point where it can affect things like on the bmx.spinning them out of the saddle down bathgate bmx tracks first straight gives the answer to why the right length is a must have on a bmx but not so on a xc/trail bike.If it were four cross on an mtb then its obviously very important to have the right length but for xc/trail riding you could get away with riding something a bit too short or too long and never actually notice where its holding you back (like its not noticable to a few on here regarding the replies so far)

Id say its going to be a problem to those spinning a lot and/or those pushing the bike to the ragged edge whilst out of the saddle (like to the point where one little mistake could end in tears).riding longer or shorter cranks might never show up as a problem for most people under xc/traily usage (not adding rock bashing and root catching) but its still important to go for the length that would be best suited for the riders leg length,riding style,usage/what they might want to use the bike for.(a 5 foot tall rider with 185`s wanting to do a 3 minute hill climb on the road for example lol)

I seem to be crank length sensitive, 180 felt like pedaling plnks, 165 feels live a total lack of leverage, 175 on the mtb and 172.5 for spinning on the road feels lovely.

Thanks for all replies. Just to answer several who asked, just I am pretty tall at 6’5″ with 37″ inside leg, hence the large 29er bike and the thoughts of long cranks to match.

i seem to recall that the ideal crank length is related to the length of your lower leg… so it might work for you (try googling – i remember an article or two about it from a couple of years ago)

i don’t really buy the extra leverage thing for people with “normal sized” legs – 175mm always seems to give plenty leverage to me!

power = work done over time

so a longer crank has more leverage but is harder to spin at the same cadence. end result, factoring in gear ratios available, is that crank length makes no real difference to power output, one length may just suit your natural cadence and riding style more.

for climbing on a geared bike, spinning a shorter crank would be more efficient for most
for climbing on a ss, a longer crank for low rev torque can have advantages

I was about to say ‘no’ until I saw your inside leg measurement.

Even so, I would advise caution. I’m 6’4″, with inside leg of 34″, and tried 180 once by mistake. It was noticeably uncomfortable and I changed back very quickly.

I’m not even sure it’s got much to do with leg length/build, TBH. I think it’s what you’re used to. Once you’re used to 175, anything else feels funny.

No idea about the physics or biomechanics; whenever I try and work it all out, my brain starts going round in circles …

I’m also 6’5″. I’ve used 180s on road bikes and there is a slight difference but not huge. Off road I never noticed any difference so don’t bother.

Too late now – just ordered a pair of Middleburn RS7/Uno 180mms !!!!!!

good choice

I’ve got a set on my SS 29er
extra leverage is good for the hills