Crank for short person! Advise

bobbydigital

I had a Cytech mechanic pick up some wheels from my house but when they saw my Cotic they said the crank arms too long for my stature and frameset.

So now I'm after some advice on buying a crank for my next build.

I will build a HT steel 29er 1 x 10.
I have 30" inseam @ 5ft 7in.
Frame will be a size small, it's an on one inbred if that makes any difference but it's a heavy frame so not sure if zee or saint cranks will be too hefty, I've never owned them so not too sure and before you start cooldad I am too lazy to go and look on the interwebs.

Are there any calculators for such things? Currently I have 175mm cranks on my cotic, should I be looking at 170mm cranks or 165mm? At the highest point my knee is about 15 degrees "rise".

Rowan404

According to the interweb a 165 would suit you best.

kirkymtb

I'd just go with what felt best. The longer the crank, the higher the torque (turning force). A technical climb often needs the highest torque you can generate. If your riding is mainly spinning on flatter surfaces you might not need the torque.

02gf74

Are there any problems with the 175mm cranks on your other bike?

For your height 170mm would be worth trying plus these tend to less common and can be cheaper on ebay.

bobbydigital

I have found some saint cranks which are apparently better than zee and should be lighter, better material I read.
I will look for 165 and 170mm, I'm pretty strong on the hill climbs so I think I can work something out with the gear ratios if needed, I never use the higher gear on my 11-40t with 34t chainring.

I don't think there's anything wrong with my 175mm cranks, just I get muscle pain on the inside of my knees if I pedal fast, so been riding in higher gears around 80-90 cadence but I've gotten into the whole bike thing in a big way and wouldn't mind doing some bike fitment just to make sure I'm not doing serious damage.

I set up my SPD pedals well so just wanted to make sure my crank arms are optimum, apparently if they are too long your knee comes up too high which puts it under more strain on your knees on the power stroke.

steve_sordy

Be aware that the shorter cranks have the same effect as changing the size of your front ring.

Going from 175 to 165 crank length will be a 5.7% reduction. So it would feel like you kept the crank the same but had replaced the 32t ring with a 34t. ie it would feel harder on the climb. If you already have knee problems that may not be desirable.

So to restore the feel of the gearing and reduce the force required through your knees, you need to do the opposite. If you go for a 165 crank, then you would need to replace the 32 front ring with a 30t. Apart from feeling more comfortable from the shorter crank, you should notice no difference when riding uphill. But you will have to up your cadence for any specific speed.

02gf74

steve_sordy wrote:

But you will have to up your cadence for any specific speed.

Or change gear.

steve_sordy

02GF74 wrote:

steve_sordy wrote:

But you will have to up your cadence for any specific speed.

Or change gear.

We are only talking about less than 6% change. One gear shift is typically 15-20%, which would overwhelm that small change. I was thinking of when he was already on the fastest gear, but I accept that I could have been clearer if instead I had said "up your cadence for any specific gear for the same speed".

The Rookie

5’10” but the same length leg, 175’s on all my bikes with no issue.

bobbydigital

I have been looking at raceface chester @ 170mm.
I don't mind trying 170mm as they are more common to find but if that doesn't work then the 165mm will be bought.

I only get knee pain from pedaling very quickly whilst sitting down, I'd estimate a cadence of 100+ as I would be in a very low gear but without almost no resistance, probably just bad form and I did have x-rays which came back as "unremarkable" which would say the knee is okay but the muscles or ligaments around it get damaged when I pedal too quickly.

Doing some testing with different ratios would be fine, all trial and error I guess.

If you image a clock face from 12 to 6 and optimum high knee height would be say 4 my knee with the 175 is at around 2 so my power stroke is starting from what I believe is a higher point.

maddog 2

165s on all my mtbs these days. Better clearance. No downsides.

Hope, XT do them but not RF (missed a trick there...)