Will shorter cranks help?

[crazycanuck]

Hey,

We were talking with our super duper bike mechanic yesterday & he suggested shorter cranks for my bikes. Main reason for the suggestion is because i'm still unable to climb out of the saddle on either bike.

Just wondering about shorter cranks & if anyone has any thoughts for me.

What do i need to know before i start wandering round the net looking for them?

Thanks
C

[tattiefritter]

How short is shorter ? I have 170mm cranks on all my own bikes (2 MTBs, a road bike and a hack) rather than the "standard" 175mm. I found changing to the shorter cranks helped me have a smoother spin but not sure they help me climb as such as you are supposed loose a bit of leverage.

Our tandem still has 175mm cranks on it and I can tell the difference, there is a definite loss of power through part of the pedal upstroke. I could always climb out of the saddle with the longer cranks I just didn't very often as I was just rubbish at keeping going stood up until I started running.

I'm 5ft 4 with short legs for my height, I have friends with longer legs who get on fine with 175mm cranks though I really wouldn't go back. I have wondered about 165mm cranks for my road bike on more than one occasion though it would mean changing the chainset out ...... (don't need to spend money on the road bike!).

Can you borrow a bike with shorter cranks to get a feel for them, I just took the plunge but I only had one bike at the time and as I really liked the 170mm cranks I specced all new bikes with that length crank, would have been an expensive business if I'd had to retrofit them all.

[OakLeaf]

The shorter the crank, the less knee flexion you'll have at the top of the pedal stroke. That'll be true both in and out of the saddle.

I'll have to pay closer attention next time I'm climbing, because I would've said the knee actually flexes more when I'm in the saddle than out - when I'm standing to climb (or accelerate), the knee is closer to being 100% extended at the bottom of the pedal stroke, so I would think the opposite knee would be less flexed/more extended as well. Not sure if that's actually true though, since I (and I think most people) tend to shift my weight from side to side when I'm standing. So maybe there's not only more flexion, but some torque as well, which might could be exacerbated by increased flexion from cranks that are too long.

I need 165s because my kneecap tracking problems become an issue when my knees flex too much at the top of the pedal stroke.

Standard for most frame sizes is 170 - how long are your current cranks?

If I were you I'd run it by your PT if you're still in contact, and/or the PTs on this board - specifically where the pain or stiffness is that you're trying to address, where in the pedal stroke it happens, and whether it's only when you're out of the saddle, or just that it's worse then.

[crazycanuck]

TF-i know there's a chickie in Perth who has a mtb with short cranks & will try and catch up with her on them. I believe we'd be talking 170mm cranks.

Oak-I'm not experiencing pain or stiffness any longer though? It's one small movement that's holding me back from mtn biking & powering down out of the saddle on the road bike

When i was in Canuckland & did a short spin on a spin bike @ a gym & I could make a complete circle then. What type of cranks are on most spin bikes?

thanks
C

[RoadRaven]

You might need to experiment
Having ridden 170 cranks on my race bikes, I have recently gone to 175 cranks on my time trial bike because of the type of riding I do on it. (I have 172.5 on my NEW road race bike)

I have heard some espouse the theory that shorter cranks can be a useful option instead on longer...

So, to sum that up... I have nothing useful to say to give you solid direction :p

[LBTC]

Hey, CC

If it helps at all to know - Bif, the Torrent you rode while you were here, has 170 cranks, while Portia, the Santa Cruz you tried briefly, has 165 cranks. Of course there are a lot of other differences between my two mtb's and more still compared to yours, but maybe you could tell the difference in the crank length??

I prefer the 165's. But I'm really short. :p

Hugs and butterflies,
~T~

[kelownagirl]

I have 165's on my old bike and I'm getting them on my new bike too. And I'm a tad taller than you. :)

[crazycanuck]

RR-you're too funny..:p

T-The only thing i remember about the Santa Cruz was it felt a bit cramped but i was on it for just a v short time @ the top of the lake. Bif felt fine & got me through the panic of getting accross the road :o :eek: and up the hills...:o

I'll visit a bike shop on the weekend & have a gander with them..

[RoadRaven]

*Rave takes a bow to only member in audience of 1 at the Comedy Show*
:rolleyes: ;)
Thanks CC - I try... maybe tooooo hard :p

CC... forgot to mention, in case u forgot, I'm 5'10"

Just to add more detail to my not-very-helpful info... :D

[crazycanuck]

RR..i'm sending you an air slap at the moment :p

Hopefully when we venture to NZ @ christmas we might have a slim chance of catching up. That way i can thwack ya! :p

[dianne_1234]

This presentation by Jim Martin suggests to me that crank length doesn't significantly affect power output:

http://www.serottacyclinginstitute.com/documents/JMartinCrankLengthPedalingTechnique.pdf

So I choose crank length for other reasons, like knee health, pedal clearance and a balanced feel.