Author Topic: Crank arm length  (Read 1339 times)

Crank arm length
« on: March 28, 2018, 01:55:31 pm »
What's everyone running?

Currently got 170mm crank arms on there, but they're coming to the end of their life. I have a spare 172.5mm crankset, reckon this might be pushing it and will probably result in death or similar?

LittleWheelsandBig

  • Whimsy Rider
Re: Crank arm length
« Reply #1 on: March 28, 2018, 02:01:52 pm »
I used to run 175mm off-road but had 180 for a while on my single speed MTB. On the velodrome, I started with 165 but quickly swapped to 170. On road, previously 172.5mm but I have defaulted to 170, which is better for my slightly restricted hip movement nowadays. I tried lengths up to 177.5 on road bikes in the past but kept getting niggling injuries that went away when I dropped below 175mm length. I'm an average-proportioned 182cm tall.

I can swap between bikes without issue when the range of crank lengths is not more than 5mm. If more than that, my pedalling action feels odd when riding the outlier bike.
Wheel meet again, don't know where, don't know when...

Re: Crank arm length
« Reply #2 on: March 28, 2018, 02:14:57 pm »
At one time I had 165s on the fixed, but it's been 170 for years now. 

I've only grounded a pedal twice, as far as I can remember.  I think I have a fairly good notion of how close I can get.

simonp

  • Omnomnomnipotent.
Re: Crank arm length
« Reply #3 on: March 28, 2018, 02:15:53 pm »
My fixie has 165mm.

If you have shorter cranks you will be able to spin faster but might feel more under-geared on climbs. I've been up to around 210rpm on the 165s. I don't recommend this, though.

One advantage of short cranks is the hip flexibility issue as LWaB mentions.

Kim

  • 2nd in the world
Re: Crank arm length
« Reply #4 on: March 28, 2018, 03:59:01 pm »
If you have shorter cranks you will be able to spin faster but might feel more under-geared on climbs.

Surely you should change the gearing to maintain your preferred gain ratio?
To ride the Windcheetah, first, you must embrace the cantilever...

Re: Crank arm length
« Reply #5 on: March 28, 2018, 09:57:58 pm »
Make both descending and climbing easier by just changing the left crank.

A 165mm crank on the chainset for descending, a 175mm NDS crack for climbing.

I have 165mm cranks even though the bike will never go near a track, never thought about changing them.
"Yes please" said Squirrel "biscuits are our favourite things."

Re: Crank arm length
« Reply #6 on: May 10, 2018, 11:22:57 pm »
Track geometry has higher bottom brackets so that they can run longer cranks. Can't remember for sure, but I think I run 175 on mine.

Re: Crank arm length
« Reply #7 on: May 27, 2018, 09:04:11 am »
Been using 172.5 for a while, not died or even came close really.

Just to clarify (which I didn't in a poorly worded OP), my concerns were for things like pedal strike and toe overlap, that kind of thing.

LittleWheelsandBig

  • Whimsy Rider
Re: Crank arm length
« Reply #8 on: May 27, 2018, 09:48:29 am »
I have toe overlap with several of my bikes but have never been particularly bothered by it. Some folk think it equals instant death though.

Pedal strike is all about knowing how far you can lean before touching and controlling your cornering to suit.
Wheel meet again, don't know where, don't know when...

Re: Crank arm length
« Reply #9 on: May 27, 2018, 10:03:47 am »
I have toe overlap with several of my bikes but have never been particularly bothered by it. Some folk think it equals instant death though.

Pedal strike is all about knowing how far you can lean before touching and controlling your cornering to suit.
Doesn't bother me on my road bike even though it's pretty bad, but on my fixie, I'd be terrified.

LittleWheelsandBig

  • Whimsy Rider
Re: Crank arm length
« Reply #10 on: May 27, 2018, 11:56:19 am »
I'm not sure if any of my fixed bikes haven't had overlap. Just drop the heel when the toe taps the mudguard or front wheel at traffic lights or U-turns and the problem goes away.
Wheel meet again, don't know where, don't know when...

Re: Crank arm length
« Reply #11 on: June 13, 2018, 08:25:41 am »
I have pretty severe overlap on mine and it has never been an issue.

Re: Crank arm length
« Reply #12 on: June 13, 2018, 09:58:42 am »
I'm not sure if any of my fixed bikes haven't had overlap. Just drop the heel when the toe taps the mudguard or front wheel at traffic lights or U-turns and the problem goes away.

Similarly for me.

Re: Crank arm length
« Reply #13 on: June 13, 2018, 09:20:04 pm »
I suspect the Harry Quinn track bike has overlap, since the top tube is only 21" and it has steep angles.  I've never known overlap cause any real-world problem, though.
Never tell me the odds.

Re: Crank arm length
« Reply #14 on: June 13, 2018, 09:33:23 pm »
I prefer 165s on fixed, but I still have toe overlap, and it's fine - you get used to knowing where your feet are in relation to your wheel, and it becomes second nature to adjust your speed/crank position/wheel angle to compensate.

Dunno whether ground clearance will be an issue, but 2.5 mm isn't a lot, really. Don't fret it.

Re: Crank arm length
« Reply #15 on: August 19, 2018, 07:00:09 pm »
I found a well researched paper that concluded 21% of your inside leg measurement was ideal. The other useful bit of info was that there are no medical issues with riders using shorter cranks than calculated but using longer cranks should be avoided.

At 60 years old I was getting a bit of hip soreness after riding my SS MTB, I was using 175mm cranks but am only 1.65m tall (short) with 78cm inside leg, the 21% calculation gives 163mm, I put 165mm cranks on the SS MTB, lifted the saddle to compensate for the shorter cranks and now I have no soreness at all, plus pedalling feels much better.

I have put 162.5mm cranks on my road bike and can ride from dawn to dusk with no issues.

Kim

  • 2nd in the world
Re: Crank arm length
« Reply #16 on: August 19, 2018, 07:14:01 pm »
Cranks that are too long for you feel too long (in a way that's reminiscent of the saddle being slightly too high).  Shorter cranks just make you pedal a bit faster.  The problem is that if 170mm cranks are too long for you, you probably think that's what cranks are supposed to feel like.
To ride the Windcheetah, first, you must embrace the cantilever...

Re: Crank arm length
« Reply #17 on: August 20, 2018, 11:08:56 am »
165 on fixed for me. 172.5 on everything else.

All my bikes (apart from the MTB) have toe overlap. Never been a problem. And let's face it - if you have overlap, reducing crank length by just a few mm is going to make no diference. Unless you went maybe 50mm shorter - which would be far from practical!  :P
Those wonderful norks are never far from my thoughts, oh yeah!

Re: Crank arm length
« Reply #18 on: August 20, 2018, 11:35:08 am »
A quick follow up to my nonsensical opening post; I clipped the floor the other week and had to buy new undergarments.