Shorter Cranks

Chris71127

I'm hoping that people will be kind enough to share their experience and opinions.

I have heard quite a lot of theories recently that it is beneficial to run shorter cranks for a few reasons. Mainly that it opens the hip angle up more than longer cranks so puts less strain on the lower back etc and puts the rider in a slightly more aero position.

The only downside appears to be less torque when out of the saddle.

I'm 6ft with size 10 feet. I have crap flexibility and currently run 172.5 cranks but am debating dropping to 170.
Am I about to make a mistake or not?

Cheers

ugo.santalucia

If you believe miracles, Nibali just did one last week, winning the Giro from an impossible position in GC... apparently all down to fitting shorter cranks... he went from being dropped to dropping everybody

First.Aspect

ugo.santalucia wrote:

If you believe miracles, Nibali just did one last week, winning the Giro from an impossible position in GC... apparently all down to fitting shorter cranks... he went from being dropped to dropping everybody

You've read "the secret pro" this week?

There's a GCN video on this topic somewhere. Basically, as you might expect, they concluded that 2.5mm either way doesn't make any descernable or measurable difference.

MikeBrew

I just dug a Sram Red compact out of the spares bin to run on a bike that I bought with a standard 53/39 crankset fitted. As well as the obvious drop in gear sizes it's also a drop from 172.5 to 170mm cranks. Works for me ! I know that a lot lot people are extremely skeptical as to whether you can feel such as small difference in crank length, but to me they seem to offer better cadence, a smoother overall pedaling action, and definitely more hamstring involvement on the pulling up part of the pedal stroke.

I think that the GCN article referred to in th post above is this one : https://www.youtube.com/watch?v=eMAxH_Ud8YE

The point I noticed here - and that the testers barely commented on - was that shorter cranks equated to a lower heart rate at a given power output. Potentially useful over a long ride.
I've heard a some people say that they can't tell the difference in a few mm and that they use what ever crank length is to hand, then you ride behind them and see their knees throwing out to the side at the top of the stroke, because their cranks are too long !

Everyone's views are going to differ on this one, and the only way forward really is to try it out for yourself.

StillGoing

Chris71127 wrote:

I'm hoping that people will be kind enough to share their experience and opinions.

I have heard quite a lot of theories recently that it is beneficial to run shorter cranks for a few reasons. Mainly that it opens the hip angle up more than longer cranks so puts less strain on the lower back etc and puts the rider in a slightly more aero position.

The only downside appears to be less torque when out of the saddle.

I'm 6ft with size 10 feet. I have crap flexibility and currently run 172.5 cranks but am debating dropping to 170.
Am I about to make a mistake or not?

Cheers

Most of that is correct. It certainly won't help you achieve a more aerodynamic position. Shorter cranks help achieve a high cadence reducing muscle fatigue of a slower cadence. But the pay off is a more cardiovascular workout. Anaerobic v aerobic. Shorter cranks will give you more clearance at the top of the pedal stroke by your saddle needing to be higher for the correct leg angle at the bottom of the stroke and the pedal being further away at the top of the stroke. The improved clearance at the top of the stroke will assist you to get into your power stroke with less resistance. I use 165mm cranks on my main bike and 170mm on the other. I can tell the difference and whilst some will argue you can't tell the difference between 2.5mm by going from 172.5mm to 170mm, that difference might just be all that you need to achieve higher cadence and improved power.

londoncommuter

Not that money is everything but I think it depends on if you're about to build a bike from scratch and have a free choice of crank length or if you're proposing replacing an otherwise completely fine one on an existing bike. Whether 2.5mm matters is somewhat dependent on how much it's going to cost!

Gavinus

I'm 5 ft 10 and traditionally ride 172.5mm cranks. I have just had a bike fitting for some clip-on aerobars at Cyclefit Manchester. On their jig they can change the crank length so you can feel the difference. As a result I have bought 165mm cranks.

In the hoods I can't feel the difference comfort wise between the two, however when in the aerobars the 165mm cranks are far more comfortable because of the open hip angle. Perhaps you can find somewhere to test the difference out.

mercia_man

Mike Burrows, designer of the original Giant TCR compact bike and Chris Boardman's Olympic-winning Lotus track time-trial buke, is a big advocate of short cranks. There are several articles from him about the topic on the internet, for example have a look at http://www.bikefix.co.uk/right-crank-length and
http://www.bhpc.org.uk/short-and-sweet- ... rrows.aspx

He uses 145mm and 150mm cranks, describing the tiny difference in length from 172.5 to 170 as "pure placebo". I use both 170 and 172.5 and cannot feel any difference. My wife uses 160 and 165 cranks and can tell the difference from 170.

MikeBrew

MerciaMan wrote:

He uses 145mm and 150mm cranks, describing the tiny difference in length from 172.5 to 170 as "pure placebo". I use both 170 and 172.5

That sounds slightly illogical as most people - me included - wouldn't expect 2.5mm to make a difference, so where is the placebo in that ? The fact is that I find that it makes a difference that I wasn't expecting.

mercia_man

MikeBrew wrote:

MerciaMan wrote:

He uses 145mm and 150mm cranks, describing the tiny difference in length from 172.5 to 170 as "pure placebo". I use both 170 and 172.5

That sounds slightly illogical as most people - me included - wouldn't expect 2.5mm to make a difference, so where is the placebo in that ?

Have a look at his articles. My interpretation of his "placebo" comment is that switching 2.5mm makes no difference - people might just think it is better. For the full benefit of short cranks, Mike Burrows says you need to go much shorter. In the recumbent world, some racers use cranks as short as 100mm.

simon_masterson

Same height, long legs, use 170mm. Ground clearance on fixed, apart from anything else. I have 172.5 and 175 as well but the former are on a bike that's currently out of action, and the latter I stripped the thread on, and haven't got round to having fixed. It used to be thought by some that longer cranks = more power, and whilst we now know that's not true, they can bring you lower to the ground, potentially giving you an aero benefit. It's often cited that short cranks can do likewise, but lower at the front isn't always more aero.

Bobbinogs

Good article here:

http://bikedynamics.co.uk/FitGuidecranks.htm#1

mrfpb

"It's only 2.5mm" (or 5mm total diameter) but if you ride for 5 hrs at 100 rpm that's a small difference x 30,000. If it makes any beneficial difference to fatigue of the hips or knees or to power output then it is worth doing.

StillGoing

Mercia Man wrote:

MikeBrew wrote:

MerciaMan wrote:

He uses 145mm and 150mm cranks, describing the tiny difference in length from 172.5 to 170 as "pure placebo". I use both 170 and 172.5

That sounds slightly illogical as most people - me included - wouldn't expect 2.5mm to make a difference, so where is the placebo in that ?

Have a look at his articles. My interpretation of his "placebo" comment is that switching 2.5mm makes no difference - people might just think it is better. For the full benefit of short cranks, Mike Burrows says you need to go much shorter. In the recumbent world, some racers use cranks as short as 100mm.

If you're turning a big circle, it is going to require more effort to turn the circumference of it at a set speed than turning a smaller diameter circle at the same speed. 2.5mm is actually 5mm smaller diameter given the full diameter of the pedal cycle. If I want to maintain a 100rpm cadence, it is easier to do it with 170mm than it is with 172.5mm.

StillGoing

londoncommuter wrote:

Not that money is everything but I think it depends on if you're about to build a bike from scratch and have a free choice of crank length or if you're proposing replacing an otherwise completely fine one on an existing bike. Whether 2.5mm matters is somewhat dependent on how much it's going to cost!

Not true. Remove the old cranks and sell them to recoup some or all of your outlay.

MikeBrew

It's also about between 15 and 16 mm less circle circumference that your foot/feet travel for each revolution - multiply that by 90 RPM for 3 hours and you can see how it helps you maintain a higher cadence....

londoncommuter

philthy3 wrote:

londoncommuter wrote:

Not that money is everything but I think it depends on if you're about to build a bike from scratch and have a free choice of crank length or if you're proposing replacing an otherwise completely fine one on an existing bike. Whether 2.5mm matters is somewhat dependent on how much it's going to cost!

Not true. Remove the old cranks and sell them to recoup some or all of your outlay.

Just bought a new bike, could have put brand new crank on for £225 but would only have got £175 for the unused one coming off. Didn't think 2.5mm was worth £50. Personal choice though.

Chris71127

Thanks for all the replies. Makes some interesting reading.

Just torn now which crankset to go for. Thinking either a rotor 3D or Praxis Turn Zayante.

If anyone has had experience with either of them I'd be interested to hear your thoughts

StillGoing

Chris71127 wrote:

Thanks for all the replies. Makes some interesting reading.

Just torn now which crankset to go for. Thinking either a rotor 3D or Praxis Turn Zayante.

If anyone has had experience with either of them I'd be interested to hear your thoughts

I have Rotor 3D24 in 165mm and SRAM Red Black in 170mm. Both are fitted with Aero Q rings, the Rotor has a P2M powermeter and both work absolutely fine.

fenix

Very interesting last post there from someone who has only posted about that supplier. Hmmmm.

I'm with Mike Burrows - I think 2.5mm is bobbins. I can't tell a difference and indeed ran odd crank lengths by accident for a few months and still didn't notice. Just get what is on sale...

ajmitchell

pros and cons of shorter cranks; pros and cons of longer cranks; as explained here https://www.youtube.com/watch?v=Yl90KFqDW-Y