Spinning

[Citius]

Actually it is. many small adult riders (<5'2") are riding medium length 170mm cranks. You simply cannot pedal at a rapid cadence like this.

So what size cranks should they be on then? And what effect would this have on their cadence? Finally, why would it even be necessary that they pedal at a 'rapid' cadence?

 

[si_c]

So what size cranks should they be on then? And what effect would this have on their cadence? Finally, why would it even be necessary that they pedal at a 'rapid' cadence?

It's all to do with circular motion, the greater the length of the cranks, the larger the circumference of your pedal motion.

 

[Citius]

It's all to do with circular motion, the greater the length of the cranks, the larger the circumference of your pedal motion.

Yes I know that. I'm asking for it to be quantified, because my feeling is that the actual differences are miniscule.

 

[MichaelW2]

circumference = 2 x pi x r
R=180 C=1131mm
R=170 C=1068mm
R=160 C=1005mm

For a small rider using Med cranks, the pedalling circle is 6cm longer.

Within correct sizes, these are small differences.
If you are already over-flexing your knees and hips, extra flexion is very inefficient

 

[Citius]

circumference = 2 x pi x r
R=180 C=1131mm
R=170 C=1068mm
R=160 C=1005mm

For a small rider using Med cranks, the pedalling circle is 6cm longer.

Within correct sizes, these are small differences.
If you are already over-flexing your knees and hips, extra flexion is very inefficient

Look, I know there are small mathematical differences, obviously. But you don't seem able to answer the questions I asked just now.

 

[bpsmith]

I read an article on this a while back. Hope I can find it as was really interesting. The author reckoned that riders managed to ride faster and for longer with shorter cranks. IIRC, he was suggested more like 160mm for even the taller riders and lower again for shorter people. He blamed the manufacturers for pigeon holing us all into the small number of options so that they could save money on producing the wider range of what we actually should have.

 

[Citius]

I read an article on this a while back. Hope I can find it as was really interesting. The author reckoned that riders managed to ride faster and for longer with shorter cranks. IIRC, he was suggested more like 160mm for even the taller riders and lower again for shorter people. He blamed the manufacturers for pigeon holing us all into the small number of options so that they could save money on producing the wider range of what we actually should have.

If there was anything in that, crank manufacturers would be frantically pushing shorter cranks on us, and if there was any physiological advantage, you can bet that the pros would already be on them. But they aren't.

 

[bpsmith]

If there was anything in that, crank manufacturers would be frantically pushing shorter cranks on us, and if there was any physiological advantage, you can bet that the pros would already be on them. But they aren't.

What size are the pros using? I bet that this info isn't out there predominantly for you to know?

Not sure, but this might be the link:

https://www.powercranks.com/cld.html

It was a while back and it's quite lengthy.

Do some Googling and there are a number of people already doing this in the Time Trial scene.

There's the gearing issue to factor in for significantly shorter crank arms if you're doing hills obviously.

 

[Citius]

What size are the pros using? I bet that this info isn't out there predominantly for you to know?

'The pros' - although they sound like a single group - are actually all individuals, so they use whatever size crank arms they are best suited to. None of them that I'm aware of are particularly coy about revealing their preferred crank length. It's difficult to keep secret anyway, as you only have to look at the team bikes when they are lined up, pre-race.

 

[bpsmith]

'The pros' - although they sound like a single group - are actually all individuals, so they use whatever size crank arms they are best suited to. None of them that I'm aware of are particularly coy about revealing their preferred crank length. It's difficult to keep secret anyway, as you only have to look at the team bikes when they are lined up, pre-race.

I only mentioned the Pro's, as you added that the Pro's Aren't using shorter cranks than those that come as standard. I am asking how you know this?

 

[bpsmith]

This debate will never be answered, but personally I do wonder why we have a variance on frame sizing of around 30% but a variance in crank lengths of only 3% if you look at the usual Shimano offerings that come as standard?

 

[Citius]

I only mentioned the Pro's, as you added that the Pro's Aren't using shorter cranks than those that come as standard. I am asking how you know this?

It's not a secret. You can look through the 'pro bike' features on the likes of Cycling News, or ask the guys themselves. Obviously they all ride different length (like any other cross section of the population) but I've not come across any that are using unusually long, or short, cranks, except on maybe one or two occasions where riders are unusually tall and long in the leg.

 

[Citius]

This debate will never be answered, but personally I do wonder why we have a variance on frame sizing of around 30% but a variance in crank lengths of only 3% if you look at the usual Shimano offerings that come as standard?

Probably because it is not deemed as necessary or beneficial. If it was, I've no doubt they would.

 

[bpsmith]

Probably because it is not deemed as necessary or beneficial. If it was, I've no doubt they would.

As you can guess, I am always tinkering and tweaking. Marginal gains worked for Team Sky remember.

 

[Apollonius]

Some very interesting data on Sky's Christian Knees here:

http://www.teamsky.com/teamsky/news/article/47612#0kMzLS4RDuI1K7Zb.97

Looks like a very high cadence to me. I have the pleasure of riding with an 85 year old ex-pro who, when beating me up most hills, rides a very high cadence. If it works for the pros.....