Crank length

Where speeds may exceed 60 kmph

Crank length

Postby Chaderotti » Mon Feb 08, 2010 9:00 pm

I would imagine this is quite debatable. My pinny runs 172.5 mm cranks. I've learned to sprint on these, I can apply all my power with maybe a bop from the front wheel.

My tack bike runs 170 mm cranks and from a standing start I'm bouncing all over the place. I also just don't feel comfortable riding the shorter cranks, I can really feel the difference. I was talking to my coach about it and he said not to move up to 172.5 because then they'll dig into the track. The whole inch shorter just doesn't feel natural.

Should I go against my coach and move to 172.5's??
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by BNA » Mon Feb 08, 2010 11:29 pm

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Re: Crank length

Postby toolonglegs » Mon Feb 08, 2010 11:29 pm

Whole inch shorter?...they are 2.5mm difference.
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Re: Crank length

Postby mikesbytes » Tue Feb 09, 2010 6:28 am

170mm is generally recongnised as been the maximum length you can run on the track, but it does depend on the height of the bottom bracket.

The issue is your riding style, practice sprinting on rollers.
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Re: Crank length

Postby Corsa » Tue Feb 09, 2010 2:22 pm

I'd be real surprised if you could even notice a 2.5mm difference. For years I trained on 170mm and raced on 172.5mm on my road bikes and felt no difference.
Technique/style as Mike pointed out. Spend a bit of time concentrating on keeping your upper body still when pedalling at speed. After a while you won't have to think about it.
And +1 on the rollers, great for technique and leg speed.
Last edited by Corsa on Tue Feb 09, 2010 3:19 pm, edited 1 time in total.
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Re: Crank length

Postby rkelsen » Tue Feb 09, 2010 3:00 pm

I'm no expert, but from what I know, 170mm is already a long crank for track use. There are heaps of track bikes around with 165mm cranks.

Also, 2.5mm is a shade less than a tenth of an inch, not a "whole inch".

Anyhow, you should listen to your coach. He is an expert. That's why he's a coach.
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Re: Crank length

Postby foo on patrol » Tue Feb 09, 2010 5:15 pm

I am with everyone elses replies. ( an inch :? )
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Re: Crank length

Postby Chaderotti » Tue Feb 09, 2010 8:14 pm

Haha woops! Must of had a blank when converting in my head :? :? :?

I went from 175 mm cranks on my malvern star, to 172.5's and that felt very natural for me, perfect even. Then going from perfection down to 170's it's completely different! To me it is anyway.
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Re: Crank length

Postby jacks1071 » Wed Feb 10, 2010 1:12 am

Chaderotti wrote:I would imagine this is quite debatable. My pinny runs 172.5 mm cranks. I've learned to sprint on these, I can apply all my power with maybe a bop from the front wheel.

My tack bike runs 170 mm cranks and from a standing start I'm bouncing all over the place. I also just don't feel comfortable riding the shorter cranks, I can really feel the difference. I was talking to my coach about it and he said not to move up to 172.5 because then they'll dig into the track. The whole inch shorter just doesn't feel natural.

Should I go against my coach and move to 172.5's??


Chad I have tested back to back 165, 170, 175 cranks on the track. 165's were best for me, I really disliked the longer ones on the track bike, just couldn't get the leg speed I wanted although I run 172.5 on my road bike. If you are bouncing usually you need to try and pedal more smoothly, bigger gear will help obviously unless you have junior restrictions.

I race with a couple of young gun juniors on the road who have restricted gearing and you'd be amazed how fast the lads learn to spin smoothly when they don't have the luxary of bigger gears.

Longer cranks resulted in more bouncing in my experience as your legs are doing bigger circles. I am about 180cm tall.

Its different for everyone though - see if someone will let you try their 165's or 175's at the track so you can test yourself without buying cranks which tends to be expensive.
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Re: Crank length

Postby bman81 » Thu Feb 11, 2010 5:37 pm

Chaderotti wrote:I would imagine this is quite debatable. My pinny runs 172.5 mm cranks. I've learned to sprint on these, I can apply all my power with maybe a bop from the front wheel.

My tack bike runs 170 mm cranks and from a standing start I'm bouncing all over the place. I also just don't feel comfortable riding the shorter cranks, I can really feel the difference. I was talking to my coach about it and he said not to move up to 172.5 because then they'll dig into the track. The whole inch shorter just doesn't feel natural.

Should I go against my coach and move to 172.5's??


There's a rider from out WA who rides 200m cranks (no, not a typo) but can't recall his name. Did alright at the national madison champs, and didn't have any trouble with cranks digging into the track. I dare say he has an appropriate bottom bracket to crank lenght relationship. That said, I'd listen to your coach but more for the reason Jacks pointed out; shorter cranks = smaller circles = potentially less bouncing about.

I found the biggest adaption from riding a road bike to riding a track bike was that there's no freewheeling on a track bike. The fixed gear just about forces you to smooth out your pedalling, where a free hub is very forgiving when you're mashing away.
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Re: Crank length

Postby rkelsen » Thu Feb 11, 2010 7:31 pm

bman81 wrote:There's a rider from out WA who rides 200m cranks (no, not a typo)

200 metre cranks? :shock:
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Re: Crank length

Postby mikesbytes » Thu Feb 11, 2010 8:15 pm

If you have junior gear restriction, then it may be a case that you need shorter cranks to reduce the gain ratio. Your coach will know what is right.
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Re: Crank length

Postby Ant. » Fri Feb 12, 2010 1:36 am

Michael Freiberg (#2 in national scratch race champs) runs 200mm cranks. His frame has a high bottom bracket which makes it okay. He's 194cm and loves his knees running mm from his chest at the top of the stroke.

Difference between your sprints on road and track has nothing to do with crank length: you have a dead spot at the bottom of your sprint with your Pinny, you apply the same technique to your track bike and at the bottom, the bike's fixed hub pushes your foot around the bottom at same speed as your downstroke, making it very jumpy.
I can't explain it well. Sprint more with a fixed, you'll sort it out. Not much to do with crank length.
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Re: Crank length

Postby bman81 » Fri Feb 12, 2010 6:52 am

rkelsen wrote:
bman81 wrote:There's a rider from out WA who rides 200m cranks (no, not a typo)

200 metre cranks? :shock:


Oops, perhaps a small typo... 200mm
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Re: Crank length

Postby brentono » Fri Feb 12, 2010 11:10 am

FME (and a repeat I know) 165mm is standard, learn to increase your cadence, :roll:
and you will find you have more control, speed for sprinting,
and POWER! :shock: (have read recent technical articles that confirm the fact)
... for the "exorbitionist" on 200mm cranks, imagine what he could do
if he learnt to pedal, and get on 165mm cranks? might get #1 :)
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Re: Crank length

Postby Chaderotti » Fri Feb 12, 2010 10:26 pm

My birthday is coming up so I'll have a bit more extra cash for doing stuff. Just got back from junior state championships or what ever. Did the 500 metre time trial and came fifth, 38 seconds.

My legs were really slowing down by the last lap so there is a lot of room for improvement with the engine.
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Re: Crank length

Postby brentono » Sat Feb 13, 2010 11:53 am

Chadrotti,
Good ride, how many years do you have in Juniors, get back to short cranks.
Can't remember the gear, could have been 86/88 but I was on 165mm cranks,
and in the State Juniors, open air, flat track, 500m TT, broke the Australian Record,
for Juniors in 36.1 seconds. :shock: Cadence counts in the TT, especially 500m.
Back in the day... B.C. Give it a try? :wink:
Cheers,
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Re: Crank length

Postby -tim » Wed Mar 24, 2010 9:12 am

165mm is generally the standard for a track sprinter. Enduros tend to like a slightly longer crank to get more leverage.

I used to run 175s on the road and 165s on the track which was quite a noticeable difference (for the same gear your feet will be moving faster on a longer crank, so spinning a shorter crank is considered 'easier'). I soon missed being able to spin on the road for went 170s for road and kept the 165s for the track and haven't looked back.

For a sprinter (participating in match sprints) you don't want to go longer than 170s because you will hit the banking unless you have an unusually high BB.

This is repeating a lot of what has been said already but I just wanted to add my experience.
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Re: Crank length

Postby Chaderotti » Wed Mar 24, 2010 6:21 pm

I think a computer with cadence could be my first investment before I play with cranks.
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Re: Crank length

Postby brentono » Wed Mar 24, 2010 6:42 pm

-tim wrote:165mm is generally the standard for a track sprinter. Enduros tend to like a slightly longer crank to get more leverage.

I used to run 175s on the road and 165s on the track which was quite a noticeable difference (for the same gear your feet will be moving faster on a longer crank, so spinning a shorter crank is considered 'easier'). I soon missed being able to spin on the road for went 170s for road and kept the 165s for the track and haven't looked back.

For a sprinter (participating in match sprints) you don't want to go longer than 170s because you will hit the banking unless you have an unusually high BB.

This is repeating a lot of what has been said already but I just wanted to add my experience.


+1 :idea:
Maybe if it gets repeated enough times, (get back to basics, learn to pedal, on 165mm, and you may be able to sprint some day)
some folks on the site may pick up on it, eh! (I'm with yah) -tim. :wink:
Go :lol:
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Re: Crank length

Postby Kalgrm » Wed Mar 24, 2010 7:15 pm

I know I have no place offering advice in this section of the forum, but I'm with the others - shorter cranks allow for a much smoother action at high cadence than those 170mm monsters you're running Chad. Shorter cranks actually increase the range of speeds you can use a given gear ratio over because a higher cadence is more easily achieved whilst still being able to apply power to the drive train.

I switched out to 145mm cranks on the 'bent (from 175s) and will never go back to even 165mm cranks on that bike. It made a big difference to the amount of power I could produce and allowed me to easily maintain cadences over 140 if needed. If it were possible to use 145mm cranks on a standard frame, I'd even suggest you give them a go before dismissing 165mm cranks as being "too short". (It's not possible to use 145mm cranks on a standard frame because it mucks up the rider position: you'd need a specially-built frame to use them.)

(Oh, and listen to what brentono says - he's a former Aussie representative on the track.)

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Re: Crank length

Postby -tim » Thu Mar 25, 2010 8:27 am

As a young bloke you should force yourself to ride a shorter crank and a low gear (less than 88 inches, not sure what the junior regulations are regarding restricted gears so 88 may be way to big). It will pay dividends when you are stronger because you will be able to spin at cadences of 200+ which are required.

Yes you may not see the results straight away as you will using a longer crank, it will take a few years. Learn how to spin while you are young because when you get older and start racing against people on 90-100+ inches, spinning out an 88 at the back of the field is no fun!! :D

PS this also goes for the road, i try to ride as much as possible in the small chainring on the flats to make myself spin rather mash...
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Re: Crank length

Postby Chaderotti » Thu Mar 25, 2010 9:15 am

165... It'll take me a long time to get a smooth pedaling rhythm going. When I first started sprinting I had a very rough pedaling stroke but now it's dead smooth with no bounce. But to go down to 165's I'll have to learn all over again!
I don't understand the 'inches' you guys are talking about regarding gearing and what not. All I know is that I'm on a 6.35 metre roll out (I think), a 48-16 if memory is on my side today.
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Re: Crank length

Postby brentono » Thu Mar 25, 2010 10:04 am

Chad,
Explained it for Emma here, hope this helps
viewtopic.php?f=39&t=21108&p=361505#p308915
Em,
Your right on your ratios, 48x16 (which is 48 divided by 16) =3
So to make it simple,

In inches (27" wheel) ratio 3x 27= 81"
... (Just remember 27 x ratio)

For roll-out WHEEL DIAMETER 680mm has 2.14 metre circumference,
your ratio 3x 2.14= 6.42 metres (they quote 6.41)
... (Just remember 2.14 x ratio)

Hope that helps,
Cheers,
BrentonO


Cheers :wink:
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Re: Crank length

Postby -tim » Thu Mar 25, 2010 12:03 pm

Yep, what Brentono said!

You will be happy you learnt how to spin while you were young. If you look at state/national track squads most of them have been riding since junior days, building up their technique by spinning restricted gears like what you are on. You often see ex-rowers etc transition to road racing but you rarely see them go to track racing due to the technique required to spin high cadences.
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Re: Crank length

Postby Chaderotti » Thu Mar 25, 2010 6:26 pm

Thanks for that guys, I'll have a chat to my coach this saturday and talk to him about it.
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