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Are any bikes based around short cranks?
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Given the current hotness of short cranks in the tri world, here's a thought that popped into my head:

Instead of keeping the same BB height, and thereby raise the rider if they use short cranks, why don't we see bikes with a lowered BB?
At a guess, lets say for an average tall rider, you spec a maximum 160mm crank. You could probably drop the bottom bracket 15mm over current designs.

Benefits that I see:
Lower CG. Not sure if this makes you more or less stable. Less I think. But probably sharpens up the handling.
Lower saddle height. Easier to mount the bike.

The big one: Reduced frontal area. Rider, bars, top tube, everything is lowered, hence Better aero.

Downsides? I can't think of any.
XS size frames might be impossible without 650C or some fancy head tube concept.
Handling might be affected in some way.
Cornering clearance would be the same as a higher BB/longer crank design

Any thoughts from the experts out there?
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Re: Are any bikes based around short cranks? [MattyK] [ In reply to ]
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I think that is my 650c Cervelo P3 aluminum that I still ride, only now with 155's instead of the 175's I rode no knowing any better. I found a brand new one in the box years ago from 99 I think, gonna build it up into a modern super bike!!!
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Re: Are any bikes based around short cranks? [MattyK] [ In reply to ]
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MattyK wrote:
Given the current hotness of short cranks in the tri world, here's a thought that popped into my head:

Instead of keeping the same BB height, and thereby raise the rider if they use short cranks, why don't we see bikes with a lowered BB?
At a guess, lets say for an average tall rider, you spec a maximum 160mm crank. You could probably drop the bottom bracket 15mm over current designs.

Benefits that I see:
Lower CG. Not sure if this makes you more or less stable. Less I think. But probably sharpens up the handling.
Lower saddle height. Easier to mount the bike.

The big one: Reduced frontal area. Rider, bars, top tube, everything is lowered, hence Better aero.

Downsides? I can't think of any.
XS size frames might be impossible without 650C or some fancy head tube concept.
Handling might be affected in some way.
Cornering clearance would be the same as a higher BB/longer crank design

Any thoughts from the experts out there?


I am short. 5' 6'' I like this idea... I really like this idea.



monty wrote:
I think that is my 650c Cervelo P3 aluminum that I still ride, only now with 155's instead of the 175's I rode no knowing any better. I found a brand new one in the box years ago from 99 I think, gonna build it up into a modern super bike!!!

Sounds awesome, please share pics when done.

Grow with data: Dynamic Sports Data | eBay store
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Re: Are any bikes based around short cranks? [MattyK] [ In reply to ]
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Most bike brands not interested in the idea. Have found one prepared to break the mould but it will take a while before you see anything.
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Re: Are any bikes based around short cranks? [cyclenutnz] [ In reply to ]
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cyclenutnz wrote:
Most bike brands not interested in the idea. Have found one prepared to break the mould but it will take a while before you see anything.

One can only dream.

Grow with data: Dynamic Sports Data | eBay store
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Re: Are any bikes based around short cranks? [MattyK] [ In reply to ]
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It's called "custom", so yes they're out there, but you won't find them from any major manufacturer in any bike shop.

And yes, a lower BB increases stability. It can also force longer chainstays, and depending on your height and position, possibly force a higher front end. Head tubes can only go so short...

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Re: Are any bikes based around short cranks? [monty] [ In reply to ]
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monty wrote:
I think that is my 650c Cervelo P3 aluminum that I still ride, only now with 155's instead of the 175's I rode no knowing any better. I found a brand new one in the box years ago from 99 I think, gonna build it up into a modern super bike!!!

Monty, I believe the BB drop on that bike is 60mm

With 160 cranks, a bike that is already 750mm BB drop could have 90mm BB drop (or at least 85). This bike would be a rocket on switchback descents, maybe more aero by having less bike frontal exposed to the wind with the rider complex a full 1.5 cm lower. Seems like a win win. I never understood why Cervelo made their BB drop so high in the old bikes. May have just been so you could have a short head tube on a higher saddle, so could get a flatter back. Butt realistically most people were riding those bikes with a zillion spacers.
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Re: Are any bikes based around short cranks? [MattyK] [ In reply to ]
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Our new XS Tactical (650) is specified with 155 crank arms.

Dan Kennison

facebook: @triPremierBike
http://www.PremierBike.com
http://www.PositionOneSports.com
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Re: Are any bikes based around short cranks? [MattyK] [ In reply to ]
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Shhh. Don't go telling everyone.
I've had the same idea. Have it built up in steel first.
I'd add a narrow bottom bracket too. Better Aero, better cornering clearance and maybe better biomechanics.
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