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Old 01-28-08, 01:01 PM   #1
ElJamoquio
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Crank Length for TT's

Stats:

Height 5'9"
Bike Inseam ~32"
TT Crank Length: 172.5 mm
Road Crank Length: 172.5 mm

Like many/most, the major factor limiting my TT position is hip angle. If I go down as far as I'd like in the bars, there's almost a dead spot towards the top of my pedalling stroke. I'm working on my flexibility, but I doubt it'll make my on-the-hoods FTP (~300 watts) equal my TT FTP (~270 watts???)

I'm pretty happy with my road crank length; but if I had to choose, I'd pick 170. If I had to blindly pick a TT length, I'd go with 165 or 167.5. Anyone go down a size or two in crank length for their TT bike?
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Old 01-28-08, 01:26 PM   #2
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um... maybe i'm getting old and senile, like roadwarrior/eldiablorojo/patentcad, but i seem to recall the philosophy was to go for longer, not shorter cranks in a TT.
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Old 01-28-08, 01:33 PM   #3
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Yep, generally people go up in length. I went from 172.5's to 175's for the TT bike and actually liked it enough to go 175 on all my bikes.
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Old 01-28-08, 01:37 PM   #4
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um... maybe i'm getting old and senile, like roadwarrior/eldiablorojo/patentcad, but i seem to recall the philosophy was to go for longer, not shorter cranks in a TT.
Nope. That's the philosphy. I'm not looking for more power, I'm looking to be more aero.
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Old 01-28-08, 02:09 PM   #5
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Nope. That's the philosphy. I'm not looking for more power, I'm looking to be more aero.
cranks aren't your answer.
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Old 01-28-08, 02:58 PM   #6
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Actually ElJamoquio is on the right track. The big thing is that he can lower the front end more because as he said the hip angle is not as acute.

Last edited by Compressed; 01-28-08 at 05:38 PM.
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Old 01-28-08, 03:37 PM   #7
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Hmmm, I was wondering the same thing.
I'm 5'9" with a 31" inseam.
I've always ridden 172.5 on the road and just bought a used P3 (my first TT bike) with 170's.
I plan to stick with the 170's for a least this season since I don't feel like buying 172.5's.
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Old 01-28-08, 04:32 PM   #8
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Originally Posted by Compressed View Post
Actually ElJamoquio is on the right track. Going down in crank length lets you lower your seat the length dropped which makes on lower obviously, the gain of this is that wind speed is usually less or calmer closer to the ground. The bigger thing is that he can lower the front end more because as he said the hip angle is not as acute.
Errr, you've got that backwards. If you go to a shorter crank length, you have to raise your seat because the pedal is closer to your body at the bottom of the pedal stroke. This may help with aerodynamics by getting your front end lower relative to your seat, but if you're on anything resembling the correct frame size, it should not be necessary.

As botto said, the rule is to go for a slightly longer crank on the TT bike. I run a 170mm crank on my road bike, and a 172.5mm crank on the TT bike, as the slightly longer crank feels a bit more comfortable at the relatively lower (90-100 rpm) cadences I use for time trialing.
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Old 01-28-08, 05:17 PM   #9
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I stick with the same length, mainly because its what I have around and dont want to do a $500 experiment on crank arm length for the 2-3 TT's I do a year. And its pretty hard to find 177.5 arms.
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Old 01-28-08, 05:37 PM   #10
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Originally Posted by elgalad View Post
Errr, you've got that backwards. If you go to a shorter crank length, you have to raise your seat because the pedal is closer to your body at the bottom of the pedal stroke. This may help with aerodynamics by getting your front end lower relative to your seat, but if you're on anything resembling the correct frame size, it should not be necessary.

As botto said, the rule is to go for a slightly longer crank on the TT bike. I run a 170mm crank on my road bike, and a 172.5mm crank on the TT bike, as the slightly longer crank feels a bit more comfortable at the relatively lower (90-100 rpm) cadences I use for time trialing.
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Old 01-28-08, 06:05 PM   #11
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Errr, you've got that backwards. If you go to a shorter crank length, you have to raise your seat because the pedal is closer to your body at the bottom of the pedal stroke.
You're correct, you can raise your seat a tiny bit with shorter cranks. But...the short cranks mean your leg doesn't come up quite as high at the top of the pedal stroke, and thus your hip angle stays a bit more open. The limiter for most people is that "crunch" at the top of the pedal stroke.

I know Jens, one of the regular TT posters on Slowtwitch, has made some mention of trying "circus cranks" (like 160s) for this reason. I dunno, but I'm on 175s on mine and thinking about switching to shorter.
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