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Old 12-06-08, 11:21 PM   #1
Cdy291
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TT bike Sizing

So you want a shorter top tube on a time trial bike right? How come I would need a 54cm Cervelo road bike but a 51cm Time Trial bike? You would think that the companies would keep the sizing the same. If you take a person that needs a 48cm road bike then their 48cm Cervelo time trial bike, which is the smallest they make would be to big. I just don't understand the shift in geometries.
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Old 12-06-08, 11:37 PM   #2
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because most bikes are not "small, medium, large" they are actual measurements. So they don't call a 51cm a 54 just because it's the size for people who usually ride a 54.
Make sense?
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Old 12-06-08, 11:44 PM   #3
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Originally Posted by Cdy291 View Post
So you want a shorter top tube on a time trial bike right? How come I would need a 54cm Cervelo road bike but a 51cm Time Trial bike? You would think that the companies would keep the sizing the same. If you take a person that needs a 48cm road bike then their 48cm Cervelo time trial bike, which is the smallest they make would be to big. I just don't understand the shift in geometries.

Just like women keep telling you.... size dosent matter long as it fits
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Old 12-07-08, 10:24 AM   #4
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To get into the correct position, you need to move your saddle forward. This effectively shortens your top tube. Shorter top tube = smaller number next to the frame size.

It should make sense that a bike you ride with your hands would be a different size than a bike you ride with your elbows/forearms.
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Old 12-08-08, 04:39 PM   #5
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Originally Posted by brianappleby View Post
To get into the correct position, you need to move your saddle forward. This effectively shortens your top tube. Shorter top tube = smaller number next to the frame size.
Thats usually not the case. Generally, the seat tube is what determines the size of a bike. A TT bike with real TT geometry should have a similar seat tube to your road bike, but a shorter top tube. With that said, I went a size smaller on my TT bike to get a bit more saddle to bar drop since I'm stupidly flexible. I ride a 58 road bike and a 56 TT bike.

To the OP, that's weird. They SHOULD keep things the same.
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Old 12-08-08, 05:54 PM   #6
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Thats usually not the case. Generally, the seat tube is what determines the size of a bike. A TT bike with real TT geometry should have a similar seat tube to your road bike, but a shorter top tube. With that said, I went a size smaller on my TT bike to get a bit more saddle to bar drop since I'm stupidly flexible. I ride a 58 road bike and a 56 TT bike.

To the OP, that's weird. They SHOULD keep things the same.
A TT bike will have a steeper seat tube thus shortening it relative to standover height. In addtion, the Top tube shortens. So, no, they should not keep things the same for the reason outlined above. In addition, because of the position one tends to achieve being the same as though you were in a road bike "drop" position, the top tube is lower on the triangle to accomodate a lower stem, and thus both the top tube and seat tube are shorter. We are not talking about randomly assigned "small, medium, and large" but actual numbers whose values have real meanings.

Last edited by DrWJODonnell; 12-08-08 at 06:01 PM.
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Old 12-08-08, 09:10 PM   #7
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Originally Posted by DrWJODonnell View Post
A TT bike will have a steeper seat tube thus shortening it relative to standover height. In addtion, the Top tube shortens. So, no, they should not keep things the same for the reason outlined above. In addition, because of the position one tends to achieve being the same as though you were in a road bike "drop" position, the top tube is lower on the triangle to accomodate a lower stem, and thus both the top tube and seat tube are shorter. We are not talking about randomly assigned "small, medium, and large" but actual numbers whose values have real meanings.
I get your logic, I hadn't thought about it that way. I busted out the ol' trig skills, and the difference from 73 to 76 degrees would make the seat tube a little under a centimeter shorter. I still kinda agree with the OP though. It would seem like a company would get more repeat customers if someone who rode a 58 cm cervelo road bike could go into the bike shop and say, "I want a 58 centimeter cervelo time trial bike" or vice versa.
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