Road bike used for tri question?

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2009-05-08 2:28 PM

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Subject: Road bike used for tri question?

From what little I have read it looks like one of the main differences between a road bike and tri bike is the seat tube angle.  The tri bike seat tube seems to be more upright - which in turn puts you more over the top of the pedals (farther forward), which helps save your legs for running (this is all in my layman's speak).  So why couldn't someone with a road bike just move their seat forward?  Granted, I know there are aerodynamic benefits, but I'm limiting my question to just this aspect of saving your legs for the run?  Is there any benefit to doing this or am I missing something?

2009-05-08 2:31 PM
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Subject: RE: Road bike used for tri question?
aneal000 - 2009-05-08 12:28 PM

From what little I have read it looks like one of the main differences between a road bike and tri bike is the seat tube angle.  The tri bike seat tube seems to be more upright - which in turn puts you more over the top of the pedals (farther forward), which helps save your legs for running (this is all in my layman's speak).  So why couldn't someone with a road bike just move their seat forward?  Granted, I know there are aerodynamic benefits, but I'm limiting my question to just this aspect of saving your legs for the run?  Is there any benefit to doing this or am I missing something?



You can, and the Cervelo Soloist was based around this concept. However, there are also other considerations about the handling, weight distribution, and the actual fit of the bike when you move forward/down. Look at slowtwitch at all their FIST fitting articles and it explains it pretty well.

John
2009-05-08 2:38 PM
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Subject: RE: Road bike used for tri question?
The two biggest differences between a road frame and a triathlon / time trial frame are that the the tri/tt frame has a higher seat tube angle and a lower head tube angle. Moving the seat forward with the higher seat tube angle (or a Fast Forward seat post) provides more power, gets the rider more aero and, supposedly, uses the leg muscles differently to save a little for the run. Now, with the seat forward, you need a longer top tube so you aren't cramped. The shallower head tube angle gives the bike more stability.

There are thousands of folks who are way faster than me riding road bikes. A road bike with a forwarded seat post and aero bars is only marginally slower than a tru tri bike.

Edited by greyg8r 2009-05-08 2:57 PM
2009-05-08 2:44 PM
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Subject: RE: Road bike used for tri question?

My understanding is also that the purpose of the tri bike's geometry is to rotate the riding position forward something on the order of 6-degrees.

2009-05-09 7:22 PM
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Subject: RE: Road bike used for tri question?
If you already have a road bike you can do what I did. I added a forward seat post, aero bars, longer stem so I am not cramped. Doing all this got me to a 80 Deg. seat tube angle. 80 deg. is steeper then some tri bikes.


Edited by keith-OG 2009-05-09 7:25 PM




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2009-05-09 8:23 PM
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Subject: RE: Road bike used for tri question?
aneal000 - 2009-05-08 4:28 PM

I'm limiting my question to just this aspect of saving your legs for the run?



Despite what you will read, there is nothing magic that will allow the tribike to save your legs for the run; only proper pacing can do that.

However, if properly positioned on a tribike, an athlete should be faster on a tribike due to aerodynamics so a given speed will (or should) be easier to maintain on the tribike.

Shane

2009-05-09 8:39 PM
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Subject: RE: Road bike used for tri question?
gsmacleod - 2009-05-09 8:23 PM

aneal000 - 2009-05-08 4:28 PM

I'm limiting my question to just this aspect of saving your legs for the run?



Despite what you will read, there is nothing magic that will allow the tribike to save your legs for the run; only proper pacing can do that.

However, if properly positioned on a tribike, an athlete should be faster on a tribike due to aerodynamics so a given speed will (or should) be easier to maintain on the tribike.

Shane



I'm glad you came out and said something that I had felt for some time - higher seat tube angle gives you better aero, but doesn't significantly "save" your running muscles.
2014-04-24 8:32 PM
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Subject: RE: Road bike used for tri question?
You could look at it this way:
A steeper seat tube angle rotates your hips so you can get down in aero, saving energy to ride the same speed...and that "saves your legs".

But that just means you're not riding hard enough.
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