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roll resistance, aero, weight, tires & posts?(7 posts)

roll resistance, aero, weight, tires & posts?jjdbike
Aug 22, 2002 9:41 AM
If anyone can provide any upto date info I would be greatly apprecitive.
I have read that aero posts are actually less aero than round wich is the opposite that I have read numerous times & counterintuitive?
Along the same lines, I recently heard that 700 X 23 have less rolling resistance than 700 X 20, again also contrary to traditional wisdom. I know that for speed, aerodynamics & weight also are important.
Can someone please substanciate or add to these issues?
Thanks very much in advance!
re: roll resistance, aero, weight, tires & posts?Part Time
Aug 22, 2002 11:17 AM
This site may interest you. I'm not sure I buy everything they are saying, but it's more information.

http://www.cervelo.com/qa/article5.html
Some dataKerry
Aug 22, 2002 5:16 PM
Whether a seat post is round or aero shape, it will have minimal effect on speed. With your legs constantly moving and coming very close to the seat post, the air is very dirty there, so shape doesn't get you much. However, you'll note that the top pros' time trial bikes almost universally have aero posts. When a few seconds can make the difference in winning or losing, you go for even minimal improvements.

At the same inflation, a 23 will deflect less than a 20, so it will have lower rolling resistance (the deflection of the casing is the primary source of rolling resistance). However, 20s usually have a higher pressure rating and also must be pumped harder to prevent pinch flats. This essentially cancels out the rolling resistance argument. 20 mm tires are slightly more aero, but pumped up hard, the handling is not great. As with everything, you face a compromise. Unless you are quite light, you'll probably have the best experience with 23s. Going to a 20 might save you a few seconds in a time trial - important if you're in contention for the win, meaningless otherwise.
Some dataAjayM
Aug 22, 2002 7:25 PM
John Cobb has stated that the "aero" seat posts are costing those pro teams a bit of time compared to a regular round tube. And as far as I've found so far he's one of the few who is posting information gathered from wind tunnel testing instead of just using the math, etc. He's also the "aero" guy who helped Trek design the USPS time trial frame, and does aero work for USPS.

Also on the tire issue, I read another article about some of the time trials in the TdF and how the teams went with wider tires on some of the courses (something like a 22 or 23mm, instead of the usual 19 or 20mm) because they wanted to reduce the risk of flats. So obviously the skinny tire doesn't improve the times that much.
Cobb says . .Kerry
Aug 23, 2002 4:10 PM
So if the aero posts are a problem, and Cobb is Lance's personal aero guru, how come the Trek TT bike has an aero post? Just one of life's little mysteries.
I wondered that myself....AjayM
Aug 23, 2002 7:30 PM
And here's the answer Cobb gave in an interview located here http://www.slowtwitch.com/mainheadings/techctr/compact.html

DAN EMPFIELD: How about aero posts? It seems to me that an aero post on a compact frame ought to be a pretty good idea.

JOHN COBB: For many years I have recommended aero seat posts to many racers. Practically all of us well-intentioned retailers have sought after, stocked and sold some types of aero seat posts. Almost every rider who has gone out to set either a personal record or some world record has had their advisor or mechanic eye their seat post to help shave off those last few seconds of speed. It seems to make perfect sense to have some thin, willowy post between your legs so that air can easily flow out the back of the bike and give more speed. But what seems to make intuitive sense doesn't always test out that way.

Using tall aero seat posts on a compact frame––though it seems like it ought to be faster––seems to actually cost time. How much slower is it? My results suggest that it might be about 45 seconds slower over 25 miles. Aero posts on traditional frames aren't as bad but still aren't as good as round posts.

DAN EMPFIELD: So what works?

JOHN COBB: A tall seat tube with an integrated post that has an aero shape but which tends to fill in the area between the rider's legs. In other words, a skinnier post does not seem to be necessarily better. But it can't just be a fat post—it has to have a trailing edge that reconnects and directs the air behind the rider. So if it's a small, thin post, a round shape is fine. Best is a well-integrated seat tube and post where it's big enough to take up some space, while also having a good aero shape.
re: Campy Record aero postNoam
Aug 23, 2002 12:14 AM
In my opinion this component was one of the best looking component campy ever made(together with the Delta brakes)