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PostPosted: Sat Sep 03, 2005 1:23 am 
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Location: Hollywood
Hey Guys,

Generally, the rule of thumb for tire aerodynamics is that you go narrow up front, and wide in the back, since the seat tube protects the rear wheel from the wind. For that reason, I purchased a pretty wide section tire, Veloflex Roubaix, for the rear. Listed width is 24mm. It's exactly like the Carbon model, only wider. Same tread, same construction. However, one thing that's keeping me from gluing it on is that the maximum inflation pressure is only 6/7 bar (100psi). I weigh between 160-170. Should I sell this tire, get a narrower one that can handle more pressure (and likely a bit lighter), or would the 100psi suffice (as the volume of air is greater)? My intention for the wider tire in the first place was to absolutely kill the corners. I had a 21mm vredestein on there, and it wasn't confidence inspiring in corners. For those who care: the tire weighs 290grams (pretty heavy, and i'm guessing lower inflation pressure will accelerate wear as well?). Rim is Reynolds DV-UL. The wheels see lots of crits, TTs, and RRs. Pretty much everything.

-Dude


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Posted: Sat Sep 03, 2005 1:23 am 


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PostPosted: Sat Sep 03, 2005 2:32 am 
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Well I don't have an exact answer to your question, but there was an article on cyclingnews a while back i think, where it was said that a wider actually has less rolling resistance.


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PostPosted: Sat Sep 03, 2005 3:26 am 
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Location: in Colorado
I'd give it a try. I have 26 mm clinchers on my training wheels and they are great for the miles I ride them.
I can ride them at 85-90 LBS with no problems. Although they are pretty slow at those pressures i don't pinchflat them and i weigh about what you do. The extra air really gives the tire alot of room for error.
When i pump them up to 100-110 they still deflect alot when you push them. Hope this helps.


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PostPosted: Sat Sep 03, 2005 3:42 am 
Why do you use such wide tyres?

19mm for TT Dry
21mm for TT Wet & Road Race Dry
23mm for Road Race Wet
25mm for Paris-Roubaix :D


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PostPosted: Sat Sep 03, 2005 4:10 am 
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Location: Hilly, Hot, and Windy
brianwchan wrote:
Well I don't have an exact answer to your question, but there was an article on cyclingnews a while back i think, where it was said that a wider actually has less rolling resistance.


Your only half right, I think? I think the fattys are faster only if it and the skinnys are both inflated to the same preassure. I.E. a 21mm @ 100psi and a 23mm @100psi. I think what they figured out in the above example was the fatty was faster. I'm almost, (almost!!!) a 100% that they figured out that a skinny tire, at "stated preassure" or "suggested preassure" which I assume is the range the tire gives, is faster/less resistance.

The article was also about some new mud tire for the Paris-Roubaix that Conti put out. It also mentioned that the tire preassures were somewhat of a secret. I think it summed up buy saying the guys were better off using a fatty a lower preassures than a skinny at lower preassure. It makes since that they would do the comparision this way, (same preassures reguardless of width) since it would seem counter-intutive. I would think a lower preassure skinny would have better mud clearence and less resistance. Guess I was wrong?

Could be wrong, it was kinda' late when i read the article.


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PostPosted: Sat Sep 03, 2005 4:17 am 
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I think it's a great idea. I have way more fun with fat tires like 28s. You get much better ride and you're easier on your wheels.
I think it makes a whole lot of sense for road riding, they will be just as fast as skinny tires and there is no point to crazy pressures on the road. I think super skinny insane high pressure tires only really excel on good wooden tracks.
More pressure doen't equal less rolling resistance in real world conditions. I think the bike industry doesn't really get this. Ask a car tire company if more pressure will make for faster rubber.


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PostPosted: Sat Sep 03, 2005 4:22 am 
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Have you actually weighed the tire? I weighed a carbon the other day and it was close to 290g.

Don't worry about the pressure. It will still have the same rolling resistance as a narrow tire at the recommended pressure, or lower at the same pressure. On the crap roads that most people ride high pressures will slow you down, decrease traction, and make you uncomfortable.

Might have saved some money and just run the carbon at 6.5-7 to get more traction. Unlike clinchers tubular tire rolling resistance doesn't increase much with decreased pressure.


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PostPosted: Sat Sep 03, 2005 5:12 am 
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Corner speed: Nearly 30 years ago I decided to do some cornering experiments. I wore 2 pairs of jeans over my wool shorts, a leather jacket over my wool jersey and of course my leather "hairnet" helmet since I was going to do something dangerous. I had 2 sets of tubular wheels, one had Clement Seta Criterium Extras (about 22mm - 220g), the other had Clement Seta Campionato del Mundos (about 25mm - 290g). My "method" consisted of going faster and faster through the same corner until I crashed. I expected that a larger rear than front would be faster, smaller tires would be faster, more pressure will corner faster. In my test, the front tire was my limiting factor not the back. This might only really show that del Mundos can corner faster than Crits. Most of the testing was on a level corner. My first downhill corner crash was the last one I wanted to do. My first uphill corner crash was even nastier. I decided that a dozen crashes that day was enough. Since then, I've never been crazy? curious? enough to repeat this test with other pairs of tires.

I had assumed that more air pressure would be faster cornering. Wrong, more pressure rolls faster in a straight line and loses less speed in sub-maximal cornering. The lower the pressure, the faster the maximum corner speed before traction breaks away and I crashed. I got down to around 70psi (under 5 bar) before concern for rim-denting stopped me from going lower. I tested up to about 150psi (10bar). The higher the pressure, the quicker the tire breaks away at the limit and the more difficult it is to hold the tire at its (slower) limit than a softer-inflated tire. Using equal size tires, less pressure in front than the rear is faster cornering than equal pressure. I usually run about 10psi (.6bar) less in the front than whatever I'm running in back.

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PostPosted: Sat Sep 03, 2005 5:26 am 
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You are truly hardcore, =4cranks. That's insane. Insane, but awesome still.


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PostPosted: Sat Sep 03, 2005 5:48 am 
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Aerodynamics: Front tire choice for TT. You have to make a decision: Narrow is faster on the straights, wider is faster in the corners. The clock continues to tick when you are in the corners. Flats cost you a lot more time in a TT stage than a road stage. A larger-section rear tire is substantially more reliable and the drag increase is trivial. I wonder who will be the first manufacturer to make a rear disc wheel intended for a 22-23mm tubular (or clincher). 22 disk vs 19 disk: Same drag, more lateral rigidity, potentially lighter. The TT frame needs to be designed for the larger section rear.

That 100psi limit fat tubular? The larger the section, the lower the optimum pressure. You might not need more than 100psi. Tandem riders commonly run 20-30psi above the "maximun" pressure. If you have a race ending with many sharp downhill corners you might put it on the front. I won one race that way.

Quote:
You are truly hardcore, =4cranks. That's insane. Insane, but awesome still.


Er, thanks I guess. I wouldn't do it again. I think I should have had a Miche the Michelin man outfit!

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Posted: Sat Sep 03, 2005 5:48 am 


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PostPosted: Wed Jan 22, 2014 4:34 pm 
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Joined: Tue Apr 12, 2011 8:08 am
Posts: 1957
Location: Pedal Square
Just found this old post via Google. Truly awesome, and ahead of times. Belated kudos!

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