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More on tire width and rollin' resistance(8 posts)

More on tire width and rollin' resistanceWoof the dog
Jan 23, 2002 11:50 PM
Here is a link to another forum. You should check it out from time to time as more messages hopefully will be added. It seems that those guys have said what I've been thinking of too.

http://www.cyclingforum.com/forums/Thread.cfm?CFApp=2&Thread_ID=647&mc=4

So yeah, how come pro riders use narrower tires for time trials? anyone care to comment?

hehehe

Woof the sly dog.
re: More on tire width and rollin' resistanceJimP
Jan 24, 2002 5:40 AM
Ok, I too have been looking at a lot of the postings about rolling resistance vs. tire width. Most of the premises sound good but don't back it up with solid research. The best words said that the wider tires tended to be heavier and have more rubber so that their rolling resistance would be more than the narrower, lighter tire. Also, a lot was said about tire pressure and that a smaller tire needs to have a higher pressure to support the same weight. Now, even if the rolling resistance of the narrower tire is the same as the wider one, it will have less wind resistance - that hasn't been disputed.
I would like to see the results of a real study on both rolling and wind resistance for tires. I know that some folks have said a lot of words about wheel, spoke, and nipple wind resistance but I ride Nimble Crosswinds so that isn't as much an issue with me. The Conti Comp GP 19mm certainly LOOKS aerodynamic on the front wheel and the Conti Sprinter 21mm feels good on the back ( and isn't as expensive to replace since it wears out faster ) .
Now that you re-opened the can of worms, lets see what others say.
Try this for size....John-d
Jan 24, 2002 6:14 AM
Two equal road rides of 25miles or more, do one on 19mm tyres the other on 23mm tyres. All things are of course equal.

I think the ride with the wider tyre will be faster because one gets less tired due to the improved ride. I think the other issues are too marginal to make much difference.

So, you start feeling that the light thin tyre is really fast, then the vibrations begin to show and the last section of the ride tails off. That's why a short test ride can be misleading, IMHO.
Done it many times, and you're rightcory
Jan 24, 2002 8:20 AM
The long way home on my commute is 22 miles. When I put 35mm tires on my Atlantis (as Riv recommends), they felt great--but I wondered how much slower they were.
Last summer I swapped among 23s, 28s, 32s and 35s (I weigh 220, so I don't go superskinny). My times on individual days varied, of course, but there was no significant correlation between tire size and time. The Panaracer Pasela 35s are supposed to run at 75psi, and they feel squishy at that pressure, so I use 85. But they weren't any slower over a number of trips.
Only thing I can think of that might affect the outcome is that I was pretty much just cruising, not going as hard as I could. If I were using max effort, maybe the small tires would be faster. But the fatties are so much more comfortable that I'll gladly trade for everyday use.
re: More on tire width and rollin' resistanceBirddog
Jan 24, 2002 8:24 AM
So yeah, how come pro riders use narrower tires for time trials? anyone care to comment?

Time trialers and triathletes use narrower tires because they are lighter and more aero. THE MOST IMPORTANT WEIGHT TO SHAVE FROM A BIKE IS THE ROTATIONAL WEIGHT!! The further outboard and bigger the circle of rotation, the more important to reduce. That's why so many triathletes opt for the 650 tire/wheel size. There is a good argument that on a flat course, 700c is actually better, but a significant number of tri-heads will tell you otherwise. One of the engineers or physicists can explain this in mechanical terms.
re: More on tire width and rollin' resistanceWoof the dog
Jan 24, 2002 11:13 AM
come on now, dog, i knew that alright! Its just a restating a question to make some people here actually think.

Do you wanna go and take a crap on a rug together?

Woof the dog.
Yes to the rugBirddog
Jan 24, 2002 6:37 PM
But first I want to chow down on a big bowl of Gravy Train, that stuff is killer!

Grrrrrr,
Birddog
re: More on tire width and rollin' resistanceguido
Jan 24, 2002 1:51 PM
Here's what one of the posters said on Cyclingforum.com:

"Rolling resistance deacreases as tyre width increases because wider tyres also have a larger circumference. A larger tyre will change its shape less than a thinner tyre will when a certain amount of weight (you and your bike) are put on it. Since much of rolling resistance comes from the tyre changing shape, less change in shape means less resistance."--Rob Coapman

That's why tubulars are both more comfortable and still fast: They don't squish like a 700x20C, therefore have less rolling resistance and corner better. A 26C or 28C slick clincher has very little rolling resistance for the same reasons quoted above, bigger around, less squishy, but their heavier rotating mass makes it harder to keep them spinning.

So a case could be made that a light tire can have greater rolling resistance than a heavier tire. That's a function of roundness, hardness, and tread design, and is always felt, always there. Weight or rotating inertial mass on the other hand, can be easily overcome, as on a flat, drafting, in a tailwind, or downhill where weight is actually an advantage. Overcoming that inertial mass will slow you down on a climb or in a sprint, though, so racers go with the lightest that will still get them to the finish line.