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tires 20 or 23 ??? help me out here(10 posts)

tires 20 or 23 ??? help me out hereAdam Steelman
Apr 25, 2001 5:27 PM
hi,
I will be in a race this week end and for the time trial I want to run my 20 tires but for the RR do you think I should run 20s or 23s. If it helps I am a small Jr. (130) Not the best sprinter. Love to climb and plan on a break. For the 23 they are the axle pro's and the 20 are a clinchers. Thanks
re: tires 20 or 23 ??? help me out herebigdave
Apr 25, 2001 8:05 PM
I like 23s for their resistance to pinch flats, but I'm 180+ pounds so, you might be just fine on the 20s. I'd go with whatever you're more confident in and have had the best luck with. Performance-wise, you'd be hard-pressed to notice a difference, IMHO.

Good luck,

--Dave
20's are noticably fasterrunstevierun
Apr 26, 2001 7:28 AM
I've two sets of axial pro clinchers 23's and 20's.
The 23's came with the bike and I thought them a bit mushy.
I bought a set of 20's and pump 'em up real hard (140psi)
The 20's are noticably faster and a bit harsher.
Plus the 20's roll more like my sew-ups used to(minus the harshness).
(I switched to clinchers two years ago and still miss my sew-ups)
Got any data?Kerry Irons
Apr 26, 2001 4:09 PM
The rolling tests done repeatedly show that, at the same pressure, narrower tires are slower than wider tires (same brand, same model). This is because the casing of a narrower tire deflects more to achieve the same contact patch area as the larger tire. Typically, narrower tires are pumped to higher pressures, which pretty much cancels this deficit. Narrower tires have a small advantage in aerodynamics. In a road race, that advantage is quite minor. Narrow tires pumped to higher pressures often "feel" faster because of the harsher ride, but you would need repeated time trial tests at fixed tire pressures to prove that your narrower tires are "noticably faster" than the same model of tire in the next wider size. All the reported data disagrees with your concolusion. Otherwise, all you have is a potential placebo effect combined with a false perception.
Well, there is the weight thing...Java
Apr 27, 2001 11:19 AM
The fact is that any tire in a 20 mm should be lighter than the same model in a 23 mm AND that's the outermost rotational weight. Not necessarily a big difference but a beneficial difference nonetheless.
The facts speak for themselves.runstevierun
Apr 27, 2001 2:52 PM
I think your "data" is wrong and based on a false assumption
that the "contact patch" between all tire sizes is constant.
Smaller x-section = smaller deflection=faster rolling
Trade off is less contact patch on ground thus
small x-section tires are dicey in wet weather.
Test it out where the rubber meets the road.
If your instinct was right, all the pros would be riding
23's or even 25's. Well, what are they riding????
A placebo effect might deceive weak-minded old me but
I don't think that the director-sportif of Once or Postal
would be fooled. That's why they ride 20's in the Tour (and even 18's on the TT (in tubulars though))
Facts?Kerry Irons
Apr 27, 2001 3:24 PM
Fact 1: the contact patch size is a function of rider+bike weight and tire pressure. If the bike and rider weigh 200 lbs, and you have 100 psi in your tires, the total contact patch will be 2 square inches, regardless of tire size. If you raised tire pressure to 200 psi (!!) then your total contact patch would be 1 square inch. Simple physics. THEREFORE if a smaller tire is used at the same pressure, it will have to flex more than a larger tire to create the contact patch. In order to avoid this problem, as I said, smaller tires must pumped to higher pressures to get to the same rolling resistance as larger tires. This is typically done and not a problem, as smaller tires are normally rated for higher pressures. This does NOT make smaller tires lower in rolling resistance than larger tires unless they can be pumped up enough to actually have less casing deflection than the larger tire. I never said wider tires were lower rolling resistance, I just said narrower tires were not necessarily lower rolling resistance. I'm not going on instinct, I'm going on published data (the old Bicycling Science journal).

Fact 2: Horses for courses. The pros frequently do ride 23s, depending on the course, road surface, and rider weight. 25s are not unheard of for the spring classics with siginificant sections of cobblestones. Remember, few pros weigh more than 150 lbs, and many are in the 130-140 lb range. They can ride a 20mm tire at lower pressures, and get comfort and traction. Narrower tires are, as I said, more aerodynamic and therefore an obvious choice for a time trial.

Back to my question, how do you measure that you are "noticeably faster" on 20mm vs. 23mm tires? Have you ever done repeated time trials on the different width tires (inflated to mfr. recommended pressure) and demonstrated this speed increase? Or are you "just sure"?
Ok- simple question....peloton
Apr 30, 2001 8:25 PM
Kerry- If your facts on tires are as you say, then why do you see the most narrow tires in time trial and track events where pure speed is paramount to success? It would seem to me that if wider tires were faster than narrow ones, narrow tires wouldn't be the choice of the best when they NEED to go fast.

Agreed, rider style and course conditions can make the results vary. I too agree wider tires might be better for some conditions. As a whole though, I would say that for pure speed a narrow tire is the weapon of choice.
Simple answerKerry Irons
May 1, 2001 6:33 PM
As I said, narrower tires are a bit more aerodynamic, so are the tire of choice in a time trial, and are typically pumped very hard. Rough roads are less of an issue, and so is handling in general since you're not in a pack. Track racing is on a perfectly smooth surface and speeds are higher, and track tires are pumped even harder. And, if pure speed - not handling, not comfort - is the issue, narrower tires offer a small advantage. My main point is that it is not a dramatic advantage, and should be balanced against many other factors. For someone who is heavy, they are typically not a great choice, all round. For someone who is light, they may make sense. But you can't make a blanket statement, as some do, that "20s are the best." 20s used to be much more popular as people went for the "narrower is much faster" routine, but the swing has definitely been back toward 23s in the past couple of years.
I can buy thatpeloton
May 1, 2001 9:25 PM
I just find the whole tire argument funny. I doubt any of us are that fast where it really makes a difference aside from personal preference. Lance or Jan could probably tt pretty fast on 25's too. It's only a matter of seconds.