iab

38s weigh a ton. Bad choice.

Mike Mills

Another thing came to mind that people tend to gloss over - the relative rolling resistance comparison is valid only at equal pressure. The thing is, large diameter tires are not available to contain high pressures such as 140 psi or more. Tubular tires are great because they can contain that really high pressure - more so than even an equivalent diameter clincher tire. The large diameter tires just can't go that high with today's rims, and tires.

What is really cool about tires like the Schwalbe KOJAK is that you can get it up to fairly high pressure (up to 95 psi) and it rolls and corners like crazy. They are also fairly light in weight (26X1.35 = 295 g; 700X35 = 330 g; 26X2.00 = 460 g). Don't think "mountain bike tire" or "beach cruiser" tire, think of the feel of a tubular tire without the harsh ride from super high pressure (even though it's a clincher).

mickey85

But remember, when we're talking randonneuring, 28's are "normal," 32's are "fat," and 35's are Brother IZ tubby...

old's'cool

Hydrated, I'm in general agreement with most of the points in your post. However, I'm not convinced by your point #2.
I'm a mechanical engineer, and I can readily envisage tire architectures that depart from a round internal cross section; what is more, I see what appear to be examples every day on passenger cars that I see on the road. I'm sure you're familiar with tire aspect ratio. These days, a 60% aspect ratio is pretty common, and 40% is not uncommon for vehicles that use very large diameter rims relative to their ride height. I find it difficult visualize a 40% aspect ratio tire with a round internal cross section. What say you?

Hydrated

You are correct... but so am I...

That low profile tire is only square looking because of its construction. Those extremely low aspect ratio tires are squished down only because they are built with such a short sidewall. But they still try to be round inside... but the sidewall is tiny when compared to the tread width... so the internal cross section comes out looking something like a squished ellipse-ish shape. What I was trying to say in my original post is that a tire has a shape on the inside that is FAR different than what it looks like from the outside. And it's never square.

noglider 

hydrated, I take your word for it, but it does seem that car tires and bike tires have different needs because of the way the bike sways deliberately through turns. Cars do their best not to sway through turns.

chipcom 

We're talking 28s, not 38s for Paris-Roubaix

Hydrated

Oh yes... you are abso-tively correct.

But you never said that we wanted to look at the dynamics of cornering and directional change on the tire. I was only looking at the physics that affect rolling resistance and cruising effort. Car tires work differently from motorcycle tires (and their little cousins... bicycle tires) in the way that they corner and steer the vehicle.

But the physics of sidewall deflection, contact patch variables, and rolling resistance still hold true for every pneumatic tire on the planet.

Cedarbat

This is an interesting Thread....allow me to throw in my own 2 psi.

I bought a pair of Vredestein fortezza SE tires several years ago, in part, because they were rated for 160psi max. I assumed that higher pressure was better, and I would routinely max them for competition events and fast group rides. The result is that I would and get "pounded" to death by every crack or divit in the road surface. They felt like they rolled much easier at the higher pressure, but there was definitely a "fatigue factor" involved. I continued to do this however, because I thought the pounding was worth the decreased rolling resistance, especially for triathlon events.

I took another look at the tire pressure discussions recently, however, when I bought a pair of used Zipp wheels which have a max psi rating of 125. There was alot of research out there indicating that there is at best diminishing returns, and at worst, a negative effect of pressures beyond about 110psi for rolling resistance, not to mention the forces it puts on the rim, especially under heavy braking. I thought back to my "beating on the bike" at 160 psi and it occurred to me that the reason I was getting pounded so badly was that my entire body weight, and the weight of the bike, was getting pushed upwards violently. That takes force or energy to do that, not unlike the additional force it takes to move a bike up a steep hill as opposed to flat ground. If a lower pressure tire can roll over the crack or divot smoothly and not have the same violent jolt or vertical movement, then the force required to lift the bike and rider is not experienced, and thus less energy is expended.

It seems to make sense to my pea-brain to think of it that way.

Mike Mills

But 28's are used in preference to 23-25's. It is done for a reason.

noglider 

Ah. It all makes sense now.

Can you recommend an article that explains rolling resistance? I'd like one I'm likely to comprehend.

Mike Mills

Precisely why I like my Kojaks and how I use them.

Mike Mills

I think my next experiment will have to be some fat tubulars. Who makes the largest profile tubular?

iab

You can get 27mm from FMB, Dugast and Challenge. Larger tubulars can be had, but they are for cross bikes, have knobby tread and will have terrible rolling resistance. Tufo and Dugast do make a 32mm cross tire with a diamond tread (for racing on grass). Not as bad as knobbies but definately not fast like a road tread.

old's'cool

OK, but my defiinition of round is a shape whose center is at x,y coordinates 0,0 and whose circumference is defined by the equation x*x + y*y = r*r, where r is the radius of the cross section.

ricohman

The ballon sized tires on my carbon Roubaix seem huge compared to the 23c the my Marinoni Special rides on.
But the larger tires indeed roll smoother and faster over rough roads. The difference in comfort is huge and at 50km into a ride I feel less fatigue.

old's'cool

It was fun while it lasted

bobbycorno

Um, no. My 650x38b SOMA B-lines are listed at 360gm. There are 700x23's and 25's that weigh more (and, not coincidentally, ride worse).

SP
Bend, OR

RFC

Have you checked out this source?

https://smtp.schwalbetires.com/tech_i...ing_resistance

Road Fan

I have a pair of Vittoria butyl diamond tread cross tubulars, 32 mm, lightly used and never flatted, for sale. PM me, anyone who wants them for an experiment.

iab

Umm, yes.

22mm tubulars are at 250 grams. Your tire + inner tube (100 grams at least) = 460 grams. You don't think 200 grams per wheel is a lot to someone who races? Guess again.

BTW, 25mm tubulars are 280 grams and 27mm are 290 grams. All a great deal under the boat anchors you're using.

Mike Mills

This thread seems to have two different factions arguing their points. However, correct each faction is, no one has yet drawn a simple distinction between them.

RACING versus RECREATIONAL RIDING

I don't know anything about the modern racing scene but I suspect few racers use true C&V bikes. Some, almost certain, most - not likely.

I thought this thread was about normal, recreational riding, not racing. Is it, or is this thread about racing and racers?

iab

Rolling resistance matters most to those who race. Otherwise, it is pretty insignificant, except to weenies.

USAZorro

At the extremes, it is far from insignificant. Calculations in one of the issues of BQ (back when it was VBQ), did calculations that showed upwards of 7 hours time difference in completing PBP due to rolling resistance alone.

iab

PBP is a race.

But does your average Joe give a crap if their 2 hour ride can be reduced to 1 hour and 50 minutes? Is your average Joe at a fitness level where thet can get the most out or rr?

So again, rr matters to racers. Otherwise, to non-racers, it is pretty insignificant.