Tuesday, August 14, 2007

It's a sport and a science (Clinchers vs Tubulars)

I just spent the evening using publicly available data from drum tests (verified somewhat under real world conditions by Lennard Zinn) to calculate whether LEW wheels offered superior performance in clincher or tubular configuration. The lessons are surprising and applicable to more than just LEW wheels.

1. Even with a reasonable weight penalty (~130g for LEW), the best clincher is better than the best tubular due to reduced rolling resistance.

2. If you use a tub, use track glue or shellack (even on road wheels) and get someone good to do the gluing. Road glue experiences more hysteresis and hence loses more energy.

3. Tubs get better, due to lower weight, at steeper gradients. However (and I was shocked by this), we are talking beyond 20% before tubs are superior, at least if the weight penalty is kept within a couple of hundred grams.

4. On flats, a clincher with similar aerodynamic properties will almost always be better than a tub, even if the clincher is substantially heavier.

5. The penalty you pay for accelerating rotating mass isn't very high, generally <1W, whereas the penalty you pay for having higher rolling resistance from a tub is >5W if you are at reasonable speed.

Comparisons were done using coefficients of rolling resistance obtained from a clincher Vittoria Open Corsa CX with a normal tube and a Veloflex Carbon with road glue. I assumed a super-light tube when calculating weight penalties as this is for a race day only setup. The Vittoria will perform slightly better with a latex tube. The Veloflex will perform better with track glue or shellack.

Moral of the story: if you are considering shelling out for tubs as race wheels, think twice. You might be better off with a similar clincher wheelset and a really nice set of tires and tubes.

My dream build:

LEW Clinchers - <970g for the pair
Vittoria Open Corsa CX - ~225g each
Superlight latex tubes - ~50 g each

11 Comments:

Blogger C-MAC said...

Yet at the same time, my dream training wheels are 32 spoke triple cross rear, double cross front Ambrosio, DT or Mavic's. At least I attained that dream. I'm not so new school after all Timbo.

11:32 PM  
Blogger timboy said...

What- clinchers have lower rolling resistance than tubs. Since when, how please explain?

This is relevant to me because I'm considering buying cosmic carbones- and was thinking of getting tubulars over clincher models.

Reasons- I like tubulars on my track wheels, they feel super fast, much faster than clinchers anyway. But I guess that can be explained by the fact that the wheels are more rigid and aero.

Dream wheels- 36 hole ambrosio rims, record hubs. mmmmmm

11:47 PM  
Blogger C-MAC said...

Look at the chart at this page: http://www.velonews.com/tech/report/articles/12493.0.html

I think people tend to think that tubs are better because people ride tubs on race wheels and always have, and therefore they tend to own better tubs (better manufacturer, higher TPI, etc). If you compare apples and apples, you need to compare the best clincher with the best tub. On this basis, the best clinchers are better. I'm recommending Vittoria Open Corsa CX for tires. I think the weight penalty on Carbones is about 200g. In that case, and considering you like flat races and they will be more durable, I'm saying rock clinchers.

11:56 PM  
Blogger C-MAC said...

By the way, Carbones are heavy, expensive and outdated. Who are you getting them off/what are you paying? Have a chat to Mitch. He will hook you up. He is the wheel guru.

Maybe you me and Al can form the Bicipolitics/Red Rooter race team, sponsored by Mitch?

11:58 PM  
Blogger timboy said...

Mitch says he can hook me up with x-treme tubs for $1700.

That's more or less the same price as for CarboneSL clinchers.

Cheap I know.

Team bicipolitics/ le coq rouge/ sponsored by le rouleur would be a smashing idea

12:14 AM  
Blogger timboy said...

I should add Carbones are very aero, bomb proof and relatively cheap.

Guys in Belgie race carbones day in day out over cobbles and shit roads- they are tough as nails.

12:16 AM  
Anonymous Phil said...

You young people, so behind the times.

I remember reading a scientific assessment of this more than a decade ago and have never understood why singles persist.

Having used both I'd have to say that todays modern clinchers are as good if not better than clinchers....the belief to the opposite is a fantasy similar to creationism.

And we wouldn't want that would we want that would we. Trust the science.

BTW, Ksyrium SSC SL's plus Open Corsas and latex tubes would do it for me.

3:47 AM  
Blogger C-MAC said...

Phil: I've known about the rolling resistance difference for a while, I just hadn't bothered to model it. The thing that surprised me is (i) how large the difference was and (ii) how little the weight penalty mattered even at steep grades. The remaining question is, how much does track glue improve the situation over road glue? And why do the AIS let riders roll on singles when they are normally so on top of this science/technology stuff?

12:37 PM  
Blogger C-MAC said...

Dude, I know what you're saying about durability. Cosmics are good on that front. Definitely performance wise you should get the clincher and, for races without too much debris, latex tubes and Vittoria Open Corsa CX tires (or a Deda Tre Giro d'Italia if you can find one or a Michelin Pro Race 2 if you can't get either of those).

This will be a rocking combination. If they are race only wheels, it shouldn't matter that latex tubes aren't that durable - still a heap cheaper than buying a new tubular if you were going to go in that direction. If you want to run a more durable combo, I'd stick with that tire and run a butyl (ie normal) tube.

10:32 PM  
Anonymous Kermit said...

I don’t think that it is a proven fact that Clinchers have lower rolling resistance than singles. From the reports that I have read, there appears to be some flawed scientific methodology.

1) The Velolex Carbon is not a particularly fast single. If you compare a Vittoria open corsa Clincher against a Vittoria CX Pista single for rolling resistance, I think you would find a different result.

2) Tyre pressure plays a huge part in the rolling resistance and is highly dependent on road surface. From the studies I have read, there is no data on the pressures that they were running. I suspect that they run the clinchers at 100psi and the singles at 200psi. Singles have the capability of running at very high pressures (ie 250psi) many people assume wrongly that the higher the pressure the lower the rolling resistance and pump them up to max pressure. This may be true on a flat surface such as wooden boards. However, on bumpy surfaces you might sound and feel fast running high pressures. However, you tend to bounce over bumps and loose traction (ie power). Singles also have the capability of running effectively at low pressures without the risk of pinch flats. This is why they may be very fast over the cobbles.

3) The road glue and tape is not ideal for singles, particularly when running at high temperatures. They are mainly marketed to Triathlets for fast changes. The Contact adhesive type glue would have minimal slippage or hysteresis.

4) When considering rotating mass, it is not the total weight of the wheel that is important it is how that weight is distributes relative to the hub. There is squared relationship to the distance (i.e. Force = Mass x radius ^2) Therefore any small weight difference in the tyre is extremely important. So too is the design of single rims that will have less mass than a clincher equivalent.

6:44 PM  
Blogger C-MAC said...

1. I'm talking about roadgoing singles. If you want to race your track tires on the road, that's a different story. What is the crr for a pista?

2. Concede. Sort of. All the numbers have tires tested at identical pressures. (i) When do you race on cobbles in Australia? and (ii) when do you run your tires at 250 psi except on a track? Whilst it's true you might want to run lower pressures on a rough surface, I don't think you have to risk pinch flats to do this with a clincher. The magnitude of pressure drop required is too low, unless you are on cobbles.

3. I already made this point. Contact adhesive makes less of a difference than a latex tube. Go clinchers.

4. Nowhere near as important as you might think. Only important at all under acceleration, and overwhelmed by rolling resistance disadvantages at speed. If you have crr data on roadgoing singles that suggests a number below, say, 0.4 (a good clincher with a butyl tube) or, more fairly, 0.25, a good worn in clincher with a latex tube, then stump up.

If you want to run the numbers on the magnitude of the effect of different rolling resistance vs weight penalties, I recommend you look at "Validation of a Mathematical Model for Road Cycling Power", Martin, Milliken, Cobb et al, European Journal of Physiology 1998.

I used crr numbers from controlled tests in tour magazine, biketechreview.com, analyticcycling.com and a few other sources employing similar methods. Whilst there are minor differences, I can't see any glaring problems with the methods for calculating crr.

Of course, none of this means you shouldn't be running nice silk single with track glue at 250psi on the boards. Preferably glued onto a disc and the deepest front possible.

8:26 PM  

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