THIS WEEK IN PRO CYCLING
Technical Q&A with Lennard Zinn - More tire talk
Dear Readers,
I have received so much mail about the " tubulars vs. clinchers rolling resistance debate that I could not resist running some of the better ones. The debate may never end, but your letter sure have raised a lot of issues that I’d never considered.
Lennard
Dear Lennard,
Something about the Vittoria slide doesn't seem right. They say that there is more contact surface area. At the same pressure, both tires, tubular and clincher, must have the same total contact area with the ground, since that is the force (pressure times area) that is resisting gravity. The shape of the contact area may be different, as the 29er converts have been arguing vociferously about 26-inch vs. 29-inch tires for years, but the total area at the same tire pressure should be the same. If you can run higher pressures in a tubular, the total contact area will be less for the higher pressure tire. Their other points may be valid, but the tire contact area argument doesn't seem totally correct.
Steve
Dear Lennard,
The letter from Vittoria claiming that tubulars' greater flexibility and shock absorption provides superior rolling resistance is crap. The more flexible the tire, the more deformation it will experience. This absorbs/consumes energy (supplied by the cyclist) and will increase the rolling resistance.
True, on bumpy roads this is a benefit, as your wheel will bounce less. On "normal" pavement, this lower tire "stiffness" will increase rolling resistance.
I recently installed "stiffer" tires on my car (I took off the wasteful, softer compound, "hi-performance" tires.) My gas mileage on the highway increased by 8 percent; actually by 2 miles per gallon! My car has a continuous mpg readout so I know exactly the mpg increase.
"Hi-performance" car tires have a softer compound to better "grip" the road; ergo, they deform more to do this; they are more flexible. This is necessary if you are a race car driver. I am not.
For 99 percent of my driving, the "hi-performance" tires are a total waste of gas and money, plus they need to be replaced after about 25,000 miles. (What a waste!).
As for bike tires, 95 percent of the time, I ride on normal pavements and I bet most cyclists do as well. I do not "bounce" around 95 percent if the time. So, for the vast majority of us riders, clinchers will provide superior rolling resistance. Like many things in cycling, facts and data take a back seat to "feelings" and un-substantiated opinions.
Jonathan
Dear Lennard,
I'm totally not buying the Vittoria explanation. This is vintage hand waving! Clearly he has a point about the deformation; I buy that part. And so I'll do some more (handwaving) since I also have no data.
Suppose that you have a tubular and a clincher system. The clincher is stiffer and the deformation process absorbs more energy. So one could imagine that the tubular system is faster. But that is just for hitting pebbles and road imperfections.
What about the real world energy loss process of tire deformation due to peddling input (a vertically modulated mass). I have not seen this referenced but it is as important as the rolling drag measurements. In this situation a softer wheel/tire could mean more energy loss (inelastic process vs. elastic). An elastic (completely rigid) wheel would be like riding without a tire at all. On a smooth surface and with a teeny strip of rubber on your rim, this would be the fastest and most energy returning wheel/tire combo. A very hard (highly inflated) tire would minimize the peddling and weight induced energy losses (inelastic energy losses).
However, some goofballs, like me, tend to run high pressures. A stiff clincher system gets even stiffer at higher P's. Therefore, at like 120psi my clincher system doesn't deform much and reduces inelastic energy losses.
My point (unsubstantiated with data) is that two processes should be considered:
● Energy loss due to road imperfections.
● Energy loss due to inelastic vs. elastic tire deformations inherent in a drive system with a vertically moving mass (a bobbing bike rider).
For the first, a supple system should be best (tubular tire or supple tubeless clincher). For the second, a rock hard system would be best (stiff clincher or any super high P. arrangement to reduce inelastic energy suck).
Obviously, the two are diametrically opposed, so like many things in life ─ and engineering ─ one must arrive at an optimum for the given situation. A smooth track situation (wood surface) one could use very high pressure. In cyclocross, one would want to absorb the very rough surface and so a supple tire system at low pressure would be faster. These jibe with reality.
Alan
Dear Lennard,
Rolling resistance is the least of reasons to consider riding tubulars.
Tubulars are lighter and incur less rotational weight, and when an ultralight clincher/tube combo is close to the comparative weight of a tubular, the ultralight paper-thin clincher/tube combo flats more easily. Even when you get a clincher/tube combo at the same weight, the rim is still heavier, although that weight gap continues to lessen. So in my mind the primary reasoning to run a tubular set-up is the weight issue (in general it equates to about one pound of rotating weight on a bike), followed by the lower likelihood of flatting the tubular. Further, when you do flat, a properly glued tubular can be ridden and controlled instead of peeling off the rim, getting jammed in your frame or fork, and tossing you over the bars, like a clincher will. Think about that next time you hit 50 down Boulder Canyon on a pair of clinchers.
Finally, in my experience of changing thousands of flat tires, the ultra-narrow high-profile aero clincher rims, extremely tight fitting clincher tires (you manufacturers know who you are), and paper thin tubes out today makes it nearly impossible to get a clincher on an aero rim without pinching the tube at least once. I am convinced after helping others change out their flats that it is easier to install a tubular than to change a tube these days. Remember the days of the fat box rim when the clincher just rolled on by hand? Ah, the memories!
Like most everyone, I train on clinchers (big fat box rims with lots of spokes), have raced on them a fair bit, and don't really care one way or another about what I have. But, when the race matters, or I am planning to spend a chunk of change on a wheelset, it most likely won’t be a clincher I have in my mind.
Jed
Dear Lennard,
I jumped on the clincher bandwagon last season after reading those studies. Before selling off all my tubies, however, I decided to try clinchers with shallow, barely aero rims at the Tuesday TT that a Spokane area club promotes on a course I have done many times with a tubular disc and deep section front tubular wheel. The result? A pr time and the motivation to try the clinchers in other situations. I then won the Idaho State Masters road race among other races as well as posting some of the fastest bike splits at the first tri and duathlons I have competed in. This season I have won once so far at the same TT course and posted the fastest solo bike split at the Post Falls Duathlon. My training is not fundamentally different this season although I did work in a gold mine for a few months which added ten pounds of upper body muscle and a little more power, but a lot more fatigue, so I don't think that factor helped or hindered as far as a new variable. I am 43 years old, have been racing for 20 years (including a dozen years of track racing in Colorado before moving to North Idaho). I am never going back to tubulars for road use and when I do get the rare opportunity to race track on lower banked concrete tracks like Marymoor near Seattle I will use clinchers.
Steve
Dear Lennard,
While the technical merits of tubulars versus clinchers is obviously too close to call, and seemingly very dependant on road surface, the smart thing to do would be to call that a wash. What is not a wash, however, is that tubulars offer a far better ride for most people than clinchers. They are smoother, more comfortable, feel like they accelerate faster, and one comparison ride ought to be enough to convince the majority of cyclists that tubulars are the way to go.
Roger
Dear Lennard,
Regarding all the tubular versus clincher stuff. I personally would rather be on a tubular in a race cornering at high speeds and staying upright in the case of a flat or a blowout. Just an old Cat. 2 talking.
Nick
Zinn's regular column is devoted to addressing readers' technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.
Zinn's column appears here each Tuesday.
