As much as I respect Jan Heine's work in debunking common cycling myths, I dismiss this article. You just cannot do a test where the variables are so small, on an open air test in a rundown scenario. There is no way that atmospheric variances do not affect the data...
Further, he still wonders whether clinchers or tubulars perform better. These tests have been done conclusively by Jobst Brandt in the 1980s. His data is there for all to see on Analytical Cycling.com. The answer is not as obvious as anyone would expect...
Anecdotal claims that he can now keep up in the paceline (because of this or that tyre) are nonsensical, as is the claim that in a paceline, rolling resistance is higher than air drag....
Heine's main point is about
suspension losses, which he claims are much more significant (i.e. more watts of lost power) than
rolling resistance and
air drag (presumably on a sufficiently-rough road surface). He describes the drastic increase in drag and slowdown felt when riding over rumble strips, which I'm sure most of us have also experienced.
Heine's musings over clinchers or tubulars is, again, not specifically about rolling resistance, but about their impact on suspension losses, which is affected by how flexible their sidewalls are and their usable range of inflation pressures. This affects how well they absorb bumps and isolate the sprung mass of the rider and bicycle. It is mainly in the body of the rider where the suspension losses happen - jiggling of the rider's flesh is powered by vibrations transmitted up from the road surface.
Brandt is either discussing rolling resistance in a very narrow technical sense, or considers that suspension losses are insignificant but offers no estimation of just how insignificant. Heine, on the other hand, has considered both. Brandt would be correct if real roads were as smooth as the steel drums used in rolling resistance tests, which is rarely the case.
...He implies that Tour Magazine invented the steel drum test - it did not and he says that tyres, for some mysterious reason, have to tested soft-ish on steel drums. Not. These experiments have been done on steel drums at all attainable pressures...
No mystery here, wider tyres are tested at lower pressures because they cannot be inflated to pressures as high as narrower tyres - this is a limitation of the tyres, not the test procedure or equipment. Within the same brand & model, wider tyres usually have lower maximum inflation pressures than narrower ones, due to the mechanical limitations of the bead/rim interface.
In any case, the premise behind the 15% tyre drop method is that wider tyres should be inflated to a lower pressure than narrower tyres to reduce suspension losses (which results in higher speed) for a given level of snakebite resistance, so it's not even a limitation.
...You just cannot do a test where the variables are so small, on an open air test in a rundown scenario. There is no way that atmospheric variances do not affect the data...
...He doesn't even publish the data...
... Of course he doesn't provide any empirical evidence for that, just a cast-away comment that is supposed to be taken seriously....
Heine does not work for a bike or tyre manufacturer and does not have access to laboratory equipment - roll-down tests on a real road are all he can do and he has described their drawbacks, so I won't knock him for that.
Tyre manufacturers don't publish suspension loss tests, I can speculate this is because:
1. There is no standard for a jiggling, vibrating human body, therefore test results would not be comparable
2. There is no standard for how rough a road surface is, therefore test results would not be comparable
3. If suspension losses are much larger than rolling resistance losses, then that would make the differences between different tyres seem insignificantly tiny, which does not help sell that brand of tyre. Much like factoring in rider weight makes the weight savings of a more expensive, lighter bike seem insignificantly tiny.
...Edit: I found another corker: "We discovered that temperature affects rolling resistance." Well, he should have also found that temperature affects air drag, but they didn't even think about that, they were too focused on finishing in time for lunch.
Which is why Heine tested at the same temperature.
Seriously, what they label as 700x35c is actually 37-622... but I'd expect you're trading weight against comfort, not speed, based on my experience comparing Delta Cruisers of different widths.
