Hi,
The argument made by Heine against roller testing is that dissipation in the rider (by transmitted vibrations) is an important component of rolling resistance (an energy dissipation term proportional to speed and roughly proportional to weight). Therefore roller tests would tend to over-estimate optimal tire pressure, since a cost of high pressures, which is increased damping in vibrating the rider, would be neglected.
If that is true it has nothing to do with the rolling resistance of the tyre as such but everything with the rolling resistance of a bicycle, his rider, his wheels and the damping factors of all of these combined.
Therefore the measured rolling resistance will vary with the impact of any of the above factors and it will change continously whilst moving from one piece of road to the next. Hell even the airpressure level surrounding the rider will effect the rolling resistance.
Now tell us, should we cover our bikes in sorbothane? Should we lose or gain weigth? Should we use saddles with or without padding? Back to steel or titanium frame?
I could be wrong but IMO the bulk (as in 95% or more) of the dissipation of energy is happening at the suspension end of the bicycle, IOW the tyres.
So, and I say this with respect, if mr. Heine wasn't measuring tyre rolling resistance but rolling resistance in general he should not have stopped at just measuring tyre rolling resistance either, wouldn't you agree?
I think they also forgot to measure the rolling resistance of the road they did the testing on as that too is a variable which can vary against yet another pile of variables as well....
For clarity's sake, I'll repeat it once again, Crr, in casu tyre rolling resistance, is a relative value allowing you to compare what can reasonably be compared. IOW it will allow you to create a picking order of preference from the testresults.
A tyre with a low rolling resistance relative to another tyre tested on a drum, in a lab, at a constant speed, constant load, is going to keep this low rolling resistance relative to that other tyre no matter what testing protocol you throw at it unless you bias that protocol to favour one outcome over the other. E.g. wildly overinflate, underflate, whatever.
Throwing in a road (which is only going to modulate reaction force R) and replacing W, a dead weight serving as a constant load, by a highly absorbant mass such as a human body, is not going to change the relative rolling resistance of one tyre to another.
Anything else, as described above, has nothing to do with rolling resistance but has everything to do with trackability.
Much in the same way a phonograph cartridge can track a groove thanks to its (electrical) load and suspension if you like.
In a similar vein a bicycle frame, wheel, you name it, can be optimised by applying well understood physics. Vertical compliance, choice of layups, variable wall thickness, pipe shapes, asymetry, etc. etc. can all be varied to obtain a particular sought after result.
The list is endless but to give one example: the current reversion to the old 27.2mm standard for seatposts because it is perceived as being more comfortable is not a mere incident. It is just applied physics nothing more, nothing less.
It too contributes to making a bike "roll" better.....
Ciao,
Being a snob is an expensive hobby.