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Originally Posted by euromodder
Is it certain that the different tyres were indeed tested with a different load ?....
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Yes, that is how it is always done.
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Originally Posted by euromodder
....If I was to study the effects of tyre size, I'd study the effect of all allowed tyre sizes on a given vehicle (i.e. always with the same vehicle weight).
In that light, I'd come to the opposite conclusion - and each and every car manufacturer is complying with that conclusion as they're fitting their eco-models with skinny tyres..........
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I think if you did that, you'd find that RRC was very close regardless because the tires are pretty closr load carrying capacity-wise. It's only when you make a major move upwards in load carrying capacity that you see significant changes,
Quote:
Originally Posted by euromodder
............If wider tyres were beneficial, surely they'd all fit those instead of narrower tyres ?............
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Except that there are cost, packaging, and ride issues to consider. Plus, isn't that what is happening?
Quote:
Originally Posted by euromodder
..........The study also has a graph (p. 35) correlating RR (actual force, not coefficient) to LI, with higher LI also resulting in higher RR. (83% correlation, and even 86% to max. sidewall load)
Higher LI (and max sidewall load) usually goes together with wider, lower profile tyres...........
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Don't forget the RRF (Rolling Resistance Force) is meaningless unless the load on the tire is the same from size to size - which it isn't. When you apply a tire the load is determined by the vehicle, so RRC is the proper graph to look at.
Quote:
Originally Posted by euromodder
..........Same with tyre weight, overall diameter - which both show a 75% correlation with RR - where increasing weight and diameter would usually indicate a wider, lower profile tyre.
All these then result in the graph on page 30, clearly indicating higher RR (actual force) for the wider tyres.........
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Be careful looking at RRF. It will lead you to incorrect conclusions.
Quote:
Originally Posted by euromodder
.........(What I'm missing in the study, is a graph of RR versus profile height.)..........
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It embedded in there if you want to study it. Which is why I've redone the regression analysis.
Quote:
Originally Posted by euromodder
........In the end, you need to overcome the actual RR force of a tyre at a given load, not a RR coefficient.........
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Sorry, but while you are correct the it is the actual force that needs to be overcome, that value is generated by multiplying the load on the tire by RRC.
Quote:
Originally Posted by euromodder
....The study concludes :
Rolling resistance rolling forces and rolling resistance coefficients did not correlate......
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I thought that was an odd way to phrase it. I think would they meant was the both RRF and RRC did not correlate to something independent that could be used as a regulatory meme.
Quote:
Originally Posted by euromodder
............But I fail to see where it comes to the conclussion that wider is better.
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It doesn't, which is why I did the regression analysis. What I found most striking was that the RRC values were significantly lower for very large tires - and that lead me to do a deeper look.