Originally Posted By: Carbon
Originally Posted By: CapriRacer
RRC = RRF / Load
I am skeptical that RRC is a constant for a given wheel and vehicle. That is to say that I am skeptical that a graph of RRF vs Load is a straight line passing through zero.
OK, I think I finally understand where your problem lies.
Just so we are clear, RRC is defined as the measured RR in terms of force divided by the load. So this is always true for every circumstance.
I think what you were trying to say was that RRC is not a constant relative to load – and you have a point. However, this is like many things within the tire industry that were once proven to be true (or a really good approximation), are now accepted as a given. Much work is done internally within tire manufacturers who are reluctant have anything published that might give a competitor an advantage, so it is never published – and I suspect that is the case here. I know that there are several ASTM and SAE procedures for measuring rolling resistance and if RRC was not a constant, then the procedures would be quite different.
At the last ITEC (International Tire Exhibition and Conference) held in Cleveland, Sept 2010, Bruce Lambillotte of Smithers Scientific Services gave a presentation that showed that some tires had constant RRC’s, some had RRC’s that had positive slopes, and some had negative slopes. I am really interested in this data because it might say that it is reasonable to assume that RRC is constant even though it isn’t – or not. In other words it might say the error is small enough to ignore – or not.
Like I said, if this weren’t true, the way things are done would be a whole lot different, so I’m inclined to think that – at worst – it is a reasonable conjecture.
