Quote:
Originally Posted by UFO
Forgive my lack of knowledge on the subject, but there seem to be two terms being used, and I'm not sure if they are interchangeable.
Can the "coefficient of rolling resistance" be equated to rolling resistance? If not, in the case of that chart posted above, what is the variable that is not stated that would convert a coefficient to the actual value that contributes to efficiency loss in driving?
I ask because in the case of aerodynamic drag, there is the Cd (coefficient of drag) that has to be multiplied by the Cda, or effective frontal area to get actual drag. Is there a similar equation that relates to rolling resistance?
|
To get RRC (Rolling Resistance Coefficient), you take RRF (Rolling Resistance Force) and divide it by the load. So to get the drag on a car, you need to know how much load is on each tire and the RRC of the tires
- EXCEPT -
Both RRF and RRC assume the inflation pressure is the same as the test value - which is typically the rated pressure. If someone wants the drag on a car due to the tires and the usage pressure is not the rated pressure, they would also need to know what affect inflation pressure has on RRC and/or RRF. There are ways to estimate this.
- AND ANOTHER EXCEPTION -
The author of those charts - Bruce Lambilotte from Smithers - had shared some additional data at a tire conference that indicated that RRC wasn't always constant. I wasn't quick enough to fully understand what he was saying - and he never actually published the data - but it stuck with me, because I had had other conversations where some folks assumed the RRC was a constant at a given pressure. I would really like to clear this up, but so far I haven't been able to.