Quote:
Originally Posted by CapriRacer
Second is that while measuring a tire's free standing diameter (that is, unloaded) as opposed to the loaded radius is the right way to do revs/mile, there is 3% factor that needs to be inserted to get the actual rolling circumference (or rolling diameter).
Put another way: If you are using the actual tire circumference, the rolling circumference is 97% of that value.
Why? I'm not sure, but I think this has to be with the belt acting like a tank track - that the effective length of track would be analogous to the circumference of the belt, and it doesn't matter how much tread is on the tire, the rolling circumference is controlled by the diameter of the belt (except we do know that tread depth plays a role in the revs/mile, so this explanation doesn't quite work.) Whatever the reason is, if you look at the tire manufacturer's values they have about a 3% - oh, let's call it shrinkage!
Most tire calculators do NOT factor in the 3%, but this one does:
Tire Size Calculator - Tire & Wheel Plus Sizing
Why? Because they asked me about it BEFORE they designed the web page. |
False. I've done rollout testing. Plenty of manual labor involved, but how else to discover the facts? Forget the 3% myth. It's busted.
I tested both LT245/70R17s, and P245/50R16s. Same results both times.
You go using that 3% nonsense, while doing 90 in an 85 MPH zone, which we do have out here in the west, you'll have a speeding ticket for 93 in an 85.