Quote:
Originally Posted by Jim Allen
Not quite sure what you mean here, Capri. Would you clarify, please?
How i measured circumference, by the way, is by marking the tire and the pavement, rolling forward one revolution and measuring the distance on the pavement (garage floor, actually). The programmer allows for increments as small as 1mm. I don't know that the programmer or the truck's PCM does any internal compensating, hence my query above, but I happen to know the designer of the programmer, so I can ask.
The other thing is that tires tend to expand a little from centrifugal force at speed. It caries from tire to tire, I guess, but even I'm not THAT pedantic! If there is a rule of thumb, I'd like to know what it is.
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Jim,
That is an interesting way to measure circumference.
Most folks would have used a tape measure around a freestanding tire - and that was what I was referring to when I made my comment about internal calibration. I can think of several ways of dealing with the tire circumference / speedometer issue - This would be just one of them.
Expansion due to centrifugal forces?
Let me put it this way: I would think that load / inflation pressure effects would be greater than the effect caused by centrifugal forces. I know of no rule of thumb for load / inflation pressure nor one for speed.