As part of the article I am writing on tires/gearing/wheels, etc., I found
that I was making assumptions about the height of the wheels we use that
appear to me subsequently to be in error.

That is, I assumed the stock Michelins were 25.3" tall and that the BFG 27
x 8.50 All Terrain Radials were 26.3" tall.

On remeasuring these tires, I now feel they are 25" and 26.15",
respectively, going by the tires I have around here.

Could those of you who run these tires who have a moment measure them
yourselves and let me know what you think is a reasonable assumption about
diameter?

The proper determination of their actual diameter is critical to
assumptions that flow through many calculations, and therefore I would
rather find out before the fact rather than after that there is an error in
my assumptions on this.

I am thinking that I will use measured tire height as the basis for
diameter assumptions because, even though actual measured rolling
circumfrence results might be more accurate, these are more difficult to
extrapolate to new tires under consideration due to the difficulty in
conducting rolling resistance testing of the possible new tires. In other
words, by sticking with actual measured tire height for input data one can
more easily extrapolate data that is useful for selecting tires, which is
the diameter that the tire measures.

For the purposes of the measurements, I judged that the best method was to
measure the tire at the edge, and discount about half of the bulge in the
middle of the tread, if there is any bulge, as being something that will be
squished flat when the wheel has weight bearing on it.

In other words, the diameter data that I collected was for tires which did
not have weight on them.

Again, this makes it more easy for us to walk into a tire warehouse and
measure the diameters of various tires off the vehicle, knowing that the
measuring methodology matched the input assumptions.

If nobody sends me back any opinions to the contrary, then I am going to
use 25" and 26.15" as the baselines for the calculations.

_______________________________________________
Derek Drew                                            New York, NY
CEO & Co-Founder
http://www.ConsumerSearch.com/
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