On Apr 25, 2008, at 7:51 PM, Elon wrote:
Why not do it on jack stands in your clean, cool garage? With the car
on the
floor, measure from the centerline of the axel to the floor because of
squat
or footprint. That radius should be slightly different (shorter) than
the
top radius. Use the shorter radius to find circumference. Then divide by
5,280 or any subset of 1 mile by your result. Chalk the tire and
count the
turns. This method may be more accurate than towing since you might not
travel a straight line between the mile markers. Since towing would
be at a
slow speed, tire growth would not be a factor just as the method I
described.
14 inch squat radius x 2 pi = 87.96 in / 12 in = 7.33 ft. circumference.
5,280/7.33 = 720 turns which are too many to count. 1/4 mile (1320 ft)
would
only be 180 wheel revolutions. -Elon
Elon:
About the circumference, derived by using pi and radius: while the
radius on the bottom half is smaller than that of the top, when loaded
-- I don't understand how that would change the circumference. That
is, the distance all the way around the tire does not change -- all of
the rubber must still roll down the road, even if the axle gets closer
to the ground.
Maybe a test under controlled conditions, like you propose, would
help. One run with a loaded tire, one with a tire that's not mounted
on a wheel. If you can explain how the circumference does change --
and prove me wrong -- I'd appreciate it. Thanks in advance.
Jon Wennerberg
Tall guy with moustache
and a pair of 2 Club hats
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