Joe:
If you leave out per-min or per-hr, what we are trying to determine is
ENGINE REVOLUTIONS-per-distance which is determined by gear train and
drive wheel "effective" tire radius (which is influenced by the
footprint). Notwithstanding tire slip and all the other losses.
Take two circles. One is a 15" radius (94.24" circumference) and rotate
it 45 deg. A spot on the circumference will rotate 11.78". Now push on
the perfect circle so that SAME CENTER POINT is only 10" above the
flattened "circumference". Now rotate the same 45 deg. A spot on the
flat patch will only have traveled 10". 10" X Tan of 45 = 10". Yep,
the distance traveled is LESS but the rotation AND circumference has
remained exactly the SAME! Admittedly, we are talking about small
effects here but circumference is not the determining factor. Many
thanks for your thoughts. -Elon
-----Original Message-----
From: Joe & Lynne Lance, Subject:Gear Ratio Formula?
(much snipped. . .) The MPH vs RPM equation, in whatever form, must
implicitly include the CIRCUMFERENCE of the tire and the distortion of
the tire along a point in the circumference by a flat spot footprint
does not change the circumference.
By "foot print" I assume you mean that a two inch length of the tire's
circumference is flat on the ground when the car is at rest. So if you
measure the distance from the axle centerline, the "drive radius" it
will be less than the tire radius.
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