Bob Douglas,
You wrote...
>Jay, Thanks for the attached. Do you happen to know if these sorts of
>figures
>are for loaded or unloaded tires? Seems like loaded radials could lose
>somewhere around 4mm on the effective radius (8mm of diameter) to the
buldge
>above the footprint. The bias-ply tires don't appear to give as much.
>This could be sort of like measuring diameter of the tire in the trunk
rather
>than the effective diameter of the tires on the road. Just curious.
Most manufacturers specify the diameter as 2 times the rolling radius. This
is different than the measured diameter, as the tire gives to the loading of
the vehicle.
Rolling radius is a means for determining the loaded diameter of the actual
tire as it is really used.
Diameter = 2 * (Aspect_ratio * Width ) + Rim_size
Where Aspect_ratio is 70 in 165 R70 13
Where Width is 165mm in 165 R70 13
Where Rim_size is 330.2mm "25.4*13" in 165 R70 13
The avove formula normally gets you pretty close, but different
manufacturers and
tire types "Radial/Bias ECT" will yield different effective diameters.
Jarrid Gross
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