In a message dated 12/1/01 1:41:23 AM Central Standard Time,
jabberwalky13@hotmail.com writes:
> Here you go, I got this from this list quite a while ago:
>
>
>
> Measure your wheel/tire across the hub. This gives the tire diameter (D).
>
> pi*D = circumference in inches (C) = 360 degrees
>
> .06 inches * 360 degrees / C = toe in degrees
>
> You can get a decent approximation for D without measuring it by using the
> tire height value posted by the manufacturer.
>
>
>
I don't know who originally figured this equation, but it is off by a factor
of 2. The reason is that toe per side is not the difference between the the
centerpoint of the wheel and the treadface; i.e. using a radius. It is the
difference between a point on the front treadface and the same point on the
rear treadface. I now understand where all my confusion came from. Whoever
originally determined this formula based it off the radius, which is
incorrect for toe. It is clearly based off diameter, as shown in the Bosch
Automotive Handbook. By using the radius you only get 1/2 of the toe
measurement per side so you can only use 180 as the divider, not 360. This
equation will now work in the following manner:
diameter * pi * toe degree / 180 = toe inch per side
putting it to the test:
diameter = 25.6"
3/8" total toe = 3/16" toe per side
Using my trig equation:
angle = arcsin [(total toe / 2) / diameter]
angle = arcsin [(0.375 / 2) / 25.6]
angle = 0.420 degrees
And confirming with your equation modified by a factor of 2:
toe per side = diameter * pi * toe degree / 180
toe per side = [(25.6 * 3.142 * 0.420) / 180]
toe per side = 0.188 = 3/16"
The two equations are now equivalent. However, those of you who used the
previous equation actually only have 1/2 the toe you though you had.
Mark
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