The rear wheel alignment spec for my car is 1/16" in per side. The alignment machine at my local shop (this is a road car) measures only in degrees. The overall diameter of the tire is 24.8". What is the correct toe-in angle for this job?
Wheel alignment question.
The rear wheel alignment spec for my car is 1/16" in per side. The alignment machine at my local shop (this is a road car) measures only in degrees. The overall diameter of the tire is 24.8". What is the correct toe-in angle for this job?
The conversion is:Originally Posted by johnhafkenschiel
Angle in degrees = 57.3 x (inches toe)/(tire dia)
This is derived from the formula 1 radian = 57.3 degrees or 2 x Pi radians = 360 degrees.
Dave Weitzenhof
0.144 degrees
sin^-1(x) = (1/16)/(24.8)
solve for x
These are essentially the same for small angles (under 10 degrees).
Dave Weitzenhof
Youse guys humble me, I suck at math. Prolly why I flunked the MCAT.
Last edited by Rick Iverson; 10.10.23 at 7:02 PM.
V/r
Iverson
Street car vs race car alignment specs
Hope that someone more technically adept (Dave W?) will pitch in to correct me if I am wrong. I think that the measurement basis for street car toe-in is different than for (typical) race car specification:
Street car = based on tire diameter (degrees or fraction of inch over this dimension)
Race car = based on rim diameter (easiest, most repeatable feature to measure from)
I do recall that some folks use a technique on their race car of scribing a shallow reference line around the (slick) tire tread with a sharp point to effectively measure toe-in @ tire diameter. Not sure if many folks use this method.
Lee
I think you're correct
Certainly makes sense. Many street car setups are done measuring (angle) on the rim also. However, the accuracy of rim toe measurement depends in large part on the rims having little to no runout.
A scribed line on the tire eliminates that source of error. Almost all of my 30+ YO Jongbloed wheels have some runout, so I use a variation of that technique.
Last edited by DaveW; 10.10.23 at 5:38 PM.
Dave Weitzenhof
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