Many aftermarket alignment kits show the adjustment range in degrees, so I thought I'd share the work I did on converting degrees to mm (seeing as most aligners report toe in mm, not degrees). Enjoy.


Step 1. Calculate the Radius (in mm) of the wheel and tyre together.

Formula (2 * tire width * aspect ratio / 100) + (wheel diameter) = wheel + tyre diameter

Executing first equation:

Wheels are 15" and tyres are 195/50R, so (2 * 195 * .5) + (15 * 25.4) =
195 + 381 = 576

576/2 = RADIUS = 288

Step 2. Calculate the angle each side wheel + tire: multiply the sin of 1 degree by the radius of the rim + tyre, to give you the mm deviation from parallel with the centreline (CL)

Formula arcsin(radius) = radians per mm

Executing second equation:
sin(1) (degree) or sin(pi/180) (radian) = 0.017452

0.017452 X 288 = 5.026293mm

Conclusion For my wheel/tyre combo every 5.026293 mm equals one degree.





I'll use the range promised by an ebay kit as an example (as below)

Adjustment range: -2.00 degrees to +5.00 degrees
Adjustment range:-10.05 mm to +25.13 mm