Dylanamus
07-04-2008, 01:45 AM
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. :thumbsup:
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.
http://i50.photobucket.com/albums/f304/Dylanamus/fordeelan.jpg
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
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.
http://i50.photobucket.com/albums/f304/Dylanamus/fordeelan.jpg
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