|Changing tire size or gears will throw off your speedometer.
This is annoying, but easy to fix by changing the speedometer gear in the
Step 1: Find out how far off your speedo is.
Example: If you drive 10 miles and your odometer advances 8.75 miles, 8.75 / 10 = .875. So your speedometer is reading 87.5% slow.
Step 2: Find out what speedo gear you need.
Example: If you find that you have an 18 tooth gear and your speedometer is 87.5% off, 18 * .875 = 15.75. So you need a 16 tooth gear which is the closest to the result.
Step 3: Locate the correct gear and install it.
Step 4: Test it!
Please note that most highway markers are not perfect, but over 10 miles it should be pretty close. You can use a longer distance for more accuracy.
I got my gear from Green Sales Company.
If you do not have a 20 degree ramp, but have some other way to get a wheel up in the air (such as a forklift).
(1/sin(20) * Wheel height) / Wheelbase * 1000
for example, If I get a wheel 23 inches high:
1/sin(20) = 2.924
(2.924 * 23) = 67.247
67.247 / 92in * 1000 = 730 RTI Score
Converting a score from a 20
20deg score * sin(20) / sin(30)
sin(20) / sin(30) = 0.781
20 deg score * 0.684 = 30 deg score
For Example, If my 20 deg RTI score is 1000
1000 * 0.684 = 684 RTI score on a 30 deg ramp
Converting a score from a 30
20deg score * sin(30) / sin(20)
sin(30) / sin(20) = 1.462
30 deg score * 1.462 = 30 deg score
For Example, If my 30 deg RTI score is 1000
1000 * 1.462 = 1462 RTI score on a 20 deg ramp
Page by Marc Reiter - last modified 01/05/00
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