Join Date: Jul 2015
Location: Carlisle PA
Red 2005 with 1SB package, chrome wheels, gauge pkg and carpeted bed.
This can be confusing! I am running Nexan Roadian 295/45-20s.
There seems to be three way to calculate the difference and the results don't agree with each other.
Overall diameter: RSA - 29.3 vs. Nexan - 30.5, correction factor of .040956.
Revs per mile: RSA - 714 vs. Nexan - 681, correction factor of .040956.
MPH: RSA - 65 vs. Nexan - 67.58, correction factor of .039692.
The tire ODs, Revs per mile and MPH were obtained from the respective manufacturers websites. I choose to use the MPH correction factor because it's the most conservative. I am open to other opinions, since I am just using my best guess.
One last point. I think I addressed this issue when we discussed tire diameter a while back. I know that it's not statistically appropriate to use 6 decimal places for a correction factor when part of the data is constrained to using 1 decimal place. I just do it for fun!