mullens Posted December 31, 2009 Report Share Posted December 31, 2009 I'm about to install a pro cal tune. Those of you who have custom or pro cal tunes, what tire circumference did you use? The tire calculator says 285/35/19's are 84.4", which calculates to 751 revs per mile. When I measured my tires it was closer to 83.5". Anybody do the GPS thing? Thanks Link to comment Share on other sites More sharing options...
Torched10 Posted December 31, 2009 Report Share Posted December 31, 2009 I'm about to install a pro cal tune. Those of you who have custom or pro cal tunes, what tire circumference did you use? The tire calculator says 285/35/19's are 84.4", which calculates to 751 revs per mile. When I measured my tires it was closer to 83.5". Anybody do the GPS thing? Thanks [/quote Well circumference of a circle is 2 X 3.1418 X the radius (half the diameter).So measure the cenetr of the wheel to the surface of the tire,and that should be it.Id use the part of the tire thats on the floor,since the tire will be depressed as it rides--te multipier I used ia actually called PI,and you can get a more precise math for the number. Link to comment Share on other sites More sharing options...
mullens Posted January 1, 2010 Author Report Share Posted January 1, 2010 Thanks...with a 13.175 radius it comes out to 765 revs per mile. I put the ruler flat on the floor and measured to center of the wheel. Link to comment Share on other sites More sharing options...
Torched10 Posted January 1, 2010 Report Share Posted January 1, 2010 Thanks...with a 13.175 radius it comes out to 765 revs per mile. I put the ruler flat on the floor and measured to center of the wheel. Pi is actually 3.14159,so the math is 82.7. in for the circumferenceA mile is 5280ft which is 765 turns---that should be it.Wonder where they got the numbers they have.Im gussing they just used the wheel size,or a much narrower tire.But phsics dont lie,so the 765 shoiuld be correct--If the tires were hot it might be a little lower turns--you might try measuring when theyre hot and see how much difference it makes in the radius.Figure they must have measured the tire not resting on the ground,and got a bigger radius,this fewer turns--bob Link to comment Share on other sites More sharing options...
mullens Posted January 1, 2010 Author Report Share Posted January 1, 2010 I didn't think of doing the 2pi r equation but it makes a lot of sense. Yes, the guys listing the circumference in the tire calculators are measuring an unsprung tire on the showroom. Even the 07-09 285/18's are listed at 84.7" which I know is way too big. I think the guys are using 82" for that tire. Link to comment Share on other sites More sharing options...
MichaelP Posted January 3, 2010 Report Share Posted January 3, 2010 Hi - What is the advantage of using the FRRP pro cal tune if you are running your car with no mods? Sorry, not trying to hijack this thread and change subject... I could not find any info in forums other than using a custom tune when changing supercharger, etc. Thanks, M. Link to comment Share on other sites More sharing options...
mullens Posted January 3, 2010 Author Report Share Posted January 3, 2010 I have a FRPP TVS on the way.... Link to comment Share on other sites More sharing options...
MichaelP Posted January 3, 2010 Report Share Posted January 3, 2010 Ok! Thanks. Have fun with the new SC and added HP ! M. Link to comment Share on other sites More sharing options...
Tob Posted January 3, 2010 Report Share Posted January 3, 2010 I have a FRPP TVS on the way.... Tousley? Link to comment Share on other sites More sharing options...
mullens Posted January 3, 2010 Author Report Share Posted January 3, 2010 Tousley? Neg....Buy Ford Racing Link to comment Share on other sites More sharing options...
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