need tire/ rev info

thefrantic1 · 05-11-2008, 07:21 PM

i put 4.30 gears in my gt and changed the parameter adjustment on the sct tune device. my speedo seemed fine at that point. i forgot to set the tire/rev setting for my nitto 275/35/20's. i went to nitto's web site and got the setting which is 753. i input the info in the tune and now my speedo is off again about 10mph. not going as fast as it shows. anyone have any info. thanks..

Fool4Parts · 05-12-2008, 12:01 PM

Try 730 rpm, maybe.

275 X .35 = 96.25mm x 2 = 192.5mm / 25.4mm per inch = 7.58" of sidewall plus 20" wheel = 27.58" overall height

2 pi (6.28) x r (1/2 diameter) 13.79" =86.6" circumference

5280' per mile x 12" = 63360" per mile / 86.6" = 731 revolutions per mile. I think. Check my math on that.

thefrantic1 · 05-12-2008, 08:11 PM

damn i must of skipped that math class. i did back it off to 725 and didnt seem to make a difference. i emailed sct also for their input but havent heard back. thats 2 + 1 = 4 maybe..oh 3..i would of never figure all that up...lol.. thanks fool4parts for the great info.

thefrantic1 · 05-14-2008, 07:28 PM

sct replied with a answer. they said the tire /rev setting is basically there for cars with auto trans for proper shifting and has no benefit for power. i am setting mine back to stock. just changing my gear setting for the 4.30's has my speedo close enough.

gman73 · 05-15-2008, 08:49 PM

I think to get your revs per min, it's 20168/tire height.

thefrantic1 · 05-15-2008, 09:04 PM

nitto's website shows a 753 as the tire/rev for mine. added it to tune and it threw off the speedo again. its not a power gain from the tune so i just changed it back to stock to keep the speedo inline. thanks

Fool4Parts · 05-17-2008, 02:30 PM

http://www.1010tires.com/TireSizeCal...&reset=yes