Reset speedometer by SCT Flash tuner

[Whipple46]

Hello guys I have a X3 SCT flash tuner and i noticed some of the options for setting my tire size to meet my speedometer. However I do not understand how to find this information, talks about 544 revs per min and goes up to 900 something. Help on this matter would be wonderful

my rear tire size is 285/35-18 (rear only right?)

and if you could point me in the right direction on where you found this info that also would be appreciated. thanks for you time guys

 

[lindertw]

go to tirerack.com and search for tires by size (you didn't mention the brand you have). when the list of tires comes up, pick one, then select "specs" for that particular tire, on the resulting page you'll see revs per mile listed.

here's an example spec page

 

[tjm73]

Measure your tire height with straight edges. Be as accurate as possible. Multiple that height (effectively the diameter) by 3.14159 (pi). That is your tire circumference in inches. Divide that by 12 and you get feet per revolution of your tire. A mile has 5280 feet. divide 5280 by the feet of your tire and you have rev/mile of your tire.

Mathematically a 285/35R18 tire is about 25.85" tall. 25.85 x 3.14159 is 81.223". That divided 12 is 6.768 feet. 5280 divided by that is 780.067 revolutions per mile.

 

[Franchi]

Yep, TJ has it right. 780 rev per mile for your tire

 

[thump_rrr]

Most tires that size are in the 803-805 range.
Set the revs per mile and verify speedo via GPS.

 

[rogcat1]

Changed the 17" wheels on my 2007 GT to 18" shelby wheels. Checked the mph on my GPS, and was within 2 mph. Close enough.

By the way, I'm running NITTO NT555 285/18.

 

[retfr8flyr]

The size of the rim doesn't matter it's the diameter of the tires that dictates the Revs Per Mile.

 

[07 Boss]

Changed the 17" wheels on my 2007 GT to 18" shelby wheels. Checked the mph on my GPS, and was within 2 mph. Close enough.

By the way, I'm running NITTO NT555 285/18.

Lol. You gave all those dimensions and didn't give us the one that you need to determine how many revs per mile or how tall the tire is, but thanks.