quick question on tire size + tune
 

i cant remember if it even effects anything or not. but since im changing the profile from 45 to 35 on my back tires, does it change anything as far as electronically (mileage, mph, etc?) because i know there are parameters for tire size in the tune files, but its not specifically for the back or front tires.

so long as the total diamiter of the tire stays the same as stock, you dont need to change a thing.

sweet :) thats what i was thinking, thank ya sir

yeah you'll need to change it. the diameter of you tires does nothing for your speedometer, its the height and since you are changing that, your speedometer will be off. Similar concept to gears...

hmm.. i used a diameter calculator and it says they are the same? /shrug

http://www.1010tires.com/TireSizeCalculator.asp

I compared 245/45/17 vs 315/35/17 and got 652.27 mm for both overall diameters.


so wait a second.. how far is the speedo gonna be off?

if the diameters are the same doesnt that mean they're the same height?

"Anything that changes the tire's outside diameter also influences the vehicle's overall gear ratio, as well as the accuracy of the speedometer and odometer."

Accoring to that tire calculation and I also did the math out on paper.. the 245/45/17 and the 315/35/17 have the same diameter, meaning the same height, both are 25.6" tall.

Thanks guys!

like i said as long as its the same height as stock tires your speedo will be the same. You dont have to change a thing. Thats why when you go with a wider tire you get a shorter sidewall. To keep the total height the same as stock.

don't worry, the speedo will be fine, they are the same height.

Remember, the height of the tire 35, 45 etc... is not a measurement, but a percentage of the width...more or less. So, a 35 is not necessarily a thiner tire then a 45.

In your case, going from 245/45 is nearly identical to a 315/35. Multiple .35 x 315 and .45 x 245 and you get the same number. Thus, these two tires have the same height.

Exactly.. which is why I said they are both exactly the same height.