I just put on 295/35-ZR19 tires on new 19" rims on the rear. Now i need to know how to calculate the diameter for LS1 edit?

Also, what is stock diameter, as a matter of interest?

 

Check the tire manufacturer's website. I know that Nitto puts their tire diameters on their website.

 

or do it the fun way

say your tire is a 275/40/17

Diameter is 17" + ((275/25.4)"*.40*2)

So diameter is 25.661417322834645669291338582677 inches


The formula is just wheel diameter (the 17) + tire width (the 275 number but that's in millimeters... 25.4mm to 1 inch) * aspect ratio (the 40 number ... 40/100 = .40) * 2 (since there's 2 sidewalls)

So if you need the circumference then just use 2 pie r or pie d

so 3.14159*diameter is the circumference in inches


so in your case 295/35-ZR19

19+ 295/25.4 * .35 * 2 = 27.12992125984251968503937007874" diameter

and a 85.231089330708661417322834645669" circumference

 

Sounds like the most accurate way would be to mark the tire and pavement, drive until the mark on the tire rotates 360 degrees, then measure the distance and divide by 3.14159

 

Thanks Horist. I was playing around with this yesterday and actually managed to figure this out. Wish i read your reply sooner!

 

The problem is, even if you put the correct number in LS1edit, your speedo will be messed up due to a software bug in LS1edit. Best way to do it is with mile markers on the freeway or use a GPS and lie to LS1edit until you have the speedo reading correctly.

 

I noticed LS1 Edit didn't change the clicks-per-mile box when I typed in a new tire size. Is this the bug?
If so, can I make the correction by changing the gear ratio as on the Vette this changing nothing else?
Also, my tire size is going from 26.7in. to 27.2in. This is only a 2% change. Is it worth changing?