How to calc new tire diameter for LS1 edit
Thread Starter
Teching In
Joined: May 2003
Posts: 27
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From: CA
How to calc new tire diameter for LS1 edit 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?
Also, what is stock diameter, as a matter of interest?
TECH Senior Member
Joined: Nov 2001
Posts: 7,036
Likes: 1
From: Lake Zurich, IL
Re: How to calc new tire diameter for LS1 edit 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
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
TECH Addict
Joined: Nov 2001
Posts: 2,551
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From: St Louis, MO
Re: How to calc new tire diameter for LS1 edit 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 
Re: How to calc new tire diameter for LS1 edit 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.
Thread Starter
Teching In
Joined: May 2003
Posts: 27
Likes: 0
From: CA
Re: How to calc new tire diameter for LS1 edit 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?
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?
