What is the @#$* truth about tire diameters.
 

I can't find a common answer to fitting different wheels and tires for my 09 vette. Some say they need to be within 5% of stock diameter...some say they need to just maintain the 1.2 inch difference plus or minus a couple tenths of an inch. What is the REAL Truth.

I would like to keep my nannies..

Trapp

Stock 245/40/18 = 25.7
285/35/19 = 26.9 that is 1.2 or 4.5% larger in rear

Option 255/35/18 = 25
305/30/19 = 26.3 that is 1.3 or 4.9% larger in the rear

Option 245/35/18 = 24.8 That is 1.2 or 4.6 % larger in the rear
295/30/19 = 26.0

Would these options work? Stock rims are 8.5 in front and 10 in back...maybe the 305's would be to wide for a 10inch rim?

any comments of knowledge..:)

Tire size
 

I'm no expert but I read where a guy was having trouble with his traction contrl, turned out his rear tire diameter was to short and the computer was fooled into thinking the car was losing traction and activating the system. Your rear tire dia should be taller. :flag:

The stock tires are 1.2" taller then the front....

you need to keep the 1.2" difference and that is the most important part of the discussion. As for overall diameter if you go too short it will have a detrimental effect on load capacity but, the number you have posted are nowhere near the point to cause issues in that area.

Stay within 3% of the overall diameter of the OE tires. No matter what the vehicle is....that is the margin of error of your "nannies". If you do that of course you will maintain the 1.2" height difference. Load rating and speed index is a whole other story for another time.........it is assumed you always maintain that , and that is directly related to tire pressure. Way to long of a discussion for this forum. Basically, NEVER go below the load index on the OE tires [87Y]....for liability and common sense reasons.