I just swapped out the stock 17 inch tires for 285/40-18 & 255/45-18 tires. I know the stock 17s were 32 lbs what is the tire pressure for the 18 inch tires. The operators manual does not say and the pillar identifies only stock 17 inch tires.
Manufactor ratings (inside door and manual) will give you the best ride, but they do not give the vehical the best tire life or performance. I work for a tire store and personally I run 40lbs in the front and 35 in the rear. That is what we run on most rear drive v8 cars and it works awesome, I havent seen any edge wear or cupping on any of those cars. plus the slightly lowered pressure in the rear helps the motivation stoplight to stoplight
Manufactor ratings (inside door and manual) will give you the best ride, but they do not give the vehical the best tire life or performance. I work for a tire store and personally I run 40lbs in the front and 35 in the rear. That is what we run on most rear drive v8 cars and it works awesome, I havent seen any edge wear or cupping on any of those cars. plus the slightly lowered pressure in the rear helps the motivation stoplight to stoplight
is that also the case for 255/35R20 and 275/35R20?
I've talked to Goodyear's director of racing development, Summit Racing, Tire Rack and various engineers in the tire business. EVERY ONE of them said for street driving to stick with the pressure listed on the door sticker regardless of tire size.
The rating on the sidewall has not a thing to do with suggesting a pressure to use while being driven.
[quote=Tominator;1337607]I've talked to Goodyear's director of racing development, Summit Racing, Tire Rack and various engineers in the tire business. EVERY ONE of them said for street driving to stick with the pressure listed on the door sticker regardless of tire size.quote]
My problem was that the tire pressure for my new tires are not listed inside the door. Would the tire pressure as provided on the Shelby GT500 not be correct for my new tires possibly due to the weight factor?
I've talked to Goodyear's director of racing development, Summit Racing, Tire Rack and various engineers in the tire business. EVERY ONE of them said for street driving to stick with the pressure listed on the door sticker regardless of tire size.quote]
My problem was that the tire pressure for my new tires are not listed inside the door. Would the tire pressure as provided on the Shelby GT500 not be correct for my new tires possibly due to the weight factor?
That is probably the case.
From my research the total load rating of a tire is at the maximum list pressure on the sidewall. In other words, the higher the pressure the higher the weight the tire will carry.
BTW, I'm not saying the above experience posted by Moshbrian is incorrect and ambient temperature must be evaluated for the sake of the argument. Hot air expands. The door sticker is a neutral listing and best or the average auto/truck.
The GT500 ain't average!
I think you'd be safe at 32 to 35lbs and it wouldn't hurt to run even higher pressure. Radials are very forgiving here where the old bias ply tires we had were easy to prematurely wear out on the outside if under inflated and the middle if too much pressure.
I've talked to Goodyear's director of racing development, Summit Racing, Tire Rack and various engineers in the tire business. EVERY ONE of them said for street driving to stick with the pressure listed on the door sticker regardless of tire size.
The rating on the sidewall has not a thing to do with suggesting a pressure to use while being driven.
Interesting. I have taken classes from Goodyear from teams in the racing development, and they have always said you need to compensate the new size tire pressure accordingly to the load capacity of the OE tire. A lower sidewall will "Typically" have a lower load rating, which may require a few more lbs. of air.
It is especially important to do this on trucks when you change sizes and load ratings "C, D, & E for instance"
I have worked for Goodyear since I was 15, and now 34 yrs old, so I do have a few years in the tire biz.
35 on all 4 corners is fine for the OP. That's what I run with the same exact setup.
Interesting. I have taken classes from Goodyear from teams in the racing development, and they have always said you need to compensate the new size tire pressure accordingly to the load capacity of the OE tire. A lower sidewall will "Typically" have a lower load rating, which may require a few more lbs. of air.
I've always wondered if they were just protecting themselves, though the Goodyear engineer designed Indy tires as well as Class 8 truck tires.
My tires get 35PSI as well....
This is a very interesting subject and I'm still in search of a definitive answer!
Tire Air Pressure 
