To those running staggered wheel sizes, what tire pressure are you using? My tires are 275/35/20 and 305/35/20. I need to check tomorrow what I have on them.

 

Those sizes should be filled to 32 PSI for the street, 28 PSI for the track.

 

There really isn't one "correct" tire pressure for all cars / tires; it depends on a lot of things.

General rule of thumb is to use the same pressure recommended by the manufacturer for the stock tires, which in our case is 32 psi.

For maximum cornering grip, the pressure might need to go down a bit . . . but that really only matters on a track; it's a real bad idea to go that fast on the street. For maximum cornering grip, you take come corners at maximum grip (tires starting to break loose) and look at the scuff marks on the side of the tire; you want the tire to roll over until the scuff marks hit the middle of the little marks on the tire. Reduce pressure to make them roll over more, increase to make them roll over less. Some guys "chalk" the sidewall to make this easier to see.

 

The door label says that the recommended tire pressure is 35. Do I use 35 on front and rear even with my bigger staggered tires?

 

Yes, size makes no difference. It will take more air to get to 35 psi in a larger tire though

 

Interesting, I didn't know they had increased it.

I wonder why . . . my guess: for fuel economy testing / rating

 

32psi.

 

Tire pressures should be adjusted for the load and speed the vehicle is likely to be operated with. Around town daily driving yeah 32 to 35 is good. My 2016 has a sticker in the door jamb that indicates Ford recommends adding 4psi if you plan on driving > 100mph. Also if you plan on loading the car up to its rated load capacity the tires sidewall will indicate the PSI required to handle up to certain weight. You probably will never load a Mustang to the limit of the tires so max PSI may never be needed. But that extra 4psi for high speed driving is a good safety measure. Also be sure to measure the pressure when the tires are cold, like in the morning before the sun heats up one side of the car. The pressure changes rapidly with heat and the pressure monitors on the newer cars will show that.

 

On the track where we go about 120 on every lap, we usually end up dropping the cold pressure, so the hot pressure is around 30, depending on the tire wear pattern . . . 36 psi cold would be around 44 psi hot which is usually way too high for best cornering grip.

That might be "safer" meaning a blow-out would be less likely, but the car would handle like it was riding on hockey pucks.

Anyway, my point is: the "right" tire pressure depends on what you are trying to achieve.