tire pressure on modern tires

[flyinlow]

I installed 18" wheels and tires in place of the old 15" wheels. Tire Rack (where I got the tires) says run the pressure that Mopar specs.

  Originally the f70-14 bias ply tires would have run 26-28psi on a 32 psi max.

  Then  I ran the 245/60 and 275/60 BFG's at about 32psi on a 35 psi max for the P metric radials.

  Now I have 245/40 and 275/40 General G max's  that have a max inflation of 51psi. What pressure is correct?  I am using 32psi for now and they seam to work well.  At only 32 out of a max of 51 do you lose a lot of load capability?

[303 Mopar]

I have generally found people grossly under-inflate their tires.  I am always around 48-49 psi on my full size tires.

[myk]

I just go a little below the maximum PSI in order to compensate for thermal expansion.  It's not like you can go off the door jamb sticker, or anything...

[RallyeMike]

Obviously, the pressure recommendation for bias ply tires from 40+ years ago no longer applies. Run the pressure recommended by the tire manufacturer. If you want to be a perfectionist, get a thermal gun, shoot it at the middle and outer edges of the tire and inflate or deflate until the temps are equal accross the tire (assuming you have correct geometry).

I have generally found people grossly under-inflate their tires.  I am always around 48-49 psi on my full size tires.

Whatever you do, don't do that! 

[MSRacing89]

I may run my car harder then others, that being said we have fined tuned pressures for our B-body big block car.  We run Mich Super Sports (max pressure 50psi) and KDW-2's.  Both fell into about the same range.  For the SS's we run 38 cold in the front and 35 cold in the rear.  After 5 to 6 laps they settle in at around 42 hot front and 38 hot rear.  So you could be somewhere in between my hot and cold settings and be looking pretty good.

[flyinlow]

Thanks , I will bump the pressure up ,go for a drive and check with the temp gun.

MSRacing , do you run those tires in cold weather ?  below freezing?

[MSRacing89]

Thanks , I will bump the pressure up ,go for a drive and check with the temp gun.

MSRacing , do you run those tires in cold weather ?  below freezing?

No sir.  Might dip into the low 40's, but not enough data to give any opinions.

[flyinlow]

Originally was thinking Nitto 555's In 295/45-18 R. and 245/45-18F. They are summer tire and I heard reviews that they felt like hard plastic in cold temps, and could even crack.  Went with the General Gmax A/S. Normally I hear General and I think rental car tire. I guess they are owned by Continental now and the Gmax's scored well in the Tire Rack tests for Ultra High Performance A/S tires.