What Tire pressure should I use?

[RogueIV]

So the OEM PSI for my car is 38 front and 36 rear on the 225/40/19 and 255/35/19.

I recently switched to 245/35/20 and 285/30/20 and the calculator is saying 36 front and 33 rear now. I always thought you had to increase the pressure when going down to smaller sidewall tires?

Not really no, it's less about the sidewall and more about how wide the tire is.

 

[JSolo]

1. Go by your door card.
2. If in doubt, here's what the good Book preaches.

View attachment 58015

I have the first size, 225/45/18 square. Trying to understand why they recommend higher pressures in the back?

 

[RogueIV]

I have the first size, 225/45/18 square. Trying to understand why they recommend higher pressures in the back?

It has to do with how the weight is distributed in the car, fully loaded. You'll have more weight in the rear in that case and require a bit more pressure to deal with that. The reason the staggered setup is lower in the rear is there's more of the tire's surface area in the back to support the weight and less pressure required. The pressure is what's keeping the tires in the desired "roundness" for the lack of a better term. It also controls how much the tire is contacting the ground.

Optimally, you should be adjusting pressures with how much people/stuff you carry in the car but this is rarely done so the Manufacturers just put the safest pressure for the max load the car is designed for.

 

[JSolo]

It's usually just myself in the car and minimal cargo (<100 lb). I'll start with 36F/38R and adjust from there as needed. My g37s ran 225/50/18F, 245/45/18R, just did 34-35 psi all around, 34 in the city, 35 when long trips. That car was around ~#3750. The gt-line is slightly heavier (#3850). But is running lower profile tires.

Hell, it came off the truck with 55psi or more in each.

 

[WRXtoStingerGT]

It's usually just myself in the car and minimal cargo (<100 lb). I'll start with 36F/38R and adjust from there as needed. My g37s ran 225/50/18F, 245/45/18R, just did 34-35 psi all around, 34 in the city, 35 when long trips. That car was around ~#3750. The gt-line is slightly heavier (#3850). But is running lower profile tires.

Hell, it came off the truck with 55psi or more in each.

How did it not explode?

 

[JSolo]

Lol.. Just goes to show what tires can handle. Because the mfg knows some idiot will put 100 psi in them

 

[RogueIV]

How did it not explode?

Truck tires are rated higher and for more payload. 55psi is pretty normal to see on the door card for a pickup. Heck I've seen door cards show 80psi.

 

[WRXtoStingerGT]

Lol.. Just goes to show what tires can handle. Because the mfg knows some idiot will put 100 psi in them

My goodness!

Truck tires are rated higher and for more payload. 55psi is pretty normal to see on the door card for a pickup. Heck I've seen door cards show 80psi.

Holy cow wow! I never knew that haha!

Learning something new every day!