Tire Preassure Question

[8695Beaters]

Well I always check my tires after I go to a shop. They never set them where I want them (since I usually don't buy stock-spec tires).

[EyesofFreedom]

First running 25 pounds in a tire...let me see here...when you replace your tires the outsides bald before the middle right!

That is because you are running the tire underinflated. The door jam spec is to have a smooth ride, not to extend the life of the tire. The engineers know the car will sell better with a smooth ride rather than a long tire life! Who wants to test drive a new car and feel every imperfection in the road!

Any shop that puts 25 pounds in a tire and lets you ride out is a shady shop to begin with. We actually had a spec sheet the had the minimal pounds it could leave with per each tire and the only thing that was 25 was a 4 wheeler tire. Even the mini tires for small trailers required 30 pounds.

That is the reason the tires are marked. Go to any new car dealership and look in the jam and then check the tire and I guarantee you most will not match pressure!

Also tire size has absolutely nothing to do with pressure! Tire pressure is calculated by the strenght and number of plys of rubber and the weight rating of the tire plus the stickiness.

Ever wonder what the a b and c ratings are?

Those are for life expectancy, grip and heat! All tires are different...because some what great traction, some want great life and you can not have a "soft" grab tire with a long life because long life tires are "hard" tires.

And lastly running 25 pounds on a standard wall tire can be dangerous because of the excessive flex action allowed in turning...which can lead to slipping or even worse a bead blow!

[8695Beaters]

I know what all the markings mean. I also do my pressures by what I feel through the wheel (I want to feel every imperfection in the road when I test drive!). Recently I have been using a formula I read about: take the vehicle weight (pounds), divide by 100, add 2 all around, and add 2 for the engine end of the car (front or rear). That's where I have been setting my tire pressures for reference points. That's what I did for my 240SX when I brought it home (it still does not run so I don't know how the pressures are working yet), but that formual has been a great starting point.

I never knew about all that other stuff though. I find that weird that the OEMs would do that, but it makes sense I guess. And no, my tires do wear evenly.