Correct Tire Pressure - very confused

[SmoothLC]

Great thread. Thanks for the info., especially NMuzj100 on the Revos.

Next time at Bridgestone, I would have asked for the same info.

 

[cary]

A real professional would get the tire load table grab the vehicle specific axle weights from a reference source and do a calculation. That's what the Bridgestone "Tire Doctor" did for me and produced the perfect pressure of 38 PSI for LT285/75R16 on the 100.

The Michelin guys pressure/heat/pressure/add is a common technique.

The OPs tire is a standard passenger tire and should use the door jamb guides. Then run the chalk, shoeshine, business card and puddle tests to fine tune.

Cha-Ching, close to the correct answer finally. What you actually do is grab the load table and see what the load capacity is for the stock p metric tire at the recommended inflation pressures, then cross reference it for your sized LT tire to the closest weight and you get your pressure. I posted a long discussion about this a few years ago. This isn't rocket science.

1) Look at the sidewall of your tire. If the sizing starts with a P, it is a p-metric tire. So does your tire say P275/65/18? If it reads 275/65/18 E, then you have an LT tire.

2) The pressures listed on your door jam are for a P metric tire. If you have an LT tire, you must increase the pressure. As NMujz100 stated, a load table is the correct way to do this. If you don't have a load table (or as commonly happens, the dealer doesn't know how to read them and convert) then a rule of thumb is add 8 psi to the LT rating.

3) When using an LT tire, the pressure you use is going to be the same regardless of if it is a C, D, or E load tire. All are rated to carry the same weight in the same size at the same pressure. The difference is the heavier rated tires have heavier sidewalls that allow higher pressures and greater load carrying capacity at those higher pressures. Max PSI of a C load tire is 50 psi, max for a D is 65psi, max for an E 80psi. At 40 psi, in the same sized tire, the C, D and E are rated for the same load.

 

[petrotk40]

here's a seemingly good document for this discussion

http://marktg.toyotires.com/file/loadinflationtable.pdf

 

[e9999]

besides tire wear and comfort issues there is also mpg of course. I have seen significant increases in mpg with high pressures. Enough that I will increase the pressure a good amount when planning to do extensive freeway driving. I've ran high pressures plenty on my vehicles and have never seen problematic center-dominant wear.

 

[Deer Whisperer]

I wouldn't over inflate too much. The higher the pressure, the smaller contact area your tire has with the road. You can get away with having a small footprint, right up until it's raining, and you have to make an emergency maneuver. If you don't have enough rubber on the road, you will not have enough traction for your vehicle to do what you want it to do.

 

[re_guderian]

besides tire wear and comfort issues there is also mpg of course. I have seen significant increases in mpg with high pressures. Enough that I will increase the pressure a good amount when planning to do extensive freeway driving. I've ran high pressures plenty on my vehicles and have never seen problematic center-dominant wear.

Meh. The cruiser ROCKS as a highway vehicle in addition to off-road. Why muck it up for a few bucks? Lets say you did 50% highway driving for the year, and could eke out 18 MPG at a higher PSI instead of 16 MPG (a 12.5% improvement). At $3/gallon, you'd only save $156 per year to sacrifice ride quality and potential handling. Not worth it IMHO. I actually got 16 MPG on a 3K mi roadtrip and run 295 Nittos. Not sure I could get 18 with them aired up to max, and the ride would be horrible.