Calculate Tire Inflation

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I bought new tires for my truck and now I'm wondering what is the proper tire inflation. Please, don't just tell me to look at the owner's manual or door sticker. I want to know how to calculate the proper tire pressure based on the tire and the weight of the vehicle.

For example, what should the pressure be when I'm running empty and the vehicle is at its lightest and what should it be when its fully loaded with cargo.

Now for specifics on my truck. Its a 2000 Chevy Silverado Z71 4x4. The owners manual and door sticker say original tires are P265/75 R16 Load Range C. However the truck came from dealer with LT265/75R16 LRD and Load Rating somewhere around 118. I ran these tires for 60k miles using 45lbs psi.

My new tires are LT265/75 R16 LRE, Load rating of 123. (The tires I wanted didn't come in LRD and I didn't want to go down a rating.) I asked the tire dealer what inflation they recommended. Of course they said 35lbs after reading the door sticker. I had them put 45lbs as I shook my head :screwy: in disbelief.

So, back to my question. For a given weight on a given tire what is the proper tire pressure to get the proper contact surface with the road?

posted by  zz71

There's got to be someone out there who knows (well at least thinks they know) something on this subject.

posted by  zz71

Did you check the rating of the tires on the tire itself. Sometimes the tire will say how much air is needed for daily driving on the tire near the tire size or close o the rim. :wink2:

posted by  Coffin Type R

The tire says something like "max weight 3400 lbs @ 80psi".

That doesn't answer my question. Even a "daily driving" recommendation from the tire doesn't help me determine the proper pressure under different load (weight) conditions.

posted by  zz71

You are probably correct. :(

It would be great if the tire manufacturer would provide such information as the proper inflation of the tires given the vehicle's total weight.

But that would mean they'd have to get it right.

posted by  zz71

The tire pressure listed on the side of the tire is to be considered the maximum inflation(80 psi. in this case). You should stick with the truck's manufactuer on the optimum tire pressure because too much pressure can cause premature steering component failure as well as bearings ride and handling problems. The tire kinda acts like a shock absorber or a buffer between the road and your truck and having too low a pressure can end up causing damage to the tire, the rim handling problems and/or poor fuel economy. Tire maufactuers cannot supply inflation ratings other that maximums because of different applications.

posted by  srober32

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