u know u have got to be the only person i have ever heared of that would call the tire manufacturer if ur within 10-15 psi of the max pressure then its fully inflated it really doesnt matter what anyone says people are going to run whatever psi they want to run so this argument isnt getting anything accomplished

 

All I know is I have never run any of my tires at the max psi. Even the tire shops don't inflate them to the max rating. My BFG ATs have about 35 psi in them, but are rated for 50 max.

 

I've always run my tire psi at the manufactures recommendation on the door jam sticker. (unless I'm off road ) Which for a my 87 f 150 is like 35 front 41 rear, unloaded, cold tire pressure. Always worked for me and I get 15+ mpg average with my 32" tires and lifted truck.

 

You have to use some common sense with tire pressures. These 1/2 on trucks often came with 4ply street tires that needed 35-40psi to hold up the weight of the vehicle. If you substitute a more rigid tire with much higher load capacity then it's not going to need as much pressure to carry that weight.. though there will be a minimum required to maintain handling and safety. Inflating to the max pressure will just produce uneven tire wear and reduce traction.

 

The pressure listed on the tire sidewall is for informational purposes only. It is there to show the maximum load that tire can carry at its maximum inflation pressure. It is not the pressure that the tire is to be run at UNLESS you need to have that load capacity. Remember its not the tire that carries the load in a wheel and tire combination, it is the air pressure inside. (think about it, let the air out and what happens??). Tire manufacturers build tires understanding that the same size tire may fit and be installed on different vehicles.. and try to build them to the most extreme application. A 31x10.50R15 will fit both an F-150 and a Ranger, but they have very different load requirements. The vehicle manufacturers will list the recommended PSI for the vehicle on the doorjamb. That is the pressure to run at for a daily driver. You could bump it up when needed for additional load capacity (hauling or towing etc) but the vehicle manufacturer usually knows what works best. If the tires have been changed in size from OE.. based on the load capacity of the new tire you can usually figure out what pressure to run at to meet the OE requirements bades on TRA guidelines (Tire and Rim Association). Generally a larger tire (larger air chamber) will need less pressure to handle the same load.

I hope this clears things up a little.

 

I hope it does too... very good post.

Do not inflate your tires according to what the tire says - it's a max pressure only! The vehicle door jamb is where you will find the correct PSI.

 

I'm not arguing. I'm telling you why you're wrong. For us to have a 2 sided conversation, we'd both have to know what we are talking about.

 

You are correct, but only for the original type tire. If you put on stiffer tires say 6 ply vs the stock 2 ply then the door jam pressures wont apply the same.

 

You are correct in that assessment, however if you were to go to a heavier construction carcass, you could effiectively get the same load capacity at a lower pressure. Generally the OE pressure recomendation for any vehicle will be lower than the max of the tire, so you would still be ok. The danger in your example would be if you went from a 6ply tire to a 2 ply.. (which isnt a very common occurrence) where you would have to go above the vehicle manuf's pressure to retain the same load capacity. The other instance would be if you went from a LT tire to a p-metric tire in the same size (ie. a LT265/75R15 to a P265/75R15) wheras the differing construction would require different pressures to handle the same load.

Be careful in trying to compare load to ply ratings... they are not exactly the same thing.. every tire will have a load index associated with it that is listed on the sidewall (usually a 2 or 3 digit number at the end of the size on the sidewall)... that is the only true way to determine the load capaciy of the tire in question. Two different size tires can both have the same ply rating.. but the load capacities can be different.

The best way to replace tires if you are changing the size or construction from OE is to first find out the vehicle requirements, then compare what you need for the vehicle to the tire you are looking at's abilities. from there you can determine the correct pressure to run the replacement tires at to maintain the necessary load requirements of the vehicle.

 

True, but I was talking in general not specifics. Problem is, if someone decided to put a set of grandpas 235 85 16 10 plys on their ranger then the #'s on the door jam would be to low a pressure for that tire. There are several scenarios. I put an LT tire on my minivan & the dealer told me that their the wrong tires for my van. Bull Ship.

 

I agree..because an LT tire will not necessarily hold the same load at the same pressure as a p-metric tire will - it can actually be lower because LT tires can have higher max pressures.. if you graphed the LT versus P-metric with the x-axis being psi and the y-axis being load capacity the curves are very different..

and I wouldn't necessarily say that the LT tires are wrong for your van..

but if a consumer is switching sizes or construction from OE, they really need to look at it on a case by case basis.

Good points Todd.

 

Thank you drivwfo. Your definitely an engineer or math major LOL.

 

Nope... been in the manufacturer's side of either wheels or tires for over the last 10 years..(and that was after a couple of years running a retail tire store..)

 

You live in IL, IN, KY or TN?

 

SoCal..

Sorry that was a little vague.. I am a National Sales Manager for a smaller tire manufacturer..