"Correct" Tire Pressures

#1

Looking for correct tire pressures on a ‘94 Chevy Silverado C1500, 2WD, reg cab, short bed. The plate on the driver’s door says “…32 psi front and 35 psi rear…” I’m running Cooper Discoverer H/T, 31x1050R 15LT tires. The sidewall says something like “…max …50 psi”.



The Cooper web site doesn’t list tire pressures but says to use car manufacterers’ recommendations. But the difference bewteen 32 psi and 50 psi is pretty significant. Suggestions?

#2

Use what’s on the door jam or the owners manual. What’s on the tire is the MAX pressure these tires can handle. The tires (and size) cover a wide range of vehicles…some lighter then yours…some heavier. Tire pressure will be different depending on what vehicle the tires are installed on.

BTW nice tires…I’m on my third set of them…Been lasting about 55k miles.

#3

Thanks, Mike. Good suggestion/info. Yes, I’m very please with these tires. Good, deep tread but yet offer a quiet ride; and seem to be wearing very slowly. 55k sounds great!

BTW, I’m weaning myself from wide or lower profile passenger tires on my truck…lol.

Thx again!

#4

The pressure listed on the sidewall is the maximum pressure the tire manufacturer thinks the tire can safely be aired up to without running into structural problems. The car manufacturer’s recommendation is the tire pressure the suspension is tuned for, so you will get the best handling and ride at that inflation. So you want to use the manufacturer’s recommendation-- the sidewall ratings are just important because you need to make sure you’re getting a tire that can be inflated up to the manufacturer’s rating, but getting one that’s rated for much more isn’t a problem.

However, there are some caveats. First off, is the 31x10.5 size the original tire size? If it’s wider than the OE size, you might want to air it up a couple of PSI’s more. Also if you’re towing or hauling a lot of weight in the back of your truck, you will also want to run them higher. When you start changing variables like load and tire size, the manufacturer’s PSI’s become less relevant and it becomes something of a trial and error process to find the optimum inflation level. You still probably will not want to ever inflate them up to 50psi, though.

#5

Perhaps those same tires could be used for other vehicles that require a much greater pressure. Go with the Chevy recommendation.

#6

Tire Guides says a 1994 Chevy Silverado C1500 2WD regular cab came with P225/75R15’s inflated to 32 psi front / 35 psi.

It is important that you compare this to what the placard says for the original tire size - as obviously that is different that what you have on there now!

If the above is correct, then the proper way to do this conversion is to calculate the load carrying capacity at the placard pressure for the placard size and then calculate what inflation pressure the new size would need to carry the same load.

And the answer is: 1 psi less for both front and rear.

For those who would like to perform the calculation, you’ll need the tire load tables (They are in the Tire and Rim Association Yearbook, but I’m not sure if you can find them on the internet) and the trick is that the P metric tire has to be derated 10% becuase it is being used in a light truck application.

#7

Lotsa great info! It appears that the consensus is to run 32/35…plus or minus 1 psi. I wouldn’t think plus or minus 1 psi would be a big deal. Also, to add maybe a few more psi for “heavy” loads.

#8

Tire Guides says a 1994 Chevy Silverado C1500 2WD regular cab came with P225/75R15’s inflated to 32 psi front / 35 psi.

Last GM I owned (84 S-15) came with three different tire sizes (depending on trim level). My 90 and 98 Pathfinder came with different tire sizes also based on the trim level. The owners manual should list all the sizes that came standard for that vehicle.

#9

Alas, I don’t have the owners manual.

BTW, when I bought the truck the tires looked new. The were inflated to 40psi. That’s another reason I was curious. I lowered them to about 35lbs at the time, but lately began to wonder. Over this winter, I noticed the two front tires looked low. Checked and they were at 25psi.

#10

“Alas, I don’t have the owners manual.”

But you do have a placard and it’s located on the driver’s door or doorpost. What does it say for both tire size and pressure?

#11

Over this winter, I noticed the two front tires looked low. Checked and they were at 25psi.

You need to check the pressure more often. :slight_smile:

#12

Check placard on the inside of driver’s door.

#13

"…C1500, 2WD, reg cab, short bed. The plate on the driver’s door says “…32 psi front and 35 psi rear…”

Yep, good idea to keep track of tire pressures. That’s what I’m doing…lol

#14

One thing you have to remember…pressure drops 1lb for every 10 degrees drop in temperature. So if you filled the tires when it was 80 outside…then checked them when it was 30…there should be at least a 5lb difference in pressure.

#15

Speaking of checking tire pressures; I’ve two ‘push-on’ type gauges (where ya push it on the stem and a metal or plastic ‘bar’ gets pushed out); the kind ya buy at AutoZone, Advance, etc. Are they fairly accurate?

Watching a NASCAR race, I’ll hear em say they changed the tire pressure a half lb. I say to myself, ‘do what? a half lb?’

#16

A “dial-type” gauge is more accurate than those cheap “bar-type” gauges, so I would suggest buying one with a dial indicator.

A half-pound difference in tire pressure will not make a major difference for the average driver, but it could make a significant difference in handling for someone driving a NASCAR race car.

That being said, I make sure that my tires pressures are consistent, and I don’t allow even a 1/2 lb. difference in pressure on the tires on the same axle. I am a bit obsessive about things like that, but a 1/2 lb difference in pressure is not really a problem for the average driver unless you fail to check and adjust pressure at least every few weeks.

#17

My every day gauges are just like yours.

But I have a precision gauge that I use for more accuracy - and it goes in 0.1 psi increments.

And our tire lab has a pressure gauge that measures to the nearest 0.01 psi (Yes, 0.01 psi). We use it when we are doing “pressure critical” testing, such as force and moment measurements where we vary the pressure, load, slip angle, and camber, to measure the side forces, and over-turning moments. Out of this we produce what is known as a “carpet plot”, which is used as input to a vehicle computer model to simulate vehicle maneuvers. It is important that small differences be discernible.

So it isn’t a great big surprise to find NASCAR using ? psi increments. I suspect they would use ? psi if they felt it made a difference.

#18

Thx VDC. Knowing that the dial type is more accurate is good. I tell ya, a problem many of us have is that it’s very difficult these days to find air. In the distant past we could pull into a gas station and there was a hose and you could help yourself; preferably after buying some gas or something to show thanks. I’m reluctant to pull into a tire store and ask for ‘free’ air. Today, gas stations that do have machines where you pay for air, well, they don’t work half the time.

#19

I agree that it is difficult to find a gas station nowadays that has an accessible air pump. Too often, cars that are awaiting repair are left blocking the pump. And, then you have the increasingly common “pay” pumps for inflating your tires.

Because of these situations, I bought my own electric tire inflator that plugs into the cigarette lighter socket. This way, I can do everything in my own driveway. Not only is it more convenient, but this way you get much more accurate pressure readings since the car has not been driven to the closest gas station. (Driving even a couple of miles can raise the pressure slightly, and this leads to inaccurate readings)

If you go to a variety of auto parts stores, you will find several brands of tire inflator on sale. The one that I use (Bionaire) is a sturdy, reasonably quiet unit and I carry it in the cargo area of my wagon. That way, if I come out of a store and find that I have a puncture, I can reinflate the tire in order to drive to the nearest mechanic for tire repair. On one occasion, I did exactly that, and it saved me from the labor of having to mount my spare just for a 1 mile drive to a tire shop.

#20

I’ve got a lil pump; takes about 10-15 mins to add 10lbs…and it gets pretty hot. It’s label says ‘300psi’; but it’s still wimpy. I guess I could invest in a bigger unit.

Capri: Impressive stuff yall do. Don’t hold me to the “1/2 psi”. NASCAR teams might well do 1/4 psi increments. Just a flip remark on my part.

Thanks for all the replies!