What tire pressure is good for my truck?

[TopoTony]

My Tundra has 18” Hankooks that show a max pressure of 51psi. The sticker on the door jam says something like 35-38psi. One tire service place set them to 50. Someone else said run ‘em at 45.
The recommendations are all over the place.
I realize some consideration is based on how much weight it’s carrying. I don’t really know that exact number. My hideout single axle has a 550 tongue weight. I’ll probably have a couple hundred pounds of gear in the bed.
Any help with a general psi number would be greatly appreciated.

 

[DutchmenSport]

It's not the weight of the vehicle the tire has to hold up, it's the air pressure against the tire rim is designed to handle. If the tire rim is designed for a max psi of 35 pounds, and the tire has a max psi of 80 pounds, putting 80 pounds of pressure in the tire on that rim will cause damage to the rim.

The psi of the rim is stamped on the back of the rim. Check it. That's the max pressure you want ON THAT RIM, regardless of what the tires says it can be.

 

[TopoTony]

Whoa…how did that fact evade myself and everyone I know? I have always thought the psi listed on the tire was gospel.
When you say, “back of the rim”, do you mean crawl underneath the truck and look on the opposite side of the rim?
I’ve just done that and see no indication of any such number. Didn’t take a pic underneath.

 

[Gary RV_Wizard]

Dutchmen is correct, but I doubt if the wheels (rims) on your Tundra are so underrated that they can't handle 51 psi. Or more. You can check it to be sure, though. Or ask a Toyota dealer to what the max psi & weight load is for the factory wheels.

The psi rating on the tire sidewall is simply the psi needed to give the tire its max-rated weight carrying capacity. It's not a recommended psi nor is it the max the tire can be inflated. The sticker on the door jam is what the Tundra engineers recommend for general use, but not necessarily maximum cargo load. And that recommendation is based on the original tires but I doubt those 18" Hankooks are originals. That pretty much makes the door sticker obsolete unless the Hankooks are the identical size as the ones shown on the tire safety sticker.

So yes, you need to know the actual weight the tire/wheels are carrying to get optimal results. Without that, you have to err on the side of caution and use the axle weight rating (GAWR) and assume the tires (2 per axle?) are equally sharing that max safe load. The axle GAWR is on those door stickers too, so get that number, divide by 2 (tires per axle) and then get that weight value from the Hankook tire inflation table. Otherwise, everybody is just guessing. But if the axle GAWR is roughly twice the weight shown for max load psi on the sidewall, that 51 psi shown there will be about right. If 10-20% less, you can safely drop the psi down a bit, maybe that 45 psi suggestion.

So if it's a guessing game, I'd go along with the folks saying 45 psi. It gets you close without being excessively harsh riding.

 

[TopoTony]

So if it's a guessing game, I'd go along with the folks saying 45 psi. It gets you close without being excessively harsh riding.

Thanks Gary, for that well thought out response. I’ll go with that guess.

 

[Boat Bum]

He's good like that.

 

[bigb56]

Sometimes it's not easy to find load & inflation tables for each brand, but I have found that just about all of the tables are the same for a given size regardless of brand. It is recommended to add a minimum of 10% to allow for side to side variations.

You may find, through experimentation, different pressures affect handling and ride with tradeoffs. A higher pressure can make for better fuel economy and less sidewall flex making for more stability while towing, but can also offer a rougher ride and reduced traction (which includes braking traction) It's a balance and you may need to experiment to find your optimum pressures while towing vs not towing and if you're like me you'll want to put a sticker somewhere with those pressures on it.

I don't think many people have had issues running a higher pressure as long as it doesn't exceed the tire and rim maximum ratings but plenty have had problems running too low of a pressure (either intentionally or through neglect/ignorance) which causes excessive sidewall flex and heat which can result in rapid carcass damage and eventual failure.

If you want to read more about tire safety check out Roger Marble's RV Tire Safety blog. He is the true expert.

 

[TopoTony]

If you want to read more about tire safety check out Roger Marble's RV Tire Safety blog. He is the true expert.

Thanks. It’s a bit of a complex science, if you really dig into it, but I’m glad there are some good general guidelines, that you fellows have shared, so I can be confidently in the ballpark.

 

[Gary RV_Wizard]

Thanks Gary, for that well thought out response. I’ll go with that guess.

The tire shop "guessed" 50 psi because they don't want to be held legally liable for under-inflating a tire, which can be a very dangerous thing. For that reason, tire shops near-always inflate for the max load carrying capacity as shown on the tire sidewall unless the owner specifically requests some other psi.. They are more worried about a lawsuit than your comfort.

I strongly encourage you to at least do the arithmetic with the axle GAWR to estimate the probably max tire load and inflate for that. But you need to know the exact tire size of those Hankooks, e.g. 255/45R20, to look up the psi value. As bigb56 suggests, you can safely use another brand's inflation table for that exact same size. Any tire that meets meets the Tire & Rubber Association standards will be very close in the inflation spec. Goodyear & Michelin inflation tables are easy to find online.

 

[CamperAL]

The place I bought my tires from (who use to do service for my RV) filled the tires with 110 lbs even though the pla card showed 80 lbs.
After I bought the tires I asked if they had to have that much PSI them and I couldn't get anyone at the shop to give me any type of an idea of what they needed. (new tires so I was depending on them to know cause they're experts right?)

On my trip south to Alabama this year (near Golf Shores, The motorhome skidded twice on me. Once while in a clover leaf and once when I moved over to the shoulder to dodge some debris. We could feel the RV slip and that scared us. I contacted the shop when back and took the RV over to let them look things over. They finally came to the conclusion I should have 80 PSI in the tires. I
had gone around and around with them on this several times.

So be careful on tire pressure when dealing with service people!! That includes buying the right tire to do the job for your situation.

 

[dave541]

The place I bought my tires from (who use to do service for my RV) filled the tires with 110 lbs even though the pla card showed 80 lbs.
After I bought the tires I asked if they had to have that much PSI them and I couldn't get anyone at the shop to give me any type of an idea of what they needed. (new tires so I was depending on them to know cause they're experts right?)

On my trip south to Alabama this year (near Golf Shores, The motorhome skidded twice on me. Once while in a clover leaf and once when I moved over to the shoulder to dodge some debris. We could feel the RV slip and that scared us. I contacted the shop when back and took the RV over to let them look things over. They finally came to the conclusion I should have 80 PSI in the tires. I
had gone around and around with them on this several times.

So be careful on tire pressure when dealing with service people!! That includes buying the right tire to do the job for your situation.

That is why I always check the pressures and re-torque the lugs when I get back from the tire shop. The owner is a knowledgeable guy and sets the shop rules to follow (don't use memory -- look up the actual pressures and torque), but the high school kid that does the routine tire swaps may get lazy and take shortcuts.

My truck recommended pressures are 32/35 front/back, and I set them accordingly. I'll go up a few pounds if towing or carrying a heavy load. Much more than that I can feel the change in handling and control. With the small portable inflators now changing pressures is easy. I haven't used my big tank compressor in over a year.