Tire pressure different on tire vs car

[PWMDMD]

Depends on the vehicle. My Tundra is supposed to be 33/35psi and if I do that the outsides of the front tires wear quickly. If I keep them at 40psi it's a perfectly even wear across the entire tire.

 

[tshephard]

Max Pressure: For passenger car tires. the max pressure is NOT where the load maxes out. For SL (Standard Load) tires, the load capacity maxes out at 35 psi (for Eurometric tires: 2.5 bar = 36 psi!), and for XL (Extra Load), the value is 41 psi (Eurometric: 2.9 bar = 42 psi!) Note" you will find tires that list a 35 psi max pressure - in which case the max load does max out at the max pressure.

https://www.govinfo.gov/content/pkg/CFR-2011-title49-vol6/pdf/CFR-2011-title49-vol6-sec571-139.pdf

"Maximum load rating means the load rating for a tire at the maximum permissible inflation pressure for that tire.
Maximum permissible inflation pressure means the maximum cold inflation pressure to which a tire may be inflated."

Now, I know that's government speak, probably written by folks that had to look up "tire", but I have to associate the two, as they did. Better source?

 

[Astro14]

https://www.govinfo.gov/content/pkg/CFR-2011-title49-vol6/pdf/CFR-2011-title49-vol6-sec571-139.pdf

"Maximum load rating means the load rating for a tire at the maximum permissible inflation pressure for that tire.
Maximum permissible inflation pressure means the maximum cold inflation pressure to which a tire may be inflated."

Now, I know that's government speak, probably written by folks that had to look up "tire", but I have to associate the two, as they did. Better source?

T - Capriracer is a tire engineer.

There is no better source. I encourage you to visit his page and read up.

It‘s an education.

 

[thunderous1335]

So if the door label said to run them at 35 psi, then whats the sense of buying tires rated to 51 psi?. Plus not understanding how the tires will perform BETTER carrying max loadsm with higher pressure, is extremely uninformed on your part. Glad I could help you understand that.,,

There is no tire you can buy where the maximum PSI rating is under 50. They do this because idiots overinflate tires way higher than they need to be because they "think it looks too low"

 

[BigCahuna]

If you have a tire inflated to 45 psi, and you don't check the pressure for a while and it drops down 10 pounds, you tire will have 35 psi in it which is fine. Now say you have a tire with 35 psi in it and don't check it and the pressure drops 10 psi, now your running 25 psi , Running a tire that low on a street car will have problems. Increased wear, sloppy handling, and lower gas mileage. Also tires with low air pressure run hotter. That's the main cause for blowouts. You have had to notice the bits and pieces of exploded car tires on the side of the road in your travels. Or tires that have come off whole, that look like they went thru a shredder. They don't even have to be loaded heavy to blow. Truck tires will often catch fire due to heat from the friction of being dragged down the road. The higher the pressure you can run, the cooler your tires will run.,,,

 

[ARCOgraphite]

The recommendation on the door, was put there to match the tires installed at the time of manufacture. That being said, his new tires do not have the same pressure ratings as the tire they put on the car in 2008. The manufacturer of his new tires say what it can it be inflated to. New tread design and capacity determine what you can inflate them to. New tires may look low on pressure if inflated to what the door label says, and may feel like they drag, going around corners. Filling to max capacity probably will make for a rough bumpy ride, if not needed. And no I've never seen a tire brand and type written on a sticker, that's why you can't assume every tire ever installed on that car has the same inflation requirement. I hope that clears this up for you.,,

You should never have to adjust pressure more than +/-3psig from placard to achieve safe load and handling and ride on a passenger car for it's normal intended usage; If you do, you bought the WRONG TIRE.

Nice try to save face - but too late

 

[mark pruett]

So if the door label said to run them at 35 psi, then whats the sense of buying tires rated to 51 psi?. Plus not understanding how the tires will perform BETTER carrying max loadsm with higher pressure, is extremely uninformed on your part. Glad I could help you understand that.,,

You're the one not getting it. The door label tells you what the pressures for YOUR particular car are, and the tire's sidewall shows what the tire's maximum capacity is.

Other cars/trucks weigh different amounts, have different springs, different weight distributions, etc... and may recommend different tire pressures than yours- higher OR lower.

Look at it this way- if you have vehicles that weigh significantly different amounts, but use the same size tire, it's not logical that they'd both require the same inflation pressure. So the tire has to be able to handle both (and any other vehicle requiring the same size, load range and speed), and the max inflation pressure on the sidewall is basically saying that it can handle vehicles that require up to 51 PSI, but vehicles that require less are just fine as well.

 

[4WD]

Good post as always. I tend to be a plus one tire shopper. Like a bit more width because I’m on sand often. Like some sidewalls because (as handle implies) - drive 4WD’s and they don’t ride well on low aspect rubber, not compliant off-road (and wife will curb gouge the rims) … And yes, like the look.
Have always used the OEM pressure on the plus one and if I get 40k it’s enough …

^^^^ Folks - I have done this for decades and have always owned multiple vehicles … Many types … Towed and off-road. Plenty cars too. The OEM did not grab that PSI/kPa number from left field. You might also note that tires are one of the longest sections in your owners manual … Think about that …

 

[Rand]

There is no tire you can buy where the maximum PSI rating is under 50. They do this because idiots overinflate tires way higher than they need to be because they "think it looks too low"

Uh what? there are plenty that spec 44psi max. without even looking hard.

 

[CapriRacer]

https://www.govinfo.gov/content/pkg/CFR-2011-title49-vol6/pdf/CFR-2011-title49-vol6-sec571-139.pdf

"Maximum load rating means the load rating for a tire at the maximum permissible inflation pressure for that tire.
Maximum permissible inflation pressure means the maximum cold inflation pressure to which a tire may be inflated."

Now, I know that's government speak, probably written by folks that had to look up "tire", but I have to associate the two, as they did. Better source?

Be very careful how you read that sentence from the regulations. It only says that the max load rating comes from the load rating at the max pressure. It does not say the load maxes it out there.

Allow me to give an example:

Let's try the P215/50R17 Toyo Proxes A20 90W SL. Go look it up on Tire Rack

Max load 1323# Max pressure 51 psi

Now go to this webpage: Toyo: Guidelines for the Application of Load and Inflation Tables

On page 17 you will find the load table for a P215/50R17. At what pressure does the SL load max out? 35 psi! Notice that All Standard Load (SL) tires max out at 35 psi (except for a few that max out at 36 psi! - and there's a long story why that is so.)

Also notice that the Extra Load (XL) tires max out at 41 or 42 psi.

And bringing us back to the OP: The vehicle tire placard lists a tire size and an inflation pressure and that is applicable regardless of who makes the tire. The load tables are essentially the same - with a few exceptions.

 

[Traction]

And to put it a different way, your tires are designed for your vehicle to be a certain size with the correct volume of air in the tire to support the weight of the vehicle at it rated load. Plus your tires are also a huge part of your suspension, and they are also like springs.