Tire pressure different on tire vs car
- Thread starter frankT
- Start date
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.
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"
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.,,,
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
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
$50 site donor 2025
^^^^ 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 …
Uh what? there are plenty that spec 44psi max. without even looking hard.
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.
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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.
Welcome to 2024, where most tires that came on your 2010 vehicles , are no longer in production.They have been replaced with tires that will be used on alot of different vehicles, with different operating pressures. And I know there are some here that want to stomp their feet and not believe that's how it is. So for those who believe what their door sticker says is law, enjoy your new tires that always look like they're going flat. And totally ruin the ride and handling, by running 32 psi in them.,,
Please go back and read the stuff in CapriRacer's posts. It's clear that you don't know what you don't know.
Future daughter-in-laws grandfather would always fill his and family members tires to the max on sidewall. He would reprimand them for not checking and being low. All of their tires had like 1/2 the contact patch, were poor in rain and snow, vehicles rode bad and wore out the middle tread very quickly.
We showed and explained to her the issues. She explained to her family and they are better. The grandfather...well...he reprimands at holiday's and fills them all to max with his inflator. They leave and air back down to placard or just above. We gave all of them tire pressure gauges and showed how to use them.
All of my vehicles are normally about 2psi over placard but adjusted based on frequent tread depth gauge checks also. They wear very evenly. FIL's Renegade is about 2psi under placard (33 vs 35) based on wear depth checks but his tires are one size larger.
I don't go by the look of being low. Many lower profile ones all look low to me. I go by wear and performance with close relation to placard. BigCahuna's posts on this actually scare me some because I know there are many people worse than that and we share the road with them.
We showed and explained to her the issues. She explained to her family and they are better. The grandfather...well...he reprimands at holiday's and fills them all to max with his inflator. They leave and air back down to placard or just above. We gave all of them tire pressure gauges and showed how to use them.
All of my vehicles are normally about 2psi over placard but adjusted based on frequent tread depth gauge checks also. They wear very evenly. FIL's Renegade is about 2psi under placard (33 vs 35) based on wear depth checks but his tires are one size larger.
I don't go by the look of being low. Many lower profile ones all look low to me. I go by wear and performance with close relation to placard. BigCahuna's posts on this actually scare me some because I know there are many people worse than that and we share the road with them.
Cant believe how many times this comes up....The sticker on your door jam is what you use for the tire pressure NOT the max pressure listed on the tire....
4WD
$50 site donor 2025
I just returned a rental - Chevy Spark - drove pretty good but picked up every crack on the freeway ?
Played with dash readings sipping coffee - 45 psi in tires - cold !
The sticker said 35 psi. This rental had 40k and these tires had 40k for sure. I bled them all to 35 psi - drove better …
Played with dash readings sipping coffee - 45 psi in tires - cold !
The sticker said 35 psi. This rental had 40k and these tires had 40k for sure. I bled them all to 35 psi - drove better …
4WD
$50 site donor 2025
In the old days, it was common for car manufacturers to specify the pressure listed on the tire's sidewall. Grandpa is probably remembering those days.
In the 1970's, government regulations stared requiring a sticker - commonly called the placard - with the tire size and specified pressure for the vehicle. At the time, pressures on the sidewall were "Rated Pressures" - meaning the pressure where the rated load maxed out.
About the same time, car manufacturers started using pressures other than what was specified on the sidewall.
Fast forward to today, and it's even more complicated as the max pressure is now listed on the sidewall and not the rated pressure.
The good news is that if you look at the tire sticker and use the size listed there, the load tables haven't changed since ....... ah ...... well, forever. They remain the same. Tire sizes have changed, but the relationship between load and inflation pressure for a given size hasn't - which is why you need to pay attention to the size. Not only does using the right size prevent the tires from rubbing (Very bad!!), but that means the pressure listed on the sticker is applicable as well.
It's there any kind of reference or formula available to derrive an approximate and appropriate pressure when changing tire sizes given the factory size and pressure?
On my Fords it was usually more than what the door decal said. On my Hyundais it's usually spot on. I use to run more than the stated pressure and found it to be beneficial with the Tauruses. Hyundais it just makes for a rougher ride. But you don't want to be below the door pressures.
A lot depends on the tires too as the OEs are usually pretty crappy.
A lot depends on the tires too as the OEs are usually pretty crappy.
