Most posts about tires and inflation warn about the problems of inflation being too low, but I recently received a question about high tire pressure and felt it deserved a few lines.
“High” pressure is relative
35 psi might be high or way low, depending on the type of tire, just as 150 psi can also be too low or too high, again depending on the type of tire and application. The bottom line is that each “type” tire and each application has an inflation that we would consider the target. Most of the “target” inflations are given when the tire is “cold,” which means at ambient temperature and not warmed up by running or by being in the sun.
At the extremes, we might have a wheelbarrow tire or farm tractor tire which is designed to operate at relatively low inflation. Some farm tires are rated at 12 psi. Some drag race slicks are also designed for pressure below 24 psi. At the other end, we find aircraft tires needing 300 psi or more.
For our purposes we can limit our discussion to passenger tires, light truck, special trailer and truck/bus type tires.
Passenger tires
Passenger tires generally have recommended inflations in the range of 34 to 39 psi, with some Extra Load tires rated at 41 psi cold. If you read the sidewall of many passenger tires, you will see an inflation pressure stated on the tire. None of these inflations are the hot inflation—so don’t set or bleed down the inflation when the tire is hot.
Many times the tire is stronger than the wheel. I have seen a few examples of wheels failing at a lower pressure than the tire when we put tires to a test of over-inflation and head toward 100+ psi.
LT (light truck) and ST (special trailer) tires
LT and ST tires have a number of different load ranges, such as “C”, “D”, “E” and some even go up to “LR-F”.
The actual psi rating for each load range is not the same for all size tires, so you must consult the Load & Inflation chart for your specific size tire. The cold inflation associated with the tire’s maximum load capacity is also molded on the tire sidewall.
In general, you will see inflations range from 50 to 80 psi, with the LR-F somewhat higher.
As with passenger tires, usually the tire is stronger than the wheel, but the inflations are still “cold”—not hot—inflations.
Truck/bus and full-size RV tires
Truck/bus and full-size RVs have higher load range and, accordingly, higher inflations—with some at 120 psi range.
One constant SAFETY WARNING
The one constant SAFETY WARNING is to not set the cold inflation higher than the rated inflation for your specific tire and load range. Also, do not bleed down HOT tires. Tire engineers know that tires will heat up. We test our tires at highway speed and above when the tire is fully loaded, and design the tires to handle the hot inflation.
Over-inflation tires make for spectacular explosions. A quick search on YouTube shows a number of examples.
What new tires can handle
In general, we see that new tires are capable of handling from 200% to 700% of the cold inflation molded on the tire sidewall when we do a burst test in the lab. With that large of a range, there is no single number I can provide other than your “cold inflation” should not be greater than the psi number molded on the tire sidewall.
The other thing to remember is that internal structural damage from potholes, curbs and road trash, as well as simple age, can reduce the maximum strength capability of a tire. Therefore, this compounds the problem of providing a maximum safe cold inflation number other than that molded on the tire.
Bottom line
- Do not exceed the maximum inflation identified on the tire or wheel as your “cold” psi.
- All inflation specs are COLD, i.e., ambient inflations.
- Confirm that your max load on each tire will never exceed the load capability for your “set” cold inflation per the published tables.
- DO NOT bleed down hot tires.
- Sometimes it is the wheel that fails.
- Improper inflation can kill.
If unsure, let a professional tire service person mount and inflate your tires on the wheels.
Roger Marble
MORE POSTS FROM ROGER ON TIRE PSI
- Do your RV tires say ‘MAX PSI 80 psi’ or something similar? Don’t take it literally
- I don’t calculate my tires’ PSI daily. Why do you?
- My RV tire pressure is showing a significant increase. Is this OK?
- Is the tire pressure too high?
- Should you adjust tire pressure when temps get colder?
- Do not adjust your tire pressure for ambient temperature
- Understanding what temperature change does to tire pressure
- A quick note on tire “MAX PSI”
- If I upsize my RV’s tires, can I lower their inflation?
*****
If you have tire questions, check out Roger’s Blog as well as his posts on RVtravel.com. There are hundreds of posts covering everything to do with tires.
If you still have a question for Roger after searching the above posts, send your inquiries to him using the form below.
RVT1243
Thanks, Roger; your column is always worth reading!
This last line of the article should be stamped everywhere tires are used. Driving a 18,000 lb motorhome makes me very aware that tire failure can be fatal.
The toughest part about maintaining tire pressure is the willingness to check and adjust it when it meets the defined ‘cold’ conditions. It often means shortly after dawn before the sun hits the rubber and/or before the rubber hits the road. Suck it up buttercup. Unless the climate changes dramatically, it isn’t like you have to do this everyday.
Roger, glad to see you are now also making reference to the wheels as well as the tires. My MH has wheels rated at 95 lbs per the Tire and Wheel Assn. standards. My tires are rated at 110 lbs (F load). The chassis is rated at 16,000 overall. So, the wheels are the restricting factor rather than the tires. Thanks for posting – your learned advice is appreciated.
Are those the original tire size and specs? My understanding has always been that vehicle manufacturers can’t install tires that exceed the wheel rating as someone might look at only the tire rating and exceed the wheel’s cold max rated pressure. ???
Hi Mikal: No, as near as I can find find out, the MH came with “D” on this particular unit – either earlier or later or some models, came with “F”. The maximum rim weight is 2,780 lbs at 95 lbs. There is also a discrepancy in the specs on the wheelbase as mine is longer than specs (GM gas chassis). The tire co. installed the F loads “…as that is what they always put on MH over 32′ “! (Mine is 34′). However, I have not experienced any flats or blowouts and keep a very close watch on both min. and max. pressure’s.
Been reading tire charts since the late 60’s. They were gospel on the farm.
Recently purchased a 2024 trailer. I hooked up and noticed it bouncing/weaving down the road. A few miles later I pulled into a rest stop and found all the tires at 90 psi or above. The previous owners said the max pressure on the tire is what he always uses. They were Goodyear Endurance tires and the chart shows they need a minimum of 40-45 psi. I set them for 50 psi (well over 100,000 miles with Endurance tires) and the bouncing/weaving stopped.
The max of 80 psi is just the max.
I then had Discount Tire look at the tread. The center of the tire was a 30% tread, while the outside was at 80%.
Our last two sets of Endurance tires ran over 40,000 miles each and they still had some tread. At 50 psi and TPMS we don’t have blowouts either.