TPMS - Newbie worried about what it shows.... is it OK?

[Alfred622]

I just added a TPMS to the motorhome. I've inflated front tires to 85# and rear to 95# which is 5# over recommended inflation based on weight they carry.

TPMS reads them cold as:
Front: 84 84
Rear: 94 95 95 94

Temperatures of all tires were close to 73 degrees (ambient)

Then I went driving for 30 miles and I see for PSI:
Front: 94 94
Rear: 105 108 109 105

and for temperatures
Front: 99 97
Rear 100 91 95 102

I'm concerned about the rear tires....

Right rear tire gained 14 PSI and outer 11.
Left rear tires gained 13 PSI and outer 11.


Outer tires ran hotter than the inners

To those with more TPMS experience than me, do these numbers look reasonable to you? If yes, what type of pressure or temperature change would you find significant?

I very much appreciate any advice those much wiser than I could offer.

[wolfe10]

And, for both tire and wheel, the PSI is cold.

Cold is defined as at ambient temperature before driving, tire not in sun, etc.

Both tire and wheel manufacturers KNOW and take into consideration the PSI increase with temperature increase. After all the Ideal Gas Law has been known for a very long time and most tire/wheel engineers knew about it from high school chemistry/physics.

[Big_Katuna]

And don’t forget to find out max inflation rating for the wheels. I ran into that on my old F53 chassis. Went to Gs but rims were rated for 80 psi. I cheated and went to 90.

[rgatijnet1]

William B wrote:

2oldman wrote:

wolfe10 wrote:
The sidewall information tell you how much air is required to carry XX pounds (the load capacity of the tire).

Max capacity. But folks on here put more air in ??

No I don't think so. The pressure on the side of the tire is the max to carry the rated load capacity of the tire. Most folks end up with lower than that number. You shouldn't exceed the sidewall number cold.

Partially correct.
The number on the side of the tire is the MAXIMUM load that the tire can carry and the air pressure is the MINIMUM needed to carry that max load. In other words, if you put in less than the printed air pressure, the load capacity of the tire will go down.
Also if you have to carry the maximum allowable weight on a tire, and you inflate it to the Minimum tire pressure as printed on the sidewall, the tire pressure will increase as you drive and the tire heats up. This is all well within the design parameters for the tire.
One other things is that if you go to a higher load rated tire like from an F to a G rated tire, and you plan on carrying the SAME load that is within the specs of the F rated tire, the tire pressure will be the SAME with the G rated tire.

[wolfe10]

William B wrote:

2oldman wrote:

wolfe10 wrote:
The sidewall information tell you how much air is required to carry XX pounds (the load capacity of the tire).

Max capacity. But folks on here put more air in ??

No I don't think so. The pressure on the side of the tire is the max to carry the rated load capacity of the tire. Most folks end up with lower than that number. You shouldn't exceed the sidewall number cold.

Correct.

Only reason to consider (improperly) doing this is that the actual weight exceeds tire capacity. If that is the case more air is NOT the answer. Selecting a tire with a higher load range IS the answer.

[William_B]

2oldman wrote:

wolfe10 wrote:
The sidewall information tell you how much air is required to carry XX pounds (the load capacity of the tire).

Max capacity. But folks on here put more air in ??

No I don't think so. The pressure on the side of the tire is the max to carry the rated load capacity of the tire. Most folks end up with lower than that number. You shouldn't exceed the sidewall number cold.

[2oldman]

wolfe10 wrote:
The sidewall information tell you how much air is required to carry XX pounds (the load capacity of the tire).

Max capacity. But folks on here put more air in ??

[Ivylog]

X4 on perfectly normal although on a longer drive you should find the inner duals will increase more than the outer tires. A 10-15% increase is normal and it does not take very many miles for it to happen. You should be concerned when you have something out of the ordinary happen which with some more miles you will understand.

On a cool rainy day I had my two tag tires increase 15+% and the other 6 only 10%...definitely not consistent with the norm. Stopped and discovered the pressure regulator was putting 100 psi into the tag’s airbags overloading the tires on the tag axle. Was able to get it back to the 45 psi it should have been putting out... never happen again. Without TPMS I would have ruined two tires, especially if it had been a hot day.

[wolfe10]

Dennis12 wrote:
Wonder why the manufacturer puts tire pressures on every tire. Them dummy's.
You will also find it on the unit. More dummy's
You can also try soaking the tires in Epson's salt. that may help.

Nothing dumb (or smart) about it. But you have to (no actually you should but don't have to) be smart enough to understand what each means.

The sidewall information tell you how much air is required to carry XX pounds (the load capacity of the tire). It certainly does NOT tell you how much the tire is carrying on your coach.

The GVWR sticker in the coach tells you the maximum each axle is capable of carrying and how much air is required to do so. Again, no claim that that is what your axle is carrying. Out for a lightly loaded weekend or are you a full timer with a hobby of collecting rocks. DIFFERENT ANSWERS.

[rgatijnet1]

Dennis12 wrote:
Wonder why the manufacturer puts tire pressures on every tire. Them dummy's.
You will also find it on the unit. More dummy's
You can also try soaking the tires in Epson's salt. that may help.

The manufacturer ONLY puts the MINIMUM tire pressure needed to carry the MAXIMUM amount of weight that the tire is rated for. Not everyone puts the maximum amount of weight on their tires, according to a four corner weight. In fact, I would guess that very very few coaches are so heavy that they reach the MAXIMUM weight rating of the tires that the manufacturer installs.

[Dennis12]

Wonder why the manufacturer puts tire pressures on every tire. Them dummy's.
You will also find it on the unit. More dummy's
You can also try soaking the tires in Epson's salt. that may help.

[rgatijnet1]

You also want to use a good tire gauge, like a Milton brand, when you inflate your tires. From my EEZtire TPMS gauge I found that the pressure is not 100% accurate. I verified this when I used one of the split inflator hoses, which ties two tires together at the same time(like two duals, or two front tires, and I found a few psi difference between what the TPMS monitor read, even tho both tires were inflated to the exact same psi.

[2oldman]

Executive wrote:
Kudos for inflating to PSI based on the weight of your rig.

How do you know how much increased pressure that is?

[10forty2]

Yep...all normal. When I first put a TPMS on my rig, it was after 2 blowouts 50 days apart with new tires. Turns out it was the tires' fault, and nothing I did....Goodyear made it right and I still run them...... with that said, my TPMS scared the dickens out of me when it started showing numbers like you posted, and I had just had the blowouts. I even pulled off the road and checked the tires to see if what the TPMS was showing was correct. It was, and the tires were perfectly fine. I found that having the TPMS added to my stress when driving, so I try not to look at it all the time.

What you want to watch the TPMS for, is abnormal and sudden changes....like a sudden drop or increase in pressure or a spike in temperature in one tire vs all the others. I've also found that the measurements that it gives are not absolute...mine tends to show a slightly lower pressure than read by an actual tire gauge, and whereas the air temp inside the tire is what the TPMS is reading, the tread temp is the main concern. I bought a laser thermometer and if I stop on the way somewhere I shoot the temp of the treads to see if there are any higher than the others, which might be indicative of problems with that tire.

[Executive45]

All normal. Kudos for inflating to PSI based on the weight of your rig. Expect 10-15# increases as you drive. Ambient temps affect your tires same as it does you. Outside tires usually a bit warmer than inside. My fronts, 315/22.5 increase from 110 to 125 generally, esp on hot days. Remember those tires are rotating on a platform that runs about 160 degrees on a hot day. IMO, your readings are correct and within tolerances. I've run TMPS for over 8 years, both on the coach and the toad....Dennis