On the road, help please!

[ghaynes755]

Tires will increase pressure with heat. Any kind of heat. If I remember posts from eh tire gurus 10% increase in pressure is normal. What didn't sound normal was you said the pressure was at 63 (not sure if that was indicated on the dash or you measured it), door sticker says 60 and you got an "UNDERINFLATED" reading. Sounds like a computer or TPMS sensor error if it gave an Under warning.

[Action]

http://www.trucktires.com/bridgeston...loadtables.pdf

Firestone is owned by Bridgestone. Follow the link on page 8 or further down may help.

>>>>>>>>Action

[switz]

With the stock Michelin LT265/70R17E tires on our 2012 Dodge, the front axle is rated 5,500 pounds and the recommended tire pressure is 60 psi and the rear axle is rated 6,010 pounds and the recommended tire pressure is 70 psi. I run the pressures 10 psi higher at each location when towing.

I use a Longacre digiial tire gage to check tire pressure while the trailer is still under the roof in the shade at the storage unit. Cold is a relevant number when the ambiant air temperature is 105+ degrees out.

[NoNameinNM]

Originally Posted by ghaynes755

Tires will increase pressure with heat. Any kind of heat. If I remember posts from eh tire gurus 10% increase in pressure is normal. What didn't sound normal was you said the pressure was at 63 (not sure if that was indicated on the dash or you measured it), door sticker says 60 and you got an "UNDERINFLATED" reading. Sounds like a computer or TPMS sensor error if it gave an Under warning.

I know-- it's bizarre. The tire pressure readings were from the dash. The lower of the two readings on the front tires before we left town that morning was 59 (recommended psi is 60 on the front tires according to the label on the door). When we got out to check the tires manually after the alarm went off, we realized the TireTek gauge I'd purchased didn't go above 60. My husband purchased another tire gauge inside a truck stop but it was junk and he couldn't get a consistent reading from it (I've just ordered a Longacre gauge that will cover the range we need, and it will be here Thursday). We did find that the gauge on our air compressor was always about two psi higher than the readings from the dash.

The next morning, at an altitude 2000 feet higher than home (with much cooler temperatures), the tires were all low and we added air. Before we left for home the next day we checked the tires again. Overall, the two rear tires each got an additional 5 psi to reach 80 psi. And on the drive home, the TPMS said that the psi in those rear tires increased by 13-16 psi, which I
found alarming. The tire supplement says an increase of 2-6 psi is normal, but the manual is generic to most automotive tires and says nothing about towing.

With the new gauge in hand, I will see how it relates to what the truck's TPMS is telling us. Then I will do my best to stop obsessing over the TPMS (I'd never obsessed over it before this incident and there's always the chance that it is faulty), and start obsessing over checking the tires manually every morning before we start, and every time that we stop during the day, and noting it, along with tire temperatures, because gosh I do love gathering data and observing trends. No... really, I do.

[Action]

The important measurement is the one in teh morning before you take off. Measuring after you have left is OK and I would not adjust pressure on a tire that has been on the road. Not until the next day.

>>>>>>>>>>>Action

[ghaynes755]

And don't be surprised if the TPMS in the truck isn't accurate to the tire gauges. Mine is off 3-5#. Dealer says that is normal margin of error. Pressures checked with two digital gauges, a Longacre and calibrated gauges at Discount Tire. All of those are in agreement. TPMS system is the only voting off of the island. Need to look and see if GMC has a calibration method.

[NoNameinNM]

Originally Posted by Action

http://www.trucktires.com/bridgeston...loadtables.pdf

Firestone is owned by Bridgestone. Follow the link on page 8 or further down may help.

>>>>>>>>Action

Thanks for the link.

Okay, we have the LT275/70R18E tires. Max weight on the front axle is 6000 pounds, recommended max pressure of 60 psi. Max weight on the rear axle is 6500 pounds, recommended pressure of 80 psi.

When we took the rig across the CAT scales our first weekend out, the weight on the truck's front axle was 4600 pounds, the rear axle was 5060 pounds, and the trailer's axles weighed 5760 pounds. I doubt that changed much this time around. Is there anything wrong with these numbers?

So if I look at that chart, it says that the maximum load on one of these tires at a cold inflation pressure of 60 is 3020, and we had about 2300 pounds on each of those front tires (assuming the truck was relatively level side-to-side) with a starting psi of no less than 59. In fact, the chart suggests that I could have run those front tires at 45-50 psi and they would not have been overloaded.

I am coming to the conclusion that something about the truck's TPMS is . Not only that, it's with little to no documentation in the owner's manual on how to adjust or override it.

Maybe it was just Saturday morning right after a blue moon?

[NoNameinNM]

It may all come down to this, which I just found:

"Your vehicle has also been equipped with a TPMS malfunction indicator to indicate when the system is not operating properly. The TPMS malfunction indicator is combined with the low tire pressure telltale. When the system detects a malfunction, the telltale will flash for approximately one minute and then remain continuously illuminated. This sequence will continue each time the vehicle is restarted as long as the malfunction exists."

When I started the truck up again after a break of probably half an hour (and reducing the pressure in those front tires by a couple of psi), the warning disappeared and never happened again. I don't remember it saying anything about a "malfunction," but the flashing with the low tire pressure warning, followed by continuous illumination is precisely what happened.

I think it's time to schedule a service appointment at the dealership to have it checked out.

[Ted S.]

I have the Firestone Transforce AT tires on my Excursion, long story but they were the only tire in stock at the next exit off I94 after a major blowout.

Anyway, they increase from 80 to 94 psi during highway tow according to the TPMS.

[NoNameinNM]

Originally Posted by Ted S.

I have the Firestone Transforce AT tires on my Excursion, long story but they were the only tire in stock at the next exit off I94 after a major blowout.

Anyway, they increase from 80 to 94 psi during highway tow according to the TPMS.

Thanks! That does help provide some sense of range that should be anticipated. From 80, one went up to 93 or 94, and the other one hit 96 for a short time.

[Al and Missy]

Your numbers are consistent with my experience. I think you had a TPMS malfunction.

Al

[Ted S.]

I also noticed the temperature affected the pressure and also the altitude. We live at 200' above sea level and crossing the Bighorns we were at near 10000, we had to air down a few pounds. I also Googled the issue and the results lead me to believe the pressure increases we were seeing was not a big concern.

[Ted S.]

Originally Posted by Al and Missy

Your numbers are consistent with my experience. I think you had a TPMS malfunction.

Al

We back checked the pressures with a manual gauge, a solid 10 lbs increase was constant at minimum. Perhaps it's the tire characteristic.

[NoNameinNM]

Originally Posted by switz

use a Longacre digiial tire gage to check tire pressure while the trailer is still under the roof in the shade at the storage unit. Cold is a relevant number when the ambiant air temperature is 105+ degrees out.

Isn't that the truth! Obviously we're not quite as hot here in Albuquerque, but I know what you mean.

I ordered the Longacre earlier today, and I'm sure we will be much happier to use it than having to mess with putting the long coil hose on the compressor back in its case (not that it doesn't do its job very well, but that hose definitely has a mind of its own!)

[NoNameinNM]

Originally Posted by Al and Missy

Your numbers are consistent with my experience. I think you had a TPMS malfunction.

Al

I agree... I'll be calling the dealership to schedule a service appointment first thing tomorrow.

You always learn a lot more from things that go wrong than from things that go right. If nothing else, I'm a lot more aware of what's going on with tire pressures and temperatures than ever before.

[switz]

I have a factory tire monitor system on my GoldWing motorcycle and we had it on the Acura. They would throw warnings in Santa Fe at 8,000 feet. The same exact pressure at 2,000 feet was okay. There is a thought about absolute pressure readings with some of the TPMS systems that get affected with altitude.

I inflated the tires when in Santa Fe by 4 psi (still under the max pressure) and the TPMS systems were happy.

Note that if there is more than one vendor of a specific tire size, the manufacturers build to the same pressure/load ratings so you are not locked into one tire company.

[mbenson1234]

Feel free to contact me at TST if you have any additional concerns.
Thanks,
Mike Benson
TST
770-889-9102

[BAB]

I have a 2014 Ram 2500 with 6.7L Cummins. I had it in a few weeks ago for an oil change and I noticed that when it was returned to me the dealer had accomplished a recall item on the TPMS. Granted, mine is a '14, but....