Might be a dumb question but how accurate is the trucks tire pressure monitoring system? I have a 2017 f350 6.7 CCSB. I have the rear tires set up around 70-75 when towing but after a couple hours of towing the tire monitoring system says the tire pressures are 80- 85 psi.

im running BFGoodrich KO2 tires. Is that accurate and is that ok for the tires if it’s above 80 once warmed up? I use a manual tire pressure gauge befor I leave so I know where the pressure is at.

thanks for any advice.

 

Touche'....................

 

Just about missed you question. Here’s the answer. A tire's maximum inflation pressure is the highest "cold" inflation pressure that the tire is designed to contain. However the tire's maximum inflation pressure should only be used when called for on the vehicle's tire placard or in the vehicle's owners manual. It is also important to remember that the vehicle's recommended tire inflation pressure is always to be measured and set when the tire is "cold." Cold conditions are defined as early in the morning before the day's ambient temperature, sun's radiant heat or the heat generated while driving have caused the tire pressure to temporarily increase.

Seeing a 10psi increase when the tires heat up is normal. My experience so far with TPMS leads me to believe they are fairly accurate.

 

I have found the TPMS to be extremely accurate +/- 1 lb in most cases.

A 10 lb increase when towing when not be unusual .

Door jam data points: It is MY opinion that the psi listed on the door jam refers to when the truck is loaded to that specification.. Then you can use your tire charts to give you a psi at any given load. The drawback is that if you have varying loads. If you pull a 5th wheel and CAT scale it then you have a reliable data point that you can inflate to: In my case I have truck + Truck Camper + a trailer for 3 different weights: 9460 lb 15540 lbs and 19,200 lbs respectively. I adjust my psi depending upon how I am hauling, it varies from 70 psi to 90 psi.

 

How accurate you consider the TPMS to be depends a lot on the accuracy of the gauge(s) that you check it against. I doubt that many truck owners have gauges that are certified. The gauges operating range and scale will play a big part in how easily it can be read. I have an inexpensive digital gauge that I use on both my dirtbikes and my truck/trailers. I run the trials tire on the rear of my woods bike at 7-9 psi and the other vehicles can range to 80 psi. Is it the right gauge for this?? Who cares...its what I'll continue to use.
I have found that I can check all of the truck tires at within .5 psi of each other at rest and then find that the TPMS shows 2 psi or so difference. Is it the repeatability of my gauge or the TPMS??
Another thing to think about is what do you consider to be cold pressure when you check. With a digital gauge, I'll see a difference between a tire that's shaded and one that's been in direct sunlight for a while (verified by TPMS), even though the truck has sat overnight.
Its my viewpoint that the TPMS is for monitoring and avoiding an issue while in transit. I'll use my gauge to set my tire pressures.

 

I just rotated my tires last week. Im running 55 rear and 65 front on the 20" Michelins. I re set the pressures with my truck gauge/filler at work. No idea if its very accurate but its one of 2 gauges I use all the time for consistency. As soon as I got on the road I flipped the dash to tire pressure and it read 67 and 69 in the front and 59 for both rears. I tried to be exact on the gauge.
So my thing is to use the same gauge and don't worry over a few pounds. The difference in the readings from gauge to TPMS doesn't bother me so much as the difference from side to side. That you may feel more than a pound or two up or down... better to be the same left to right... Im going to be looking at that more because I think the right one always shows a bit higher than the left... See that's the problem for me... the TPMS is 4 separate sending units... each could be different at the same actual pressure... whereas the gauge is one unit across all 4 tires...
Find the pressures that work empty and loaded and how the contact patch is and ride with that pressure on whichever gauge you use.
Its like stepping on the scale to see your weight. No 2 are the same.

 

Mike, good advice.

If you want to see how accurate your TPMS is. Park your truck North-South orientation on a sunny day somewhere before noon go out and turn on your truck and look at your TPMS read outs. They should be 1-3 lbs psi over the other side of your truck that is in the shade. The sun exposed tires will heat up more than the tires in the shade and depending upon ambient air temp and where you live the difference can be a little as one lb and as high as 3 lb. Here in S Tx with nights in the low 70's and days heading towards 100 by mid day you can get a 2-3 lb difference.

When I got to check my psi I do it out in my barn where the truck is inside and all my psi should be equal side to side.

If you are like me you got tire agues all over the place. When I got my F 450 sans TPMS and had to rely upon my tire gauges I dug out all of them I think about 9 total. I then checked A tire using each gauge I was SHOCKED at what I discovered. I had differences of over 30 psi and out of the 9 I had 3 gauges that read the same +/- 1 lb. I then repeated them on another tire that took a differs PSI (rear Vs front). I ended up keeping 3 and tossing 6 others. Some were old, some newish, some digital, some analog.

What I found was the tire gauges that agreed with each other also agreed with the TPMs. If you want to optimize your tires. What I did was take my AC unit out to the barn and one morning when the ambient temp was about 70 I equalized Left - Right psi and I used door jam psi. I have now done it "cold" and L/R is within .5 psi of each L/R tire. Next step was to find the contact patch because its NOT the PSI, its the contact patch loaded and unloaded. The door jam give you a 'at weight' PSI, not unloaded PSI (note, I could be wrong on this, but door jam provides only 2 data points, PSI and a Max weight loaded, I will assume the PSI given = with max weight loaded, I am open for correction).

Contact patch: Couple of ways, dust or wet test and you can see visually the size of the contact patch. I adjust when the tires are hot in 2 lbs increments +/- to get full contact.

Before someone starts screaming "Charts is the Bible" let me assure you its not the Bible, it is your guide and the charts are in 10 or 5 psi increments. I do use the charts, AFTER I have CAT scaled to get me as close as I can, but my final results and confirmation come from my visual contact patch inspection and adjustment.

 

Recommended on this forum, I bought this tire gauge and it matches the TPMS in the truck every time. Seems very accurate.