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Discussion Starter · #1 ·
My Truck:
2017 Ram 1500 5.7
3in spacers in front, 2in coil spacers in rear
35x12.50r 20s on XD wheels

Issue factory 39psi tire pressure is too high causing my tires to wear in the middle

I would like to lower the TPM pressure to 28-32psi, this way I can run highway pressures at 35psi without the light coming on.

Problem, the only dealer I can find that is supposed to have the capability in the Denver area is Larry H Miller (The worst service ever in the history of dealerships, will never take my truck back. They had my truck for 3 days to check fluids, left 3 messages for advisor to call me back, had to call Ram customer service just to speak to my advisor, so I could pick up my truck)

Looking for someone local to me, who has the appropriate tools to adjust this for me (willing to pay third party $50 or so to do this for me)
Would also like to have the tire size adjusted in the computer to fix speedo if available.
 

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I have a hard time believing 39 psi is too high for any tire that anyone is putting on one of these trucks. You will have trouble finding someone to adjust your threshold down to 28, that's almost as low as I go for driving on sand and you will be putting yourself at risk of a blowout a la late 1990's Ford Explorer
 

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Discussion Starter · #4 ·
I have a hard time believing 39 psi is too high for any tire that anyone is putting on one of these trucks. You will have trouble finding someone to adjust your threshold down to 28, that's almost as low as I go for driving on sand and you will be putting yourself at risk of a blowout a la late 1990's Ford Explorer
I want to start by saying that after years of experience, (ASE Certified Master Technician, Factory Trained, Engineering degree) You only make yourself sound ignorant when you do not know what you are talking about. The door placard is for the factory tires, based on load and tire ratings of the tires that came on the truck. The factory tires that were on my truck running at 39PSI were wearing the center of the tire (5000 mile tire rotations). The center of the factory tires after less than 15000 miles was 3/32nds of an inch lower than the outside.

In regards to 39PSI being too high, I think that 39PSI is too high for even tire wear period. The tires that I replaced them with are ~2 inches wider, @ 39PSI after another 13-14,000 miles I have 5/32nds inch difference between the center and outside tread patches. That is a considerable difference in tread depth. I have performed a chalk test as well, which shows that the center 3rd of the tire is making nearly all of the contact patch.

When tires cost about $1200 per set, it only makes sense to get even tread wear.

There are several ways to find the correct (safe PSI) for a vehicle's tires.
For example one of the easiest ways:
My truck is rated at 3900 GAVR F&R
My Tires are rated at 3195 each @ 80psi F&R

Using basic math & some common sense.
Tire pressure for a Max load:
3195 * 2 (2 rear tires) = 6390 lbs @ 80psi (load capacity of tires)
3900 / 6390 = ~61% ( I need to run about 61% of 80PSI in my rear tires for a max load on my truck)
61% of 80PSI is 48-49 PSI (keep in mind this would be for a max load)

Now for the actual weight:
The heaviest Factory Ram 1500 trucks total weight is about 5670lbs across all four tires
Without going to a scale or getting too fancy.
All 4 tires on my truck are capable of supporting 12780lbs @ 80PSI
5680 / 12780 = ~44%
44% of 80PSI is ~35PSI

Now take into account the 20% tolerance before a tire is considered low (The threshold that most TPMS lights come on is 20% from the factory)
20% of 35PSI = 7PSI
35PSI - 7PSI = 28PSI

After doing the math You can see that 28 PSI would be about the minimum. With that being explained, I personally would run the tires on my truck right around 34 PSI.
 

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I want to start by saying that after years of experience, (ASE Certified Master Technician, Factory Trained, Engineering degree) You only make yourself sound ignorant when you do not know what you are talking about. The door placard is for the factory tires, based on load and tire ratings of the tires that came on the truck. The factory tires that were on my truck running at 39PSI were wearing the center of the tire (5000 mile tire rotations). The center of the factory tires after less than 15000 miles was 3/32nds of an inch lower than the outside.
That's cool if you disagree; if one of my dispatchers let a truck leave my lot with tires 30% below the specified threshold I'd can him
 

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Lowering the tire pressure probably won't solve the problem. Go to Firestone or Tire Rack. I'm not sure who has the best info. Most tire manufacturers will say that center wear is usually from underinflation. Yes, I said underinflation. At high speeds, tires crown from centrifugal force. This results in that crown having to collapse and slip (tread walk too) right before it makes contact with the road. This is the most common cause of early need for replacement of tires. Anytime you put a wider tire on a set of rims, this problem is exaggerated. Offroad tires always wear faster as they were designed around lower speeds and not even concerned about treadwear. I saw the math. Still no justification for unsafe, overheated temps and squishy cornering. It is not just your life you are risking
 

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If you inflate to 39 to get the light off, it will come back on at 35 psi? I thought it was lower than that to trip the light - unless the 17's are different.
 
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