lowering tire pressure
Token Redneck
Joined: Jun 2007
Posts: 9,339
Likes: 350
From: Breckenridge, TX
Yeah, unless you can get an actual load index table from the tire maker the math problem is the next safest bet. Just sub in the lower load index if there are two on the tire like above for a dually, to account for sidewall deflection on the rears to make sure nothing contacts.
Fleet Mechanic
Joined: Jul 2003
Posts: 1,815
Likes: 24
From: Houston
Yeah, unless you can get an actual load index table from the tire maker the math problem is the next safest bet. Just sub in the lower load index if there are two on the tire like above for a dually, to account for sidewall deflection on the rears to make sure nothing contacts.
I have always gotten the load index table from the manufacturer, but I really like the math you laid out for us up there. I have never seen that before but it makes perfect sense.
I actually did the "chalk" method on my current tires before I got the load inflation table and was surprised to find that I was only a couple psi off front and rear from the chart.
People are always shocked when I tell them I run my tires as low as I do, but mathematically it works out. Thanks for the info.
New User
Joined: May 2016
Posts: 3
Likes: 0
My 2016 f250 calls for 65 psi on the door jam sticker for all four tires.
In the owners manual there is a procedure for re-learning the TPMS.
I'm gonna try this because I don't like 65 all the way around. No need for 65 psi on a unloaded bed or hitch.
In the owners manual there is a procedure for re-learning the TPMS.
I'm gonna try this because I don't like 65 all the way around. No need for 65 psi on a unloaded bed or hitch.
Posting Guru
Joined: Jan 2006
Posts: 1,490
Likes: 16
From: Arizona/Texas
What size are your tires? You must have a low payload to only need 65 psi all around.
Senior User
Joined: Dec 2014
Posts: 137
Likes: 1
From: S/E Michigan
I run my 15 350 6.7 SBCC 20" wheels at 65 Empty. The TPMS goes off at 60-62 on my truck. The TPMS can be programed / lowered by your FRIENDLY dealer. It's in the BCM settings.
My Door Sticker calls for 65F 80R
My Door Sticker calls for 65F 80R
Laughing Gas
Joined: Jul 2012
Posts: 1,210
Likes: 20
From: prince george, bc canada
I must be older than most on here. I grew up when 32 psi was a "normal" tire pressure. Went up to a whopping 40 psi if some heavy work was involved. I regularly run 35-45 psi in my company duty that carries mild loads, and I dropped to a D rated tire as well. My personal 08 duty rolls on E rated 35s. With my 4000lb slide in camper I max these tires at 65 PSI. When I leave on my 750 mile off road huntin trip in 2 weeks I will be rolling 25-30 psi. I think this whole over inflation thing the world thinks is correct came plain and simply from manufacturers striving for max fuel mileage. I agree that we need a way to get rid of that stupid tpms thing. I have been able to tune it out, just like I can with my wife....but you always know its there.
4wd Low
Joined: Jun 2006
Posts: 14
Likes: 8
I must be older than most on here. I grew up when 32 psi was a "normal" tire pressure. Went up to a whopping 40 psi if some heavy work was involved. I regularly run 35-45 psi in my company duty that carries mild loads, and I dropped to a D rated tire as well. My personal 08 duty rolls on E rated 35s. With my 4000lb slide in camper I max these tires at 65 PSI. When I leave on my 750 mile off road huntin trip in 2 weeks I will be rolling 25-30 psi. I think this whole over inflation thing the world thinks is correct came plain and simply from manufacturers striving for max fuel mileage. I agree that we need a way to get rid of that stupid tpms thing. I have been able to tune it out, just like I can with my wife....but you always know its there.
New User
Joined: May 2016
Posts: 3
Likes: 0
275/65 20 10k gvw
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Laughing Gas
Joined: Jul 2012
Posts: 1,210
Likes: 20
From: prince george, bc canada
I run 35-1250-17s. The max pressure I can put in them is 65psi. My slide in camper weighs 4000lbs. I ran this camper with D rated 35s and the maximum 50 psi and had a quite a bulge so I went to the E rated tire. Its rougher unloaded but my camper is on 85% of the time.
New User
Joined: May 2016
Posts: 3
Likes: 0
From: Dartmouth Nova Scotia CAN
Lol! I had so many conflicting pressures on so many forums that I wrote to the tire manufacturer. This was their response (even though I told them the door pillar says 75 front and 60 rear for our 2008 F350 DRW Lariat):
Regarding your email stating:
---------------------------------------------------------------------
Hi. I am carrying approx. 5000 lbs in the box (truck camper). The door label reads 75 front and 60 rear but, the online forums say to have the rears at 75 - 80 so there is less friction with the road causing heat buildup. We have air bags on board pumped up to 45 psi. Please advise what pressure we are safe with. Thank you.
---------------------------------------------------------------------------------------------------------------------------------------------------------
I’d like to use my passion for BFGoodrich products to offer you the following information:
The best air pressure recommendation for the original equipment size tires is to use the inflation pressure as specified by the vehicle manufacturer. For your 2008 Ford F-350, they recommend for your front tires to have the PSI of 75 and the rears to have a PSI of 80. They have determined the optimal inflation pressure for load, ride, handling, rolling resistance and treadwear performance.
When carrying more weight than usual, it can be recommended to have the maximum tire pressure of 80. Below you will find what your tire can carry at its PSI.
Tire Pressure
75
80
Maximum Load
3020lbs
3195lbs
Regarding your email stating:
---------------------------------------------------------------------
Hi. I am carrying approx. 5000 lbs in the box (truck camper). The door label reads 75 front and 60 rear but, the online forums say to have the rears at 75 - 80 so there is less friction with the road causing heat buildup. We have air bags on board pumped up to 45 psi. Please advise what pressure we are safe with. Thank you.
---------------------------------------------------------------------------------------------------------------------------------------------------------
I’d like to use my passion for BFGoodrich products to offer you the following information:
The best air pressure recommendation for the original equipment size tires is to use the inflation pressure as specified by the vehicle manufacturer. For your 2008 Ford F-350, they recommend for your front tires to have the PSI of 75 and the rears to have a PSI of 80. They have determined the optimal inflation pressure for load, ride, handling, rolling resistance and treadwear performance.
When carrying more weight than usual, it can be recommended to have the maximum tire pressure of 80. Below you will find what your tire can carry at its PSI.
Tire Pressure
75
80
Maximum Load
3020lbs
3195lbs
New User
Joined: May 2016
Posts: 3
Likes: 0
From: Dartmouth Nova Scotia CAN
When you submit your request, you have to fill out the type of vehicle you are driving; including DRW. I have written them back to confirm they picked up on it...
New User
Joined: May 2016
Posts: 16
Likes: 0
I'm so glad I came across this thread. With LT275/70Rx18E tires on a 2016 F-350 SRW, which indicates 65 front and 80 rear, I lowered the rears to 70. I don't carry any weight in the back. The ride is so much better now (less bumpy). And no TPMS warnings.
One thing I do need to do though is a few more highway runs. After lowering the rears I was experiencing some shaking driving down the highway, but only exactly at 70 MPH. Any faster or slower and it was fine. But I think that may have been related to just one particular stretch of highway (well, a rather long stretch) because I couldn't replicate it on a different highway at the same speed. Perhaps it was just the way that stretch was paved. Not sure but I'll try it again tomorrow.
One thing I do need to do though is a few more highway runs. After lowering the rears I was experiencing some shaking driving down the highway, but only exactly at 70 MPH. Any faster or slower and it was fine. But I think that may have been related to just one particular stretch of highway (well, a rather long stretch) because I couldn't replicate it on a different highway at the same speed. Perhaps it was just the way that stretch was paved. Not sure but I'll try it again tomorrow.
New User
Joined: May 2016
Posts: 10
Likes: 1
only cause I have to understand something in my own language of rookie;
Whatever PSI I need to run divided by max tire weight rating
(60/65) * (2600 * 2)
multiplied by max tire rating * 2 (located on sidewall of tire) mine is 2600
should equal weight at that particular axle, Correct?
so to carry max capacity I would have to be well over my max tire capacity of 65. I simply have the wrong tire for towing and hauling up to the max rating for the truck itself.
So If I am going to tow or load the truck, I have to get it weighed and then calculate the new numbers, to ensure I am within the allowable weight. right?
so depending on what weight I have at the axle, will depend on my psi I need to be at.
Whatever PSI I need to run divided by max tire weight rating
(60/65) * (2600 * 2)
multiplied by max tire rating * 2 (located on sidewall of tire) mine is 2600
should equal weight at that particular axle, Correct?
so to carry max capacity I would have to be well over my max tire capacity of 65. I simply have the wrong tire for towing and hauling up to the max rating for the truck itself.
So If I am going to tow or load the truck, I have to get it weighed and then calculate the new numbers, to ensure I am within the allowable weight. right?
so depending on what weight I have at the axle, will depend on my psi I need to be at.