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Old 12-27-2017, 10:43 AM   #1
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Tire Pressures

I have question about what pressures I should have my Tow Vehicle tires at.

The door sticker gives 38psi for front and rear tires, and specifies the tires as P235/70R17.

The current tires are: (https://www.discounttire.com/buy-tir...t-s-at/p/17958) you may have to pick a store to see details.

Pathfinder Sport S AT
P245/70R17 108S
The tires say max is 2200lbs and the max 51psi.
Truck is a 2007 F-150 towing a 2018 Jayco X19H
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Old 12-27-2017, 10:58 AM   #2
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Simple answer is you can go up to 51psi on those tires. But really, psi should be adjusted to fit the tongue weight, or adjusted tongue weight if you have a WD hitch. See if you can find an inflation table from Pathfinder and adjust accordingly after weighing the truck/trailer combo. Lastly, if your trailer is heavy, you might want to consider E-rated tires.
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Old 12-27-2017, 01:44 PM   #3
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Quote:
Originally Posted by himandher818 View Post
I have question about what pressures I should have my Tow Vehicle tires at.

The door sticker gives 38psi for front and rear tires, and specifies the tires as P235/70R17.

The current tires are: (https://www.discounttire.com/buy-tir...t-s-at/p/17958) you may have to pick a store to see details.

Pathfinder Sport S AT
P245/70R17 108S
The tires say max is 2200lbs and the max 51psi.
Truck is a 2007 F-150 towing a 2018 Jayco X19H
The correct inflation pressure - by the book - would be to inflate the replacement tires to a PSI that will provide the same load capacity the OE tires provided at 38 PSI.

Sometimes the manufacturer of that kind of tow vehicle will provide optional tire inflation pressures for towing. If so, they will be in the owner's manual. If not there, the manufacturer's recommendations are valid.

Personally, I would inflate the rear tires to 51 PSI when towing something, if for nothing more than to take some of the flexibility out of them.
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Old 12-27-2017, 09:13 PM   #4
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Agree when towing or carrying a heavy load run those soft P tires up to 51 psi.

P tire when used on a truck have different load and pressure characteristics than LT tires. Something to keep in mind when using minimum load pressure charts
1. P tires max capacity comes at 35 psi so using higher pressures doesn't gain any capacity but does stiffen the tires carcass for better load handling.

2. P tires load capacity when used on a truck or trailer is reduced by dividing its capacity by 1.1 per fed regs.....so your 2200 lb rated P tire is reduced to 2000 lb per tire. Your F150 probably has a 3800 RAWR so your ok there.
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Old 12-28-2017, 05:35 PM   #5
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Quote:
Originally Posted by himandher818 View Post
I have question about what pressures I should have my Tow Vehicle tires at.

The current tires are:
P245/70R17 108S
The tires say max is 2200lbs and the max 51psi.
Because your tires are not the exact size as the OEM tires on your door sticker, you can ignore the door sticker and instead use the Tire&Rim Assn (TRA) load/inflation table. A wealth of info is at the following link:

TRA Load/Inflation Tables

Scroll down to page 16, then down to P245/70R17 to see the load inflation table for your tires.

PSI . Max Load (lbs.)
----.-------
26 . 1,918
29 . 2,017
32 . 2,116
35 . 2,205

You should NEVER inflate the tires to less than the actual load on the tires, but it's okay to add more PSI, up to the max on the sidewall. As JIMNLIN noted, and as the load/inflation table indicates, inflating your tires to more than 35 PSI will not increase the load capacity of the tires, but it will stiffen up the tire and result in a cooler running tire.

I always tow with my rear P-series tires inflated to the max PSI on the sidewall.

To do tire inflation right, you have to weigh the wet and loaded rig and know how much weight is on each axle. Divide the weight on each axle by the number of tires on that axle to get the approximate weight on each tire. Then apply the load/inflation table first thing in the morning before the tires have rolled.

Now for the complications. When you run car tires on a light truck, you have to adjust the load inflation table. This is explained on page 5 of the file above. It says:
Quote:
P-Metric or hard metric tires on Light Trucks
When a P-metric or metric tire is installed on a light truck (SUV, pickup, minivan), the load capacity of the tire is reduced by a factor of 1.1 as prescribed by the Federal Motor Vehicle Safety Standards (FMVSS). For example, 305/50R20 has a maximum load capacity of 3086 lbs. If this tire is fitted to a light truck, then the actual allowable load capacity for the tire is 2805 lbs. (3086 lbs. divided by 1.1). If you replace the original tires with the exact same type (P-metric, hard metric, LT-metric, or flotation), size designations, and ply as the tires that were originally installed, just follow the vehicle’s tire information placard for proper inflation pressures. If, however, you apply a ‘Plus zero’ or plus-1, etc., fitment to a light truck, you must discount the replacement tire’s load by the 1.10 factor and ensure that the replacement tire has sufficient load capacity by inflation to support the load of the originally installed tires.

This load reduction factor is prescribed by Federal Motor Vehicle Safety Standards (FMVSS) and is based on the expectation that passenger type tires (P-metric) may experience more severe loading and usage conditions when applied to light trucks.
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Old 12-28-2017, 06:16 PM   #6
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Quote:
Originally Posted by SmokeyWren View Post
Because your tires are not the exact size as the OEM tires on your door sticker, you can ignore the door sticker and instead use the Tire&Rim Assn (TRA) load/inflation table. A wealth of info is at the following link:

TRA Load/Inflation Tables

Scroll down to page 16, then down to P245/70R17 to see the load inflation table for your tires.

PSI . Max Load (lbs.)
----.-------
26 . 1,918
29 . 2,017
32 . 2,116
35 . 2,205

You should NEVER inflate the tires to less than the actual load on the tires, but it's okay to add more PSI, up to the max on the sidewall. As JIMNLIN noted, and as the load/inflation table indicates, inflating your tires to more than 35 PSI will not increase the load capacity of the tires, but it will stiffen up the tire and result in a cooler running tire.

I always tow with my rear P-series tires inflated to the max PSI on the sidewall.

To do tire inflation right, you have to weigh the wet and loaded rig and know how much weight is on each axle. Divide the weight on each axle by the number of tires on that axle to get the approximate weight on each tire. Then apply the load/inflation table first thing in the morning before the tires have rolled.

Now for the complications. When you run car tires on a light truck, you have to adjust the load inflation table. This is explained on page 5 of the file above. It says:
You may be quoting information from two completely different sets of standards/instructions. One is applicable, FMVSS and the other is not, FMCSS.

You will not find inflating tires to the load carried as a valid recommendation in the FMVSS standards.

Taking information out of context from tire manufacturer's SOPs requires the information to be applied to a situation that is relevant.

For vehicles - non-commercial - built using FMVSS standards the correct tire inflation pressure is found on the vehicle's tire placard. Exceptions will be found in the vehicle's owner's manual.

Setting inflation pressures for plus sized tires are industry standardized. The new recommended cold inflation pressures for the replacement tires will be derived from the load capacity the OE tires provided when inflated to the recommended cold inflation pressure (s) found on the vehicle's tire placard.

Almost all of what I've said here can be confirmed by researching chapter #4 of this reference.

https://www.ustires.org/sites/defaul...TruckTires.pdf
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Old 12-28-2017, 06:41 PM   #7
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Originally Posted by FastEagle View Post
You may be quoting information from two completely different sets of standards/instructions. One is applicable, FMVSS and the other is not, FMCSS.

You will not find inflating tires to the load carried as a valid recommendation in the FMVSS standards.

Taking information out of context from tire manufacturer's SOPs requires the information to be applied to a situation that is relevant.

For vehicles - non-commercial - built using FMVSS standards the correct tire inflation pressure is found on the vehicle's tire placard. Exceptions will be found in the vehicle's owner's manual.

Setting inflation pressures for plus sized tires are industry standardized. The new recommended cold inflation pressures for the replacement tires will be derived from the load capacity the OE tires provided when inflated to the recommended cold inflation pressure (s) found on the vehicle's tire placard.

Almost all of what I've said here can be confirmed by researching chapter #4 of this reference.

https://www.ustires.org/sites/defaul...TruckTires.pdf
What?
This is not rocket science.
Inflating tires based on load is not alchemy.
This has been beaten to death so many times I thought this topic was dead.
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Old 12-30-2017, 12:07 PM   #8
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If you pry it out of the tire OEM, you can get the load / pressure charts from them specific to the tire you are using. Key note: DO NOT TELL THEM THE VEHICLE THEY ARE ON! They will just default to the vehicle OEM recommended pressures to pass the buck. I always get charts for the tires I am using. Currently that is BFG KO2's. I developed a healthy respect for the recommended pressures of the folks who actually did the R&D and made the tires. Comes from decades of commercial truck tire experience. I never rely on generic third party pressure recommendations.
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Old 12-31-2017, 04:16 PM   #9
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Originally Posted by Cowpie1 View Post
If you pry it out of the tire OEM, you can get the load / pressure charts from them specific to the tire you are using. Key note: DO NOT TELL THEM THE VEHICLE THEY ARE ON! They will just default to the vehicle OEM recommended pressures to pass the buck. I always get charts for the tires I am using. Currently that is BFG KO2's. I developed a healthy respect for the recommended pressures of the folks who actually did the R&D and made the tires. Comes from decades of commercial truck tire experience. I never rely on generic third party pressure recommendations.
In the attached reference you will find the following statement in bold red letters. When researching other tire manufacturer’s SOP documents you will always find that statement. It’s a tire industry standard for all vehicles built and certified in accordance with the building standards for safety found in FMVSS.

Warning! Never use an inflation pressure lower than what is recommended by the vehicle manufacturer.

https://www.toyotires.com/media/2125...s_20170203.pdf

Tires fitted to vehicles in the commercial trucking industry use a different set of regulations and standards (FMCSA). One is not applicable to the other.
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Old 12-31-2017, 09:38 PM   #10
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Tires fitted to vehicles in the commercial trucking industry use a different set of regulations and standards (FMCSA). One is not applicable to the other.
Not true at all.
A FMCSA uses the same FMVSS specs and same tire mfg recommendations.
If you have any fed regs for that opinion please post it for our members who have or use commercial vehicles.
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Old 12-31-2017, 10:56 PM   #11
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Originally Posted by FastEagle View Post
In the attached reference you will find the following statement in bold red letters. When researching other tire manufacturer’s SOP documents you will always find that statement. It’s a tire industry standard for all vehicles built and certified in accordance with the building standards for safety found in FMVSS.

Warning! Never use an inflation pressure lower than what is recommended by the vehicle manufacturer.

https://www.toyotires.com/media/2125...s_20170203.pdf

Tires fitted to vehicles in the commercial trucking industry use a different set of regulations and standards (FMCSA). One is not applicable to the other.
That is generally true of P rated tires on SUV's and 1/2t pickups. When you get into 3/4t territory or higher and LT tires, the blanket OEM recommended pressures are based on the pickup loaded to GVWR. In the case of my 2015 Chevy 2500... 60 front, 70 rear. given that there is about 2500 lb difference between empty and gross on my pickup, those OEM recommended pressures far exceed the tire OEM recommendations when the pickup is unladen. And it is based on the tire they put on at the factory. A different tire will call for different PSI based on loading.

Once one gets into LT type tires, the same principle applies on running pressures that match the load as it does with larger commercial tires. Of course, the tire maker will default to the vehicle OEM regarding pressures when they can to "pass the buck" on liability to the vehicle OEM.

And FMCSA does not dictate tire pressures. It is based on the tire OEM recommended pressures for the loading on the tire. The very same thing being discussed here. I defy you to produce the FMCSA 393.75 regulation that has actual required tire PSI on any given tire. For instance, a single 22.5 low pro tire in a dual configuration may require 100 PSI for maximum 17K lb on a drive axle. On the same axle, using wide based single low pro 22.5 rubber, the recommended pressure in 95 PSI. Michelin wants 105 PSI on it's 22.5 low pro steer tire, whereas Yokohama wants 100 PSI on their low pro 22.5 on their steer tire. The FMCSA does not dictate minimum and maximum tire pressures. They default to the tire OEM.

This copied from the 393.75 regulations regarding tires is the only mention of tire pressures....

(i) Tire inflation pressure. (1) No motor vehicle shall be operated on a tire which has a cold inflation pressure less than that specified for the load being carried.

(2) If the inflation pressure of the tire has been increased by heat because of the recent operation of the vehicle, the cold inflation pressure shall be estimated by subtracting the inflation buildup factor shown in Table 1 from the measured inflation pressure.
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Old 01-01-2018, 11:38 AM   #12
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What?
This is not rocket science.
Inflating tires based on load is not alchemy.
This has been beaten to death so many times I thought this topic was dead.
May not be rocket science or alchemy, but being new to towing, it is something I am not very familiar with. I was having trouble putting together useful information and determining of the information out there what was valid and what was not valid information. Didn't realize it had been beaten to death.

Cowpie, JIMNLIN, FastEagle,SmokeyWren, ralphie,

Thanks for your input. Using the information you have given, this is what understand.

The orginal tires (P235/70R17) at 38 psi show the max load as 2149 (page 16 of link posted by SmokeyWren. The current tires (245/70R17) show a 2205 at 35 psi, which is greater than the original at 38. So since I generally used 38psi I was still good, and 35psi or greater is what would be required to match or exceed the original load capacity.

Increasing the psi would not increase the load capacity, but would make the tire stiffer and give a buffer before the weight capacity was impacted.

Taking the 2149 and 2205 values and dividing them by 1.1 gives 1953 and 2004. Both exceed the axle rating of 3400. Actual scale value for truck with a full tank no passengers is 2160 on the rear axle. Assume I can maintain a TT tongue weight of 550 plus 100 for the WD hitch gives an additional 650 on the rear axle adding in 700lb for the passengers and cargo and assuming 1/2 will be on the rear axle I come up with an additional 1000 on the rear axle for total of 3160. This is well below the rating of the tires at the 38 or 35 psi values so even maintaining those min values should be sufficient.

With all this in mind, I should be good with the pressures at 45+ psi. and could go higher. I did inflate them to 45 psi, and felt every little bump in the road with the truck empty.

Am I understanding what you guys are saying?
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Old 01-01-2018, 11:48 AM   #13
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I would keep your truck tires inflated to the pressure shown on the sidewall of the tire. THat is the min pressure required for the max weight the tire can carry. Down the road, if you wanna go to a Cat scale and get real weights, then ok, you can adjust then. For trailer towing, I ran my 16" LT tires on my Dually to 80 PSI as listed on the sidewall. Underinflation causes tire failures.
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Old 01-01-2018, 06:41 PM   #14
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With all this in mind, I should be good with the pressures at 45+ psi. and could go higher. I did inflate them to 45 psi, and felt every little bump in the road with the truck empty.

Am I understanding what you guys are saying?
Sounds like a good plan.
The wifes '16 1500 chevy crew cab 4wd short bed has P255/70-17 and a 51 psi tires.
When pulling my 10k car hauler and a 7600 lb blue tractor I pump the rears to 51 psi.
When not towing or hauling a load I drop the rears to 32 psi for a much softer ride. The front tires don't change when empty or loaded so I keep them at 38 psi years round which works best for this particular truck.
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