Tow Vehicle Tire Pressure

[nagel]

Do others increase / decrease the tire pressure in their tow vehicle when they are pulling the trailer? My truck specs say 35 psi for all 4 tires, but nothing about adjusting when towing.

I'm thinking I want to increase the tire pressure in the rear tires maybe to 40 psi when pulling the trailer. Thoughts? Is their a formula for figuring this out or should I leave it at 35? I'm thinking with the added tongue weight, it could cause the tires to "smash down" a little bit.

[gmw_photos]

It has been said that a safe bet is to use the door sticker for min psi number, and the tire sidewall for max. Sometime, like on P tires, it's the same number.

One of our trucks is a Ford F350 dually. These are LR E tires, 80 psi max. The door sticker says 75 front, 60 rear. That's what I have run for the last 13 years in them. This is the second set of tires, the first set aged out at 10 years with plenty of tread remaining. Almost all the miles have been towing either the large GN horse trailer or my equipment trailer loaded with Bobcat or other heavy stuff. Point is, in my case, running the door sticker recco has and still does work well. All pressures set cold, before leaving the barn, and never readjusted during the run.

As always, your mileage, pressures, habits and beliefs probably will vary.

[1320Fastback]

45/80/40 when towing and 45/45/15 when not.

Front/Rear/AirBags

[CavemanCharlie]

My local mechanic and tire dealer says to keep them at the maximum tire pressure listed on the side of the tire and he pumps them up when he services the truck. My pickup truck dealer says to use the listing on the door pillar of the truck and when I take the truck to be serviced by them they let the air back out. lol

It all depends on who you want to believe.

[TurnThePage]

It REALLY sucks when heavy duty truck owners respond with heavy duty specific info, when they should know that this is NOT about a heavy duty tow vehicle.

In the past, when I've run D & E rated tires on my half ton pickups, I ran them near the OEM recommendations (35 - 40 PSI) for daily driving, and they performed fine. I found that no more than 55 PSI was ever needed for even the heaviest loading (well above GVWR). Now, I've seen the light, and run the wimpy P rated tires, and just air them to max when towing. Otherwise they're at the OEM recommendation.

[cougar28]

I always go by what tire mfg states on the tire never by what the vehicle door pillar says.I never inflating more than stated cold max and never lower more than 15% of max pressure.By doing this never had a tire wear or overheating problem. Remember what happen to Ford with the Firestone tire a few years back and all the rollovers that happen.

[nagel]

To all, Thanks for the responses. I've actually been away traveling and working so have not been able to check back in. Anyway, yes my truck is is GMC Sierra 1/2 ton. The door sticker refers to a P rated tire. I did put a 10 ply tire on (I think that is a E rated tire). The door spec is 35 pounds. The tire says 40 up to 80 max. If I run over 40 without towing it is very rough and shaky. Maybe another issue, but many parts are new except for shocks and really can't believe that will cause that issue. Anyway, thanks for the input and I think this did spark some other questions and answers.

[gmw_photos]

Here's a pretty interesting blurb from a major tire supplier:

Maximum Inflation Pressure

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.

For the reasons indicated above, It is also normal to experience 'hot' tire pressures that are up to 5 to 6 psi above the tire's recommended 'cold' pressure during the day if the vehicle is parked in the sun or has been extensively driven. Therefore, if the vehicle's recommended 'cold' inflation pressures correspond with the tire's maximum inflation pressure, it will often appear that too much tire pressure is present. However, this extra 'hot' tire pressure is temporary and should NOT be bled off to return the tire pressure to within the maximum inflation pressure value branded on the tire. If the 'cold' tire pressure was correctly set initially, the temporary 'hot' tire pressure will have returned to the tire's maximum inflation pressure when next measured in 'cold' conditions.

A tire's 'maximum inflation pressure' may be different than the assigned tire pressure used to rate the tire's 'maximum load'. For example, while a P-metric sized standard load tire's maximum load is rated at 35 psi, many P-metric sized standard load performance and touring tires are designed to contain up to 44 psi (and are branded on their sidewalls accordingly). This additional range of inflation pressure (in this case, between 36 and 44 psi) has been provided to accommodate any unique handling, high speed and/or rolling resistance requirements determined by the tire and vehicle manufacturers. These unique tire pressures will be identified on the vehicle placard or the vehicle's owner's manual.

[Terryallan]

trailer_newbe wrote:
“”You, DON'T account for heat. The engineers have already done that. You always set them cold. If they are at correct pressure, the heat buildup is normal. Now, if one gets low that will create excess heat that can raise the pressure to the point of a blowout.

Mark””

I do not agree. The manufacturer list the MAX pressure on their side wall. Granted they usually say cold, but anyone who thinks they engineered all road temperature conditions, I have a bridge across the Grand Canyon I’ll sell you. Set to 80 PSI then drive through Yuma on a 120 degree day, bad idea. I’ve aired to 80 PSI then hit the road and observed 86 PSI, which I’m good with, but where I live the temperature (and more importantly) the asphalt gets so hot it starts to melt. You can’t just air to max (cold) and take off, because you need to compensate for the time of year and where you are heading.

Thing is. If you keep airing down the tires when they heat up. (Not a good thing) When they do cool down after driving. They will be severely underinflated, if not flat.

as for the time of the year. Cold PIS at 80F. Is completely different than cold PSI at 30F. Even though the gage reads the same. So you have already compensated.

Always have to add air in the winter, because they were aired to cold psi in the heat.

[rbpru]

I left Indiana in an ice storm an 29 degrees, TT tire pressure was 55# cold pressure. A few day later I was in the Texas panhandle and 80 degree weather, at a gas stop my TT tire pressure was 80# hot pressure. A couple of day later I was in Albuquerque NM with 3 inches of snow and temps in the 30s.

When I reached Phoenix the temp was mid 70's and the cold TT tire pressure had returned to 55#. I spent 58 days touring around AZ, NM, UT and back to IN. When ever I checked the cold pressure it was always within a few pounds of the 55# I left home with.

These were OEM "C" rated ST China bombs doing what they were designed to do. I replace then after 18,000 mile because they were seven years old.

I now have a set of ST tires rated "D" at 65# and "C" at 55# with almost 20,000 miles on them. I keep them at 60# because of the harsher ride.

It is the same with my "P" rated truck tires. When towing, I set them at 40# and go, although the truck came with tire pressure sensors. TPS are not a bad idea if you fret about your tire pressure.

[JIMNLIN]

I just air them to 70 PSI as I'm not hitting max cargo weight anyway and I don't worry about hot roads as I know there is plenty or room to grow pressure wise.

I've seen my 16" load E tires on my GN equipment/flatdeck trailers, which were kept at 80 psi cold set, go to 90-92 psi on hot pavement/110-113 outside ambient temps on all day runs at interstate speeds.
No problems with doing so. These type trailers can run close to max axle loads every day.

[rbpru]

Almost all tire manufacturers have load vs pressure data on their tire models.

Few folk care, they just use what works for them.

[trailer_newbe]

Agreed

[opnspaces]

trailer_newbe wrote:
“”You, DON'T account for heat. The engineers have already done that. You always set them cold. If they are at correct pressure, the heat buildup is normal. Now, if one gets low that will create excess heat that can raise the pressure to the point of a blowout.

Mark””

I do not agree. The manufacturer list the MAX pressure on their side wall. Granted they usually say cold, but anyone who thinks they engineered all road temperature conditions, I have a bridge across the Grand Canyon I’ll sell you. Set to 80 PSI then drive through Yuma on a 120 degree day, bad idea. I’ve aired to 80 PSI then hit the road and observed 86 PSI, which I’m good with, but where I live the temperature (and more importantly) the asphalt gets so hot it starts to melt. You can’t just air to max (cold) and take off, because you need to compensate for the time of year and where you are heading.

It's not usually cold, it's always cold. I've never seen a tire that did not specify PSI cold. That being said my Suburban specifies 55 psi for comfort and for 80 PSI when towing. I just air them to 70 PSI as I'm not hitting max cargo weight anyway and I don't worry about hot roads as I know there is plenty or room to grow pressure wise.

[TurnThePage]

35 PSI nearly put me in the ditch. 44 PSI was perfectly stable.