Tire air pressure

[Cummins2014]

The work truck I'll adjust air pressure accordingly to what is loaded by a slight amount. I found that unless I'm fully loaded to the kilt, 65-70 PSI works fine. I keep an eye on the pressures once driving for a while, especially when it's extremely hot out. Fully loaded, 70 PSI can quickly turn into 75+ PSI doing 65+ mph with the heat.

Part of being a good/responsible driver is keeping an eye on those tire pressures while towing heavy.

I air as said to 80 psi cold towing a fifth wheel , not concerned at all with whatever that pressure gets to after getting heated up , I have on seen my dash TPMS those rears being nearly 90 psi , they are designed to do that , as you know thats why its always cold inflation you go by ,not guess work what they will get to when heated up . My fifth wheel @ 95 psi. , I will see 105-108 on my TPMS .

 

[Grumpy8811]

I air as said to 80 psi cold towing a fifth wheel , not concerned at all with whatever that pressure gets to after getting heated up , I have on seen my dash TPMS those rears being nearly 90 psi , they are designed to do that , as you know thats why its always cold inflation you go by ,not guess work what they will get to when heated up . My fifth wheel @ 95 psi. , I will see 105-108 on my TPMS .

exactly, pressure buildup in tires as they heat up is accounted for in the design.
aka tire pressure are taken when cold, cold meaning the truck has been sitting still for a period of time and the tire is at ambient temp .

whats the other side of it... you get an approximately 1 psi change in static pressure for every 10 degree F change in tire temp .
in other words if the weather changes temperatures considerably so does the air pressure in the tires.

finally the tire inflation placard in your vehicle when considering the idea these are heavy duty trucks, some which ride around fully laden all the time while others never carry anyweight should be treated more as a suggestion than a fact of life that must be adhered to.. observant users can tune their tires for their particular situation .

 

[AH64ID]

Yet, load inflation tables reflect minimums. We don't know the load in question but it isn't as if 40 psi is appropriate and the user is inflating to 80. For a big fifth wheel on a SRW, 80 may not be far from the minimum given by the tables. After all, for a 3500 SRW the door sticker says 80 psi rear axle. If 10 or 15 psi over what is given by the tables is used to improve handling characteristics, that's well within an acceptable margin that may already be there for cold days, slow leakers, seasonal changes, uncertainty/imbalance of loading, etc.

Per the tables they reflect the “appropriate inflation pressure”.

Anything over “appropriate” would be considered overinflated, thou it does take more than a few psi over table psi to start to see the negative effects of overinflationy. I’d also rather be overinflated than underinflated.

As for the door sticker, just like the tire, that’s pressure at max load, heck these trucks used to have a light load button but some lawyers probably got involved thanks to uneducated operators.

 

[Jim W]

As for the door sticker, just like the tire, that’s pressure at max load, heck these trucks used to have a light load button but some lawyers probably got involved thanks to uneducated operators.

Mine never worked on my truck. Had the truck at the dealer three different times trying to have the LIGHT load button to work on my truck.
I for one am glad it is gone just a waste of money and design time for a function that would not work.

 

[AH64ID]

Mine never worked on my truck. Had the truck at the dealer three different times trying to have the LIGHT load button to work on my truck.
I for one am glad it is gone just a waste of money and design time for a function that would not work.

It worked fine on the trucks I used it on, so I wouldn’t condemn it. It would be far better for trucks to have it if they needed it than living with a tire low light for reduced pressure when empty.

 

[Turbo Terry]

And what air pressures do you run pulling the 27 th 5 th wheeler

 

[AH64ID]

And what air pressures do you run pulling the 27 th 5 th wheeler

60 to 80 depending on how heavy the trailer is loaded and what’s in the bed. My RAW is under 6K with a light trailer and empty bed, I’ve weighed it as low as 5,500.

 

[Jim W]

John, I do no big deal about the low tire pressure light on. As I check my tire pressures every month along with my wife's car. I have never had a flat tire on my truck (knock on wood) in the 17 years I have own my truck.

When the truck is empty, I run 50PSI in the rear and the front are at 60PSI. But my tires are not stock, so I used the tire manufactures air pressure guide for the mass that the tires are supporting.

 

[User113]

This discussion reminds me of my younger and more carefree (i.e. stupid) years when I owned a Jaguar. The recommended "tyre" pressures listed on its glovebox sticker were based on speed, not weight. One inflation pressure for speeds "up to 100 mph" and a higher pressure for speeds over that. Presumably you're allowed to drive from 0-100 mph at the higher pressure so that you can continue on to 101 mph and beyond because those cars were not equipped with a central Tire Inflation System!

I seems to me now that there is so much latitude in tire inflation pressures that, aside from either extreme (i.e., really high or really low), it doesn't really matter all that much. Which is a good thing, as there are so many clueless drivers out there!

 

[AH64ID]

This discussion reminds me of my younger and more carefree (i.e. stupid) years when I owned a Jaguar. The recommended "tyre" pressures listed on its glovebox sticker were based on speed, not weight. One inflation pressure for speeds "up to 100 mph" and a higher pressure for speeds over that. Presumably you're allowed to drive from 0-100 mph at the higher pressure so that you can continue on to 101 mph and beyond because those cars were not equipped with a central Tire Inflation System!

I seems to me now that there is so much latitude in tire inflation pressures that, aside from either extreme (i.e., really high or really low), it doesn't really matter all that much. Which is a good thing, as there are so many clueless drivers out there!

I’m not sure if there is more latitude or rather tires are built better and most vehicles on the road have TPMS.

Tires also have seem to higher speed ratings these days. My tires are rated for 106 mph, which is above the speed limiter. Loaded it’s rare to exceed 76 mph, so there is still quite a bit of load margin even if I’m at 100% of the rated weight.

 

[lpennock]

This discussion reminds me of my younger and more carefree (i.e. stupid) years when I owned a Jaguar. The recommended "tyre" pressures listed on its glovebox sticker were based on speed, not weight. One inflation pressure for speeds "up to 100 mph" and a higher pressure for speeds over that. Presumably you're allowed to drive from 0-100 mph at the higher pressure so that you can continue on to 101 mph and beyond because those cars were not equipped with a central Tire Inflation System!

I seems to me now that there is so much latitude in tire inflation pressures that, aside from either extreme (i.e., really high or really low), it doesn't really matter all that much. Which is a good thing, as there are so many clueless drivers out there!

Back before tires were speed rated, the manuals would tell you to add 10psi for extended high speed running. For truck/bus tires there was also a load rating decrease above certain speeds (usually 75mph). With speed rated tires the pressure and load rating changes are factored in to the speed and load ratings so no changes are required.

 

[AH64ID]

Toyo has this in their commercial tire. … and we shouldn’t even get into LT vs ST ratings a margins

 

[crispyboy]

I have the light load button on my old truck. There is a technique for changing the load status. Turn the ignition on (no start), adjust the pressure and push the button.
During the winter or on a long trip with no trailer I use the light load setting. 45R/60F. It makes quite a difference in how the truck behaves on the highway. During the warmer towing season I use 70R/65F.

 

[Grumpy8811]

This discussion reminds me of my younger and more carefree (i.e. stupid) years when I owned a Jaguar. The recommended "tyre" pressures listed on its glovebox sticker were based on speed, not weight. One inflation pressure for speeds "up to 100 mph" and a higher pressure for speeds over that. Presumably you're allowed to drive from 0-100 mph at the higher pressure so that you can continue on to 101 mph and beyond because those cars were not equipped with a central Tire Inflation System!

I seems to me now that there is so much latitude in tire inflation pressures that, aside from either extreme (i.e., really high or really low), it doesn't really matter all that much. Which is a good thing, as there are so many clueless drivers out there!

I agree.. my FIL is one of those clueless people, he is a builder. ... I went ahead of time to one of our properties 300 miles away... he shows up later complaining his arm is sore... ask him why, says the truck seems like it wont stay on the road...

I go outside.. I see the problem, he just completed a 300 mile drive with about 7 psi in the front tire..
I suspect if the vehicle had a warning lite, he still wouldn't notice.

 

[Killer223]

Per the tables they reflect the “appropriate inflation pressure”.

Anything over “appropriate” would be considered overinflated, thou it does take more than a few psi over table psi to start to see the negative effects of overinflationy. I’d also rather be overinflated than underinflated.

As for the door sticker, just like the tire, that’s pressure at max load, heck these trucks used to have a light load button but some lawyers probably got involved thanks to uneducated operators.

Where do I find these load charts? I search and all I get is max psi is 80.

 

[lpennock]

Where do I find these load charts? I search and all I get is max psi is 80.

Her is a link to the Toyo site that provides that info.
https://www.toyotires.com/tires-101/tire-load-and-inflation-tables/

Same info from Falken Tires
https://www.falkentire.com/load-inflation

There are some differences in 17" LT tires from the two sites. This is due to the fact that at one time TRA limited 17" tires to 3195lbs. If you have a 17" you need to verify which is the correct table to use by looking at the max load for your tire.

 

[AH64ID]

Her is a link to the Toyo site that provides that info.
https://www.toyotires.com/tires-101/tire-load-and-inflation-tables/

Same info from Falken Tires
https://www.falkentire.com/load-inflation

There are some differences in 17" LT tires from the two sites. This is due to the fact that at one time TRA limited 17" tires to 3195lbs. If you have a 17" you need to verify which is the correct table to use by looking at the max load for your tire.

Does the TRA not limit 17’s anymore? I remember when they started limiting them.

 

[lpennock]

Does the TRA not limit 17’s anymore? I remember when they started limiting them.

I don't know for sure that they changed but I would believe they have because the Falken Wildpeak AT3W which is a new design now has 17" tires listed as high as 3970lb. When TRA brought in the 3195lb limit they grandfathered old designs to the higher limits so I'm guessing that since the new Wildpeak is back to the higher limits TRA has changed the requirement.

 

[AH64ID]

I don't know for sure that they changed but I would believe they have because the Falken Wildpeak AT3W which is a new design now has 17" tires listed as high as 3970lb. When TRA brought in the 3195lb limit they grandfathered old designs to the higher limits so I'm guessing that since the new Wildpeak is back to the higher limits TRA has changed the requirement.

Interesting, I do recall some tires never adapting the limits while other tires changed over quickly without even redesigning the tire.

It’s been a long time since I’ve shopped 17” tires though

 

[lpennock]

Quick search on discount tire website for a LT285/75R17 comes up about 50/50 index 121(3195) and index 128(3970). The 128 rated ones are newer designs like BFG KO3, Falken AT4W and Toyo R/T with the 121 rated being older designs like Toye AT3 and Nitto Ridge Grappler.