What air pressure in my TV tires?

[henkelphoto]

Hi guys!

I recently changed out the "P" tires on my Ram 1500 to "LT" tires with an "e" load rate. The tires have a max pressure of 80psi

While just driving with no trailer, I'm using 40psi in the tires, but I'm curious what you guys think I should put in them while towing. Would 65psi be too much? Not enough"?

[Gary RV_Wizard]

We could only guess. You need to have axle or individual wheel weights (from a scale) to evaluate what psi the tire should have. You use the loaded weight and the tire makers load-inflation tables to determine that.  So, what is the full tire size designation (LT xxx/yyRzz) and tire brand & model (to select the right tables). And the approximate weight carried on the front and rear axles, with and without the trailer.

Odds are the LT tires use a different table than the previous P tires, even if identical size. The "E" load rating, however, only changes the maximum, not what is needed for a less than max load.

[steveblonde]

The pressure indicated on the TIRE is the manufactures recommended pressure. When swapping out the origanal tire recommended for the truck always use the pressure indicated on the tire, when towing you should be at 70 - 80psi loaded
Go to the tire manufactures website
The tire guide on the drivers door is for the tires the truck came with in your case P not Lt

[donn]

Both the previous posts are right and wrong.  80PSI is likely the max pressure to carry the max load for the tire.  However 80 will quite likely exceed the wheel mfg pressure rating.  You need to find out what load and pressure the wheels are rated for and not exceed that.

[Gary RV_Wizard]

Your truck is loaded more heavily when towing, especially if the trailer is a 5W, so the weight on the tires goes up and more psi is needed to support the load. More psi also stiffens the sidewalls a bit and improves stability somewhat in turns and cross winds. Whether you need to go to the full 80 psi on the new tires depends on the actual loading. A typical truck-size 16" tire in LRE is good for about 2650-3050 lbs at max inflation (80 psi), but most 1500's  won't get anywhere near a 6000 lb load on the rear axle. If I had to guess, I'd say maybe 60-65 psi for towing. That would give you about 2400 lbs per tire in carrying capacity (equivalent to LR D at max load),

Were the original P tires load range E? Usually not. Typically a pick-up with P-type tires will be a LR C but have the XL designation, which permits inflation to 42 psi and carries a somewhat grater load than a standard "C" @ 36 psi max.

[steveblonde]

Both the previous posts are right and wrong.  80PSI is likely the max pressure to carry the max load for the tire.  However 80 will quite likely exceed the wheel mfg pressure rating.  You need to find out what load and pressure the wheels are rated for and not exceed that.

this is also right and wrong lol the wheels made on todays trucks are ALMOST all rated to 80 psi and aboveand hae been for several years the old steely wheels were different
most factory wheels are made by allcoa for Ford GM and Dodge

 https://www.arconic.com/alcoawheels/catalog/pdf/brochures/alc_specdataguide.pdf


you can search the Allcoa site for your wheels

https://www.arconic.com/alcoawheels/north-america/en/product-search.asp

[LarsMac]

Hi guys!

I recently changed out the "P" tires on my Ram 1500 to "LT" tires with an "e" load rate. The tires have a max pressure of 80psi

While just driving with no trailer, I'm using 40psi in the tires, but I'm curious what you guys think I should put in them while towing. Would 65psi be too much? Not enough"?

I believe that running at half the recommended pressure, no matter what the load on your vehicle, will reduce the life of your tires, and could damage your sidewalls. That could create a problem when you are running under a load.


 

[Lou Schneider]

I recently changed out the "P" tires on my Ram 1500 to "LT" tires with an "e" load rate. The tires have a max pressure of 80psi

While just driving with no trailer, I'm using 40psi in the tires, but I'm curious what you guys think I should put in them while towing. Would 65psi be too much? Not enough"?

Your truck has a recommended tire pressure placard on the driver's door.  That's a good starting point.

Beyond that, weigh the truck with the trailer attached and get the actual weight on each axle.  If you can't weigh the truck, estimate the weight on each axle.  Then look up the required inflation pressure in a tire load vs. inflation chart for your tire size.  Just because a tire is rated to hold 80 PSI without damage doesn't mean you should use that much pressure unless the load requires it.

Like Gary said, 65 PSI is a good off the wall guess.

If you want to go further, Toyo Tires provides a very comprehensive Tire Load and Inflation Guide including a downloadable PDF giving load vs. inflation pressures for all of the tires they manufacture. 

Two items of interest:  First, the inflation tables are based on Tire and Rim Assn. reference charts so the information is valid across other brands.

Second, the inflation pressure for a given load stays the same, regardless of the tire's load rating.  Higher rated tires merely allow higher inflation pressures if the load requires them.

The pressure indicated on the TIRE is the manufactures recommended pressure. When swapping out the origanal tire recommended for the truck always use the pressure indicated on the tire, when towing you should be at 70 - 80psi loaded

I believe that running at half the recommended pressure, no matter what the load on your vehicle, will reduce the life of your tires, and could damage your sidewalls. That could create a problem when you are running under a load.

If "recommended pressure" is the maximum PSI indicated on the tire sidewall, that's wrong.  The tire pressure should be matched to the load, as noted above.  Note that in many cases the charts recommend as low as 35 PSI in an 80 PSI rated tire if it's appropriate for the load.

[FastEagle]

OK, I’m going to explain this using tire industry standards.

First I have to ask this question, were the replacement (LT) tires recommended and installed by a tire retailer? I ask that because they would use tires that are approved for the swap-over.

The “P” tires you replaced are not what most people think they are. That’s because the vehicle manufacturer factored in the mandatory load capacity reduction for “P” tires used on the pick-up truck (It’s about 10%) when they fitted them and set their recommended inflation pressures.

Tire inflation pressures for automotive vehicles - that includes your TV - are set to a PSI value that is deemed appropriate for the fitment on your vehicle. The standards clearly instruct the vehicle manufacturer to do so. So, what is shown on the tire placard, certification label and in the vehicle’s owner’s manual is the correct recommended cold tire inflation pressures. Deviations, if there are any, will be described in the vehicle owner’s manual.

The inflation pressures for the Original Equipment (OE) tires are the benchmark - so to speak - for all subsequent recommended inflation pressures for that vehicle. This is, in part what the standards say; Replacement tires must provide the load capacity the OE tires provided (Via Inflation). To do that a tire inflation chart/table for the OE tires and another for the plus sized tires must be used to determine the new recommended inflation pressures for the replacements. Find the OE tire load capacity provided by the placard recommended inflation pressures - those values have already been reduced to comply with the derating standard. Use the results to find the psi value that will equal or exceed the load capacity the OE tires provided.

A savvy tire installer will know all that stuff and will tell you what they did, make a notation in your vehicle owner’s manual and place an auxiliary tire placard with the new recommended tire inflation pressures next to the original placard. (NHTSA allows that to happen). 

[scottydl]

I can only assume that the OP is even more confused now than when the question was first asked!

Aside from the technical specifications, I'd agree with some of the other responses that you first need to (1) get your entire rig loaded (truck, truck + trailer, and trailer ... see this Forum Library article for instructions), and (2) download the load inflation tables for the make/model of tire you have installed.

Once you have those numbers, we can help figure out the best range(s) for your front and rear tires when towing.

[Gary RV_Wizard]

I'm sure you are right, Scotty. This is a simple problem once the weight and tire size are known. We are debating with each other, but henkelphoto hasn't come back with any information that could help find the answer.

[steveblonde]

I deal with tire shops on a daily basis they have all without a doubt recommened the tire pressure on the tires so thats what i stick with

[Gary RV_Wizard]

Meaning the max load pressure shown on the sidewall?  That's the legally safe recommendation for them - the tire cannot be "underinflated" if they set it to max. On a passenger car or SUV that won't be much problem even if excessive, but with heavier duty tires it could be.  Especially if henkelphoto jumper up in Load Range, which he may have done..

[henkelphoto]

Hi guys! Sorry I haven't been back on here for a while, dealing with life stuff.

Anyway, I won't be able to get the truck or trailer weighed for a few weeks. Right now, I have had the truck weighed, but since changing the tires and adding a couple of other accessories, I need to re-weigh it.

The tires I purchased (BFG KO2 "LT") are the same size as stock tires (Goodyear SR-A "P"), 265/70R17. After looking at both sets of tires, the load range stayed the same as "e".

After reading through all the posts here, I would say any further comments will be counter-productive until I get the truck/trailer weights. I'll come back to this post when I get those weights.

Thanks to all! And Happy New Year!

[UTTransplant]

A bit of a hijack from the OP, but we use the 60 pounds front, 80 pounds rear Dodge recommends. My issue is when not towing. DH used to leave the rear at 80 pounds, but that makes for a dreadful ride! We now lower them to 60 rear when not towing, like the front, and I am much happier. Could we go lower? The bed always has 300 or more pounds in it since we have a pull out shelf on it with some other gear we always carry (fuel, DEF, tools).

[FastEagle]

Tire inflation pressures are a subject with too many anecdotal answers.

This document has the "by the book" answers. Not many read it because they already have a solid mind set to what is best for them.

https://www.ustires.org/sites/default/files/CareAndService_PassengerAndLightTruckTires.pdf

[kdbgoat]

Years ago I bought oversize tires for a full size 4 wheel drive 1985 Blazer. The shop was a very old one, and had an excellent reputation. Mr Ewing overinflated the tires, then started slipping a dollar bill under the outside edge while letting the air out. When the bill grabbed, he stopped. He then checked the pressure, wrote the front and rear on a 3x5 card and put it in the glove compartment. I ran those tires for 50,000 miles+ using those pressures and never had any odd treadwear. I'm not saying that is the right way to get the proper inflation, but he seemed to know exactly what he was doing, and it worked for me.

[Old_Crow]

Years ago I bought oversize tires for a full size 4 wheel drive 1985 Blazer. The shop was a very old one, and had an excellent reputation. Mr Ewing overinflated the tires, then started slipping a dollar bill under the outside edge while letting the air out. When the bill grabbed, he stopped. He then checked the pressure, wrote the front and rear on a 3x5 card and put it in the glove compartment. I ran those tires for 50,000 miles+ using those pressures and never had any odd treadwear. I'm not saying that is the right way to get the proper inflation, but he seemed to know exactly what he was doing, and it worked for me.

I've always done that when running extra wide tires on my(or my customer's)hot rods or trucks.  Running the stock size 30x9.5-15's on my Wrangler, the door calls for 28, but I ended up at 25 with the Hankook's I'm using now.

[Gary RV_Wizard]

The tires I purchased (BFG KO2 "LT") are the same size as stock tires (Goodyear SR-A "P"), 265/70R17. After looking at both sets of tires, the load range stayed the same as "e".

It's not perfect, but since the size & load rating are the same, start by using the recommended pressures shown on the tire sticker on the driver door post. Also, along with that should be another sticker that shows front & rear axle max load ratings. That info can be used as an estimate of the tire load, even though it is a "max". When towing you can set the tire pressure high enough to support the max load. It's likely higher than necessary, but until you can get a scaled weight its better than guesswork.

Can you provide a photo of those two stickers, or copy the salient info int a message here?

I've attached a sample axle load sticker. In this example, the rear axle can carry up to 6084 lbs.  If fully loaded and evenly balanced, that would be 3042 lbs per tire.  Usually the loading is not quite equal, so you should allow for a bit more.

[FastEagle]

It's not perfect, but since the size & load rating are the same, start by using the recommended pressures shown on the tire sticker on the driver door post. Also, along with that should be another sticker that shows front & rear axle max load ratings. That info can be used as an estimate of the tire load, even though it is a "max". When towing you can set the tire pressure high enough to support the max load. It's likely higher than necessary, but until you can get a scaled weight its better than guesswork.

Can you provide a photo of those two stickers, or copy the salient info int a message here?

I've attached a sample axle load sticker. In this example, the rear axle can carry up to 6084 lbs.  If fully loaded and evenly balanced, that would be 3042 lbs per tire.  Usually the loading is not quite equal, so you should allow for a bit more.

I'm glad you posted that placard. Let's talk about it. The inflation pressures recommended by the vehicle manufacturer (50 PSI & 70 PSI) Exceed the GAWR axles those tires are fitted to. The total GAWR is much greater than GVWR. GVWR is the limiting factor. The axles and tire pressures both provide load capacity reserves for the maximum GVWR. There is no way, as depicted that those recommended tire inflation pressures need to be manipulated. Those tires cannot be overloaded without overloading the vehicle.