F250 Tire Question

[JohnUSA]

I have a 2002 F250 Super Duty Crew Cab 7.3L and had the tires replaced. The tire that was recommended and purchased was a Firestone Destination AT - LT285/75R16 this a D load rated tire.

Before I left the tire shop I asked what tire pressure I should be running in these and the answer was to use the pressures indicated on the info panel inside the door jam. OK, if that is correct then these tires should be running 60 psi in the front and 70 psi in the rear. I checked the pressure in the tires and the tire shop put 48 psi in all four. IS that because the tires are D rated and not E?

If the recommended tire for that truck is a load rating of E then it would probably handle the recommended air pressure but these tires are D and not even the tire shop followed Ford's recommendation. So the questions I have are as follows:

1. What pressure should these tires be at?
2. Should load rating D tires even be on this truck? This is a work truck not a street rod.
3. What happens if someone else mistakenly puts 70 psi in the tires and hauls a load with this truck like I almost did?

Firestone is telling me that this tire in a D rating will handle a larger load than the E rated tire because the D rated tire is a 285 and the E rated tire would have been a 235. I'm not saying they are wrong but that doesn't sound right to me.

I would greatly appreciate hearing what you think.

[RopinandRidin]

It sounds like the guy that put your tires on just didn't fill them up correctly. I don't understand Firestone's logic as far as far as a D rated tired of one size being stronger than an E rated tire of another size because the strength of the tires is stated by the letter. E's are stronger than D's. I'm not a tire expert though, so I don't know....

All I've ever put on my trucks are E rated tires because I was told that the weight and work that my truck did needed the strength of the E's.

[BTBBT]

The Letter scheme for rating tires is meaning less and less these days. What you want to do is get the rating off the side of the tire itself. It will tell you the max load per tire in both a single and dual config. and at what max pressure. That is the max you want to run it at. That is the max that tire can 'officially' run at according to the manufacturer. The reason they rate them D or E has more to do with the construction of the tire, not the actual load rating. There are load rating tables that give you the max load at specific pressures, I think a little searching on Firestone's website should turn those up. Those tables are what you want to go by. But for now and always, never exceed the rating on the side of the tire.

And yeah, the guy at the shop only put enough air in them to get the beads to seat and that's it. Pure lazyness and a complete lack of regard for the job if you ask me.

[Smiley1]

Originally Posted by JohnUSA

I have a 2002 F250 Super Duty Crew Cab 7.3L and had the tires replaced. The tire that was recommended and purchased was a Firestone Destination AT - LT285/75R16 this a D load rated tire.

Before I left the tire shop I asked what tire pressure I should be running in these and the answer was to use the pressures indicated on the info panel inside the door jam. OK, if that is correct then these tires should be running 60 psi in the front and 70 psi in the rear. I checked the pressure in the tires and the tire shop put 48 psi in all four. IS that because the tires are D rated and not E?

If the recommended tire for that truck is a load rating of E then it would probably handle the recommended air pressure but these tires are D and not even the tire shop followed Ford's recommendation. So the questions I have are as follows:

1. What pressure should these tires be at?
2. Should load rating D tires even be on this truck? This is a work truck not a street rod.
3. What happens if someone else mistakenly puts 70 psi in the tires and hauls a load with this truck like I almost did?

Firestone is telling me that this tire in a D rating will handle a larger load than the E rated tire because the D rated tire is a 285 and the E rated tire would have been a 235. I'm not saying they are wrong but that doesn't sound right to me.

I would greatly appreciate hearing what you think.

Congrats on the purchase of those tires. I run those exact tires in the same size and load rating. Pay no attention to the sticker on the door as the sticker is for the factory set tires.

I run 60 PSI in the front and back. Its wearing just fine at that PSI. I up the PSI to 65 on front and back when I tow heavy.

[SmokeyWren]

Originally Posted by JohnUSA

I have a 2002 F250 Super Duty Crew Cab 7.3L and had the tires replaced. The tire that was recommended and purchased was a Firestone Destination AT - LT285/75R16 this a D load rated tire.

Before I left the tire shop I asked what tire pressure I should be running in these and the answer was to use the pressures indicated on the info panel inside the door jam. OK, if that is correct then these tires should be running 60 psi in the front and 70 psi in the rear.

No, that is not correct. The PSI on the Federal Certification Label applies only to the size tire that's also on that label, and it applies only when the truck is loaded for bear. For bigger tires or lighter loads you need less PSI.

I checked the pressure in the tires and the tire shop put 48 psi in all four. IS that because the tires are D rated and not E?

No, that's because the tire jockey doesn't know his job. But he got close to the correct PSI for your tires on your truck. See below.

1. What pressure should these tires be at?

Depends on the weight on the tires. You need different inflation PSI for an empty truck than you do for one that's loaded to the GVWR. Details at the end of this post.

2. Should load rating D tires even be on this truck?

Load range indicates only the max PSI that can be put in your tire. It has nothing to do with how much weight the tire can handle. The tire industry knows this, and they have finally done away with load range and replaced it with Service Description, which is made up of tire load index (weight capacity) and speed symbol. Your 285s have Service Description 122R. Decoded, that means they are designed for a max weight capacity of 3,305 pounds and a top speed of 106 MPH.

3. What happens if someone else mistakenly puts 70 psi in the tires and hauls a load with this truck like I almost did?

Hopefully they will be fired for not knowing how to do their job.

However, it's not a huge no no. Normally, the tires should be inflated to a max of 65 PSI, but LT tires can (and should) be inflated 5 to 10 PSI more than the max on the sidewall under some conditions - such as sustained high speed (over 70 MPH) with a heavy load. So if you're driving on I-10 from Junction, Texas to the Arizona line at the speed limit (75 in NM and 80 MPH in Texas), then you can overinflate your tires more than the numbers on the sidewall. (See the Goodyear link below for more on this.)

Firestone is telling me that this tire in a D rating will handle a larger load than the E rated tire because the D rated tire is a 285 and the E rated tire would have been a 235. I'm not saying they are wrong but that doesn't sound right to me.

Believe it, then get educated about tire specs and inflation.

LT285/75R16D, regardless of brand, has a max weight capacity of 3,305 pounds @65 PSI.

LT235/85R16E has a max weight capacity of 3,042 pounds @ 80 PSI.

So in this case the Load range D tire will handle more weight than the load range E tire? Not because of the load range, but simply because the bigger tire has more weight capacity, even at a lower max PSI.

Okay, back to what is the proper inflation for your new tires.

The short answer is to weigh the truck on a CAT scale at least twice - once when unloaded and once when loaded for bear. Get your axle weights per the scale ticket, then divide by two to get the approximate weight on each tire. Then apply a load/inflation table for your exact size of tires.

Here's the load/inflation table for size LT285/75R16 mounted on single wheels (not duals).
PSI. Load (max)
---. ----
35. 2,130 pounds per tire
40. 2,340
45. 2,540
50. 2,755
55. 2,925
60. 3,110
65. 3,305 (max for tire load index 122 or the old load range D)
70.
75.
80. 3,750 (max for tire load index 126 or the old load range E).

Notice that your sidewall says max weight of 3305 at 65 PSI, but that size tire also comes in a load range E with 3,750 pounds weight capacity at 80 PSI from, for example, BFGoodrich AllTerrain. But you'll never need more weight capacity than 6,610 pounds on an axle. With 6,610 pounds of weight on your rear axle, you're going to be grossing more than 11,500 on your truck = severely overloaded on your SRW pickup with 8,800 pounds GVWR. A '99-'04 F-350 SRW with 16" wheels and 9,900 pounds GVWR would also be severely overloaded with that weight. So you certainly do not need a tire with more weight capacity than your load range D tires.

Example: One CAT scale ticket I have when on the road towing my 5er said 4,440 pounds on the front axle and 5,180 on the rear axle, for a GVW of 9,620 on the two axles (15,960 GCW). So that was 2,220 on each front tire and and 2,590 on each rear tire. So the above load/inflation tables says with those tires and that load I'd need 35 PSI in each front tire and 45 PSI in each rear tire. I'd probably add a smidgen to that and run 40 front and 50 rear on that trip.

Note that my F-250 is a 4x2, so 4x4s will weigh a few hundred more on the front.

Bridgestone/Firestone publishes a load/inflation table for some commercial tire sizes, but not for your 285s. But all load inflation tables regardless of tire manufacturer will be identical for the same size/type tire (controlled by the Feds an TRA). So you may have to go to a Goodyear or a Toyo truck website to find the load/inflation tables, and you may have to go to the "truck" tire website instead of the car/SUV/light truck website to find the load/inflation tables

Here are some links to get you started on your studies: The Goodyear doc has a wealth of info, including the load/inflation tables for the sizes of tires they make. The RMA quotes the Tire and Rim Assn. (TRA) load/inflation tables from a few years ago, and the TRA is the authority on load/inflation tables in the USA (and probably Canada too). Michelin includes only "real truck tires" in their tables, apparently because they think only real truck drivers are smart enough to apply the load/inflation tables. I haven't studied the Bridgestone/Firestone link lately, but a quick glance indicates they include only "commercial use" too, since yours are not included.
Bridgestone/Firestone load inflation tables

Goodyear load inflation tables

Michelin load inflation tables

Tire and Rim Assn master load inflation tables

[JohnUSA]

Thank you all for the great feedback and it was extremely helpful. I will go the through the links attached and try to understand what each of the tire ratings mean. I thought 48 psi was on the low side but not knowing what the tire specs actually mean I just wasn't sure what to put in them.

I called the tire store that put them on the truck and will be talking with the owner on Monday or Tuesday to let him know the pressure that was in the tires when I left the store and get confirmation as to why I was not told about the difference in pressures between the D and E tires. Thanks again.

[JohnUSA]

I talked with the tire store owner, actually he called me early this morning. He swapped out the tires for the same tire in a load range E. There was a little price difference between the tires I purchased and the new ones but there were no haggles, just very good customer service. Now I feel safer knowing I can use the recommended tire pressures and carry the loads I need without second guessing. Again, thanks for all your feedback and this story had a happy ending.

[JohnUSA]

I fully expected the new tires to ride rough but they don't. In fact I cannot tell any difference in the ride (60 psi front / 70 psi rear) but it does seem to steer easier. Maybe it's just me but I like the overall feel better.