Lt Vs Passenger Tires

ETMegabyte · May 23, 2011

My '03 GMC 2500HD came with LT rated tires. I bought it used from a dealer, and it had a Fisher 8' MM2 HD plow on it, so the LT tires make sense...

A little background info on the truck. It has the Vortec 8100 motor, Allison tranny, plow and tow prep packages, etc. Heavy duty truck...

But during the summer, I don't do much that would be considered heavy. Occasionally pull a popup camper, or a trailer for my single motorcycle... Some trash to go to the dump. Things like that. Things your standard S10 could easily handle...

My question is whether I could put Passenger rated tires on it for the summer. I am aware that it is a heavy truck, but it's not any heavier empty (which my truck bed typically is) than my father's F150 fully loaded... My father's F150 also has a LD 7.5' plow on it as well. If the passenger tires are safe for him to use both loaded and plowing in his 1/2 ton F150, would they still be safe in my empty 3/4 ton truck during the summer?

I only ask because typically passenger rated tires are less harsh with bumps and such, so putting passenger rated tires on the truck during the summer theoretically should improve the ride some... Right?

Any thoughts?

tyhuck · May 23, 2011

I wouldnt put anything lighter than an 8ply (load range D) rated LT tire on a 2500. Regardless of how much you tow or load into the truck, you should always run an LT tire on that heavy of a truck. I wouldnt even suggest running a P rated tire on a half ton. Hell, I ran LT rated tires on my Jeeps and my S10. If your father-in-law is running a plow on P rated tires, hes asking for trouble. You have to also take into acount that the front tires will be carrying a load regardless of the load in the bed. That 8.1 is a heavy engine. Maybe not as heavy as the D-max, but still a big sucker. I would be more worried about steering and handling on the front end with lighter tires than I would be on the rear. P rated tires will cause you to lose stability at higher speeds because of the lighter duty sidewall. The ride will be softer, but to me, its better to have a little more bump and avoid the risk of a blowout.

Im no expert, but I do have some tire shop experience behind me.

8.1HD/ALLISON · May 23, 2011

+1 on above statements.

brianf60 · May 23, 2011

You can put P rated tires on there no problem. Just keep in mind the total weight of the truck and your load and the max safe rating on the tires. The lower pressure will give you a softer ride and the tires will be cheaper.

Matt_ · May 23, 2011

A common ride quality issue for guys with 3/4 ton trucks is that their tire pressures are being run for max capacity of the vehicle as opposed to the actual DD weight. If you're still running 70-80 psi when unloaded, that's what's killing your ride.... Not the LT tires.

Try dropping the pressure to 50-55 and see how it does. (Note, to be safe you should look up the TRA Inflation Tables and make sure 50-55 is a good pressure for your tire size based on vehicle weight.)

Matt_ · May 23, 2011

Also, most tire shops wont mount a P rated tire on an 8 lug wheel.

My shop would not install a tire with a lower weight or speed rating that what the OEM called for..... basic liability issues.

tyhuck · May 24, 2011

A common ride quality issue for guys with 3/4 ton trucks is that their tire pressures are being run for max capacity of the vehicle as opposed to the actual DD weight. If you're still running 70-80 psi when unloaded, that's what's killing your ride.... Not the LT tires.

Try dropping the pressure to 50-55 and see how it does. (Note, to be safe you should look up the TRA Inflation Tables and make sure 50-55 is a good pressure for your tire size based on vehicle weight.)

+1 and ditto.

I always ran 10 ply tires on my 2500s, but I only ran them at about 50 psi in the rear because I didnt run it loaded. The fronts I ran at factory specs. That usually gave me a good wear pattern on the 245/75/16s I used to run. Ide usually bumped it up to about 60-65 when loaded because I never maxed the truck out.

ETMegabyte · May 24, 2011

A common ride quality issue for guys with 3/4 ton trucks is that their tire pressures are being run for max capacity of the vehicle as opposed to the actual DD weight. If you're still running 70-80 psi when unloaded, that's what's killing your ride.... Not the LT tires.

Try dropping the pressure to 50-55 and see how it does. (Note, to be safe you should look up the TRA Inflation Tables and make sure 50-55 is a good pressure for your tire size based on vehicle weight.)

You know, I hadn't really thought of that... My tire pressure does not change between Summer and Winter. As I recall, they're at 70 or 75psi... I'll look for the TRA Inflation Tables and see what it tells me. The hard ride is really the only thing I have an issue with when driving it during the summer (other than it's massive gas consumption and oil consumption - but I knew that when I bought it!)...

I have another thread here about getting another set of rims so I can have a summer and winter set... I want to keep the current set as summer tires, as they're very good on-road and light off-road (Cooper Discoverer ATR) but aren't quite grippy enough for plowing in my opinion, and get another set of studded tires for winter plowing...

My question here was for when the current Cooper's wore down, and whether I should change to P-rated tires... My current thought is that I will probably stick with LT rated tires year round... I hope the tire pressure thing helps with the ride... I'll let everyone know my thoughts once I make that adjustment...

ETMegabyte · May 24, 2011

I always ran 10 ply tires on my 2500s, but I only ran them at about 50 psi in the rear because I didnt run it loaded. The fronts I ran at factory specs. That usually gave me a good wear pattern on the 245/75/16s I used to run. Ide usually bumped it up to about 60-65 when loaded because I never maxed the truck out.

Part of my issue is that the sticker on the driver's door on my truck is missing, so I'm not quite sure what the "factory specs" are. Stupidly enough, when I downloaded the owner's manual for the truck (specifically to find out what the sticker is supposed to say), it says to check the sticker... Figures, right?

I run the tires at (I think) 70psi... The tires themselves say max cold pressure of 80psi...

I don't suppose anyone has an '03 GMC Sierra 2500HD that can post a pic of the sticker on their driver's door? At least that would give me a starting point...

I also wonder if having the plow on the truck in the winter would change the pressures I should run at...

I'm not ashamed to say I'm a little clueless here... My old plow truck, an '88 Sierra 2500 came to me with P-rated tires, but it was mostly a yard truck, so a blowout wasn't really a concern to me. This truck is newer, nicer, and driven more during the summer and on the road than my old one ever was. I never really had to think about tires and pressure and such...

ETMegabyte · May 24, 2011

I don't understand why information is so hard to come up with... I just wanna know how heavy my truck is!!!! This would be SOOOOO much easier if the stupid sticker on the door was there... Arrgh...

Anyway, the only information I could find was from eBay motors, which says the curb weight of my truck is between 5402lbs and 5631lbs... I got this from here. I'm guessing the "range" is due to the different motor/tranny options... Since I have the largest gas motor, and heaviest transmission (the Diesel engine is only slightly heavier than mine), I'm going to go with the upper limit here as a starting point just to be absolutely safe. So, Assuming curb weight is 5631 lbs, and add some equipment, and a few people, and we're somewhere around 6000lbs minimum...

GVWR is 9200lbs.

Using those numbers as a reference, that would mean that each tire would need to carry between 1500 and 2300lbs (minimum vs max weight).

So I looked at the TRA Inflation Table, and here's the pressure/weight lists it gave me for my tire:

35/1700
40/1865
45/2030
50/2205
55/2335
60/2480
65/2623
70/2765
75/2900
80/3042
95/3415

The TRA Inflation tables say my tire (LT245/75/16) in single configuration can do 1700lbs per tire at 35psi. So, theoretically, I could run my tires at 35psi as long as I don't put anything in the bed... The TRA table says at 55psi the load can be 2335lbs per tire. So, unless I'm reading this all wrong, that means that even at FULL LOAD, I should be able to keep my tires at 55psi all the time... Right?

And if I want a softer ride when the truck is empty or nearly empty, and adding in a bit for a margin of safety, I would be perfectly safe at 40psi... Right?

Would this adversely affect tire wear if I keep it around 40psi? How about performance or gas mileage? Still clueless, but trying to learn...

Thanks

-Eric

Matt_ · May 24, 2011

Remember there's a lot of weight added with the plow prep packages and such.

But yeah, it looks like you can run them around 40 unloaded. I would probably start with 50 though and see if your ride is good that way you don't have to worry about airing up a bit more if you throw a load in the bed or have a full cab. Or try 50 front / 40 rear... that's a big engine you have there! The fronts are carrying significantly more weight than the rear when unloaded.

For fully loaded, you need to look at the rear GAWR, not the GVWR divided by 4.

Just curious, what does your door placard say for tire size, air pressure and GAWRs?

tyhuck · May 24, 2011

I always ran 10 ply tires on my 2500s, but I only ran them at about 50 psi in the rear because I didnt run it loaded. The fronts I ran at factory specs. That usually gave me a good wear pattern on the 245/75/16s I used to run. Ide usually bumped it up to about 60-65 when loaded because I never maxed the truck out.

Part of my issue is that the sticker on the driver's door on my truck is missing, so I'm not quite sure what the "factory specs" are. Stupidly enough, when I downloaded the owner's manual for the truck (specifically to find out what the sticker is supposed to say), it says to check the sticker... Figures, right?

I run the tires at (I think) 70psi... The tires themselves say max cold pressure of 80psi...

I don't suppose anyone has an '03 GMC Sierra 2500HD that can post a pic of the sticker on their driver's door? At least that would give me a starting point...

I also wonder if having the plow on the truck in the winter would change the pressures I should run at...

I'm not ashamed to say I'm a little clueless here... My old plow truck, an '88 Sierra 2500 came to me with P-rated tires, but it was mostly a yard truck, so a blowout wasn't really a concern to me. This truck is newer, nicer, and driven more during the summer and on the road than my old one ever was. I never really had to think about tires and pressure and such...

The sticker should have said 45 in the front for a gasser, and 80 in the back. But we have already determined that you dont need that much in the rear if unloaded. Ide say you wuld be safe with 50 -55 psi in the front and around 50 in the rear. Just remember to bump the pressure up when loaded or plowing.

ETMegabyte · May 24, 2011

Just curious, what does your door placard say for tire size, air pressure and GAWRs?

That's part of the problem. No door placard...

ETMegabyte · May 25, 2011

Would this adversely affect tire wear if I keep it around 40psi? How about performance or gas mileage? Still clueless, but trying to learn...

I think this is the final hurdle before I start making changes... I know on P rated tires, lowering the tire pressure changes the wear patterns significantly... Is this also the case for LT Rated tires? Also, this thing has a HUGE motor, and gets like 8mpg now. I'd hate to make changes to the pressure to improve ride if it's going to cut my gas mileage in half or make it so the thing can't steer around a corner...

Any comments?

newdude · May 26, 2011

Factory tag should be 60lbs for the front, and 80lbs for the rear. 2007 and up can vary.

Running too low a psi would increase your rolling resistance, and give you poor mpg. Higher psi would help gain mpg. Too high a psi will wear the center of the tire out faster than the sides, and too low a psi will wear down the side treads. I ran 60lbs on my last truck with 245/75/16's and they wore pretty good. 8 to 10 ply tires have stronger construction as well to support all the load and the empty curb weight of 3/4 ton trucks. Heck, 1/2 ton trucks, mostly pre 1999 sometimes came with LT tires. My friend has a 1995 K1500 and it came with LT245/75/16 E load Firestone Steeltex on it. Thats what the door placard lists and the Steeltex were OEM as far as we could see (had 55,000 miles when he bought it).