I'm trying to figure out what the difference is between P and LT tires, and how all that applies to a truck such as my F150.

I assume that LT tires wear longer and have stiffer sidewalls and that P tires are more comfortable at the expense of load capacity and longevity.

I'm not sure why my truck has P tires. Maybe to give it a car-like ride?

I have the standard P235/70R17 tires here:

http://www.hankooktireusa.com/product/oe_RH03-P.pdf

It looks like they make an almost identical LT tire in a LT245/70R17:

http://www.hankooktireusa.com/product/RH03-LT.pdf

Comparing the tires gives us the same nominal rim width, a rim width range within half an inch and identical tread width.

The diameter of both tires is within half an inch. My extremely poor math skills tell me this is less than a 1% difference.

I have no idea what most of those other columns are, like ply rating and stuff. All I can figure out is that I think, physically, they are compatible.

Anyways, my question is if I changed to the LT tires when my OEM tires wear out, what change should I expect? More tire life? Better or worse handling? Less bulging when loaded? A harsher ride? If so, how harsh? If the truck is "designed" around a P tire, will an LT tire cause all sorts of problems? (By this I mean, for example, perhaps the frame is tuned to expect a certain amount of tire damping so a stiffer sidewall could cause the truck to change its character completely? Or maybe the suspension system will be unable to compensate for the change?)

I just noticed that the the tread depth is 16.5 on the LT and 12 on the P. Shouldn't that equate to a much longer service life?

I'm not dissatisfied with the P tires I have right now, but it does seem a bit weird to put car tires on a truck. I read somewhere that they have to derate the tires a bit to do this, which sounds even weirder.

Loaded up, the P tires seem to bulge a bit more than I expected, even at max pressure, which isn't very high. However, they seem to work okay.

I'm just trying to learn here. Any input is appreciated.

 

The general difference is in weight rating. When using a P-designated tire in a truck application, you must subtract a certain percentage from the weight rating (9-10%, I believe) to keep the tire "in spec".

There are several other differences, most of which I don't recall off the top of my head. As I foggily remember, the LT-designated tires have a stronger sidewall, and are actually designed with service on a truck, whereas P-designated tires are designed strictly for passenger car useage, where ride quality is often the most dominant design decision.

Here's a fairly lengthy discussion from another board I frequent (mostly GM Suburban guys).

http://oursuv.com/oldsubforum/Forum/...ges/11205.html

-blaine

 

Thanks! That was pretty helpful. (I'm sure glad FTE doesn't use that forum software!)

The best reply was:

http://oursuv.com/oldsubforum/Forum/...ges/11211.html

I'm still curious how it would affect the ride and how you would air them up. Wouldn't a 10 ply tire would need more than the 38PSI that is listed on my door jamb. Are there other brands to consider? I searched tirerack.com but I must be searching wrong.

Still learning.

 

That type of forum software was very common about 10 years ago, before broadband was common. It's much more suited to low-bandwidth applications, and in corporate environments that may not use a GUI-based OS.

Anyhow, door-jamb pressure values are almost always aimed at comfort when used with P-designated tires. Anything in a D or E (i.e. LT-designated) load range most certainly WILL need more than 38 PSI to not be underinflated.

-blaine

 

If you are used to running P rated tires on your truck and do not do a lot of hauling or towing then switching to LT tires will give you a very harsh ride. They are stiffer and built more robustly. The ride will be a lot more lumber wagon like than before. Also, if you are thinking you can put an LT tire on your truck and that will increase your towing/hauling rating it will not, because you still have to consider the brakes and suspension. I used to bust tires 8 hours a day every day. Most people who bought LT tires for their truck that had P tires on it complained of the ride changing, but the did get a longer life and usually with an LT tire you have more options as far as tread pattern/purpose.

 

Thanks! That is some really good info there. My truck is only used for hauling and towing stuff around town and it isn't my primary vehicle. However, it does spend a lot of time taking me to Bojangles for some reason. Sometimes I'll take it 2-300 miles on the highway but I don't think the ride would be that bad on a fairly smooth highway, would it? Are 10 plys too extreme?

I'm really just interested in less bulging under load, more safety and longer tread life. Its just a work truck. I just want it to work without hassling me. I expect to keep it until I die, or 500,000 miles, whichever comes first.

(Finding 17" LT tires hasn't been easy, or I have been looking in the wrong place. Either way, the way these OEM tires are wearing it looks like they will last to 50,000 miles at least.)

Oh yeah: You wouldn't use the door jamb air pressure requirements for LT tires, right? My door jamb says 38PSI and the tire says 41PSI max. I assume an LT tire is going to run in the 50PSI+ range? How will I know exactly what pressure to run?

 

You could go up to a 6 ply (C rated) LT tire, but 10 ply is way too much for an F150 under most circumstances. As for pressure, that mostly depends on the load and tire width, and LT tires don't need more when everything else is equal.

 

One thing to keep in mind is that the LT tires generally need to run at a higher air pressure. The P tires have a thinner sidewall so they can flex and buldge more without generating as much heat as the thicker LT sidewall. The higher PSI makes them stand taller and so they flex less to generate the same heat.

Calvin

 

For any truck, LT tires are a must in my opinion. On my F250 SC I have Load range D LT tires and guess what? It rides like a truck. It makes me feel good when hauling a load of crap to the dumps or pulling a trailer. It always amazes me to see Suburban or Expedition size rigs with passenger car tires on them. These can be loaded up pretty good with people and all there stuff. Definately over the load renge of P rated tires. Ever see the guy going down the highway way overloaded and tires bulging to the max? He scares me. Just my opinion though.

 

Actually, some bulging may be perfectly normal with radial tires. I actually remember that a roommate a long time ago (20+ years) inflated the tires on his Buick by look, and not using a gauge -- he had one blowout, and another tire looked like an egg. I checked one tire and he had almost 80 (!!!) PSI there.

In any case, don't underestimate P tires -- I just checked my tires, the spare (P235/75R15) is rated 2183 lbs at 41 PSI while the current tires (LT24575R16C) are rated 2205 lbs at 50 PSI while the previous tires (LT23575R15C) are rated 1985 lbs at 50 PSI. So go figure....

 

I am running a load E on my F-150. They are Cooper Discoverer ATR's. The ride is much stiffer! I have the 18" Lariat wheels so I was limited to tire companies and ply ratings. I would have gone with a C range but I could not find any. I tow a travel trailer almost every other weekend in the spring, summer and fall so I needed the extra ply rating. The stock P rated tires were not up to the task. I ran out of tire load way before I ran out of payload on the truck itself. The tires, while stiffer when not towing are rock solid and stable when I do tow. If I had 17" wheels I could have about gotten any range I wanted. I have to run 70 PSI in the Coopers. They are rated all the way to 80 but there isn't enough weight on the tires to justify 80 PSI. THey run cool at 70 even at 100 deg heat while towing. I hope this helps. THe tires are rated at 3260 lbs each. It does drive differently and some bumps that I went over before that I didn't notice are very noticeable now. THe truck will actually jump sideways a bit when not towing. I tried running less air pressure in them and it was absolutely terrible! It wouldn't stay on the road... it almos felt like the truck was floating. I tried running more air in them and it wouldn't hold a line.... drifting. At 70PSI it is perfect.

 

What LT tires are available/suggested for 17" wheels? I can't figure out how to get tirerack.com to show them. If it matters I suppose I want load range C (6 ply?) tires and I have a 7.5" wide rim. I'd like to keep the OEM 30" diameter, or within 1/2 inch either way, so my speedometer doesn't get out of whack.

 

What is the stock size on the truck now? It will be listed in your door jamb also.

 

Goodyear silent armor make an XL load tire in that size. Yokohama Goelander has an XL tire in that size. I am sure there are more. This is from Tire rack. I will check Cooper's site also. There are also som off brand tires that are made in that size. They are name brand manufacturers with different tire names. They have excellent tread life and ride quality. Summit and El dorado and Sport King are a few. Are you looking for a highway tire, or an AT tire, or a mud tire?

 

P235/70R17

Highway use.

I'll check out the ones you listed.