Difference between LT and P metric?

[Huhwhye]

I would like to know what is the difference because we can't get an answer from the tires shops or from Bridgestone other than the usual marketing mumbo jumbo.

Looking at size 265-75-16, Bridgestone Revo AT come in both a Pmetric and LT version.

The tires are obviously different. LT has 1/16 more tread depth and .3" more tread width but cost $30 more per tire and a Load Range C 2470 @ 50psi

The P metric rated "standard load" has a rating 260l lbs @44 psi. Which is strange because you would think a Light Truck tire would hold more weight than a Passenger Car tire? Right? I don't know?

REVO SPECS from www.tirerack.com

So is there a difference in construction?
The way the test and rate the tires?
Is 1/16 of tread worth $120 more for a set of tires?
I don't know.

[ April 22, 2005, 09:10 PM: Message edited by: Huhwhye ]

 

[Steve S]

lt=light truck p= passenger

 

[Huhwhye]

That's precisely the mumbo jumbo I'm talking about.

feel like I'm banging my head into the keyboard.

You couldn't tell I already knew that from my post? Let me quote myself

"The P metric rated "standard load" has a rating 260l lbs @44 psi. Which is strange because you would think a Light Truck tire would hold more weight than a Passenger Car tire? Right? I don't know?"

I want to know why the different specs and price. And which is a better value?

[ April 23, 2005, 12:48 AM: Message edited by: Huhwhye ]

 

[Steve S]

Just guessing a lt should be somewhat more heavy duty .I don't know the difference.I myself would call or go to a tire shop and ask the tire guys.

 

[Huhwhye]

Tire shops have no idea. I can't see how they are more heavy duty with lower weight ratings on the LT and both weigh about the same.

 

[jorton]

Check to see if the P has a 4 ply tread and LT has 8 or 10 ply tread.

The P tire is a good daily driver and the LT is for heavy hauling and towing.

 

[CapriRacer]

Where to start?

Ply: Don't pay any attention to this 4 ply / 6 ply / 10 ply stuff. It was replaced long ago with "Load Ranges" in LT tires. "Load Range" is much less confusing because many folks think that a "10 ply tire" ought to have 10 plies - they never did - and modern tires, with their high strength cords, don't need 10 plies to get the strength. Typical Load Range E (formerly 10 Ply Rating) LT tires have 2 ply sidewalls (polyester) / 4 ply tread (2 polyester / 2 steel).

LT metrics: The design intent of LT metric tires is between the soft, cushiony P metric tires and the stiff, but durable MRT (Medium Radial Truck) tires. So P metric tires are based on a design standard that allows more flexing, where the standard for LT metrics require less flexing, (and therefore less load). What you get with an LT metric is a more durable, perhaps retreadable casing, although hardly anybody retreads these things - but that's the design intent nevertheless. However, you only get this if you follow the LT metric inflation standards - which means higher inflation pressure for the same load.

One of the little known quirks is that when P metrics are used in a light truck service (Pickups SUV, etc.), the load rating is reduced by 10%. This goes back a long ways, and is probably part of the standard to account for the stiffer suspensions in these vehicles. So if you do the calculation, the 2601 # max load referenced above gets reduced to 2365 #.

Probably the largest consideration here is what did the vehicle come with from the factory. LT metric tires have a much higher spring rate than P metrics, and changing the tire's spring rate can have some unintended, perhaps dangerous, changes in the handling of the vehicle. Springs, shocks, and sway bars were all designed by the vehicle manufacturer with the original type of tire, and it's properties. Caution and common sense go a long way in this department.

It's probably best to stay with the type of tire the vehicle manufacturer specified, rather than re-engineer the vehicle.

Hope this helps.

[ April 23, 2005, 08:15 AM: Message edited by: CapriRacer ]

 

[Huhwhye]

Thanks that does help alot. So are you saying the plys may be made of different size cord or material? Because they both have the same plys and the weight difference probably accounts for the extra 1/16" of tread depth. Strength is a big concearn but at an extra $30 a tire I don't know if its worth it there are other tires in that price range I feel are better.

The original tires on this truck, a 4x4 Tacoma had 3 flats in 3 different tires. Had 2 flats in one trip and had to borrow a spare from another truck. And 2 were fatal, a side puncture and a pinch flat. All the 3 flats were from pathetic causes for a 4x4 tire.

Also staying original usually isn't in the vocab of an off roader. This tire is for a 4x4 and were looking at a larger than stock tire size by an inch. The factory tire was a P265-70-16 BFG Rugged Trail and were junk off road.

 

[Juan]

I used to sell tires at Sears years ago. Short and simple: the LT tires have a stronger sidewall (more plys) than the P tires. Since they don't flex as much, they are a little harder on the tread, hence a little more tread.

 

[srivett]

A little more about load. Your vehicle is rated for a specific amount of weight IF your tires load ratings meet the requirements. If you have a really heavy vehicle you could possibly put tires on that do not allow you to carry a payload. An older V10 dodge single cab weighs something like 9000 pounds dry so you'd want LT tires on that thing if you wanted to pull a 5th wheel.

Steve

 

[CapriRacer]

"So are you saying the plys may be made of different size cord or material?"

Yes, an LT metric would use beefier cords than a P metric. However, don't think this makes for a better tire. While the casing would be stronger, the strength is there primarily for the increased inflation pressure, and actually detracts from some performance parameters that aren't related to strength - such as temperature generation - meaning speed capability.

"....the weight difference probably accounts for the extra 1/16" of tread depth."

Probably! The difference in materials results in minor changes in weight - all other things being equal.

One of the reasons LT metric tires have increased tread depth is because of their intended application - more of a commercial use. This is not usually a good way to go for consumer types of use.

"All the 3 flats were from pathetic causes for a 4x4 tire. ......The factory tire was a P265-70-16 BFG Rugged Trail and were junk off road."

I've always had some problems with the way OE manufacturers do tires for pickups and SUV's. On the one hand they try to get the look of a beefy, off road tire, then specify rolling resistance levels that prevent the use of appropriate tread compounds. They also demand soft riding tires. This results in tires that aren't much good for what they look like they should be good for. I know this is OK since most folks are so "appearance" oriented, but I think it's basically dishonest, and creates an unrealistic expectation in the consumer's mind. I think it is better to give a customer something that looks like what it's supposed to do.

But going back to your situation. If you intend to go off roading, a more compliant tire will absorb bumps better, so I'm thinking a P metric tire would be better. But one where the tire is designed for off road usage.

Hope this helps.

[ April 24, 2005, 08:44 AM: Message edited by: CapriRacer ]

 

[1sttruck]

'P' tires are often speed rated while 'LT' tires are load rated. As previously noted the '8 ply' and such has been replaced by 'load range', where C, D, and E are common on light (pickup and SUV) trucks. To add to the confusion there is also a 'load index', like 93, 118, etc., which notes a load like '2500 lbs max'. Some assume that load index is the same as load range and try to use larger, lower air pressure tires that can carry the same load, but load range also denoted side laoding for towing.

 

[CapriRacer]

Actually both P metric and LT metric tires are both "load rated" and "speed rated".

Usually P metric tires are "Standard Load", but there are some "Extra Load" P metrics.

Many LT metric tires have speed ratings - usually in the Q range, but more recent offerings are in the S range.

Hope this helps.

 

[MNgopher]

Capri is pretty much dead on the difference between LT and P series tires.

I put LT 245/75/16 Bridgestone Dueler AT's on my '99 F150 and it was one of the best things I have ever done for the truck.

The P series tires have to be derated for use in light truck applications by 10%, thus while it appears a P series tire in a size has a higher rating, in reality, it is lower than the same size in a Load Range C tire. A little known quirk, but it is true.

My tires carry an "S" speed rating, which was the same as the stock P series tires.

I like the LT series tires for the stiffer sidewalls, as that firms up the ride and elimanates some of the wallowing feeling I had with P series tires.

 

[Matt-TDI]

I will say this much; LT tires are definitely much heavier... I work both almost every day (although I'm beginning to do alignments now as well, so doing tires isn't something I do full time anymore). Many manufacturers have the same size in both P and LT ratings. I can tell you from having to put them on stock shelves and also mounting them up and LT tires are without a doubt much heavier and thicker in construction.

 

[Big O Dave]

Essentially, LT tires have a number of characteristics which differentiate them from P-metric tires:

* LT tires are typically designed to hold higher air pressure, which allows them to carry a heavy load continuously (not just occasionally) without overheating and failing. All load range "C" tires can be inflated to 50psi, "D" goes to 65psi and "E" goes to 80psi. There are higher load ratings, but these three are the ones commonly used on light trucks.

* LT tires share more with high-performance, speed-rated tires (such as H and above) than they do with standard tires (such as T and below), in terms of tire construction. This is because, like high-performance tires, LT tires are designed to minimize the creation of internal heat and to be able to endure elevated internal heat levels for long periods. Typically, LT tires are made of higher quality materials than P-metric tires, and their construction is much more robust, with heavier sidewalls and denser, higher quality steel belts.

* LT tires are designed to endure greater physical abuse than P-metric tires, and some LT's (such as the Michelin XPS Rib and Traction) are made exactly like big rig tires, using all steel construction (instead of polyester cords, for example). LT's can handle sidewall abrasions more effectively than P-metrics and are suited to off-road and construction site driving, to name a couple of examples.

* In many cases P-metric and LT tires (of the same size) hold the same maximum weight, or the LT's hold slightly less. This is due to the way the two types of tires are rated - one for temporary maximum load bearing and the other for continuous maximum load bearing.

The trade offs for these strengths include significantly higher weight, stiffer ride and more rolling resistance (yielding less fuel economy).

This is just a "primer," but it gives you a start with regard to the general physical characteristics of LT tires. Hope this helps!

 

[1sttruck]

If you have a heavier vehicle you need to be paying attention to the recommended load range and the tire pressure. My recommened load range E tire pressure ranges from something like 45 psi to 80 psi for the rear tires depending on load and speed. The speed rating is almost kind of a moot point.