tiredler- what does "109S" mean? I have a 2000 F-150. The door sticker says to use the following: 255/70R17 109S. I thought the S was a speed rating but what about the 109?

 

It just came to me, I recall the tire catalogs state, if you put P metric tires on a light truck the load rating is less than stated on the side wall.

It seems strange that they would make a P metric 265/75-15, that clearly is a light truck tire size, but warn you that if you use it on a light truck, the load rating is less.

All you have to do, to compare the difference between a P metric, and an LT tire, is pick then up, the LT tire is a lot heavier.

 

This one's not the easiest to answer in short form. No one comes right out and says it directly. It basically has to be a conclusion that is drawn. The best way to do that is to ask the question "why do truck tires get a load range that refers to ply's and passenger tires don't?" In a nutshell, the more plys the stronger the tire and it's ability to resist flex. You wondered how I made a comparison between the two terms. There is no comparison between these two terms, and that's the problem. People use a tires max load as the determining factor when they are comparing tires without understanding that a D rated tire is not, by definition and classification, as strong as an E rated tire. So to make a long story short, so I can get off the computer, which in turn will get the wife off my back. Higher load range/ply rating = stronger sidewall strength = greater risistance to horizontal load.

 

I have done some further research. On my own: Oh My God! EviroCon is right. Load range refers to the strength of the sidewalls to handle sideways stresses. As the web sight put it the rear truck tires when towing tend to squirm more and these horizontal stresses are what the resarch Load Range refers to; the D and E designations. The Maxium Load refers to the vertical weight. So my P tires seem to have what it takes to handle the vertical load 2601 lbs but not the horizontal squirm or sidewall load.

 

Does that apply to whitewalls also?

 

Yes. All tires are subject to both vertical and horizontal load. So they all have a corresponding Maximum Load (Vertical) and a Load Range (Horizontal).

 

the 109 is a European load index #, it's really not used here, but it refers to a corresponding weight rating 109=2271max load capacity @ max inflation

 

Again i ask where do u get the maximum load=vertical load, and load range = horizontal load info???

maximum load capacity is the maximum weight capable @ maximum inflation.
Load range is a term that has replaced the old term "ply or ply rating".
ie 4ply rating=load range B
6ply rating=load range C
8ply rating=load range D
10ply rating=load range E..and so on. i Have never seen any correlation between max load=vertical load, and load range = horizontal load

 

LT tires are made in several load ranges. the higher the load range, the stronger the cord use in constructionof the carcass. The belt package and the bead area are also beefed up. The stronger cord, bead,belt allow for higher inflation pressures, hence higher load capacities. The tires lateral strength is increased as well by the use of the stronger(heavier) materials, and the increased inflation pressures.

 

tiredlr- Your last post just answered your own question on how you can correlate load range with horizontal forces. Keep in mind that saying load range=horizontal, and a tires max load=vertical is a over-simplification, or a breaking down of the entire issue into it's most useful variable for the purpose of determining whether or not a tire is the proper one for the job. In this case towing a 9000# trailer. If I were trying to determine the best tire for mudding I might choose a different variable to focus on. Now I have a question for you. If, as you say the higher the load range, the higher the load capacity, i.e. E tires have higher load capacities than D tires, then how is possible for a D tire to have a higher max. load rating than a comparible E tire?

 

The Good News: Carmax where I bought my F250 is going to replace my P tires for LT Load Range E. The truck from the factory calls for 50 lbs up front and 70 in the rear. The P's only carry 35.

I asked Jeeves about the difference between the designation Load Range and Load Capacity. It seems to me the difference hinges on this. Load Capacity is the amount of weight a tire can sustain in a static or stationary position. In my case the P's are labeled 2601 lbs. This appeared more than sufficient to me. But as I have learned thanks to you all and to Jeeves there is another very important factor.

That is most normal beings do not keep there vehicles stationary very long. So the forces of the weight, bumping and turning of the wheels cause other forces to come into play on the sidewalls. These are the so called horizontal forces. Yes the old ply ratings and the current C, D, E ratings are I guess the same thing. The site I found used the word similar to squirm etcetera for the movement of the tire under load.

Anyway this has been a great exprience for me ending with my call to Carmax. They immediatle said "If the tires are not the right ones we will replace them." I drove out there and their examination confirmed that the tires are not adequate. I expect to have the correct tires on it within a day or two.

Thanks to you all again. This is the first vehicle I have purchased from Carmax. Their used vehicles are sold almost as if they were new. They are very high quality and they have been great to me. If you put your Carmax car in their shop for service they give you a loaner. Does anyone know of a used car dealer that does that?

Florida here I come!

High Road
F250 Diesel Crew pulling a 31 King of the Road.

 

SIZE FOR SIZE A LOAD RANGE E TIRE WILL ALWAYS HAVE A HIGHER LOAD CAPACITY THAN A LOAD RANGE D. IT IS POSSIBLE FOR A LOAD RANGE D TIRE TO HAVE A HIGHER CAPACITY THAN A LOAD RANGE E, IF IT'S ALARGER SIZE TIRE(MORE VOLUME OF AIR). AN EXAMPLE A 285/75R16 LOAD RANGE D,MAX LOAD #3305@65PSI VS A 245/75R16 LOAD RANGE E ,MAX LOAD #3042 @ 80PSI. THE TERMINOLOGY MAX LOAD RATING AND LOAD CAPACITY ARE THE SAME. IF A TIRE HAS A MAX LOAD RATING OF 3042, IT WILL HAUL THAT WEIGHT SAFELY VERTICALLY, HORIZONTALLY . END OF STORY

 

I was just going to chime in with the same thing.

Load ranges mean absolutely jack.

It's all about the max load rating of the tire.

 

I do not think we are coming to the correct conclusion here. One member hit it on the head when he said that my P tires will work for a little while but they will not last long. And several said they were afraid I would wind up in a ditch. It is not because of the Maximum Capacity that they said this but it is because the Load Range or Ply rating is not sufficient to take the abuse over time.

5200 lbs of capacity is enough to carry my tongue weight. P tires are rated Standard Load carrying 35 PSI and Extra Load carrying 41 PSI.

 

HighRoad,

No mattter how you look at it, P tires are not designed to be on a 3/4T Truck and tow a 5th Wheel.

I'm in a Travel Park in Florida at the moment. Numerous 3/4T/1T trucks here that tow 5th Wheels and regular trailers and all the guys I know personally use Light Truck tires.

Consider yourself fortunate that the dealer is going to switch them out for you. I have bought Michelins and Continentals (E). They are not cheap. But, you need them.

Ray