Somebody explain "tire weight class" to me.

Discussion in 'Tires | Wheels' started by BadDog, Mar 17, 2005.

  1. BadDog

    BadDog TRC Staff Staff Member

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    I know "class D" and "class E" and what is recommended for what. But how is it my 285/75-16 Class D tires are rated for more weight than my old 245/75/16 Class E tires? I went with them based on the weight rating, but obviously I'm missing something about the class rating system since it seems it should go in hand with the weight rating...
     
  2. RJF's Red Cummins

    RJF's Red Cummins TRC Staff Moderator

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    The larger size maybe?
     
  3. BadDog

    BadDog TRC Staff Staff Member

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    But I don't understand why it's not consistent for weight? How is it a 2" larger diameter tire has a lower class and higher weight capacity?
     
  4. Burt4x4

    Burt4x4 Well-Known Member

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    Good question, mabye the sidewall ply has to do with it? 8ply vs. 10ply? What really is that anyway?

    HighJack ~ did you have to modify your rig to get the 285's to fit? Are you at factory hight still? What year is your rig again? I am definatly going bigger than the 245's I have now...
    End HighJack ~ :D
     
  5. BadDog

    BadDog TRC Staff Staff Member

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    Mine is an '02. '01-'02 can run 285/75-16s (basically, 33s) with little or no effort. I didn't crank the bars *at all*, and mine have never rubbed anywhere but on place there is a useless "bump" on the plastic fender liner on the driver's side. Looks like maybe there was something going to go back there at one point, but nothing there on mine. Anyway, I turned the tire to the point where it would rub intermittently (but only when turned just right AND leaving a parking lot or something uneven). I then heated it with a heat gun and shoved some 2x4s in between the tire and the hot/soft plastic. Let it cool a bit and then heated it again from the outside (inside the fender) and let cool again. Removed 2x4, liner held new shape minus bulge, and no rubbing to this day. Some claim they had to trim the bumper air dam or space the bumper out 1/2" or so, but I have never touched it.

    Now, the '03+ are a different story. With the change in sheet metal came a slightly smaller wheel opening. I've seen several reports of having to "crank" quite a bit to fit 285s with no rubbing. Some cranked and trimmed and spaced the bumper to get rid of all rubbing. Basically, for '03+, 285s are right on the edge of what you can run without a lift. And I wouldn't recommend it since "cranking" or any lift mechanism out there (ranging from "cranking" and "keys" to full "kits" is going to cause longevity problems for the CVs. I would just stay with 265/75-16s or similar for these trucks.

    IMO, I would *not* lift it beyond factory spec unless you are willing to sacrifice durability and dependability for looks, which is what it amounts to if you don't really NEED the bigger tires. How much functional difference is 265 to 285 anyway? I went to the largest tires possible without lifting to drop my highway rpms and because the "roller skate" look of the 245s didn't appeal to me. So I got the largest tires I could fit with no mods, lowered my rpms, got better clearance for fire road and camp duty, and improved the looks (IMO) without sacrificing anything but the cost of the tires.

    I'm pretty much the anti-lift representative here so, take it for what it's worth, but I wouldn't lift any tow/daily driver rig that was not also expected to do serious off-road duty. The trade-offs are just not worth it in my book.
     
  6. Burt4x4

    Burt4x4 Well-Known Member

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    Oh yes I totaly agree with you 100% on not lifting my towrig. I have zero intentions on changing my suspension. This is my tow rig not my offroader, I got that coverd:pimp: I do want bigger tires so 265's are on my radar in the near future. Thanks for clearing up the differnt years for me toowaytogo
     
  7. BadDog

    BadDog TRC Staff Staff Member

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    Great, glad I could help. It's amazing how many people seem to think that "crank the bars" is a good way to get some "free lift" or "level their truck" and they really don't seem to understand what that means (and costs). And this in turn leads to IFS's undeservedly bad rep for durability.

    Now that we are WAY off in left field, lets return to your regularly scheduled "tire weight class" discussion... ;)
     
  8. BadDog

    BadDog TRC Staff Staff Member

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    LOL! And I thought I was just ignorant or overlooking something. Can it be that ALL OF US are just blindly listening to tire class "requirements" and making decisions based on that "class", without a clue what it means?

    Load rating I can understand. N pounds per tire and all that. Very straight forward and no confusion, who would want or need "classes" for tires if that's all it was? Usually a "class" is used to represent how several different factors work together for overall "ability" so that you just look at the class, and don't have to know exactly how the pieces fit together. For instance, speed ratings for tires have to do with internal heat resistance, compound, centrifugal force resistance and so forth all combined into a "rating" that at a glance tells you if it's suitable for the cars intended use.

    I can't help but wonder if load range class is the same. And if so, what makes it different than just weight rating? Maybe it's somehow relating side-wall stiffness to resist "wagging" or "pushing over" with load, where the weight rating is just how much it can reasonably support rolling down the road? In other words, weight alone is a maximum and "load rating" tells you how well it can control the load. Which would explain why the taller side wall 285/75-16s have a higher weight rating but are only Load Range D; and the shorter side wall 245/75-16s have a lower weight rating but are Load Range E. Makes sense, but I want to hear from someone that knows how this fits together...
     
  9. Super Trucker

    Super Trucker Well-Known Member

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    Load range applies to the # of plys where load rating is the amount of load it can carry. Normally as the range goes up so does the rating.
     
  10. BadDog

    BadDog TRC Staff Staff Member

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    I've heard that about being related to the number of plies too. But if it's just number of plys, why not just say, number of plys? Why come up with the whole load range thing? I'm sure that's part of it, but I'm betting there is more.

    And as I said, my specific tires are load range "D" and have a higher weight rating than my old "E" tires did. That's what has me confused.
     
  11. Super Trucker

    Super Trucker Well-Known Member

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    As an example in big rig tires of the same basic size. 12x24.5 bias ply load range F tires have a lower rating than 12Rx24.5 load range G tires. Which have a lower rating than 12Rx24.5 load range H tires.

    I think "load range" is a hold over from the older days when it meant that "LR" had "X"# of plies. But when you change the size of the tire the weight rating could go up or down as with your tires.
     
  12. BadDog

    BadDog TRC Staff Staff Member

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    So basically, load range is pretty much irrelevant, just look at the weight rating? That's basically what I did when I chose my tires, but I've always had a nagging feeling that I was somehow missing something and maybe making a mistake. Thanks for the info…
     
  13. Super Trucker

    Super Trucker Well-Known Member

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    Load range does mean something when coparing the same size tires. I went from LR "D" tires to LR "E" tires in the same size for the heavier weight rating. Also as LR goes up so does the amount of air in the tires. In the big rig tires I listed above the max psi is 90, 110, and 120 as the LR goes up. The cost goes up with each jump of LR in the same size tires.

    But when changing sizes you might be able to get the weight rating you need in a cheaper lower LR tire of a different size.
     
  14. BadDog

    BadDog TRC Staff Staff Member

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    Ok, I see that. But if I understand correctly, even in the same size tire, you could just go my weight rating and pretend there was no such thing as a "load range", and things would be no different. The max pressure is also directly specified, so I see no use at all to the load range. It seems to add nothing of value. :dunno:
     
  15. Super Trucker

    Super Trucker Well-Known Member

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    Well in some ways its like 1/2 ton vs.1 ton trucks. In the old days a 1 ton truck could carry 2000 lbs. But now say a 2wd C3500 that tares at 7k and has a gvwr of 10k, that should be a 1.5 ton truck.
     
  16. BadDog

    BadDog TRC Staff Staff Member

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    Sweet! Perfect example to beat that home! I wasn't looking at it in the right light oh "history" and the way that stuff just lingers on forever... :doah: waytogo
     
  17. BadDog

    BadDog TRC Staff Staff Member

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    Bringing this back to the top to tie into some good references and comments in the latter part of this thread.
     
  18. mbwagoner

    mbwagoner Well-Known Member

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    The wider the tire the higher the capacity
    The higher the load range the higher the capacity

    There is a point where they pass each other and a lower load range will have a higher capacity due to it be wider. The load range effects how much presure you can put into the tire, allowing more weight. An E range tire will be stiffer and feel more solid than a D as well.
     

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