Tire load range question

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1joester2

1joester2

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Aug 4, 2008
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Upstate, NY
I have load range "D" tires mounted on my 24" C.

Having had a few tire issues in the last week (they're original to the MH and it's time to replace them) I wonder about installing load range "E" tires instead.

If I understand correctly, it's basically an 8 ply VS 10 ply change. I imagine there would be a slightly stiffer ride, but my feeble mind tells me they would be a better tire in general.

Am I missing something like heat generation or traction, or ???
 
Actually, tires don't have "plies" anymore, so 8 vs 10 ply is just another antiquated term retained for marketing purposes, to give a relative indication of load capacity for those who don't like or understand the Load Rating index or tire loading tables. a "10 ply" tire is as strong as a 10 ply tire would have been, if that type of construction was still in use.

That said, an "E" tire probably is a bit stiffer in the sidewall than a "D" of the same make and model. It may or may not be stiffer than some other manufacturers "D" or "E".  That's because the Load Range index letter for a truck tire denotes relative carrying capacity within a tire model line and does not necessarily compare exactly to a similar letter in a different model or brand of tire, nor does it mean any specific weight carrying capacity. Confusing, eh? 

I'd go for the E rating unless a D already  provides a substantial margin in weight carrying capacity. You learn that by asking for the load capacity in lbs (the max value is stamped right on the tire sidewall) and comparing it to your actual axle weights. If you already have 25% or so extra capacity with the D rating, there is little or nothing to be gained by paying for a higher capacity tire.
 
Door jam placard ratings:
front = 4300 lbs
rear= 8600 lbs

OEM tire ratings from the sidewall:
Max load single = 2335 lbs @ 65 psi
Max load dual = 2150 lbs @ 65 psi

So I was sold an RV with the rear tires at maximum capacity? I would have thought Coachmen would have a safety margin.

Looks like load range E is the way to go.
 
It would appear that your rear axle GAWR is determined by the tires (4x2150=8600).  It's possible, and even likely, that the axle itself is rated for more than 8600# but the tires will only carry that much, thus the GAWR.  Changing the tires won't change the GAWR, unfortunately.

We have a similar situation on our front axle.  The GAWR is 9350#, exactly the maximum load rating of the original tires.  The axle itself is rated at 10500#.  We have since upgraded to load range H tires, but that doesn't change the GAWR of the coach, even though we would seem to have a bigger load capacity.
 
I guess I'm confused as to why that would apply to the rear axle only.

Just the same, I think I'm leaning towards the "E" tires, and I think a trip to the scales is in order next time we travel under full load.

Joe

I pulled out the original paperwork and found this:
Actual manufacturing weights (this is dry weight, unloaded)
LF- 1650 lbs
RF- 1660 lbs
LR- 2840 lbs
RR- 3030 lbs
I suppose I could add the fuel water, food, and other supplies to come close, but I will still weigh the unit fully loaded when I have the chance.
 
I guess I'm confused as to why that would apply to the rear axle only.
Click to expand...

Because the front axle is limited by the axle rating, not the tires.  Find out the manufacturer and part no. of your rear axle and lookup the actual rating and it's almost certainly higher than your GAWR of 8600#.

You have a decent payload based on those dry weights, but actual loaded weights are still recommended.  Then you can set your tire pressures correctly as well.  If your final loaded weights are still under the GAWR ratings, then there is no pressing reason to go to a higher load range tire as it won't change the GAWR anyway.
 
What concerns me is that the RV paperwork suggests 65 psi per rear tire, and that's the maximum raing on the tire itself.

Joe
 
I would get the E tires, even if you do not at this time reach the max axle capacity. Some day you might and I would be real nervous if the tires were at max as well. The axle probably won't break, but the tires???  It's probably not a lot more $$, though I could be wrong on that score.
 
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