Is Your Extra Heavy Class C Too Much For Your Tires?

[ron_dittmer]

While internet shopping for tires for my E350 small rig, I stumbled on THESE "E" RATED TIRES with a load rating that is 500+ pounds more than a typical "E" rated tire. If my rig was extra heavy and I dealt with an occasional blow-out, I would surely look into one of those 3 choices. An extra 2000 pounds of tire load capability on the rear axle, and 1000 pounds on the front would be surely be something I would consider. I am sure the ride will be rougher, but for an over-loaded rig, the ride would be my least concern.

[ron_dittmer]

pnichols wrote:
So Ron ... I wonder how the Roadian tire gets it's 3195 pound rating with only 83 lbs. of pressure? Maybe super stiff/thick material in the sidewalls that support the weight instead of relying on air pressure in a chamber supporting the weight?

Something doesn't smell right here. :h

(Where is a tire design engineer when you need him.)

I agree, it doesn't seem to add up.

I found the same exact tires sold by Tire Rack as well as Tire America. The 3195 pound rating and 83 psi max matched. So it's not a typo.

[pnichols]

So Ron ... I wonder how the Roadian tire gets it's 3195 pound rating with only 83 lbs. of pressure? Maybe super stiff/thick material in the sidewalls that support the weight instead of relying on air pressure in a chamber supporting the weight?

Something doesn't smell right here. :h

(Where is a tire design engineer when you need him.)

[ron_dittmer]

beachcomber_1 wrote:
Remember while looking at tires for more capacity, that rims have max pressure rating . My E450 have 80 psi max pressure rating.Raising the tire pressure rating should never exceed the rim rating

The Nexen Roadian CT8 HL tire with a 3195 pound rating for $134.91 has a max tire pressure of 83 psi, just 3 pounds over the rating of the E450 steel wheel. I would think that is within the margin of safety.

The General Grabber HD for $190.99 has a 90 psi max which is uncomfortable.

[beachcomber_1]

Remember while looking at tires for more capacity, that rims have max pressure rating . My E450 have 80 psi max pressure rating.Raising the tire pressure rating should never exceed the rim rating

[pnichols]

pianotuna wrote:
Hi Phil,

From a tire tech site:" For example, a LT235/85R16 Load Range E tire is rated to carry 3,042 pounds when inflated to 80 psi and used in a single application, but only 2,778 pounds when used in a dual tire application at the same inflation pressure.

This reduction in rated load capacity results in slightly larger tires being specified for the application that can better withstand the additional stresses experienced when a single tire goes flat and the three properly inflated remaining tires are required to temporarily carry the load at reduced speeds to remove the vehicle from immediate danger."

Hmmm ... I agree with the concept of duallies having a secondary function in addition to raw weight carrying capacity. That secondary function - that to me is very important - is to provide tire redundancy for safety in case one tire of a dually set should fail. However, using tricky specification manipulations - without so stating the purpose - to indirectly keep us consumers "safe" is doing us a disservice - IMHO.

I've always envied dually pickup owners because - unlike dually tired motorhomes - their trucks are rarely ever loaded anywhere near their max rear tire carrying capacities, so having four tires in the rear truly does provide outstanding backup in case one (or even two - one on each side) should fail because most of the time the one tire remaining on the one (or each) side can still carry the truck for many miles, if not indefinitely.

I've actually had that experience with our Class C. I drove several miles with one rear tire flat until I reached a small town with a tire repair shop open. Of course the Load Range E tire on the one side was way overloaded, so the motorhome felt bouncy and unstable in the rear. BTW, that overloaded Michelin tire went on to perform flawlessly for several years after that. The failed Michelin tire went flat due to failure of the plain old everyday rubber valve stem that came stock on the E450, so I was able to continue using that tire, too ... after replacement of it's valve stem (all are metal ones now).

Of course the best in the heavy rear of a motorhome would be for each tire to have a "true" load carrying capacity equal to at least one-half of the weight being carried in the rear. That would make our dually Class C motorhomes have about the rear tire redundancy safety and reliability that dually pickups have when used as a daily driver.

[pianotuna]

Hi Phil,

From a tire tech site:" For example, a LT235/85R16 Load Range E tire is rated to carry 3,042 pounds when inflated to 80 psi and used in a single application, but only 2,778 pounds when used in a dual tire application at the same inflation pressure.

This reduction in rated load capacity results in slightly larger tires being specified for the application that can better withstand the additional stresses experienced when a single tire goes flat and the three properly inflated remaining tires are required to temporarily carry the load at reduced speeds to remove the vehicle from immediate danger."

[pnichols]

BFL13 wrote:
Phil, a nitpic---the back duallies don't get the full 2680 as when single.

Right you are - if one agrees with what's published for single versus dual tire ratings. That was an oversight on my part (not enough morning coffee) ... because I intended to seem to agree with what's published.

HOWEVER, maybe deep down inside I don't agree with what's published about the dual tire versus single tire load carrying differences - because in certain applications it doesn't pass the common sense intuition smell test.

Why should dual versus single tire arrangements list different load carrying capacities ... if 1) the tires in dual configuration never touch, and 2) the tires in dual configuation still have adequate air flow between them so as to provide (real close to) the same cooling as a tire in single configuration?

To better help with 1) and 2) in my E450 MH's situation so as to keep the rear duallies inherent strength intact under a variety of situations - for all six tires I changed from the stock Load Range E 225/75R16 tire size to the Load Range E 215/85R16 tire size. The E450's stock rims and wheel well clearances presented no issues with this slightly narrower and taller tire size.

Since the 215/85R16 size is slightly narrower, the inner sidewalls of the tires are further from each other. This insures that the sidewalls never touch and also insures better cooling air flow between the tires. As a bonus (the most important to me), the taller profile also provides approximately 3/4 inch more ground clearance everywhere on the motorhome's underside.

I need a solid engineering explanation as to why the weight carrying difference between single tire service and dual tire service exists under all usage conditions? It's not intuitive.

[BFL13]

Phil, a nitpic---the back duallies don't get the full 2680 as when single.

[pnichols]

Some time ago in these forums there was a discussion of certain new higher weight-carrying rated tires that are available in "Load Range E" sizes.

I seem to remember that the discussions at the time pointed to the purpose of these higher ratings being to provide for four-tired (and hence narrow) delivery trucks that can be small overall ... but still be able to carry heavy cargo for use around cities. This being especially helpful in Europe now - but gradually being needed everywhere in high density populated areas all over the world - for material delivery by trucks that could be narrow for the streets and low to the ground for more convenient access at delivery sites.

My comments on these tires are:

1) Are these higher rated tires U.S. sourced? (Myself and some RV owners still prefer that.)
2) Of course a six-tired E450 or 4500 can still be fully served with six 2680 lb. tires, since 6 X 2680 lbs. equals 16080 lbs. total, and 4 X 2680 lbs. equals 10720 lbs. in the rear.
3) Do these higher rated tires carry more weight only with higher inflation pressures ... or are they able to do it with only 80 lbs. of maximum pressure due to stiffer/heavier material being used in their construction? Of course with heavier construction, the ride of an RV using them will have a stiffer ride at any given pressure.
4) If these tires are able to carry more weight due to heavier-duty construction, then they may be close to what I've wanted for quite some time - a "tougher tire" than the typical 10-ply rated Load Range E tire. In other words, a 16 inch rim/~31 inch tall Load Range G (12 ply rated?) tire for use on Ford E450 and Chevy 4500 based motorhomes that is more puncture-proof at 80 lbs. of pressure on down (the pressures used below 80 lbs. of course depending upon the weight of one's motorhome).

My goal is a more puncher-proof and blowout-proof tire - for both getting to/from rough off-highway exploring and camping areas, plus more safety from blowouts on the open road.

[Desert_Captain]

My E-350 has a RAWR of 7,800# and my tires are rated at 2,680 max. Since I will not be pushing the RAWR any further these E rated tires have more than enough capacity. I do bump the rear psi to 75 {from medium load of 65 psi} when running heavy and/or towing my bike and trailer {2,220#}.

Running heavy I put 65 in the fronts and medium load bump that down to 60. Also, when towing I air up my rear air bags to 50 psi to help compensate for the tongue weight {it is a single axle trailer}. The ride in either configuration is smooth and steady and passing tracks are hardly noticeable.

Works for me.

:C

[pianotuna]

Hi,

Nice find, Ron.

I was under the maximum weight for the vehicle (E-450) but overweight for the tires. I went to taller wheels and a tire that was adequate. It was not cheap--but it IS safe.

[carringb]

BFL13 wrote:
But what about the axle? Where is that wrt GAWR?

The RAWR of the E450 is 9,500 pounds. The axle itself tolerates overloading, by a lot, without issue. But you'd certainly want to upgrade the rear springs to maintain ride height and bump-travel.

[ron_dittmer]

I checked my clicky link and it works for me. That 3195 weight rating are the three choices my "clicky" takes you to. For reference, in single application, a typical "E" rated tire is 2680 pounds. That is significantly more load capable per tire regardless of how you add it up.

If your axles are also over-loaded, that is another topic. I was only sharing this information to address tire blow-outs.

[rjstractor]

The link only went to the home page. I did a search for E350 tires and found what I believe are the 3 tires you referred to. They have a 3195 lb per tire rating but it doesn't say what they are rated for in a dual configuration. If they are have similar ratings (expecting that it will be slightly lower) in a dual configuration they may be worth looking into.