RV Tech Q&A: November 2018

Selecting Trailer Tires

I currently tow a 37-foot fifth-wheel with a gross vehicle weight rating (gvwr) of about 14,000 pounds. In three years, it has had three blowouts while we were traveling. I am having difficulty getting consistent recommendations for the type of tires I should be using.

I currently have ST235/80R16 Goodyear Endurance tires on the rig but have been told
by different RV and tire stores that I should be running 14-ply tires instead of 10-ply, that I need steel-belted radials and that I should use a 235/85 size tire.

In view of the lack of consistency in recommendations, how do I select the proper tire for trouble-free running?

Robert Kiger | Redlands, California

The easy answer to your questions is to use radial tires, Robert, since that’s what most trailers are running these days. Steel-belted or fabric-belted is a hardware choice made by each manufacturer, but as long as the rest of the specifications are good, the radial-ply material is less important than the overall tire suitability.

The use of “ply rating” is fairly rare these days, although the rating still appears on special trailer (ST) tires. Today, most tires are described as “load range E” or “load range G,” and so on. Those load range E ST235s you have are rated at 3,420 pounds each for a total of 13,680 pounds of capacity, assuming yours is a dual-axle trailer with four tires. You should keep an eye on your axle weight because those tires are OK but don’t offer a lot of extra capacity for payload wiggle room.

If they could fit your trailer’s wheel wells and tire-to-tire axle spacing, the Endurance ST235/85R16 tires are rated at 3,640 pounds each for an extra 880 pounds combined capacity, which would be a decent cushion and worth considering for next time. ST tires are recommended for trailers, but you can also successfully use light truck (LT) tires, as long as they’re rated the same as or higher than the tires you’re replacing. In any case, always make sure that the tire and inflation pressure you’re running doesn’t exceed the wheel rating.


Sewer Smell

I own a 2016 Highland Ridge Open Range 3X377FLR. When we flush the toilet, there’s a sewer smell. I have taken it back to the dealer twice for this problem that still exists.

Last year I got up on the roof and pulled the vent cap to check for a restriction or blockage. That’s when I discovered the vent pipe was too tall and was hitting the vent cap. Because the trailer was still under warranty, I did not cut the pipe but instead took it back to the dealer for the third time — this time with a clue as to what the problem could be. The dealer told me that the technician cut the pipe back ½ inch so it would clear the cap. The problem has gotten better but still persists until the tank gets to about half full, and then it subsides until we dump the tank. The smell then returns until the tank is half full again.

I contacted the manufacturer, Highland Ridge RV, by email about this issue, but all I got was crickets.

Gil Meyers | Queenstown, Maryland

The vent-cap pipe solution is one method, Gil, and you might also try replacing it with one of the higher-efficiency vent caps available from the aftermarket. When the holding tank reaches half full — which I’m guessing you are monitoring by way of the notoriously inaccurate level indicators that came with the RV — the fluid is deep enough to fully submerge any solids in the tank. This stage also allows the holding-tank chemicals to circulate all around the tank interior. There may be considerable debris stuck to the tank walls, as that could explain the odor when the tank has been dumped. Regular use of one of the black-tank cleaning products on the market, such as the new Tank Blaster from Thetford, could help considerably with residual debris removal and odor control.


Condensation and Grade Driving

I have two questions. First, when we camped in Athens, Texas, it rained every day, and the left side of the camper in the cabinet above the TV was dry, but on the right side, the same cabinet was wet. The moisture was not like it leaked from rain but rather from condensation. We had to leave the door open so the air from the air conditioner would keep it dry. As soon as we closed the door, it was wet again.

Second, I read somewhere in Trailer Life that a reader used 4WD to descend a mountain grade. How does 4WD help while descending a mountain grade?

Mark Bevill | Blanchard, Louisiana

The condensation evaporates on the back side of the door when it’s exposed to the drier room air. There must be a source of moisture inside that cabinet, perhaps a damp piece of padding on the bottom of the cabinet or moist insulation or something. Empty the cabinet and look closely at all the surfaces and material, and you’ll probably find your moisture source.

I don’t recall us publishing anything about 4WD helping on a downhill grade, so I can’t address that specifically. In general, 4WD will not help on a downhill from a traction perspective, although there’s an element of accuracy here. Shifting into 4WD low range in the transfer case means the powertrain has a significantly lower (higher numerically) gear reduction between the engine and axle. In the old days with manual locking hubs, you could leave the front axle hubs unlocked, so even with the vehicle shifted into 4WD low range, you would be working with the rear axle only, and the front axle would still be freewheeling. That extra gear-train reduction would help make better use of the engine-compression holdback, and in turn help you move more slowly down the hill. To avoid over-revving the engine, you’d need to move at a very low speed, in the 30-to-40-mph range at maximum, so these maneuvers are typically reserved for short distances.

As such, although it can be done with old-style manual 4WD systems and locking hubs, but not newer auto-locking hubs, very few people use 4WD to aid with downhill driving. As a choice for a tow vehicle, 4WD offers more traction on loose surfaces, and low range gives slow-speed control for backing into campsites and such. Additionally, some truck manufacturers are offering a hill-descent feature that aids in safe off-road hilly driving.

See Related Story:
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