Brand: LT tires are best choice for trailer-towing truck

Q: We have a 28-foot travel trailer that we tow with a 2012 Ram 1500 4X4 with a 5.7-liter engine. The trailer has a loaded weight of approximately 7,700 pounds. I suspect tongue weight is just over 900 pounds.

I have an Equalizer weight transfer hitch that has built-in lateral stabilization. The truck has "P" standard equipment Goodyear Wranglers on it. I have kept the pressure at the recommended 36 psi. I have asked tire dealers and RV dealers about proper tire pressure, but have not received a definitive response. I believe the sidewall of the tire indicates a maximum psi of 40. When the trailer is loaded and hitched up, I do not notice any "squat" in the tires. Do you have any recommendations for proper tire pressure while towing? I will also probably be replacing the truck tires within the next year. Would it be better to go to an "LT" tire versus a "P" tire? An aggressive tread is not necessary as most of my miles are highway. I do some ice fishing, so an all-weather tread is adequate.

A: The trailer weight and tongue weight are probing the upper limits of your truck's towing capacity. According to the vehicle's specs, maximum trailer weight is 8,900 pounds and max tongue weight utilizing a receiver hitch is 1,045 pounds. Perhaps the key specification is the GCWR — gross combination weight rating. This is the maximum weight of the truck/trailer combination. For your rig, that number is 14,000 pounds. The GVW — gross vehicle weight — of your truck is 6,350 pounds fully loaded. If your truck is fully loaded — fuel, people, gear and payload — while towing your trailer, you are flirting with the very upper limits of the GCWR for the truck — 14,050 pounds. In practical terms, you have barely enough "truck" for the job.

Regarding tires, I think the LT — light truck — tires would be a better choice for your vehicle for the simple reason that LT tires can carry a higher load than the same size P-series passenger car tires. It's a bit confusing, but a P-series tire fitted to a light truck/SUV can only carry 91 percent of its rated capacity. Why? Higher center of gravity and more likely to be overloaded when fitted to a truck, so tire makers have to build in an extra margin of safety into P-series tires.

LT tires, on the other hand, feature heavier body plies, bigger beads, more tread depth and in general a stronger, more heavy-duty design that allows higher inflation pressures to carry heavier loads. P-series tires are lighter, more fuel efficient and ride better. LT tires may ride somewhat harsher when the truck is empty or lightly loaded but are stronger and better suited to heavy loads and towing, for which you qualify on both counts.

Comparing Bridgestone Dueler A/T RH-S P275/70R17 versus their Dueler A/T RH-S LT275/70R17, the P-series tire when mounted on a truck/SUV can carry 2,305 pounds at 44 psi. The LT tire, on the other hand, can carry 2,470 pounds at 50 psi.

If you are going to run the P-series tires, I'd suggest inflating them to 44 psi. But I certainly think the LT series tires would be a better choice for your truck.

Motoring Note — In regards to possible causes for intermittent operation of a remote keyless entry/start system, this from Mike Grant: "What type of car does this guy's neighbor park in his driveway? I had a friend who had a similar problem when trying to start his car at home. His neighbor had a simiar, one year older car and would unlock his car, then lock each time he left his house. So home from work (1), then out to the store (2), then return (3), and off to work the next morning (4) and BINGO, that's four false strokes for my friend's car, which was well within range, and the security system locked him out. Might be worth checking for such crosstalk."

Excellent suggestion, Mike, thank you!

Paul Brand is the author of "How to Repair Your Car" and "How to Repair Your Truck and SUV," published by Motorbooks.