RV clinic & performance

straight talk from the TL Tech team

Tow-Rating Topics

In the last several years I've seen letters relating to problems encountered when the tow vehicle and trailer are not properly matched. I'd like to learn about selecting the best combination before I make my next purchase to avoid future problems. Is it sufficient not to exceed the vehicle's maximum tow rating, or, based on your experience, is there a recommended "rule of thumb" such as not exceeding 80 to 90 percent of the maximum tow rating? Would your recommendation be the same for hauling either a travel trailer or a fifth-wheel?

If one does not specifically require a longbed pickup for the model of a fifth-wheel trailer chosen, are there other considerations for having a longbed versus a shortbed? Does the longer wheelbase of a longbed pickup offer better towing characteristics than a shortbed truck of the same model? Would this be true for either a travel trailer or a fifth-wheel?

What is the tradeoff between staying with a lower axleratio option and using a larger engine, as opposed to using a higher axle-ratio with a smaller engine? For example, a Chevrolet/GMC truck with an automatic transmission and a 4.8L engine with a 4.10 axle will provide the identical tow rating as a 5.3L engine with a 3.73 axle ratio. Which combination is preferable?

R. PAUL MERCER

TUCSON, ARIZONA

* Wow, your questions cover a lot of ground. Based on the queries we receive, I'd bet a lot of people have similar concerns, so we'll give it a whirl.

There is no "rule of thumb"for utilizing only a certain percentage of a manufacturer's tow rating. However, we get a lot of letters from people who say they wish their rigs had more power, and the more reserve you have, the happier you'll be with performance. I like a 20 percent margin because most people underestimate the weights of their tow vehicle, trailer, passengers,fuel and cargo by about that much and this leaves a cushion.

Assuming the cabs are the same, longbed trucks have longer wheelbases, and all other factors being equal, longer wheel bases are more stable platforms for towing. All of this applies to both fifth-wheel and conventional trailers.

All other factors being equal, optional larger-displacement engines perform better for heavy trailer towing. Smaller engines use less fuel while idling and under a light load (solo). However, since gasoline engines need richer air-fuel ratios as they approach full throttle, as load increases the smaller engine (assuming the same truck and load) reaches the point where it needs a richer mixture sooner than its larger cousin. That is the main reason why the fuel economy of small engines tends to drop by a greater percentage than larger engines when they're towing. In order to spec out the best engine foryour use, you have to consider what percentage of the time you intend to be solo or towing and what level of performanceyou demand.

Trailer Wheel Heat

We recently purchased a used travel trailer, a 1994 Coachman 25-foot model, and before towing it 30 miles to our house, I replaced the bearings and added grease. After pulling the trailer 30 miles, I noticed the rims and back of the hub of the first set of wheels were extremely hot! I adjusted the brakes and I still get some drag on the first set but not on the second set of wheels. Is there anything else I need to do?

DAN MANOLAKIS

DENVER, COLORADO

* There may be several factors at work here, Dan. Brake assemblies and wheels on RVs get hot for several reasons including dragging brake shoes, dragging brake magnets, improperly-adjusted bearings or a brake control that's incorrectly feeding current to the trailer brakes when the tow rig brakes are not applied.

Since you just did the bearings before moving the trailer, that's where I'd start your search. Check the retaining castle nuts for proper adjustment and wheel freedom of motion. Now check all of your brake wiring connections including the positive feed lines and the ground wires. Use a multimeter to test for current flow at the axle magnets with the trailer plugged into your truck and the truck running, but no one touching the brake pedal. There should be no current flow until the brakes are activated on the tow vehicle, then there should be current detected at each wheel.

Copyright T L Enterprises, Inc. Aug 2001
Provided by ProQuest Information and Learning Company. All rights Reserved