E. WHEELS & TIRES

Tires are of supreme importance. Selecting the correct ones for your application is a task well worth your utmost attention. Tires may appear simple; after all, there are four on your automobile and everybody uses them. But sorting out all the sizes, shapes, numbers, treads, services and compounds can be an arduous task for a trailer. The number of combinations is limitless . . . and confusing to boot. Then there’s the wheel and all of the available bolt patterns, widths, offsets, disk styles and its capacities. It is easy to appreciate a manufacturer’s dilemma in stocking specialized wheels and tires, especially if several models of trailers are part of their line. Not only are size and fit an issue, but tires can have a profound effect on the stability of your whole rig. More information regarding the effect on stability from the tires can be found in TRAILERS-How to Buy & Evaluate.

In general, tires used for trailers must have high cornering stiffness which usually translates to stiff sidewalls. Trailer service tires, designed for use on trailers only, can be counted on to contain the features necessary for towing. They have stiff sidewalls and a cross section similar to the old “78 series” tires. These are the best choice for your trailer. If standard passenger car tires are to be used, their capacity must be reduced 10% to obtain a realistic carrying capacity when used on a trailer.

Radial tires have elicited a lot of controversy. They have been used on trailers with some success, even though their sidewalls are considered to be not stiff. Government testing has shown radials to be superior in cornering stiffness, although it does seem to depend greatly on the individual brand of tire and the actual load. Radials also hold the road to a certain point, generally above the load for an equivalent bias belted tire. The disadvantage is that when the higher give out point is reached, road holding decreases as cornering rate increases whereas a bias belt tire will continue to hold at its generated higher rate. 18 Inflation pressure is also important-marginal or under-inflated tires have reduced cornering stiffness and definitely reduced load carrying ability. Be sure to check this out before towing. Volume 3 discusses these load and tire characteristics in more detail.

Circumstances unrelated to your choice often dictate the tire you will use such as a garage full of used tires, or “my friend has a good deal” or … whatever. Just be sure you are determining the capacity correctly and taking into account the trailer’s eventual use and complete weight when you attempt to arrive at the actual capacity required. Tire capacities are marked on the outside face, making it easy to assess their capacities.

Insufficiently strong wheels can crack and come apart. Wheel failures are not something to risk. A standard passenger car rated at 4800- Ibs gross will have 4 wheels with a capacity of 1360-lbs each. Two of these on a trailer give a toting capacity of 2700-lbs less 10%, or 2430-lbs-a rather marginal number for most trailers-and certainly not the tire to use with a 3500-lb axle. Wheels, (or rims), are very often the determinate of overall capacity. Wheel capacities are not as easy to assess as tires, but they are extremely important. It is folly to use a tire rated at 1680-lbs and a wheel at 1300-lbs. Wheel capacities are sometimes stamped on the inside rim and should be checked if you have any questions. The best source for this information is the manufacturer.

Black steel wheels are a popular choice and usually readily available; they can be fitted with hub caps for a little class. These wheels with no markings and a 5-hole pattern can range in capacity from 1100 to 1800-lbs. Unfortunately, the hub cap nodes on wheels vary considerably and finding hub caps to fit can sometimes be a real chase. Painted steel spoke wheels (shown in Figure 3.28) dress up the looks of your trailer quite a bit.

They also are devoid of hub caps, eliminating the confusion in attempting to get the right size and fit. Commonly used on trailers these days; they not only look nice, but provide a place to wrap a locking chain. Fancy magnesium wheels also look great but are expensive and an invitation to thieves. The available wheels and tires are constantly changing and being upgraded. Whatever you buy, it is important to understand and know the rated capacity.