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Tires and Towing: Before Your Customers Hitch Up, Check Weights, Load Capacities

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Are your customers trailering boats, cars, horses or campers this season?

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They are? Well, are they checking the lug nuts on their trailers on a regular basis? Do they know how much air pressure their towing vehicle tires need?

The most likely answer: an emphatic “No.” You are the one these people should be talking to about trailers.

This year, factory-to-dealer deliveries of recreational vehicles will set a quarter-century mark, with more than 330,100 units shipped. That’s a gain of 2.9% over 2003. Baby boomers will add to the trend as they enter their prime RV years. Expect the number of RV-owning households to climb another 15% by the time 2010 arrives.

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And, in the February/March 2004 issue of Boat/U.S. Trailering magazine, the top three reasons for roadside trailering breakdowns were listed. Heading the list was flat tires.

Bearing failure was number two, and tow vehicle problems came in third. Other top issues were axle and wheel problems. Do you see yourself fitting into this service matrix?

You should. How many half-ton pickups with a 24-foot trailer in tow can’t support 1,000 pounds at the hitch? You’ve seen serious trailer squat and trailer dive, and you’ve seen the front axle of tow vehicles nearly off the ground. And, the driver of an out-of-trim rig may experience a loss of steering and braking, precisely when he needs them both. Too many towables are not properly trimmed for highway running.

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That’s where you come in. You already know about trailer tires (and if you don’t, see the Tire Focus feature on page 45). Why not learn what you can about hitches so you can offer the whole package? It’s not difficult.

You already know that ST tires ®“ special trailer tires ®“ are designed differently than the average passenger or light truck tire. They’re required to support 10% more weight than an equivalent P-metric size tire. Wheels also play an important part in trailer towing safety.

All wheels are rated for maximum load and inflation pressure, which must be compatible with tire ratings. If you don’t find this marking on a wheel, that’s a red flag. In other words, it’s dangerous to mount a tire rated to support 3,000 pounds on a wheel rated to support only 2,000 pounds.

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Hitching Up

Now, on to hitches ®“ and how they impact tires. Hitches are grouped into five classes ®“ Class I, II, III, IV and V. Each grouping is based on trailer and tongue weight.

Hitches also come in a variety of configurations, from a ball-mounted type on a step bumper all the way up to a heavy-duty system that can transfer the trailer’s tongue weight through the tow vehicle and trailer frames.

For example, a Class I hitch is a light-duty drawbar hitch rated to accommodate 2,000 to 2,500 pounds GTWR (gross trailer weight rating) and 200 pounds of tongue weight. It is available as part of a step bumper, as a separate bumper-mount or as a combination bumper/frame mount.

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The number 200 signifies vertical pounds of tongue weight ®“ the amount of weight the trailer puts on the tongue or ball of the hitch. A basic rule for tongue weight is that it should never exceed 10% to 15% of gross trailer weight or maximum allowable towed vehicle weight.

You can find this rating, which reflects the safe loaded weight of the trailer, on a metal tag on the trailer frame. The trailer and tow truck ratings, working together, keep your customer’s investment protected.

Note that too much tongue weight will cause both the tow vehicle and trailer to sway. Too little can also cause trailer sway.

In most cases, a Class I fixed tongue hitch is used on small pickup trucks attached to a step-type rear bumper. While this type of hitch is safe when used as directed, one that bolts directly to the frame is preferred.

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Generally, a Class I hitch is used to tow trailers for very small boats or small, pop-up travel trailers. In other words: very light towing applications.

A Class II hitch, the most common one sold, is used primarily on full-size pickups and SUVs. It is designed for heavy-duty applications, such as towing mid-size travel trailers and large fishing and pleasure boats.

The Class II hitch generally supports 3,500 pounds of gross trailer weight and 300 pounds of tongue weight and is either frame mounted or receiver style.

On a receiver-type Class II hitch, expect to find some variations. One type features a ball-mount permanently built into the hitch assembly, while others use a receiver with a removable ball-mount that fits into a square hole.

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Weights and Measures

But before you take on the Class II hitch, you need to understand GVWR ®“ gross vehicle weight rating ®“ which is the total allowable weight of a fully loaded tow vehicle.

GCWR ®“ gross combined weight rating ®“ takes into account the combined weight of the tow vehicle and trailer, including passengers, cargo and fluids. If the tow vehicle weighs out at 7,000 pounds, the weight of the trailer cannot exceed 3,000 pounds.

To determine tongue weight (TW), take the tow vehicle and trailer to a public scale. Place the tow vehicle’s rear tires just off the scale deck. This will leave the trailer ®“ and only the trailer ®“ on the scale deck and still hitched. Record this weight.

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Next, unhook the trailer from the tow vehicle and weigh the unhitched trailer. The difference between the trailer weight while still hitched to the tow vehicle and the weight of the unhitched trailer is the tongue weight. Remember: Until you weigh the trailer, you can’t act on anything. You have to know the weight on each axle and where the payload is located in case it has to be repositioned.

What about the motorsports enthusiast who wants to tow a 3,600-pound racecar on a trailer with a maximum permitted gross weight of 6,000 pounds? On paper, that’s a reserve of only 2,400 pounds.

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 Note that this is before the driver heads for the track. There will be spare tires held by metal brackets welded in place. A winch will be needed to pull the car on and off the trailer. He’ll also probably bring tool cabinets, spare parts, lubricants, a generator, jack stands, coolers, lawn chairs, and so on.

With that gear, most of that 2,400-pound reserve is eaten up. That’s why weighing a trailer before every use is mandatory. So are tire inflation checks and load distribution options ®“ including a review of the load/inflation capacities of all tires.

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In the Class III hitch category, several types are available that can handle gross trailer weights (GTWs) from 3,500 to 12,000 pounds and tongue weights of 350 to 1,200 pounds. Most are designed to accept a two-inch drawbar.

Most, if not all, Class III hitches are designed to be used with a weight distribution system, the purpose of which is to transfer some of the tongue weight to the tow vehicle’s front axle and some to the trailer’s axle(s) for greater stability.

 Weight distributing systems employ the principle of leverage. Two spring bars and an adjustable/tilt ball-mount make the system work by allowing a wide range of adjustments for trailer leveling and weight distribution.

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The spring bars work like the handles of a wheelbarrow. They are inserted and locked into holes underneath the ball-mount and extend rearward toward the trailer. Chains at the ends of the spring bars are hooked to specifically hinged brackets attached to the trailer tongue.

Using a lever, often a steel pipe, the bars are lifted upward to the tongue and pinned in place. The wheelbarrow analogy works this way. As the wheelbarrow handles are raised, the weight is shifted forward on the wheelbarrow.

When properly adjusted, about 40% of a 300-pound tongue weight (120 pounds) will be delivered to the front axle of the tow vehicle. Another 120 pounds will be delivered to the rear axle(s) of the tow vehicle, and 20% (60 pounds) will be transferred to the trailer axle(s). This results in a nicely balanced tow vehicle-trailer package that is stable and easy to control.

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True, it takes a bit of homework and some hands-on experience, but in a relatively short period, you can become the trailer-towing expert in town.

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