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It’s Time To Get Hitched!

Adapted from articles in Tire Review

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There are customers you will serve in the tire shop business who spend some of their time pulling a trailer behind their vehicle. These may include customers who are trailering boats, cars, horses or campers for recreation. Or your customer may be the owner a lawn care service who trailers the tools of his trade to and from job sites.

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Whichever type of driver they are, they will be dependent on your expertise when it comes to servicing their towing needs.

As an experienced technician or mechanic, you will probably be the one who has to educate them about their trailers. Find out if your customer is checking the lug nuts on their trailers on a regular basis. Ask them if they know how much air pressure their towing vehicle tires need. Most likely, they will answer an emphatic “No.”

Their lack of performing preventive maintenance makes you the one who these people should be talking to about trailers.

Can you guess the top causes for roadside trailering breakdowns? According to the February/March 2004 issue of Boat/U.S. Trailering magazine, the top three reasons for roadside trailering breakdowns were:

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#1 Flat Tires;
#2 Bearing Failure; and
#3 Tow Vehicle Problems.

Other top issues were axle and wheel problems. So, 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 may have seen serious trailer squat and trailer dive, or even seen the front axle of tow vehicles nearly off the ground. These problems cause the driver of an out-of-trim rig to experience a loss of steering and braking, precisely when he needs them both. The fact is, too many towables are not properly trimmed for highway running.

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That’s where you come in. First, you’ll need to learn about trailer tires. And you might as well learn about hitches so you can understand the whole towing package? But don’t worry – it’s not difficult.

ST Tires
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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(Well talk more about tires later in this article.)

Getting Hitched
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 and is 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.

Class III
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.

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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.

Distributing the Weight
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.

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.

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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.

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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Trailer Tires Are Special
Though the trailer tire market is relatively straightforward, a few points deserve mentioning. First, it is essential that customers select the correct tires to match their application and capacity requirements. Tires with the special trailer (ST) designation are generally built differently than tires with the passenger (P) or light truck (LT) designation. Load carrying capacities of ST tires are greater than standard tires.

As with any tire, proper inflation is important. But with trailer tires in particular, sidewalls flex if they’re underinflated. And flexing – though desirable in passenger tires for handling – is disastrous in trailer applications. Flexing leads to trailer sway, which can lead to accidents. It’s for this reason that experts generally do not recommend using passenger or light truck tires on trailers.

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The stiffer sidewalls of ST-designated tires help control sway problems, but proper inflation is also necessary. So they must be kept to the maximum recommended pressure at all times.

ST tires also have reduced tread depths that help with straight tracking. Which is why some ST manufacturers design these tires with a solid-center rib design and reduced tread depth that allows the tire to stay cool under load.

Other Essentials
Another problem – flat spotting – can occur if trailer tires are underinflated and under load for an extended time. You may want to warn your customers not to store their trailers under load for long periods of time.

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You also should ensure customers are using the appropriate load range-rated tires for their applications – it’s a matter of safety.

Customers also should be advised not to mix bias and radial tires and to use the same brand on the same axles.

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