Beasts of Burden
Picking the right tow vehicle
Story Wayne Scraba
During the dog days of summer – at least in our neck of the woods (tourist country) – a common site is an overworked RV stranded on the side of the road, hood up and engine steaming. Honestly, just because a given car, truck or RV can have a hitch fitted doesn’t make it a tow vehicle.
It doesn’t matter if you’re hauling a trailer for a collector car, camping, boating, powersports, biking or a race car, the single most important piece of equipment you’ll require is a capable tow vehicle. Without a truck (motorhome, van, etc.), you simply cannot move your trailer with any kind of safety to the final destination. Obviously, every hobby has different demands, and that means everyone will likely place different stipulations upon the tow vehicle. Some folks prefer the comfort and convenience of a motorhome. Others appreciate the versatility of a pickup truck, while others value the passenger-carrying capabilities only a van or a Suburban can offer. Still others have trailers and equipment so large, a conventional pickup truck is actually out of the question. In any case, to ultimately arrive at your destination (and to arrive safely), there are a number of things to consider.
So which combination is best suited to trailering? That depends upon your requirements, but no matter what your personal towing preference, you still have to purchase the right tow vehicle (with the right equipment) to get the job done. If there is any secret to trailer towing and setting up a given vehicle for the task of tugging a trailer, it involves determining the total combined loaded weight of the tow vehicle and the trailer. This weight is referred to as the Gross Combination Weight Rating or GCWR. Each and every truck, car or motorhome has a maximum GCWR that will allow for satisfactory performance when towing.
How do you arrive at the GCWR? It’s not that difficult. Most trailers will have a “Trailer Manufacturing Rating” stamped on the trailer ID tag (usually affixed to the left front of the trailer frame). This tag will indicate the weight of the trailer. Next, you have to figure out how much equipment you’re going to carry. This includes the weight of everything in and on your trailer, including support equipment, tools, spare fuel, oil, water and so on. The total loaded trailer weight is then added to the total loaded weight of the tow vehicle. Keep in mind that the total weight of all passengers, luggage, supplies and other equipment loaded into the tow vehicle must be included in the total GCWR figure (more on GCWR later).
In order to determine tongue weight, most automotive manufacturers point out that you can simply use 10 percent as a basis for dead-weight hitches and 12 percent as a basis for weight-distributing platform hitches (sometimes called an equalizer hitch). When towing a trailer, you have to add the tongue load to the GVWR (Gross Vehicle Weight Rating) of the tow vehicle, because the truck will be carrying that weight too. The manufacturers also suggest it’s a good idea to weigh your trailer and the tongue separately after the trailer is loaded. Carefully planned trailer loading can be used to juggle the tongue weight percentage.
Once GCWR and tongue weight have been calculated, you can determine the type of hitch assembly required for your tow vehicle. The lightest type of hitch is commonly referred to as Class I assembly. These are light-duty pieces designed for a maximum trailer weight of up to 2,000 pounds and a tongue weight of no more than 200 pounds. The common rear step bumper found on a truck is capable of handling this weight (both trailer weight and tongue weight). A ball size of 17/8 inches is typically required for use with these lightweight trailers. Few, if any, serious equipment (boat, race car, etc.) trailers fall into this category.
Class II and Class III hitches are almost always skipped over by the Detroit automobile manufacturers, simply moving to the large Class IV hitch assemblies when the trailer weight exceeds 2,000 pounds. The one exception to this rule is certain pickup trucks with rear step bumpers carrying a 4,000-pound trailer weight rating and a 400-pound tongue weight rating. A two-inch diameter ball is required in all applications up to 4,000 pounds.
The typical Class IV hitch package is designed for use with trailers up to approximately 8,500 to 10,000 pounds with tongue weights of between 800 and 1,200 pounds. There are a number of different tow vehicles capable of pulling a trailer in this range, but always remember that a trailer of this size is large. Class IV equipment normally consists of a hitch platform that is bolted to the truck frame through pre-punched holes. The hitch ball, anti-sway and equalizing equipment must be purchased from aftermarket sources. Hitch ball diameters are commonly in the 2-inch to 25/16-inch range with platform hitch packages. Certain Class IV platforms are welded to the frame in addition to the bolting procedure. This is acceptable as long as the welding process is done correctly.
Class V hitches are similar to Class IV versions, but they’re larger. For the most part, Class V hitches were originally designed for commercial or agricultural applications. Where a typical Class IV hitch will be based around a 2-inch square receiver, a Class V receiver measures 2½ inches and is rated at 10,000 pounds. With a weight distributing assembly, the total weight rating typically goes up to 14,000 pounds. This sort of hitch is typically limited to use on full size, one ton or larger trucks.
What about equalizing devices? According to the manufacturers, trailers that exceed 4,000 pounds mandate some sort of weight distribution device. In practice, this system is based upon a weight-distributing hitch, which disburses tongue weight to all axles of the tow vehicle and trailer. This allows vehicles to tow heavier trailers with less sagging at the rear and improves steering and brake control. A weight-distributing hitch system includes a hitch head that fits into the receiver-tube opening, spring bars, and hook-up brackets that connect the spring bars to the trailer frame.
The last type of trailer hitch assembly commonly found on light-duty trucks is the fifth-wheel assembly. Fifth-wheels are hitches in the bed of a pickup that include a plate, like on a big rig, whereas a gooseneck is a ball in the bed that gets mounted directly to the frame. There are two types of fifth-wheel assemblies manufactured today. The first design has a fifth-wheel mounted on a bar, which is supported by brackets mounted to (or over) the rear wheel fender housings. The kingpin is then mounted to the trailer. The second type of fifth-wheel hitch features a kingpin mounted in the bed or box of the pickup truck while the actual fifth-wheel is attached to the trailer. The fifth-wheel hitch is not supplied by any truck manufacturer. Instead, it is supplied by the trailer manufacturer or an aftermarket vendor such as Reese or Draw-Tite.
The tongue weight or load of a fifth-wheel or gooseneck trailer is often greater in percentage than that found in a conventional tag-along trailer. Because of this, you have to be very careful with the truck GVWR, as well as the maximum allowable payload of the tow vehicle. Due to the weights involved, most big fifth-wheel or gooseneck trailers mandate trucks with dual rear wheels.
In all cases from Class I to the large fifth-wheel rigs, you should first consult the trailer-towing guides provided by the Detroit vehicle manufacturers. A lengthy list of GCWR packages for all of their respective trucks is included in those trailer guides. It’s a very good idea to peruse this list of specs completely before deciding on the truck for a given application. One word to the wise: The use of a truck that is too heavy for the intended trailering application is always better than using one that is too light.
Generally speaking, the larger the truck and trailer package, the larger the tire required. Tires are best selected by the “bigger is better” method. All modern trucks have a certification/tire label on the rear edge of the driver’s door or in the Incomplete Vehicle Document in the cab (the Incomplete Vehicle Document is used when a truck is converted into a motorhome or other custom body). This label shows the size of the original equipment tires mounted on the truck when it was new and also shows the inflation pressures needed to obtain the gross weight capacity of your vehicle. This is called GVWR or Gross Vehicle Weight Rating. The GVWR includes the weight of the vehicle, all occupants, fuel and cargo (don’t confuse this with GCWR – which includes the trailer weight). The certification/tire label also tells you the maximum weights for the front and rear axles (called Gross Axle Weight Rating or GAWR). To find out the actual loads on your front and rear axles, you need to go to a weigh station and weigh the truck. You should never exceed the GVWR for your vehicle or the GAWR for either the front or rear axles on the truck.
Don’t forget about the truck spare tire either. Spare tire location and the method of deployment can also prove important in trailering combinations. Some trucks might be best equipped with a box-mounted spare, while others are best arranged with under-chassis assemblies. Many manufacturers offer special crank-operated spare tire carriers or glide-out models that simply take the drudgery out of spare tire removal and installation. Remember that the type of trailer you tow can have an influence on the operation of the crank-out mechanism. In addition, the type of spare is also consequential. When the truck is loaded to maximum capacity and you have to get somewhere with a fully loaded trailer, you’re far better off with a matching (correct capacity) spare than a generic tire.
Harnessing the Power
Trailer wiring harnesses are another prime ingredient of towing. Most truck manufacturers offer factory-installed trailer wiring harness assemblies as standard or optional equipment. The first type available is a common five-wire harness. This is a light-duty harness for use with trailers without brakes (typical Class I trailers). The second type of harness available on most pickup trucks is a heavy-duty, seven-wire assembly. It’s designed for use with trailers exceeding Class I, which require the use of trailer brakes. In some instances, the connector is not included with this harness, but all of the applicable wiring is routed to the rear of the truck and tie-wrapped to a frame member. If that’s the case, you have to supply the correct connector for your specific trailer and trailer brake arrangement.
The electrical system on the tow vehicle will also require upgrading in towing applications. Remember that the truck now has to contend with a number of added loads on the power supply and storage system. These loads include the need for charging the trailer battery(s), additional lights, trailer brakes and so on. Because of this, all of the Detroit manufacturers offer heavy-duty alternators in the amp range of 100 to 130+. These heavy-duty alternators are designed to cope with the increased demands placed upon them, and in most cases, they’re either part of a towing package or available optionally. The same applies to heavy-duty batteries. Start with the largest capacity battery available for your truck. In most applications, a battery carrying a 600+ cold-cranking rating will be required for towing purposes. Another electrical option that is readily available (and ideal for race car haulers) is an auxiliary battery. Most Detroit truck manufacturers offer a dual-battery setup. Although this does not ensure double the cranking power, it does guarantee that you will have at least one fully charged power source. Most auxiliary batteries are rated at 500+ CCA. That’s enough capacity to boost-start the truck (or the car on your trailer) if necessary. In addition, this battery can supply power for any number of accessories that might come into use while running or parked.
When it comes to engine, transmission and rear-axle combinations for towing, opinions are diverse. However, virtually everyone agrees on one thing: If you tow in any type of terrain with grades, bigger is always better. For example, we’ve had extremely good luck towing on the flatlands of the Great Plains with a small displacement V-8 pickup. The moment that same truck rendezvoused with the Rocky Mountains, it howled, “Enough!” Mother Nature can become a great equalizer in these situations, and you’ll end up kicking yourself for not purchasing the largest power source available for the GVWR of the truck you select. All three Detroit truck manufacturers offer a wide array of engine, transmission and rear axle choices. In each of those situations, the truck manufacturer can provide a recommended powertrain combination for a specific GCWR package.
Here’s how the math works (and intertwines): The Sierra crew cab 4X4 has a GVWR of 7,000 pounds. With the 403hp 6.2L engine, six-speed automatic transmission and 3.42:1 rear-axle ratio, along with a heavy-duty cooling package, GMC has determined the maximum trailer weight (loaded) is 9,300 pounds. That means the GCWR (Gross Combined Weight Rating) of the rig is 16,300 pounds, including the truck, trailer, everything on the trailer and everything in the truck (including you and your passengers). Similar recommendations (minimum engine size, transmission type, rear-axle ratio, truck GVW) are made for every truck manufactured.
Keep in mind that the power output of the engine, the transmission combination and the rear-axle ratio can add up to much improved reliability in the total trailering package. In most of today’s trucks, you can specify either an overdrive automatic or, in select cases, an overdrive manual transmission. These gearboxes typically feature an overdrive ratio of roughly .70:1 in high gear. Simple math proves that a pickup truck fitted with a 4.56:1 rear axle and a .70:1 overdrive works out to a remarkable 3.19:1 overall ratio. This allows you to tow in the highest non-overdrive gear, but when the truck is empty, you can operate it in overdrive. Properly equipped, the truck will live longer, will perform better under load and will prove easier to drive.
Built to Haul
Extra capacity cooling systems are important in a towing application (that should be a no-brainer). As trailer size and the overall package weight increases, so does the demand for additional cooling. The normal powerplant coolant operating range will increase as the truck is burdened with additional weight or long grades. At the same time, the transmission (automatic) will also require additional help and so will the engine oiling system. As you’re no doubt aware, a certain amount of powerplant cooling is provided by the lubricant. As the demands on the engine increase, the need for additional cooling also increases.
For the most part, trucks equipped with air conditioning are fitted with larger capacity radiators, heavy-duty clutch fans (often with increased pitch on the fan blades) and/or auxiliary electric fans. These features all ensure that the maximum amount of air is pulled through the radiator. In addition to this increased cooling efficiency, you should also consider factory-fitted, heavy-duty transmission coolers (for automatic equipped trucks), heavy-duty radiators and auxiliary engine oil coolers. All of these items can be included in the manufacturer’s heavy-duty cooling system, towing package, or combination of the previously mentioned components. The heavy-duty automatic transmission cooler can include a larger radiator tank and/or separate transmission oil cooler. The auxiliary engine oil cooler is just as the name implies – a separate radiator is plumbed into the engine’s oiling system.
Heavy-duty suspension components are normally determined by the GCWR ratings, but many of the manufacturers do not include heavy-duty shock absorbers or large diameter stabilizer bars in their entry level towing packages. Does four-wheel drive offer a towing advantage? Not if you tow in normal conditions. Obviously, it’s some assistance when towing in snow or mud, but for most auto enthusiasts, that isn’t a pressing issue. You’ll often find that four-wheel-drive trucks actually have a lower GVWR and lower GCWR than their two-wheel-drive relatives.
Auxiliary or larger capacity fuel tanks are also good towing investments. The added range is more of a convenience than anything else. But if you find that filling a small tank frequently becomes a chore, you’ll quickly appreciate more fuel capacity. Electronic speed or cruise control is also a perfect option for towing. Large mirrors (the latest trucks offer large electric mirrors) are another serious bonus. Rear cargo lamps can prove beneficial when hooking up at night and can also be useful when loading the bed when shrouded in darkness. Other interesting truck hardware that’s applicable to towing includes underhood lamps, reel-style trouble lamps (mounted underhood with enough cord to reach the rear of the truck), additional behind-seat storage, roof marker lamps and a host of comfort and convenience options. In the end, take the time to peruse the respective manufacturer sales catalogs. In many cases, there’s plenty of good trailering equipment available right from the manufacturer, but you have to find it.
When all is said and done, the right beast of burden for towing depends upon the load you’re hauling. So, choose your options and your trailer carefully. You won’t be sorry.