Towing Tech

Pulling You Weight

How much can you really, legally, tow?

Some years ago at an RV show, while inspecting a 40-foot Teton fifth-wheel, the potential buyer was told he could pull it with a 3/4-ton pickup. I laughed. When the customer asked about my reaction, I explained there was no 3/4-ton that could carry the trailer’s 4,000-plus-pound pin weight nor tow its 20,000-plus-pound loaded weight.

The frowning salesman questioned my credentials (I was technical editor at an RV magazine) and got quite irked when I advised the customer he’d also need a license endorsement to drive it in his home state.

Much to the salesman’s disgust, the customer walked out armed with the truth about towing capacities.

Tow ratings are big business in pickups, bragging rights perhaps second only to horsepower and torque. Vehicle manufacturers present the maximum-weight scenario when it comes to towing capacities of pickups. The opposite is quite often the case with trailer builders that often offer the lightest weight regarding empty trailer weights.

In both instances, reality and gravity tend to get the last word.

Such numbers are critical if you are a contractor and tow anything with your pickups. Tow more than what your particular truck is really rated for and your company is wide-open to insurance and liability issues.

Do the Math

Curiously, two of the primary numbers you need to determine your truck’s maximum towing capacity rarely appear on the government-mandated door jamb certification label and tire rating label: Gross Cargo Weight Rating (GCWR) and your truck’s weight as equipped.

Note: Only the vehicle manufacturer has the authority to set or adjust GCWR.

Let’s build a generic 1-ton regular cab 4WD diesel dually pickup with fictional but typical numbers (all in pounds): Base weight 7,500; GVWR 12,500; payload 5,000; GCWR 29,000; max conventional tow 14,000 (8,000 without weight-distribution hitch); max fifth-wheel tow 21,346; GAWR front 5,500; rear GAWR 9,350; and empty axle weight 4,300 front, 3,200 rear.

The first thing you should notice is the axle ratings add up to more than the truck’s max loaded weight of 12,500 pounds, and the payload rating is less than what the rear axle can accommodate given its empty weight. But that doesn’t increase GVWR, GCWR or payload.

Next you’ll see the tow rating is GCWR less base weight and a 150-pound EPA “standard” driver.

If your foreman’s called “Moose” for a reason, the fifth-wheel hitch hardware added 75 pounds, you carry 50 gallons of diesel in a refuel tank, a small cooler and a tool box, take another 700 pounds off the max rating.

Tart up the truck with fancy audio/video, a winch, heavy-duty bumper, mud flaps, side steps, and all that additional weight comes off GCWR as well. It’s not that hard to take more than a thousand pounds off any full-size truck’s rating.

And that compact loader or backhoe you put on the equipment trailer might have a full fuel tank too, perhaps some attachments, and some material to or from the jobsite that are not included in its touted operating weight.

Get out your calculator and start subtracting, or better yet, go to a truck scale and find out what it really weighs on each axle, and be sure you check it with and without the trailer and any weight-distributing hardware attached.

Subtract the scaled weight of the truck plus any employees from GCWR (you’ll need engine, axle ratio, drive, and body configuration) and the result or the quoted maximum tow rating, whichever is lower, is your pickup’s actual towing capacity.

New Tow Ratings Coming

Most tow ratings carry a “properly equipped” caveat or something similar outlined in the owner’s manuals, manufacturer trailering guides and websites, and frequently on the hitch itself.

A full-size pickup rated at 10,000-12,000 pounds “conventional towing” may be limited to 5,000-8,000 pounds without a weight-distributing hitch, sway control, or both.

Failure to do so can stress truck components beyond design limits, produce undesirable handling and braking characteristics, and exposes you, your company or municipality, and employees to liability.

If anything goes wrong it won’t be the pockets of your $25 per-hour employee that lawyers seek as the primary target.

While the proper equipment and liability issues remain, there is a new standard for tow ratings being phased in. These are the first such standards and won’t stop the bragging rights, but they will make such comparisons apples-to-apples.

In Surface Vehicle Recommended Practice J2807 the Society of Automotive Engineers (SAE) spells out a set of standards for rating GCWR and maximum trailer weight rating (TWR).

These new rules are to be in force by the 2013 model year. Some manufacturers are quoting tow ratings according to J2807 already, and that is the asterisk to look for if you want the apples-to-apples data.

Coming To Terms

Myriad ratings apply to trucks, and until you’re familiar with these terms, your towing safety and liability could be in jeopardy:

• GAWR – Gross Axle Weight Rating. The maximum load that can be carried by any specific axle. It includes the weight of the axle, brakes, wheels, tires, all the truck weight on it, and payload. Most frequently exceeded with plows, slide-in campers, fifth-wheel/gooseneck pins and heavy receiver loads.

• GCWR – Gross Combined Weight Rating. The maximum total rated weight of your truck, trailer, payload, fluids and occupants. Most frequently exceeded with overweight trailers.

• GVWR – Gross Vehicle Weight Rating The maximum total weight of the truck, occupants, fluids, cargo and trailer tongue weight. Most frequently exceeded with large campers and overweight dense loads like sand.

• TWR – Trailer Weight Rating. The maximum loaded weight of the trailer, including fluids, cargo and breakaway system battery.

• TVTW – Tow Vehicle Trailering Weight. The weight of the truck used to determine the TWR, including options, two occupants, and hitch.

Also worth knowing is tire weight capacity, shown on the sidewall with max load at what pressure. The service description (a number/letter like 126Q following the size) corresponds to a maximum load and speed for the tire.

New Tow Ratings

SAE’s J2807 makes the pickup manufacturer’s tow and cargo ratings more realistic and level across the field much like horsepower ratings are handled. Every manufacturer will be required to test in exactly the same way to certify their stated towing capacities and cargo weight ratings.

For example, rather than allowing for just a driver, the new standard requires that a driver, passenger, hitch weight and any options that a third of customers order be included for the tow vehicle weight.

Trailer axle loading and trailer tongue standard testing specifications are in J2807 to preclude any fudging based on the lash-up. J2807 also mandates no weight-distributing hitch that might minimize a load that would otherwise exceed rear GAWR.

A range of performance variables is addressed, including but not limited to: Acceleration from zero to 30mph, zero to 60mph, and 40 to 60mph; repeated launch, forward and reverse, up a 12-percent grade; minimum cruising speed on the Davis Dam 12-mile grade, temperature at least 100 degrees F and the air conditioning on high, without any loss of coolant, warning lights or service codes.

J2807 also requires the tallest available axle ratio (this is why today’s tow ratings vary by axle ratio) be used; testing will include both with and without a weight-distributing hitch to meet specific handling criteria; the parking brake must hold on 12-percent up/down grades; braking distance limits from 20 mph without trailer brakes, with different distances for vehicles that have and do not have trailer brake requirements, and keeping inside an 11.5-foot lane in braking tests; and limits on hitch-related structural deflection and deformation.

Many of the values set in these tests vary by single- or dual-rear-wheel trucks, and duallies with GVWR greater than 13,000 pounds are excluded. At this point, that’s the realm of medium-duty 450/4500 Series and up, but with ever-escalating pickup truck numbers it may come into play and create a loophole like lifting GVWR a few pounds for a different set of emissions, economy and/or tax standards.

SAE’s new standard should simplify real-world towing ability and put all the competitors on a level battlefield. But you’re still in command of how the towing ability is used.

Minding Your Tongue

One of the biggest mistakes contractors make in towing is exceeding the pickup’s maximum hitch tongue weight. This leads to overloading the truck’s rear suspension, creating significant handling and braking issues.

Every pickup has a set limitation on how much tongue weight can be placed on the hitch (noted in the owner’s manual), and every hitch shank has a load limit (noted on the shank) as to how much it can support.

The two capacities ratings are not always equal, but the lowest number always takes precedence.

For instance, the majority of ½-ton pickups only allow 500 pounds of tongue weight while ¾- and 1-tons with 2-inch receivers generally max out at 1,200 pounds. The newer HD pickups with 2 1/2-inch receivers are usually rated to support up to 1,800 pounds tongue weight.

Vehicle manufacturers also require 10- to 15 percent of the trailer’s loaded weight on the hitch ball.

So if you are towing a loaded trailer that tips the scales at 9,700 pounds, you should have between 970 and 1,115 pounds on the tongue (hitch ball), with 12- percent being ideal as that gives you a little leeway toward being too heavy or too light.

(Too little tongue weight leads to trailer sway and too much adversely affects the pickup’s braking and steering.)

The easiest way to ensure tongue weight is set in accordance to the pickup manufacturer’s requirements is to use a scale such as those offered by Sherline ( Sherline’s scales are capable of reading tongue weights up to 5,000 pounds, although the 2,000-pound-capacity model is sufficient for most pickup trailer towing applications.

Load the trailer and support it on the trailer jack. Place the scale, resting on a short piece of 2Ă—6, under the trailer coupler and slowly raise it into the coupler until the jack is supporting the weight of the trailer tongue.

Read the dial on the scale. If the weight is too high or too low, adjust the position of the load or equipment on the trailer until the number is correct.

Moving a piece of equipment, such as a 9,000-pound compact loader, six inches forward or back on the trailer can change the tongue weight 600 pounds. So load positioning is critical if you want to be in compliance with the pickup manufacturers’ towing guidelines.

If a piece of equipment is going to be hauled on the same trailer all the time, it’s good to paint or mark the trailer bed to indicate where the bucket edge or a tire needs to be positioned to keep that weight balance correct.

–Bruce W. Smith