Story and photos by H. Kent Sundling
You might think a one-ton dually is a big truck and that anything with dual rear wheels could handle most towing jobs. But a dual-wheel single-rear-axle hauler truck like a Peterbilt, Freightliner or International can be a viable option if you tow 20,000-pound trailers often.
Class 3 one-ton pickup trucks have regularly increased their payload and towing capacity over the years, sometimes from structure and powertrain changes, sometimes from marketing hype. At the current rate, one-ton dualies’ torque and horsepower could catch up to those of semitrucks before the end of the decade. The new trailer towing standards set by the Society of Automotive Engineers may slow that trend, but at some point with 20,000-pound plus trailers, you may need a higher-capacity truck with more stopping power.
Starting in 2011, the Big Three raised the gross combined vehicle weight rating on one-ton dualie pickup trucks from 26,000 pounds to 30,000 pounds. One-ton Class 3 dualie pickup trucks are the Ford F-350, GMC Sierra 3500, Chevrolet Silverado 3500 and Ram 3500. Class 3 trucks have a gross vehicle weight rating between 10,001 and 14,000 pounds. This includes single-rear-wheel one-ton trucks, even the Hummer H1.
You will see one-ton dualies towing trailers and hauling welders and slide-in campers. Then you'll see quite a few just driving around like cars, which makes sense when you figure what another car payment, insurance policy and oil change would cost for an extra car; so why not just pay a little more for fuel on a truck you already have?
Class 6 trucks have a GVWR between 19,501 and 26,000 pounds — almost twice as high as Class 3 and one step down from over-the-road semitrucks. Some conversion trucks in this class de-rate their axles to get into the Class 5 rating disguised as a large pickup truck. Trailer tow rating is harder to pin down. Truck manufacturers basically determine the maximum trailer weight. Many Class 6 trucks as a cab and chassis have their GVWR and GCWR retagged by the body upfitter. Upfitters add features like beds, running boards, interiors and even their own warranties.
If you tow through mountains often, having an oversized truck with air brakes and an engine brake will ease the excitement coming down the fast side of a mountain. Engine brakes are in the diesel engine head, like in over-the-road semitractor rigs. It involves an extra lobe on the camshaft to open an extra exhaust valve to release cylinder pressure in the compression stroke, taking the power out of the engine to slow down the truck.This is more effective at slowing a truck than the exhaust brakes in one-ton diesels that shut off the exhaust flow after the turbo to build up back pressure in the cylinders.
Class 3 one-ton diesel dualies from the Big Three have improved their trucks’ braking ability over the last decade with larger disc brakes and exhaust brakes. Class 6 trucks — such as the Ford F-650, M2 Freightliner, International Durastar, Perterbilt T-330 and Kenworth T-300 — have air brake and engine brake options like over-the-road semitrucks.
Have you noticed that when your truck is loaded, it may point its headlights at the stars and doesn't set level? Even though semitrucks are loaded most of the time, you won't see much of a change in headlight angle, and the whole truck will squat a little when loaded or empty. Most semitrucks use rear air suspensions that automatically level themselves. Air ride may be the answer to truck squat in future Class 3 trucks, but for now it's a suspension option on Class 6 trucks.
A GCWR of 26,000 pounds is an important number — not enough room here for a debate over commercial driver’s licenses, but any truck with this rating or lower won’t need an air brake endorsement on a driver’s license. Once you go above 26,000 pounds, a 12 percent federal excise tax for commercial trucks kicks in.
Class 6 diesel trucks are very powerful, occupying a whole other realm of torque — more than 1,000 pounds-feet. These trucks have larger diesel engines and more towing power. They aren't designed for racing but for slower, more controlled liftoffs. Class 3 pickup trucks win the battle with speed and acceleration.
But with large air brakes, engine brakes and weight, Class 6 wins the contest for stopping a trailer. It’s also nice to have a heavy truck pulling the trailer; it gives you more control when you brake going downhill, keeping the tail from wagging the dog. And if you were to lose your trailer brakes, these big trucks will stop you better than a Class 3.With Class 6 trucks, you are also looking at a truck designed for more than 1 million miles instead of a target of 300,000 miles for a good diesel pickup truck. But then there is cost and how many years to divide it by. Class 3 dualies can cost over $60,000; Class 6 trucks as a finished conversion can cost over $130,000. Class 3 diesel engine warranties are 100,000 miles; Class 6 diesel engine warranties can be 750,000 miles.
Does that mean you could pay 7.5 times more for a Class 6 than a one-ton dually? That makes paying twice the price seem cheap for a Class 6. Since we're talking big money, what about fuel mileage? Since the EPA doesn't rate either truck class, my experiences with both classes have seen 15 mpg on an M2 Freightliner running empty and 9 mpg with a 20,000-pound trailer. Tractor trailer over-the-road rigs with GCWR of 80,000 pounds typically get 7 mpg.
Compare that with what you read here on the 2011 Heavy-Duty Hurt Locker gas mileage comparisons on the Class 3 dualies.