Ram pickup towing capacity may be too ambitious
The new 2013 Ram HD 3500 DRW with a towing capacity of 30,000 pounds makes me stop and think about stopping. The HD 3500 jumps towing capacity in the segment by 7,000 pounds or the weight of another pickup truck that you can, theoretically, now carry along.
If this kind of maximum trailer weight becomes the standard, we might need a new non-commercial driver’s license for big trailers. The commercial driver’s license test is certainly good experience, as is the driving test. We’ll assume the new Ram will be able to handle the new load rating the automaker is promoting, but what about the trailer? Semitrailers have been required to have antilock braking systems since 1991. They even have a light on the rear to show officers if the ABS is working.
Semitrailers have powerful air brakes, too. Most trailers towed with pickup trucks nowadays have electric drum brakes without any form of antilock brakes. You won’t find electric drum brakes on any vehicle that hauls passengers; electric brakes are not the best, but they are the least expensive.
Stopping a pickup truck with a 30,000-pound trailer is still the most important problem. Ram’s exhaust brake is good at slowing down a truck, but it’s not as powerful as an engine brake found on semitrailers. Engine brakes, commonly called Jake brakes, work off the rocker arms in the cylinder-block heads that hold the exhaust valve slightly open near the top of the compression stroke to “decompress” a diesel engine. This effectively turns the engine into a giant air compressor. Additionally, Class 8 semitrailers have powerful air brakes.
The next problem is suspension; yes, the new Ram has a beefed-up front and rear suspension setup, but the rear suspension is still a Hotchkiss leaf-spring configuration. Leaf springs squat under load. Imagine a 30,000-pound gooseneck trailer with a 25 percent tongue weight equaling 7,500 pounds.
From zero to 7,500 pounds and mostly on the rear axle, the new Ram’s rear could drop several inches. This affects the headlight angle and, more importantly, the rear differential pinion angle. If the drive train levels out too much, the rear axle can start hopping and the universal joints could pop. A couple of decades ago, semitrailers solved the problem of star-gazing headlights and pinion angle squat with self-leveling airbag suspensions that keep semi’s level when both empty and loaded. Airbags even helped braking, handling and improved the overall ride.
The stats on the new 3500 Ram look good on paper: 50,000-PSI high-strength steel frame, improved transfer case, higher-load transmission and an upgraded 6.7-liter Cummins turbo diesel engine with 850 pounds-feet of torque. We like that Ram used the same automatic transmission found on its 4500 and 5500 trucks. With a gross combined weight rating of 37,600 pounds, this new Ram 3500 DRW with a loaded trailer is close to half the total gross weight of a Class 8 over-the-road big-rig tractor-trailer. Semitrailers on public interstates can legally gross 80,000 pounds. The 2013 Ram 3500 dually combined weight is just a hair under half that weight.
We should also note that the Ram HD’s automatic transmission design, which is geared down in the low gears to start under a load without lugging the diesel and axle, is similar to a Peterbilt with full-floating drive axles. It carries weight on the axle housing and not the axle shafts.
But is the new Ram 3500 half as strong as a Peterbilt or Freightliner? Semitrailers can have 24.5-inch steel wheels with air brakes, engine brakes and tandem twin-screw axles. Transmissions can be eight to 18 speeds. Axle ratios are similar, with mostly 3.55:1 and 4.10:1 gears; however, the 850 lb-ft of torque on the Cummins Ram HD versus the 1,200 lb-ft of torque generally found on semitrailers isn’t even close.
However, there may be a case to be made for the new Ram 3500. The brakes on the Ram HD 3500 are 14 inches; on a new Peterbilt, they are 16.6 inches on a front 12,000-pound axle, making the Ram HD brakes larger than half the size. Additionally, tires on the Ram HD 3500 are 10-ply and E-rated; Peterbilt’s are 14-ply and G-rated. And the wheels are more than half the size and strength of a semitrailer. Finally, frames made from 50,000-PSI steel have ratings that are similar, except when considering double-framed tractors.
By certain specs, the new Ram HDs look to be more than half the truck of a Class 8 semi tractor. Of course, we don’t have all the specs on the new Ram 3500 yet but added to my wish list would be a set of upgraded 12-ply (F-rated) tires like the Ram 4500/5500 and a rear airbag suspension, at least as an option.