Is the 2013 Ram HD 3500 Half a Semi?


The new 2013 Ram HD 3500 DRWwith a towing capacity of 30,000 pounds makes me stop and think about stopping. The HD 3500 jumps towingcapacity in the segment by 7,000 pounds or the weight of another pickup truck thatyou can, theoretically, now carry along.

If this kind of maximum trailerweight becomes the standard, we might need a new non-commercial driver’s licensefor big trailers. The commercial driver’s license test is certainly goodexperience, as is the driving test. We’ll assume the new Ram will be able tohandle the new load rating the automaker is promoting, but what about thetrailer? Semitrailers have been required to have antilock braking systems since1991. They even have a light on the rear to show officers if the ABS is working.

Semitrailers have powerfulair brakes, too. Most trailers towed with pickup trucks nowadays have electricdrum brakes without any form of antilock brakes. You won’t find electric drumbrakes on any vehicle that hauls passengers; electric brakes are not the best, butthey are the least expensive.

Stopping a pickup truckwith a 30,000-pound trailer is still the most important problem. Ram’s exhaustbrake is good at slowing down a truck, but it’s not as powerful as an enginebrake found on semitrailers. Engine brakes, commonly called Jake brakes, workoff the rocker arms in the cylinder-block heads that hold the exhaust valveslightly open near the top of the compression stroke to “decompress” a dieselengine. This effectively turns the engine into a giant air compressor.Additionally, Class 8 semitrailers have powerful air brakes.

The next problem issuspension; yes, the new Ram has a beefed-up front and rear suspension setup,but the rear suspension is still a Hotchkissleaf-spring configuration. Leaf springs squat under load. Imagine a30,000-pound gooseneck trailer with a 25 percent tongue weight equaling 7,500pounds.

From zero to 7,500pounds and mostly on the rear axle, the new Ram’s rear could drop severalinches. This affects the headlight angle and, more importantly, the reardifferential pinion angle. If the drive train levels out too much, the rearaxle can start hopping and the universal joints could pop. A couple of decades ago, semitrailers solved theproblem of star-gazing headlights and pinion angle squat with self-leveling airbagsuspensions that keep semi’s level when both empty and loaded. Airbags evenhelped braking, handling and improved the overall ride.

Thestats on the new 3500 Ram look good on paper:  50,000-PSI high-strength steelframe, improved transfer case, higher-load transmission and an upgraded6.7-liter Cummins turbo diesel engine with 850 pounds-feet of torque. We likethat 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 DRWwith a loaded trailer is close to half the total gross weight of a Class 8 over-the-road big-rig tractor-trailer. Semitrailerson public interstates can legally gross 80,000 pounds. The 2013 Ram 3500 duallycombined weight is just a hair under half that weight.

We should also note that theRam HD’s automatic transmission design, which is geared down in the low gearsto start under a load without lugging the diesel and axle, is similar to a Peterbiltwith full-floating drive axles. It carries weight on the axle housing and notthe axle shafts.

But is the new Ram 3500half as strong as a Peterbilt or Freightliner? Semitrailers can have 24.5-inchsteel wheels with air brakes, engine brakes and tandem twin-screw axles.Transmissions can be eight to 18 speeds. Axle ratios are similar, with mostly3.55:1 and 4.10:1 gears; however, the 850 lb-ft of torque on the CumminsRam HD versus the 1,200 lb-ft of torque generally found on semitrailersisn’t even close.

However, there may be acase to be made for the new Ram 3500. The brakes on the Ram HD 3500 are 14inches; 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 theRam HD 3500 are 10-ply and E-rated; Peterbilt’s are 14-ply and G-rated. And thewheels are more than half the size and strength of a semitrailer. Finally, framesmade from 50,000-PSI steel have ratings that are similar, except whenconsidering double-framed tractors.

By certain specs, the newRam HDs look to be more than half the truck of a Class 8 semi tractor. Ofcourse, we don’t have all the specs on the new Ram 3500 yet but added to mywish list would be a set of upgraded 12-ply (F-rated) tires like the Ram 4500/5500and a rear airbag suspension, at least as an option.


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