In our post on truck payload capacities, one of our readers asked about the physical differences between trucks rated for different payloads. I'll take a crack at describing this, but space limitations necessitate painting with a broad brush. Feel free to add additional info in the comments. To start, we can break things down into three basic categories - single-rear-wheel trucks under 8500 lbs GVWR (half-tons and some "light" 3/4-tons), single-rear-wheel trucks over 8500 GVWR (all "true" 3/4-tons and some 1-tons), and dual-rear-wheel trucks (the remaining 1-tons).

The easiest difference to spot between the two categories of single-rear-wheel trucks is the number of wheel lugs. Lighter-duty trucks will have 5 or 6 lugs (I seem to remember Ford using 7-lug wheels, too), while heavier-duty trucks will have 8. If you come across an older (early 90s) GM 2500 - normally a 3/4-ton designation - and see 6 lugs, it?s not a true 3/4-ton truck. That is, it won?t have a GVWR over 8600 lbs. The same is true for late-90s non-Super Duty Ford F-250s. On the other hand, the recent Chevy 1500HD had 8-lug hubs and a GVWR over 8500 lbs. It was, except for the badging, a true 3/4-ton truck, and many customers who expected half-ton ride and gas mileage were not impressed.
If we?re looking at a newer Ford or Dodge 4x4, the heavier-duty truck will have a solid front axle instead of independent front suspension (IFS). Heavy-duty GM trucks retain the IFS, but use cast-iron lower control arms and a wider track (which gives more room in the wheelwells for larger tires and allows for more ?wheel cut?, or steering angle). Out back, larger rear axles are used. A half-ton truck might use a 8.5? rear axle (referring to the ring gear diameter), with 3/4-ton trucks using 9.5-10.5? rear axles and modern one-tons using 11.5? axles. Similarly larger axles and diffs are used up front. Some 3/4-tons and all one-tons get the more complex full-floating arrangement, which eliminates the weak C-clips used in semi-floating axles. Deeper (higher numerically) ratios are used in these axles.

Transmission and transfer cases in the heavier-duty trucks are, as one would expect, much stronger and heavier. It?s even possible to find a real shifter on the transfer case. The manual transmissions used often have a deep ?granny? first gear, and one will occasionally find provisions for a PTO. Driveshafts will be larger in diameter and will have larger U-joints.

In the engine compartment, you?ll generally find the same small-block V8s used across the board. The difference comes in the diesel and big-block powerplants that are available in the heavier trucks. Such engines need a stronger drivetrain that carries a weight and fuel-economy penalty, so they?re reserved for use in the heavier trucks that are not currently covered by CAFE standards. Heavier-duty trucks will be equipped with larger cooling systems, for obvious reasons.

Frames are obviously built heavier on the 3/4- and 1-ton trucks. In some cases, they?re significantly different in design, despite the common appearance of the bodywork that sits on top. The spring rates are considerably higher front and rear, with progressive rates used in the rear to maintain some semblance of ride quality while unloaded. Shock absorbers will have higher damping rates to control these stiffer springs (although it seems that they?re often not up to the task).

What I?m trying to impress on everyone is that there?s some significant differences between the different trucks. It?s a lot more than different badges and a set of fender flares. Ford has made those differences obvious by splitting off the Super Duty line, where as GM and Dodge have maintained common bodywork and interiors. That?s an indicator of each automaker?s prefered marketing tactics and desire to commonize expensive tooling.

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