Ask Autoblog: What determines a truck's payload capacity?
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, its
not a true 3/4-ton truck. That is, it wont 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 were 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. Its 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, youll 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 theyre 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, theyre 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 theyre often not up to the task).
What Im trying to impress on everyone is that theres some significant differences between the different trucks. Its 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. Thats an indicator of each automakers prefered marketing tactics and desire to commonize expensive tooling.
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Reader Comments (Page 1 of 1)
Finished.Law.School 10:26PM (12/18/2005)
Question: What determines a trucks payload capacity?
ANswer: How many obese people will fit in it before mpg ratings are affected.
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Kamil 10:26PM (12/18/2005)
Wow, thank you for going through all that trouble just to answer my question, I really appreciate it.
-Kamil
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Eric 10:26PM (12/18/2005)
My question is, Is there a difference between the "true" 3/4 ton and the 1 ton trucks where the moving parts meet the non moving parts, like the wheel bearings and brakes? Also the only diffrence that I have found in examining, for example, a 1 ton dodge, in tow rating is it will go up with the lower rear end raito, example the dodge truck is rated around 13K towing with a 3.73, while the 4.10 is rated above the 15K range. To further this raito the Ford 1 ton "tow boss" has a rear of 4.30 and is rated at 19K lbs and requires dual rear wheels. all of the others gain by using single rear wheels becouse you can subtract the weight of the second set of tires. likewise a 4x2 has a higher tow raiting than a 4x4 due to the weight issue.
-Eric
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murse 10:26PM (12/18/2005)
Another interesting thing to take note of is that Ford is the only of the domestics that uses a completely different chassis for their O8500 trucks. Both Dodge and Chevy use upgraded versions of their U8500 frames up through 3500 designated trucks.
Ford 250 and 350 pickups use the same basic chassis as their 450 and 550 trucks, with the F-150 being a unique platform.
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murse 10:26PM (12/18/2005)
Another interesting thing to take note of is that Ford is the only of the domestics that uses a completely different chassis for their O8500 trucks. Both Dodge and Chevy use upgraded versions of their U8500 frames up through 3500 designated trucks.
Ford 250 and 350 pickups use the same basic chassis as their 450 and 550 trucks, with the F-150 being a unique platform.
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Eric Bryant 10:26PM (12/18/2005)
Eric,
The answer to your question is "maybe". On some models, there's differences in brake sizes between 3/4- and 1-ton models. If the 1-ton uses a larger rear axle (most do), then usually the wheel bearings are larger, as are the axle shafts.
Tow ratings are often established not by the strength of the running gear, but by engine size and axle ratio (as you pointed out). It often comes down to the vehicle's performance during worst-case situations - can the combination be accelerated and decelerated at a safe rate, and will the vehicle's cooling system be up to the challenge? Often, the difference in this type of performance between a 3/4-ton and a 1-ton is negligible.
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David Thompson 10:26PM (12/18/2005)
"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)"
Keep in mind the GVWR has crept up over the years. My '66 GMC 3/4 ton has a GVWR of 7500 lbs.
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Gary Blomquist 10:26PM (12/18/2005)
Actually, my 2005 Dodge Ram 2500(3/4ton) 4X2, Cummins diesel, Quad Cab, long bed has roughly a 2,500 lbs. payload capacity. That's 1 1/4 tons, not 3/4 ton.
As for towing lbs., I learned a lot participating in the Motorhome.com forum, on the net. An example of what one must consider when towing is that your payload weight must be deducted from the advertised vehicle manufacturer's tow weight limit...I.E. If you have a Chevy Astro that's rated to tow 5,000 lbs. of trailer, you should only tow safely at roughly 80% of that limit.
Tow ratings are figured with one average weight driver in the tow vehicle, and a full tank of fuel. Passengers, and cargo weight must be deducted from your tow weight of your trailer. Also the average vacation trailer has a dry weight and a gross weight. If you buy a trailer with a dry weight that just marginally is within your safe lbs. limit for towing with t.vehicle payload lbs. added in, you might not be trully safe on the road. Most travel trailers are not towed "bone" dry, but carry food, coolers, filled fresh water tanks, food preparation things, clothes, etc. All that weight is added to the dry weight of your trailer plus what your carrying in your T. vehicle over and above the driver and a full tank of gas.
I pulled a tent trailer with an Astro that was rated for 5,000 lbs of trailer, but failed to consider my cargo and additional passengers in my Astro on these vacations. In addition, my tent trailer was loaded up pretty good. I think for years I was probably towing at or nearly at 100% of the Astro's advertised ability.
Well, that's not safe for me or others on the road.
When buying a T.V......follow the over-kill methodology....and buy something that can tow twice as much as your trailer and still not be working hard, enginewise, brakewise, or suspensionwise.
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Dave 10:26PM (12/18/2005)
Wow, getting called out twice in a week, it's like a new record for me over here at AB...
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