Payload Calculation Question

boblynch

Adventurer
How is a vehicle's GVWR determined and why is it lower than the axle ratings?

Consider the Ford F350 as an example. The 08 F350 SRW Long Bed has a GVWR of 11500. The combined axle ratings are 13000lb (front 6000 and rear 7000). If you subtract the base curb weight of 7773 (front 4765 and rear 3008) you get a delta of 5227 (front 1235 and rear 3992).

The published payload is 3640 lbs. So what happened to the 1587 lbs? The OEM 18" wheel/tire setups are rated for about 3500 per wheel/tire so they are not the limiting factor. Frame, brakes, etc. must play a role. Can anyone shed light on this one?

I'm considering the merits of a beefed up F350 vs. a SRW-conversion of a F550.

Bob
 

James86004

Expedition Leader
I think if you assume the term payload refers to evenly distributed material in the bed of the pickup, then you get closer. 7000 Gross Rear Axle Weight - 3008 lbs rear axle curb weight gives 3992 lbs for a payload, which is only 352 lbs more than the published payload. The 352 lbs can be accounted for by the fact that the rear axle is not centered under the load. If you make a shear and moment diagram of the truck, you will find how much force a given payload exerts on the rear axle.

Or, you can put the rear axle on a scale, and start adding payload until the rear axle weight reaches 7000 lbs. Then remove the payload and weigh it. I bet it will be 3640 lbs.

Here is an explanation for a shear and moment diagram:

http://en.wikipedia.org/wiki/Shear_and_moment_diagrams
 

RobinP

Observer
boblynch said:
How is a vehicle's GVWR determined and why is it lower than the axle ratings?

Consider the Ford F350 as an example. The 08 F350 SRW Long Bed has a GVWR of 11500. The combined axle ratings are 13000lb (front 6000 and rear 7000). If you subtract the base curb weight of 7773 (front 4765 and rear 3008) you get a delta of 5227 (front 1235 and rear 3992).

The published payload is 3640 lbs. So what happened to the 1587 lbs? The OEM 18" wheel/tire setups are rated for about 3500 per wheel/tire so they are not the limiting factor. Frame, brakes, etc. must play a role. Can anyone shed light on this one?

Payload is the GVW minus the curb weight (weight of vehicle, no passengers, including fuel, oil, coolant, and accessories). In your case 11,500 - 7773 = 3727 lbs. The base curb weight probably doesn't include liquids, so subtract a further full tank of fuel and all oils etc and I bet you get 3640 lbs.

Hope this helps,
 

boblynch

Adventurer
James86004 said:
I think if you assume the term payload refers to evenly distributed material in the bed of the pickup, then you get closer. 7000 Gross Rear Axle Weight - 3008 lbs rear axle curb weight gives 3992 lbs for a payload, which is only 352 lbs more than the published payload. The 352 lbs can be accounted for by the fact that the rear axle is not centered under the load. If you make a shear and moment diagram of the truck, you will find how much force a given payload exerts on the rear axle.

Or, you can put the rear axle on a scale, and start adding payload until the rear axle weight reaches 7000 lbs. Then remove the payload and weigh it. I bet it will be 3640 lbs.

Here is an explanation for a shear and moment diagram:

http://en.wikipedia.org/wiki/Shear_and_moment_diagrams

Thanks this makes sense... Bob
 

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