Help a newbie understand tow weight vs payload regarding engine stress?

[ahparker]

I'm sure this is very simple and obvious, but not quite understanding tow weight vs payload as it concerns engine stress.

I understand that roughly 10% of trailer weight goes to tongue weight and counts against your payload capacity, but is pulling the same weight, say 1k#, whether on a trailer or in the bed the same amount of work for the engine? Or put another way, IF payload was magically 7k# and that load fit in the bed, would that be the same amount of work vs towing a 7k# trailer? Just thinking about a 2.7 max tow rating and trying to understand better (I know you probably shouldn't pull 7k# with a 2.7).

Or is there some magical formula that changes the amount of work to be done when weight is pulled on a trailer? It seems like it would all be "sprung mass" as I understand it.

Hopefully this question makes sense and thanks in advance for responses!

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[redline]

Depending on the trailer and how you load the trailer it can be 10 to 15% As a rule but not guaranteed. Get yourself a tongue weight scale, weight the trailer before you buy it and make sure you are with in spec…

if you are thinking RV , you have to remember WDH , propane, food, water, cloths and the other 1000 lbs of shit you through into the trailer all have an impact …

 

[mla_anderson]

Specifically as it affects stress on the engine, there is no difference between payload and trailer weight. The engine has to move the same weight either way.*

The difference is in the frame's ability to take the load. When you have a trailer the frame takes a fraction of the load (see @redline above).

*Not entirely true as a trailer adds a wind load that a regular payload won't.

 

[ahparker]

That all makes sense, so basically maxing out on payload is still far below the max ability/capacity of the engine to do work.

I know GVW or whatever it is shows what the max weight of the vehicle can be. Is there a spec that says what the combined max weight is for a vehicle that includes payload and tow weight?

 

[LD50]

Since you're specifically asking about engine stress, getting up to speed will cause the same amount of stress regardless of where it is located. Once at speed, the type of trailer will have a much larger effect on the continued stress and load that the engine is under. My 3500 pound RV would pull every bit as hard or worse than my 8000# boat because there was so much extra wind resistance from pulling that giant box down the road.

 

[BLoflin]

That all makes sense, so basically maxing out on payload is still far below the max ability/capacity of the engine to do work.

I know GVW or whatever it is shows what the max weight of the vehicle can be. Is there a spec that says what the combined max weight is for a vehicle that includes payload and tow weight?

Vehicle has GVWR which is As Built weight (with full tank of gas) and all payload and passengers.

In fact Payload is determined by subtracting GVW (As Built) from GVWR.

The other number you are asking about is GCWR (Gross Combined Weight Rating), that is the max of Tow Vehicle (including Payload) and Towed Vehicle (i.e. trailer).

The GCWR is published for each model/engine/tow pkg/rear axle ratio, but is not on the door sticker. You need to find your vehicle config in the Ford RV and Trailer Towing Guide. The GCWR ranges from a low of 9500lbs to 19,500lbs depending on config.

For example assuming you have a SuperCrew Cab, short bed, 3.5V6 Turbo, 3.55 rear axle and 4x2, your GCWR is 16.5k. If you have Max Tow it is 19.4k.

However, as others have said, towing (for example) a short low trailer of bricks weighing 6k is different than towing a 6K RV that is 11' tall and 30' long. The trailer length x height will affect sway (due to cross winds or big trucks passing). The frontal area of an RV (height x width) will affect acceleration and perhaps top speed.

 

[Buyer2021]

Not disagreeing with any of the posts already made about placing an equal payload in a trailer vs the bed.

But if you have a choice of placing an equal payload in the bed or in/on a trailer (staying within vehicle limits in both cases) I'd suggest the well-placed load in the bed will almost always be less stressful on the engine in the real world. A pallet of something (e.g. grass sod, cinder blocks, bags of whatever, even hay bales) are examples where you may have a choice of placing the load on a trailer or in the bed.

Reasons I suggest that (remembering equal weight of the payload and within rated capacities):

• With a trailer there's the weight of the trailer itself and its own rolling resistance
• The frontal area of the trailer with its load will almost assuredly be worse than that of the load in the bed (remember wind resistance increases exponentially with speed and is often the biggest factor when towing a trailer)

All may be relatively moot for short-distance low-speed hauling, but if hauling for a distance at highway speed and you have the choice ..... the load-in-bed will IMO likely be 'less stressful' / require less 'work' on the part of the engine. A likely real-world indicator of that will be better gas mileage.

 

[GEN14OWNER]

I'm sure this is very simple and obvious, but not quite understanding tow weight vs payload as it concerns engine stress.

I understand that roughly 10% of trailer weight goes to tongue weight and counts against your payload capacity, but is pulling the same weight, say 1k#, whether on a trailer or in the bed the same amount of work for the engine? Or put another way, IF payload was magically 7k# and that load fit in the bed, would that be the same amount of work vs towing a 7k# trailer? Just thinking about a 2.7 max tow rating and trying to understand better (I know you probably shouldn't pull 7k# with a 2.7).

Or is there some magical formula that changes the amount of work to be done when weight is pulled on a trailer? It seems like it would all be "sprung mass" as I understand it.

Hopefully this question makes sense and thanks in advance for responses!

I pulled 1000lbs OVER my "rated capacity" today in my RCSB 5.0. "Truck wise", yes it was a little squirrely.

"Engine wise"... I could have easily loaded more.

 

[Calson]

The key number is the GVWR for the vehicle which takes into consideration the engine and the transmission and the gear ratio for the axle(s). Too great a load on the engine can reduce the ability of the motor oil to protect the bearing surfaces and shorten the life of the engine. For towing I want a low gear ratio to both protect the engine and to maximize acceleration when merging with traffic at an onramp.

The drivetrain stress is based on total load and not where that load is located, i.e. the bed or in a trailer.

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