Tow Vehicle Analysis w/ Surprising Result (for me): F250 gas versus F250 diesel

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GaryB

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Jul 29, 2006
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Evansville, IN
Thanks to the help of many of you, I think I?ve finally I?ve gotten the hang of this tow vehicle sizing for a 5er.? In the process, I?ve discovered something interesting.? Please correct me if I?m wrong in the following analysis.? It is possible for a gas-powered F250 4x2 5.4L V8 truck (3.73 axle, crew cab, long bed) to be able to safely tow more than a turbo diesel-powered F250 4x4 6.0L V8 (3.73 axle, crew cab, long bed).? The reason is related to the extra weight that the diesel and 4x4 package (roughly 1000 lbs) put on the rear axle (suspension).? Since both models above are ? ton trucks, they have the same suspension and GAWR (max rear axle load rating).? Despite that the diesel has a much higher GCWR and tow rating due to its engine and drive train, these values are not always the limiting factors.? If weight on the rear axle is the limiting factor, then the gas engine may be able to effectively tow more than the diesel.

I?m not trying to turn start a debate - I?m just trying to understand if I?m correct or if I?m missing something here.? If correct, the purpose of this thread is to caution novices (like me) that they need to consider more than just tow ratings versus trailer weights when deciding on a tow vehicle.

Using values from the 2006 Ford Towing Guide, the gas truck has GCWR = 16000 lbs, tow rating of 9600 lbs and GVWR = 9400 lbs.? Assuming the loaded truck weighs 7000 lbs (with people, gas, hitch,etc.), that means the true carrying capacity of the truck = 9400 ? 7000 = 2400 lbs.? Assuming that 25% of the king pin weight rests on the rear axle, that means the gas powered F250 could tow a max loaded 5er weight of 2400 / .25 = 9600 lbs without overloading the suspension and GAWR.

The 4x4 diesel has GCWR = 23000 lbs, tow rating of 15900 lbs and GVWR = 10000 lbs.? Assuming the loaded truck weighs 8000 lbs (1000 lbs more than gas truck due to extra weight of diesel and 4x4), that means the true carrying capacity of the truck = 10000 ? 8000 = 2000 lbs.? Again assuming 25% of king pin weight rests on the rear axle, this means the diesel F250 could tow a max loaded 5er weight of 2000 / .25 = 8000 lbs without overloading the suspension and GAWR.? This is 1600 lbs less effective towing capacity than the gas engine.

Of course, if we compared a 350 series (1 ton) diesel engine instead against the same 250 gasser, the diesel would regain its true towing advantage since the GVWR and GAWR would increase considerably.

So there must be two distinct sets of factors to consider.? One is GCWR and towing ratings which are functions of engine, drive train and axle ratio.? Diesel has a big advantage here.? The second set is GVWR and GAWR which are functions of frame, suspension, axle and tires.? Here, the diesel really has no advantage, especially when offset by its extra weight.? What matters here is the payload or cargo carrying capacity of the truck (which dictates the suspension and GAWR).? Depending on which set of factors is limiting, the above result is possible.?

By working through this example, I think it?s finally ?clicked? for me!? Please let me know if I am mistaken on anything I?ve said above.? Thanks so much for everybody on the forum for walking me through this stuff.? I can now choose a tow vehicle with greater confidence!

Gary
 

Gary RV_Wizard

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Feb 2, 2005
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73,944
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At our Silver Springs FL home
That scenario and a variety of others is entirely possible, Gary.  That's why you have to do the atithmetic on all the numbers, not just GCWR or Max tow capacity. I hope we haven't implied anythng to the contrary here.

A 4x4 nearly always has a lesser carrying capacity than a 4x2, because of weight of the 4WD mechnism. A diesel is stronger but heavier, as you say. Same for a 5 or 6 speed tranny versus a 4 speed.  And a dual rear wheel truck has less advantage than it might otherwise, because the extra pair of wheels detracts from the added capacity of the bigger axle.
 

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