BACK2GAS

Just curious...

Does anyone know how manufacturers arrive at their towing and payload numbers?

Is it calculated purely on how the vehicle is equipped or real world assessment? These are numbers that we come to depend on, use to determine our purchases and the loads we carry. I'd be interested in how they arrive at the number.

Obviously manufacturers want to leave room for upgrading to larger trucks with higher payload and towing limits so they can't have an F150 encroach on F250 territory.

The question isn't meant to be argumentative I'm just curious as to how they arrive at their numbers.

What makes a truck capable of towing 13k, but not 13.5k or 14k? How do they arrive at the idea that 13k is the MAX? What's the limiting factor? Power, torque, weight, power vs. weight, frame strength, brakes, weight vs. brakes?

It's not an answer that goes, "Well it's bigger, that's why it can tow or haul more..." While this may be true, it's not really the question I'm asking.

It could also be that nobody on the forum actually knows. And that's ok too.

smokeywren

I'm not a a chassis engineer, so I can't tell you the exact answer. But I'm highly educated with an MBA from a good graduate school and years of using logic to develop automated computer systems. And I've been a car nut all my life, and I read a lot, so I can give you an idea.


There are two primary weight ratings that determine the max weight of a trailer you can tow without being overloaded - GCWR and GVWR. There are several other weight ratings too, but in a nutshell if your truck doesn't exceed the GVWR then the suspension and brakes are not overloaded. If your truck doesn't exceed the GCWR, then the drivetrain should have enough power and torque and gearing to pull your trailer over hill and dale with breaking a sweat.


Gross Combined Weight Rating (GCWR) is the maximum weight the combination of truck and trailer can weigh without being he slowpoke holding up traffic and without overheating anything in the drivetrain when climbing grades. The chassis engineers compute the theoretical GCWR based on logic and mathematics. Then they build test "mules" with the right combination of engine, drivetrain, chassis, bed, cab, etc., load a trailer with dead weight to reach the test GCWR, then actually tow that trailer up a steep highway to verify that their theory holds up in the real world.


One such highway used by Ford is Highway 68 from Laughlin NV to Kingman AZ - about 30 miles of steep grades coming out of the Grand Canyon and heading up to the high plains of Arizona.


If the tow vehicle cannot maintain the minimum speed required, or if anything in the drivetrain burns up while climbing that grade, the test vehicle is repaired, the test weight is reduced, and they continue testing and reducing weight until the vehicle passes the test. If the tow vehicle passes the test with flying colors, then more weight is added to the trailer and another run is made.


Gross vehicle weight rating (GVWR) is the maximum weight on the tow vehicle's axles that it can carry without exceeding the weight ratings of any of the components of the suspension and drivetrain, including the frame, brakes, springs. shocks, wheels, tires, axles, bearings, etc.

BACK2GAS

Interesting. So they literally trial and error trucks, changing drivetrain parts and combinations seeking a failure point. Thanks for the response.

atwowheelguy

The Gross Combined Vehicle Weight Rating (GCVWR) is determined by a series of tests as specified by the Society of Automotive Engineers and described in their SAE J2807 standard. It is available from the SAE for $74. It was developed in 2008 and revised in 2010, 2012 and 2016. It now includes vehicles up to 14,000 GVWR. Toyota adopted it in 2013. Ford, GM and Ram adopted it in 2015. Any built before that are rated at whatever the manufacturer said it was. Now, whatever weight they can load up and still pass all the tests is the GCVWR for that truck.

http://www.trucktrend.com/how-to/tow...-the-standard/

http://standards.sae.org/j2807_201602/

smokeywren

The problem with SAE J2807 is that it ignores payload capacity of the tow vehicle. GCWR is rarely the limiter as to how heavy a trailer you can tow without being overloaded. GVWR, and payload capacity based on GVWR, is usually the limiter on tow vehicles with single rear wheels (SRW).


GCWR will tell you the max combined weight can PULL without overheating anything in the drivetrain and without being the slowpoke holding up traffic on steep grades. But most modern pickups can pull a lot heavier trailer than they can carry the hitch weight of that trailer without exceeding he payload capacity of the tow vehicle.


Don't confuse GCWR and GVWR. GCWR is the combined weight of the rig. GVWR is just the max weight on the axles of the tow vehicle.

atwowheelguy

How is it a shortcoming of J2807 that it has nothing about payload in it? It was never intended to address payload or GVWR. It addresses towing. The OP asked how the manufacturers determined towing and payload limits. They determine towing limits by the J2807 test. Payload limits are determined by each manufacturer without any regard to towing capability.

The test standard says the tow vehicle must not be overloaded. So it must have 10% of the trailer weight on the tongue without exceeding GVWR or GAWR.
It was revised in 2016, but you can see the 2012 edition here:http://fifthwheelst.com/documents/j2807.pdf

smokeywren

Two problems.


1] That's in the fine print. "Nobody" reads the fine print - they just go by the certified GCWR, or "tow rating" which is GCWR minus the shipping weight of the empty tow vehicle. Ford has had similar language in their annual towing guides since at least 1997, but as evidenced in various towing forums, including this one, it's ignored. Folks take the tow ratings a gospel and are upset when the "weight police" explain that they're overloaded when towing at anywhere near the tow ratings.


2] 10% tongue weight is unrealistic. Average tongue weight is about 13% of gross trailer weight of a tandem-axle trailer, and is almost always over 11%. If you use 10% tongue weight in your computed estimates, you're probably going to be overloaded. 10% tongue weight of a 7k trailer is 700 pounds. But 13% is 910 pounds. That extra 210 pounds of tongue weight is the downfall of most estimates of gross vehicle weight of the tow vehicle.

Dirttracker18

Here is a concise overview



I hope that clears it up a bit.

atwowheelguy

Did you read the standard?

The standard says that the vehicle GCVWR will be determined by the test. The test vehicle may not be overloaded during the test. The tow vehicle must have any option sold on more than 33% of the vehicles and must have the trailer towing package installed and must have 300 lb. of people in it. Right there in black and white. If they say a maximum trailer weight is 10,000 lbs., they had to test a vehicle towing a 10,000 lb. trailer with 10% tongue weight without overloading the truck. It doesn't say a 10,000 lb. travel trailer or toy hauler with 13% tongue weight. My understanding is that 5%-7% is the recommended tongue weight for boats.

Address all complaints to the Society of Automotive Engineers for not requiring testing of every vehicle with every possible travel trailer, cargo trailer or boat. They just must not know what they are doing. I doubt that the standard was written for vehicle consumers. It was written for vehicle manufacturers. I guarantee you that they read the fine print.

Feathermerchant

So if the truck can carry the driver and tow a trailer without being overloaded, SAE J2807, it passes. Great. If you camp alone and carry no tools, firewood, and have no other mods on your truck, you're golden.
Does that sound realistic at all?
Standards can be written. That does not mean that they are useful. Countless people come into the towing forum only to find out that they cannot tow their new trailer due to being overloaded because family.