Recently I posted a series of questions on various Facebook group pages similar to the following:
“The GCWR and the tires/rims are the same for a 250/2500 and 350/3500 vehicle and the only difference between the two is the GAWR and GVWR. What is the most likely metal load bearing component on these vehicles that will be different?”
The answers varied; some were correct and others were a good try. Before I reveal the answer, perhaps a review about the load ratings and powertrain are in order. For some, this may be new knowledge.
What is GCWR?
Gross Combined Weight Rating—The GCWR is the maximum allowable weight of the tow vehicle and any towed vehicle combined. The GCWR may be found in the “Owner’s Manual” or in the tow vehicle brochure for the model year you own, usually provided by the dealership. The GCWR is assigned by manufacturers and includes the powertrain's capabilities such as engine, transmission, axles, and gear ratio. Any of the powertrain's components, or combinations of, may create the weakest link in the powertrain. This information may also be found in Fifth Wheel Street's "Tow Ratings" menu.
Gear Ratio—Mechanically, the differential gear ratio is not necessarily the weak link, but rather a ratio of power reduction or increase to the wheels depending on the ratio. When considering the same brand and model vehicle, a differential ratio of 3.42:1 will cause the engine and transmission to work harder than if the ratio was 4.10:1 with the same amount of weight hauled or towed. The tow vehicle will still move the weight regardless of the differential gear ratio. But a lower transmission gear may have to be used move the weight, therefore increasing engine RPM, and fuel cost, and may increase additional stress on the engine and/or transmission, therefore increasing the risk of premature wear and breakdowns. You may note that two identical vehicles with the only mechanical difference being the gear ratio will have different GCWRs and maximum towing capacities. See the Ram examples below or on this page: How Much Can a One Ton Truck Tow Without Exceeding Ratings?
Gross Axle Weight Rating (GAWR)—The GAWR is found on the certification label and it's usually located near the driver’s side door. The certification label will list the GAWR for the front and rear axle assemblies. The GAWR is the maximum allowable weight on the axle assembly measured at the tires.
Gross Vehicle Weight Rating (GVWR)—The GVWR is found on the certification label and it's usually located near the driver’s side door. The GVWR is the maximum allowable weight of the fully loaded vehicle, including liquids, passengers, cargo and kingpin or tongue weight of any towed vehicle.
The GVWR, as required by National Highway Traffic Safety Administration (NHTSA), primarily considers the weakest link in the load bearing components such as the frame, axles, springs, brakes, rims and tires. Based on the lowest component rating within the load bearing components, manufactures assign the GVWR. One of NHTSA's safety requirement for GVWR is that the vehicle is expected to stop within a required distance when it is fully loaded to the max GVWR. This is appears to be a primary safety concern of NHTSA when tow vehicles are overloaded by too much pin or tongue weight coming from the trailer. Some owner's manuals may state: "The towing vehicle's brake system is rated for operation at the GVWR—NOT GCWR. Separate functional brake systems should be used for safe control of towed vehicles and for trailers weighing more than 1,500 lbs. when loaded." Exceeding the GVWR can result in premature mechanical failure and failure to stop within a safe distance resulting in serious injury or death.
NOTE: All vehicle manufacturers emphatically warn that GCWR, GVWR and GAWR should never be exceeded for the reasons of safety and vehicle longevity.
Additional resource: 49 CFR 571 - FEDERAL MOTOR VEHICLE SAFETY STANDARDS
The typical powertrain consists of the following components or assemblies.
1. Engine—Provides power to the following:
2. Transmission—An assembly of parts, including the speed-changing gears, a transfer case for some vehicles, and the propeller shaft by which the power is transmitted from an engine to the following:
3. Drive shaft(s)—A mechanical component for transmitting torque and rotation that is usually used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement between them.
4. Differential—A device, usually, but not necessarily, employing gears, which is connected to the outside world by three shafts, chains, or similar, through which it transmits torque and rotation. The size of the differential gears control the gear ratio and directly increases or decreases the towing capacity.
5. Final drive—The final drive is the last in the set of components which delivers torque and rotation from the differential to the drive wheels. These final components include axles extending from the differential, brake assemblies, rims and tires.
Braking down the question to arrive at the answer
“The GCWR and the tires/rims are the same for a 250/2500 and 350/3500 vehicle…”
When reading the 2013 Ford truck towing capacity chart (shown below), some of the F250 and F350 vehicles have the same GCWR. When this occurs, it could be due to the fact that both vehicles have identical powertrains. Even if there are slight variations in individual parts, the fact remains that both powertrains have identical GCWR and both are rated to tow the same amount of combined weight and are equally capable of controlling the load. Some of the other brand manufacturers provide better details than what you see here. It is rare to find other brand models similar to the F250/350 listing that have the same GCWR.
“…and the only difference between the two is the GAWR and GVWR.”
Why would there be a difference?
Notice in the highlighted examples above that the maximum loaded trailer weight's difference between the two vehicles is only 100 pounds. This could be because the F350 is 100 pounds heavier. Unfortunately this example does not conveniently show the GVWR or the GAWR as some other vehicle brands do. To view Ford's GVWR listing, there's another page to access. Now this is where it gets crazy. On the Maximum Payload Package Selector page is the listing of the GVWR for six configurations of the F250 and F350 trucks and there are 23 different ratings ranging from 9,900 pounds to 14,000 pounds. It can be easily confusing to which of the GVWR belongs to the trucks shown above. On the Chassis Specifications page, it states the GAWR as follows:
|Max. Front GAWR||F-250/F-350 4x2||F-250/F-350 SRW 4x4|
|5250 lbs.||5600 lbs.|
|Max. Rear GAWR||F-250||F-350 SRW||F-350 DRW|
|6290 lbs.||7180 lbs.||9650 lbs.|
Notice that all F250s rear GAWR is 6,290 pounds and as mentioned above, some of these trucks have the same GCWR as the F350s. Is that because one axle assembly is different? Not necessarily. I’ve already established that both powertrains are effectively the same, knowing that both have the same GCWR.
Is it the rims or tires? No. At least not in this example. Most new vehicles sold are equipped with the appropriate load bearing rims and tires. Wheels and tires can affect the load ratings. All rims and tires should be rated to meet or exceed the load that vehicle was built to carry. Proper tire inflation pressure is also important. The number one most reported insurance claim is the result of RV damage received from sudden release of air from tires.
Clearly, for the general consumer and novice, selecting the correct truck for the job can be difficult. Consumers have to be diligent in evaluating those numbers which will most likely require a visit to the dealer. Fortunately, consumers now have a new and nifty, free web-based app available that will tell them the safest trailer weight a vehicle can tow and not exceed the GVWR, GCWR and TWR. The RV Tow Check 3.0 is the only app of its kind that supports all manufacturers weight safety and longevity requirements. Also, RV Tow Check complies with the GCWR and GVWR SAE J2807 TWR Calculation guidelines. RV Tow Check displays realistic vehicle towing capacity for fifth wheel and conventional trailers simultaneously and provides instant results when selecting various kingpin or tongue weight percentages.
Ta-da! Drum roll, please.
“What is the most likely metal load bearing component on these vehicles that will be different?”
The most likely answer to the presented question is circled in the picture below.
Typically, the engine and transmission are capable of towing a great amount of weight. This was recently proved when a Toyota Tundra towed the Space Shuttle and a VW Touareg towed a 747 jumbo jet. (See here)
A personal opinion: When towing heavy loads, avoid differential gear ratios below 3.73:1. (On the other hand, with the continual increase in diesel engine torque, gear ratio appears to be becoming less of a factor. Only time and real testing will tell.)
Why is this information important?
1. As stated in my first version article, Before You Buy That RV, Truck or Other Tow Vehicle:
"Some vehicles may have a high GCWR and maximum towing capacity but the tongue weight or pin weight of some trailers may exceed the vehicle's rear GAWR. Always pay close attention to the gross axle weight ratings. Be careful not to assume the vehicle's maximum towing capacity will handle the pin or tongue weight of any trailer."
2. In the case of an owner who has a three-quarter-ton truck with a rear GAWR that is too light for the trailer's kingpin weight or a family that has a three quarter ton SUV or van which has never been considered able to tow a fifth wheel or gooseneck trailer, the common corrective action has been to upgrade to a bigger truck, select a lighter trailer or add aftermarket helper springs and/or air bag suspension kits to the existing truck. Modifying the rear springs is permissible, but it's important to note that doing so does not change the tow vehicle's Certification Label, that is, unless a professional adds an additional Certification Label showing the new rear axle load rating. Many RVers have installed the mentioned modifications on their three-quarter-ton trucks and have successfully towed fifth wheels. (Consider reading this article: The Truth about Altering Vehicle Weight Certification)
There is an alternative and it may significantly save the owner of a three-quarter-ton truck or SUV or van some money. Any one of these vehicles, including trucks with suspension lift kits, may be capable of towing fifth wheel or gooseneck trailers by equipping it with an Automated Safety Hitch System.
Automated Safety Hitch System
After interviewing Joe Jamieson, who is the CEO of Automated Safety Hitch, Inc. and the inventor of the Automated Safety Hitch System (ASHS), it didn’t take long to realize the hitch system is one of the most innovative RV safety products on the market. With this system you could tow a big fifth wheel or gooseneck trailer with most three-quarter ton vehicles.
As Jamieson, who has both a degree and an extensive working background in aeronautics, guided me through the plant, he explained the details of the manufacturing process. When it comes to construction, Jamieson does not take shortcuts. When asked why he goes the extra mile, his reply is, “So I can sleep well at night.”
During my test drive I towed a heavy two axle horse trailer filled with a bunch of junk and I could easily stop just by activating only the brake controller. Very little pressure is required to brake with the vehicle’s brake pedal. Turning around tight corners and maneuvering through traffic is a breeze with the steerable axle that automatically locks straight when not doing slow tight turns.
I recommend this system for owners of three-quarter ton vehicles who want to tow a larger trailer which has previously been limited to one ton or larger trucks. Call Joe at +1 (940) 320-3008 or visit his website.
Read FWS's founder's complete hands-on review:
Note: Fifth Wheel Street., nor any associated entities, nor its founder have any vested interest in the Automated Safety Hitch, Inc.
Q: What about axle air springs (bags) like the Firestone Ride-Rite - Want they increase my load capacity?
A: No. Here is a direct quote from Firestone/Ride-Rite: "Please remember that air springs do not increase the load carrying capacity of your vehicle. *DO NOT EXCEED THE VEHICLE'S RECOMMENDED GROSS VEHICLE WEIGHT RATING (GVWR)"