How to Increase Your Truck's GVWRby Richard Rowe
Unless you're the proprietor of a certified coach builder, legally speaking there's no way to increase your truck's gross vehicle weight rating (GVWR). This rating comes from the vehicle manufacturer, and is equal to the truck's curb weight plus towing capacity plus cargo capacity. The truck's weakest link defines its weight limitations. This might be the suspension, springs, tires, axles or any other weight-bearing portion of the chassis. Private vehicle owners, however, can do a lot to increase a truck's cargo and towing capacity.
Identify your truck's weakest link by researching its weight-bearing components. For example, say a given truck has a pair of Dana 44 axles rated at 3,500 lbs. (for a total of 7,000 lbs.), 99-load tires rated at 1,709 lbs. each (for a total of 6,836 lbs.) and springs with 5 inches of travel at 270 lbs. per inch (1,350 lbs. per spring, for a total of 5,400 lbs.). This example is fairly typical in that spring stiffness is the limiting factor at 5,400 lbs.
Replace or reinforce the weakest link with something of a higher weight rating. In the example, the truck owner might opt to install a set of stiffer leaf springs. If the new leaf springs have 5 inches of travel at 500 lbs. per inch of travel, the new spring rating would be 10,000 lbs. (500 lbs./inch x 5 inches of travel x 4 wheels). In the world, this incredibly stiff spring set would result in a jouncy, rock-hard ride whenever the truck runs without cargo. It is for this reason that many truck owners choose to install supplemental air-bags that offer extra support only when required.
Replace the next weakest link. In this example, the stock tires 99-load index rating (1,709 lbs. apiece) is the limiting factor. Replacing those tires with a set rated at 2,469 lbs. (load index rating 112) will bring total tire ratings up to 10,596 lbs.
Install a set of heavier-duty axles. In the example, the truck's pair of Dana 44 axles limits the its load capacity to 7,000 lbs. Replacing them with a set of stronger Dana 60 axles (rated at 5,500 lbs. apiece) will bring the axle rating up to 11,000 lbs.
Continue replacing the weak links in your truck's load-bearing components in this way until they're all within your target range. In this case, that would be about 10,000 lbs. On an average truck, you may need to replace (in this order) the suspension bushings, driveshaft U-joints, the drive shaft, transfer case and transmission. Consider installing a supplemental transmission oil cooler to avoid overheating the transmission under load.
- Manufacturers make the springs your truck's weak link for a reason. It's far better to allow the springs to bottom out under heavy loads than to risk blowing a tire, breaking an axle or U-joint or busting the transmission. Keep the spring rate lower than everything else so that it gives before anything expensive gives way.
- Towing a trailer can drastically alter your truck's weight distribution. Consider installing a bed-mounted "goose-neck" hitch to put the trailer's weight right over the rear axle instead of hanging off the bumper.
Things You'll Need
- Metric and standard sockets, full set
- Metric and standard wrenches, full set
- Screwdrivers, full set
- Penetrating oil
- Cutting tools like grinders, reciprocating saw and torch
- Welder and welding supplies
Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.