Operating Beyond the Pavement

The solution for many departments is to purchase a readily-available stock truck chassis and modify it in some way. The modifications take many forms, from steel bumpers to roll-cages to special skid plates. One of the most common mods is to replace the factory dual rear wheels with super singles.
The benefits of changing the dual rear wheels are two-fold. First, with dually’s, mud or sand can get caught between the tires. When the truck is moving these types of soft soils, it creates a “suction” that drags on the wheels and makes getting stuck more likely. Second, many super single tires can be purchased with very aggressive tread patterns better suited for off-road use than the stock tires.
So, if you are interested in a super single conversion for your next brush truck, here are some of the common things that you should consider.
Weight Ratings:  It’s a simple fact that dual rear wheels will have a higher weight rating than single rear wheels, so to go to a single rear wheel will limit the available axle capacity on the back of the unit. On a class V truck (i.e. Ford F550’s and Dodge 5500’s), the largest tires that are available to fit that size axle will only have a load rating in the neighborhood of 6500 lbs. Consequently your axle rating will be limited to 13,000 lbs. However, because of the way Ford and Dodge rate their total GVW, you may still have the full GVWR. Make sure you get a weight projection in advance to make sure the truck can hold what you want.
Lift Kits: A common question is whether super singles require a lift kit. The answer is not necessarily. The stock tires on a Class V chassis are usually about 32-34 inches in diameter. There are a couple of similarly sized aftermarket tires that can carry the load and will therefore fit on the chassis without the use of a lift kit.  However as a rule, the more aggressive the tread the larger the tire so if you want an extra aggressive tread, you will probably need a lift kit.
Warranty: Do super singles void the original manufacturer’s warranty? Like so many things in life, it depends. Obviously, the chassis supplier won’t provide a warranty on work they didn’t do. So if they didn’t install the wheels or the lift kit or any other component, those won’t be covered through the chassis manufacturer. Further, if there is reason to believe that any of the modifications caused a failure in other components, those won’t be covered either. So it’s important to work with an installer that has a good relationship with the chassis manufacturer and has been trained on what they allow and don’t allow. That way if there are any problems, they can be there to stand behind the product.

Doug Kelley, KME Wildland Product Manager
Posted: 10/23/2015 9:53:19 AM
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