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Operating Beyond the Pavement: Super Single Vs. Dual Rear Tires

Doug Kelley, KME Wildland Product Manager

Brush trucks have many shapes and sizes—maybe more than any other type of fire apparatus. But, they all have one defining characteristic: they are meant to operate beyond the pavement. The problem is that there aren’t any commercial truck chassis available on the market that are purpose-built for off-road use. 4×4 is a start, but it’s not the whole story. And sure, there are surplus military trucks, and more than a few departments have those. But, those ex-military trucks often have limited availability and, more importantly, their condition is usually unknown in advance. So, that makes it difficult to plan a fleet replacement just how and when you need it.

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 F550s and Dodge 5500s), the largest tires available to fit that size axle will only have a load rating in the neighborhood of 6,500 pounds. Consequently, your axle rating will be limited to 13,000 pounds. 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 to 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. 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 it didn’t do. So if it 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 it allows and doesn’t allow. That way if there are any problems, they can be there to stand behind the product.

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