Dually or DRW are terms that refer to a vehicle having Dual Rear Wheels - that is, a pair of wheels on each side of the rear axle.
While usually these vehicles are pickup or utility trucks, some large vans also have dual rear wheels.
The purpose of having two rear wheels is to increase overall capacity with regards to stability and safety margins while carrying heavy loads or towing a substantial amount of weight.
Dual rear wheel vehicles almost always have different specifications for front and rear wheels:
Front: The front wheels usually have a substantial positive offset, to allow for axle hubs that extend a significant distance past the brake rotors and calipers, without the wheel and tire extending past the fender.
Rear Outer: The rear outer wheels usually have a substantial negative offset, which allows the wheel to be properly spaced from the mounting surface where it comes in contact with the rear inner wheel, and to ensure that the tires of the rear pair of wheels do not contact or rub each other.
Rear Inner: The rear inner wheels have a substantial positive offset like the fronts, allowing the wheel and tire combination to be a sufficient distance from the outer wheel while sharing the same mounting surface; the positive offset moves the wheel inboard, towards the center of the vehicle.
Dual rear wheel vehicles provide significant advantages when it comes to payload and towing capacity, but present additional challenges when it comes to proper fitment.
During purchase of aftermarket wheels, when using the OEM wheel diameter, the rear inner wheel is often re-used, with only 4 wheels purchased - the fronts and rear outers. However, if a larger than factory wheel diameter is used, specialty aftermarket rear inner wheels should be purchased as well to ensure that the diameter of all 6 wheels on the vehicle remains the same.
The dual rear wheels on these vehicles must also be fitted to the vehicle with sufficient tire spacing - it is a significant safety hazard for the rear tires to rub together; the friction and stress from this can quickly damage the sidewalls of even large, multiple-ply truck tires, especially under load. Sidewall damage can lead to tire blowouts.
Additional information on Dually or DRW vehicles and fitment can be found in other articles in our FAQs.