An axle extension member configured for attachment to an axle flange of a truck may be used to modify the truck from a standard track configuration to a wider track configuration to accommodate super single wheels. Methods for adjusting track width of a truck axle are also provided. The axle extension member includes an annular spacer portion and a spindle portion configured to receive an extended length axle shaft therethrough. The annular spacer portion is configured to abut and attach to an outboard face of the axle flange. At least one attachment feature is configured for attaching a disc brake assembly to the axle extension member.