Jan 09 2009
Tag Axles
What is a tag axle? It is a trailing axle that is usually mounted behind the drive axle. It is a non driven axle equipped with two wheels one on each side.
What does it actually do? They add to the carrying capacity usually 10,000 to 20,000 pounds. It decreases the distance from the rear most axle center to the further rear most portion of the vehicle. This increases the departure axle of the rear overhang of the coach body and frame, making the rear of the coach frame less liable to contact the roadway on uneven ramps or sloped surfaces. The extra axle is usually equipped with an extra set of brakes.
The differences of the tag axles; the deep dish like tag axle is identical to that of the drive axle ahead. There is also the tag axle that looks like the front wheel, rather than the drive. Some are steer able, they offer less tire wear and help to reduce the turning radius by stimulating a shorter wheelbase during tight maneuvers. The reverse rim, similar to the front wheel, can load the wheel bearing at, or near, the dead center of the wheel. Which means the bearing carrying that wheel would be directly in line the center of the tire tread. If the single wheel on the tag axle is mounted with the deep dish facing out, like the duals on the drive, except with no inner wheel, the bearing is wheel inboard. This increases the bearing load greatly, requiring a larger and stronger bearing and a stronger frame mount.
Some have automatic following tags. Another way uses an airlift of the tag which lifts the tires off the roadway. The final style unloads air, leaving not much more of the weight of the tag assembly on the road. Both the lifting and unloading type need some operator input by pushing buttons.
Does a tag axle help with driving and handling? If a single axle is properly balanced, aligned, and the running gear are set properly, they say there isn’t a noticeable difference between the tires.
