A tag axle is located behind the drive axles on a heavy vehicle.
Understanding Tag Axles
A tag axle is an auxiliary axle positioned at the rear of a truck, tractor, or trailer, specifically behind the main driven axles. These additional axles are not typically driven themselves but are used to help support weight and distribute the load more evenly across the vehicle.
The primary purpose of adding a tag axle, or its counterpart the pusher axle, is load management. As mentioned in the reference, "The decision to spec either configuration is generally based on load balancing of the vehicle." By adding extra axles, the gross vehicle weight rating (GVWR) or gross combination weight rating (GCWR) can be increased, allowing the vehicle to carry heavier loads while staying within legal weight limits per axle.
Tag Axles vs. Pusher Axles
The video referenced titled "When to use pusher axles over tag axles" highlights the key distinction between these two types of auxiliary axles: their position relative to the drive axles.
- Tag Axle: Located behind the drive axle(s).
- Pusher Axle: Located in front of the drive axle(s).
Both configurations serve the purpose of load balancing and increasing carrying capacity, but the choice between them often depends on factors like weight distribution needs, suspension requirements, and vehicle maneuverability characteristics.
Why Vehicles Use Tag Axles
Vehicles such as dump trucks, concrete mixers, heavy-haul tractors, and some buses utilize tag axles for several reasons:
- Increased Payload: Allows the vehicle to legally carry more weight by distributing it over more axles.
- Load Distribution: Helps balance the weight across the chassis, reducing stress on the frame and other components.
- Compliance: Enables the vehicle to meet axle weight restrictions imposed by road and bridge regulations.
- Stability: Can contribute to better vehicle stability when carrying heavy or unbalanced loads.
In summary, when you see a heavy truck or bus with extra axles located towards the rear, behind the wheels that power the vehicle forward, you are likely looking at a tag axle configuration, primarily installed for enhanced load balancing and capacity.
