|Unit Code: |
|Pusher Axle applications vs. Tag Axle applications - |
|Pusher axle (air lift axle in front of the tandem Drive Axles)
Tag Axle (air lift axle behind the tandem Drive Axles)
Pusher axles are found most commonly on Dump trucks due to the fact that Florida law allows them to scale 44,000 lbs on the tandem and 20,000 lbs on the front with flotation tires, or a gross of 64,000 lbs. When the pusher axle is added this allows 6,000 more lbs up to a total legal gross weight of 70,000 lbs.
This then led to their use on Heavy Haul tractors, but unlike dump trucks where a substantial amount of the weight of the load can be transferred forward, it is not possible to front load the tractor and take full advantage of a weight transfer. The front steer axle of the empty 4 axle heavy haul tractor typically weighs about 11,000 lbs and the rear tandem will weigh about 12,000 lbs empty. Even when we have the fifth wheel slid ahead of the tandem 24” to 36” we find that when we reach the 20,000 lb limit on each of the two drive axles we will only have about 7,000 lbs on the pusher axle, and the weight on the front steer axle has gone down to about 7,000 lbs. This is a total of about 54,000 lbs on the tractor.
When we install the detachable tag axle behind the drive axles we will leave the king pin on a 120” swing clearance gooseneck placed directly over the center of the tandem drive axles. Then we will load the tag axle to the full 20,000 lb limit of our over weight permit as well as 20,000 lbs on each drive axle. The cantilever effect of the tag axle will transfer weight to the front steer axle up to 14,000 lbs or more, which is an increase on the front axle from 11,000 lbs empty to 14,000 lbs, or a total of 3,000 additional lbs. Our new total with 14,000 lbs on the steer, 40,000 lbs on the drive tandem and 20,000 lb on the tag axle is 74,000 lbs on the tractor in the tag axle application vs 54,000 lbs in the pusher axle application. This represents an increase in payload capacity of 20,000 additional lbs.
One additional advantage of the detachable tag Axle application is that when we decrease the weight on the air lift axle to make turns the weight transfers right back directly onto the drive tandem which is where we want it. This also decreases the weight on the front steering axle. In the Pusher Axle application with the fifth wheel slid 24” to 36” ahead of the center of the tandem additional weight will be transferred onto the front steering axle causing a serious and unsafe overload situation to occur.
Tom Fouche, Pres. Phone 352-622-3199
Mid-State Equipment, Inc. Fax: 352-236.3085
PO Box 1119 www.heavyhaultrailers.com
Ocala, Florida 34478 e-mail: email@example.com