TAG AXELS

tag axle is non driven axle behind drive axle

MPG comparing to 6x4 is about 7-10 percent better depending on how big axles you have what kind of transport tires .....

 

Tag axes and push axes are popular in Europe, especially in UK.

They make 6x2 trucktors, usually all is controlled with ECAS.

yeah, I saw converted to 6x2 US trucktors in Russia too.

How do they do it? There is only one drive axe in truck, the other rear axe is free rolling axe. In case of tracktion problems ECAS dumps air from tag axe air bags and add air to drive axe and when truck accelerates ECAS inflate tag axe air bags.

There are lift axes, there is one more air bag that lifts tag axe.

Lifting lowering is ECAS controlled too and it depends on load, but there are Tag Axe controll buttons in cabine.

Benefits - less price then 6x4 truck, less weight. But for bad roads like in ex-USSR, snow, mud 6x4 are better anyway

Read more about this here.
http://inform.wabco-auto.com/intl/scripts/intl/pdf/815/00/27/8150100273t2.pdf

 

I'll answer the only part I understand.

A tag axle is a non-driven axle (aka: dead axle) located behind a drive axle. A non-driven axle located in front of a drive axle is called a pusher. Tag and pusher axles may, or may not, be liftable and may, or may not, be steerable.

 

http://www.flickr.com/photos/phatboyjim_truck_pix/3682207248/lightbox/

Just example

 

A tag axle is a axle that is in the position of one of your normal drive axles.
Usually the rear drive position but can be in the position where the front drive axle normally is.
The big difference is that it is just a carry axle , it does not have a diff or side-shafts.
It is like an axle on a trailer.
It makes the truck lighter and there is less loss from friction as there is no 2nd prop shaft , diff or side-shafts.
This results in a lowering of fuel consumption.

The down side is lower traction as you now have one less drive axle.

A 2,5 diff ratio sounds very fast unless using very low profile tires IMO.
Never seen this on a class 8 myself.

 

Steerable axes are usually UK feature. They use steerabel pushers.

 

there is no 2.5 ratio as much i know

fastest meritor should be 2.64

also they have non steered lead axle


......

but another important thing usually non steered lead axle tractors use lot more tires than non steered tag axle

 

yep, becouse steered pusher is linked to steering box and lead axe can not be linked.. But there are self steered axes, and electronics lock them at higher speed, usually over 15-20 MPH

 

Here is a pic of one done on a freightliner columbia for the batesville caskit company. Hope this helps.

KH