TAG AXELS

Con-way Truckload started equipping their class 8 tractors with tag axles.
Basically the front drive axle is only axle connected to the drive shaft. The rear axle is a dummy axle. The front of axle is a steel plate, no ring or pinion.
It is lighter, and less friction.
Ours are equipped with rapid dump valves to help increase traction.
Personal opinion, there is a safety issue with this design coupled with super singles = less drive traction.
But bean counters don't have to drive them.

 

Wrecker/Tow Truck drivers love tag axles, they make a killing towing stuck tag axle trucks out.

 

Fastest Meritor RT40-145 is 2.47.

With a 10-Direct, 2.47 and 22.5LP would be 1373 rpm at 65 mph.

My RTLO-13, 3.58 and 24.5LP is 1403 rpm at 65 mph and gets excellent fuel mileage with a 14.0L Series 60.

C13 used to like to be geared a little shorter than that but I havnt kept up with the newer versions.

 

BTW, there is one hidden trap in US trucks if you cinvert it to 6X2. There is central diff lock only, and not all the owners want diff swap so we usually move rear diff on front diff place and remove one differential fully. It realle saves fuel. When truck gets in stuck driver press Traction help button and ECAS deflate rear air bags and inflate front ones, but if one wheel skids only, no diff lock driver can use.

 

it is like a variation of 8x4

Pusher axe


One more pusher axe


A la Turka

 

Ouh, sometimes Robson drive is used to help start with tag axe down