Single Powered axle on 3 axel truck

It's called a tag axle, not a second drive axle since it's not powered (driven). Only there to support/spread weight. The truck I'm getting this week is a tag axle truck. Saves weight, and maybe some fuel, but in less than perfect driving conditions you have no option to engage the interaxle for more traction. This will be my first experience with one, but a lot of companies are going to them for fuel economy. In a "twin screw" (both axles can be driven), even though the interaxle is not locked, the parts in both axles are still turning. Similar to a four wheel drive.

 

From what our euro members have said, I would put the driving axle in the front and the tag behind it . Also a dump or lift on the tag seems to be the way to go. It is an interesting idea!

 

We had them and it worked OK in good weather, but drivers said they they really sucked in the snow, I've seen them get stuck on flat ground in the ice. The front axle was driven, the rear was a tag.

 

you need front driven and rear tag
it is better offroad and in snow/slippery conditions safer and use far less tires

and you need lift device for tag

 

as for 6x2 in winter they are better than 6x4 , especialy when empty , we run 8x4 and when it is empty during winter it is not capable to turn in front of my house on slightly slope with about 16000-16500lbs on both drive axles , so you need something to push your drive wheels to ground ......


take a look at this , 6x2 110 000lbs , worst norwegian roads , you can find there 15% slopes

 

If you can lift the tag axle they are far superior both loaded and unloaded in snow and ice compared to a twin screw without difflocks. The important thing when driving on snow or ice is to have as much weight as possible on the drive axle. In Scandinavia most trucks are single drive and we have much worse winter weather most US truckers ever experience.
Spec the truck with the tag axle behind the drive axle. Also make sure that the drive axle has lockers. Best is of course if you can both dump and lift the tag axle, but dump is a necessary. The good thing with lift is that every time you go empty or with very light load use safe both fuel and tires.
Having a 2 axle truck pulling trailers is like begging for trouble in the winter as there is no way of getting more weight on the drive = more traction as the balance is fixed between front and rear axle.

 

Not sure if it is Meritor or Dana, one of them has a convertible single drive tandem.
Rear axle uses same axle housing as a normal driven rear axle, but without the differential, and other related hardware, and no drive-shaft between the 2 axles.

Later on, for example at trade-in, differential and other parts can be installed in the axle housing, add driveshaft between the two axles, and you have tandem drive.

 

Yep, I'd recomend front axle drive, rear tag, like Germans build their 6x2 trucks. In England they love pushers.

To lift ore not to lift.... I sugest to use non lift tag axle is easier to build. The tractiom help valve (electronically controlled) is used only. This valve dumps air from tag axle air bags (level system pums drive axle to keep ride height). It is enought to start. No lift bag, no additional valves, no additional weight and electronics