Single & Dual Driven Axle Tandem Question

on a 3 axle tractor you have a steer and 2 drives. A basic model does not have limited slip or a locking power divider. This means that if one wheel slips, the other wont move.

The power divider works as an dif between the 2 drive axles. If you put big tires on the fron axle and small on the rear, the power divider allows the tires to spin at different speeds and minimize tire scuffing. (this is highly NOT recommended though since it could burnout the power divider.)

Your differentials allow left and right wheel positions to spin at different speeds. This is helpfull on turns since the outer wheel has a longer track and needs to spin faster.

So, if one tire hits mud, the power divider puts all the power to that differential and the dif put all the power to the spinning wheel. The truck will always power the easiest wheel to spin, so the one not gripping will spin. If you lock your power diveder, the dif for the spinning wheel put its power to that wheel, but the other dif still gets 50% of the power. if its wheels grip the truck will still move. This be comes a problem on the side of the road. Pulled over to the side with left wheels gripping and right not, you could have power to both difs with power divider locked, but still have both right wheeles slip on mud or grass.

Heres where dif locks come in. (not many trucks are equipped) They lock both left and right wheels together. If left or right have grip the truck will move. With power divider locked and diffs locked you have true 4 wheel drive and it any wheel position grips the truck will move. You shouldnt use dif locks very long because the wheels are locked to the same speed. this means any turn will scuff tires.

Contrary to popular belief...on dry road, a 6x4 truck distributes power to all 4 wheel positions. (not just the front or just the rear) This is why its hard to do a wheeie in a truck. As soon as the front come off the ground, they spin and the rear looses all power. If you lock the power divider, it theoretically is possible with enough HP but extremely unlikly in a stock road truck.

So, benifits of 6x2. Without the power divider and extra dif, you should pick up .3 mpg. Thats a lot of extra weight, and mor importantly, gears that resist the hp of the engine going to the road. Loosing the extra gears can reduce drive line hp loss by 10-30 HP. You also can use trailer tires with less rolling resistance on the dead axle. These would be torn up by the torque of a drive axle, but not by a dead axle. using trailer tires instead of a drive tire can result in about .2 mpg increase. If you have a locking dif you can still get out of trouble. In this case though, you want a dump valve on the dead axle. This allows you to take the air out of the suspention on that axle and put all the weight on the drive axle. this may keep the drives form spining if they were supported by the dead.

A better config is a lift axle. While light or empty you rase the dead axle saving money on tools, tire wear and rolling resistance.

Up side to 6x2 is less parts to replace and better mpg. Downside is, compared to a 6x4 with dual dif locks and a locking power divider, it could be come stuck more. Most 6x4 only have a locking power divider and a 6x2 with locking diffs will do better then a 6x4 without locking diffs. Another down side is snow and ice. Having more gripping wheels is better. Lastly, your jake will only work on 2 wheel positions insted of 4. This can make engine braking on a slippery surfaces more of a problem.

For me, id prefer the 6x2 setup as it is way cheaper to maintain and cost less fuel. The handing ishues arn't an ishu much and they don't perform much worse.

 

No super single spiel ...?

I use (trailer) tires on a tandem axle drive tractor
Goodyear 661... Lots of hp/torque too. No problem .


P.S. I think there called "all position tires"

 

all position and trailer tires are different. All position can handle the torque....strait up trailer tires cant

 

6x4 have better control with off road or snow.

 

6x2 are popular in Europe and in UK. The main benefit is weight difference. Big fuel economy.... ouh, I can see.. Seems to me fuel milage is the same.

6x2 are good for good roads, but when it is winter they all ride with lift axle up. In Europe it is allowed to lift loaded axle temporary, for tracktion help and electronics down the lift axle when truck runs over 15-20 mph.

6x2 truck got more solenoids, valves, fittings, air lines... so not so reliable as 4x2 ore 6x4. So I'd think twice before purchasing 6x2