Want to know more about tag axles

[jadatis]

In different topics I read about Tag axles, and I think many dont know what you can do with it.

As far as I know its an axle that can even be lifted of the ground, but can also be put more pressure on the suspension ( excuse me if I use wrong word, I am Dutch) so more weight is carried by the tag-axle, but this influences the weight on rear and front axle.

On Trucks in the Netherlands , where I live , I often see such an axle , and sometimes they are placed behind the rear/drive-axle , but sometimes in front of that so in between front and rear axle.

So main question is here, if my idea is right , and every Tag-axle can be lifted off the ground , and you can vary the pressure on suspension.
And I want to know what tag you all have, in front of rear/drive or behind placed.

For tirepressure, weight on axles ( or better seperate wheel(pairs) ) is important , so if one axle is overloaded , you can play with the pressure on Tag to get lesser weight on that axle, but not always.

1: if Tag behind rear/drive-axle.
If more pressure on Tag ( not tirepressure) lesser weight on rear axle and more on front axle, and the other way around .
2: if Tag in between front and rear ( in case of 3 axles total) , more pressure on tag gives lesser weight on front and rear axle , but mostly on rear lesser weight, because tag is placed close to the rear axle, but can be wrong about that.

So once my question is answered, this topic can be used to get a general idea about what you can do with it.

[ChassisGuy]

RV tag axles do not lift.... at least none do that I'm aware of. Tags are located behind the drive axle. Some steer, some don't. Weight distribution is usually 1/3 on tag and 2/3 on drive. This is usually not adjustable but that can be worked around.

[Dtwallace]

I think there is a general misunderstanding as far as weight transfer as you indicated but not in the exact wording.
In general, s tag axle is behind the drive axle, thus the term tag along. When this axle is in front of the drive axle, we called it simply a lift axle.
The big difference in placement is determined where you need weight taken away from.
I'd like to use a dump truck as an example, you seen lift axles on dump trucks forward if the drive axle. When the dump truck is loaded to capacity, the drive axle and the steering axle will be supporting 100percent of the weight. At this point they are both over loaded.
So we drop the lift axles that are between the drive axle and the steering axle to remove weight from the two over loaded axles.

Now let's look what the tag axle does for us.
Same truck, same load, but this time the we have a tag axle behind the drive axles. We drop the tag axle and weight is removed from the dive axle only, not both drive and steer.
Also in this case, a very minute amount of increased weight may show up on the steering axle if we over do air pressure on the tag.

Air pressure, should always equal or just below the drive axle air pressure.
The reason for this? A too light of weight on the drive axle will effect traction.

Tire air pressure should be adjusted as recommended by manufacturer.

I used the straight framed truck as an example since you wanted a take on why behind or in front of the drive axles. As you can clearly see, the front mounted drop axle has the advantage for weight distribution, but the vehicle turning radius may suffer.
Some motor coaches have a tag that will lift off the ground completely. I'm more familiar with the ones that just get light at the press of a button, or when backing up.
Hope all that's clear, looking forward to your reply
DTW

[pwhittle]

My RV tag axle can be lifted for tight turns via a switch on the dash. The pressure is adjustable via a pressure regulator to change the amount of weight carried by the tag axle. It is behind the drive axle.

Paul

[bruceisla]

My Newmar tag does not lift ... it just "unloads".

[TonyDi]

Originally Posted by bruceisla

My Newmar tag does not lift ... it just "unloads".

Mine works the same way.

[gemert]

My tag axle also lifts to assist in tight turns. I can adjust the pressure in the tag to vary the weight on the front axle if need be. The tag, if in auto, will automatically lift as soon as I start going more than 5MPH or go down when below 5MPH.

[Kiawah]

The tag, if in auto, will automatically lift as soon as I start going more than 5MPH or go down when below 5MPH.

I think you just wrote those backwards.

When moving forward over 5 mph, the tag would lower to carry the correct amount of weight. When less than 5 or turning, the tag raises slightly so the coach can turn easier without scuffing the tires, and at that point the tag is carrying less weight.

[hypoxia]

Very good explanations above.

My tag lifts completely off of the ground. I suppose the reason some don't is the additional expense of the lifting mechanism.

With the tag down the turning radius is larger, lifting it allows a tighter turn. At a ski resort this winter a bus driver told me he lifts the tag to put weight on the drives for traction up the mountain.

The latest thing in tags is a steerable tag; when the coach turns the tag also turns.

[jadatis]

OK , learned already this here.

A "tag"axle is called lift-axle when its placed in front of the rear/drive-axle.
The motorhomes on this forum have only Tag-axles , wich are tag behindd the rear axle.
Some are fixed , so you cant do anything about the loaddivision.
Some can be lifted , or pressure on them can be set to zero so no load on Tag.
So a 2 way adyusting.
But also Tags exist that can do all, lifted, and a analog setting of the pressure on it.

About the weightshifting a tag gives, if its adjustable.
For that an fictiv example.
Front: weight 10000 ( whatever kg or lbs).
Rear: weight 20000
.

Wheelbase ( front /rear ) 20 feet.
Tag-axle 5 foot behind rear axle .
Asume Tag first lifted of the ground zo weight on it zero ( asume tag itself has no weight).

If Tag set to such pressure on suspension that weight on it gets 5000.
Then by leaver working, you can calculate what weights are added or lowered to front and rear. First rear 25/20(foot)x -5000=- 6250 so less weight on rear axle so it gets 13750 .
Front -5/20 x -5000= +1250 so more weight on front axle .
So new weights
Front axle weight 10000+1250= 11250
Rear axle weight 20000- 6250= 13750
Tag-axle weight......................5000
Total weight ............................30000 and was 30000

So call that minute weight difference on front, but in real the difference is not 5000 on tag so in the end the weightdifference on front can be minute, as DTWallace writes.

At the bottom of page it gave similar topics and one wrote about more wear on Tag-tires. Mayby this topic can explain that in the end and we can see what you can do about that .

[gemert]

Originally Posted by Kiawah

I think you just wrote those backwards.

When moving forward over 5 mph, the tag would lower to carry the correct amount of weight. When less than 5 or turning, the tag raises slightly so the coach can turn easier without scuffing the tires, and at that point the tag is carrying less weight.

LOL you're right! Sorry.

[Dupdyke]

03 dynasty 42' 8 tires was all wheel weighed and he adjusted the tag air to put about 5000 lbs on tag it put 800 more on front, still way under max, and took a bunch off the drives. I was told in wet grass drive slow lift tag for traction. Drives a lot smoother with pressure on tag.

[jadatis]

@Dupdyke

How did he determine the 5000 lbs on Tag?
But 800 more on front is about in line with my example.
If you would measure the distance between front and rear axle and rear and tag, and you would calculate the way as in my example, you would come to those weights.
In this case for instance more then 20 foot between front and rear, and lesser distance between rear and tag.

But I think that some vehicles wich owners think that are fixed, so you cant adyust anything, can in fact be adyusted.
Once owned a normal car for wich you could pump up the shockbrakers to give more pressure on rear axle for when you had heavy loads.
Only needed a normal tire-pump for it.

So if you think your tag is fixed, go look under the vehicle and see if you can find some tubes that seem to go to the suspencion or shockbreakers.
Mayby the tags then can be adjusted, but not from within the car, but with a pump somewhere at a valve in the rear.

Most motorhomes have a pretty constant weight, so once you know the weights on axles and adyusted the tag, you can forget it for years.
Then write down the pressure you filled, so you can check that once in a while.

[Crasher]

In my area an undriven axle that it behind the drive axle is called a tag. It there is an undriven axle in front of the drive axle/axles, it is called a pusher axle. Many motorhomes come with non adjustable proportioning valves that determine the ratio between the drive and tag. Some are 60/40 (60% of the rear weight on the drive and 40% on the tag) while others are 75/25. Also some are adjustable. Few of the newer models will lift the tag off of the ground. When pressurized, the tag suspension may have between 40 psi and up to 80 psi. when they are "dumped" for a turn or automatically "dumped" when in reverse, the pressure will drop to about 20 psi in the bags. There has to be some pressure in the air bags to help prevent the tag tires from sliding when coming to a stop. Below 10 mph, the anti-lock brake system disengages and the tag wheels would slide on wet or any loose surface. I have replace the proportioning valves with manual regulator valves allowing me to adjust the tag pressures to suit the load. On a 43-45' coach with a tag, for every six pounds taken off of the tag, one pound will come off of the steer and all seven pounds will go to the drive axle. In my case, I took 4200# off of the tag which took 700# off of the steer and added 4900# to the drive axle. Now, I have the most stable, well mannered motorhome I have ever driven. Better traction, better weight distribution and excellent braking.