All the tag axel does is allow for extra weight capacity so that manufacturers can add extra weight or length than the frame was built for. My opinion would be to get one without a tag axel if possible.
I would agree with s.harrington. That is espceially true for a class C. The advantage is quite simply that it gets you by with a condition that would be overloading of the chassis if you did not have one. But the problem is that no class C chassis was designed for the use of a tag and all of them were added on by the RV manufacturer. The extra axle is just what the name implies, and axle that "tags" behind the drive axle. The tires will scrub when you turn so they won't last as long as the other tires on the RV. Another down side is that you now have eight tires to deal with, rather than six. Quite often, there is no brake on the tag and those that do have are very often of little use. That will mean extra load for the origional brake system. There are some owners who claim that the extra axle and wheels add some degree of stability. Not sure if that is valid. Reviewers will tell you that the tag can cause traction issues when traveling on wet or slick roads or on unpaved ones.
All of this comes from reading as I have never owned a motorized RV with a tag, and I never will.
Don't you have self steer tag axel's over, there it's like having a front axle as a tag so when you turn the rear wheels steer themselfs cutting out scuffing and reducing the effort it takes to pull round,it works the same as towing a car with an "A" frame, where ever you pull it, the front wheels turn to follow,thus you can have the extra payload without the drag,you would still be wearing anoter set of tire's out but not so quick & I agree with Kirk trying to cross a ditch can lead to loss of traction,good luck Bazzer. Beam me up scottie :laugh: :laugh: sent by pidgeon?
Sure, you may be able to get tag axels which can steer or lift off the ground, but these are additional mechanisms which need maintenance and can break.
As mentioned, a Class C (van) chassis was not designed for a tag axel, so adding one may not be an optimal design choice. On a chassis specifically designed for tag axels (some class A or bus chassis, perhaps) it may not be as bad an idea, but make sure you really need the exra weight handling capacity and it is worth the additional problems.
2 other negatives to keep in mind - the tag axel cuts down on storage space, and on toll roads, may cost you more (particularly in Tollklahoma )