6 axle with 60" spread on tractor

I don't have the details, but some states will permit high tandem weights, but the permit cost may be enough to warrant a tag axle or Jeep if you are hauling that weight often.

 

I think that most 55t trailers have long necks, or the flip-neck. In my observations there is a break point where 4 axle tractors make sense, and then heavier than that you are back to a three axle tractor with a heavier steer axle. Once you get to that point jeeps come into play and the drop axle usually hinders more than helps. The other fellows have much more experience though; perhaps they will chime in.

 

You will never need a 2 axle Jeep because your 55 tin trailer will not have enough neck to move weight forward onto the drives and steer axles.

 

I probably didn't make myself very clear; I believe that most 55 ton applications would work well to have a 4 axle tractor. Once you get bigger than that is when you start getting into jeeps and the 4th axle may not help. Does that make sense?

 

I'd rather add a drop axle to the truck than I would want a single axle jeep. Either way, you're going to need a long enough neck to make it work, probably more so with the jeep.