How big of a dozer can I haul?

Two things that you should consider, is the step deck strong enough on the outer rails to support the weight, track machines, Dozer at that size are usually wider then 8'6" so the weight is going to be condensed on the edge of the trailer, and if the center of the tracks are on the edge that means its mostly steel on steel which has a tendency of slipping and could come off the trailer.
The other issue you might have is the beaver tail and ramps might be too much of a incline going up onto the flat part of the trailer, plus the grousers on the Dozer will tear them up if you do this often enough.

 

Someone posted this a while ago....

 

It takes a really big dozer to be over 8'6" wide at the tracks. An LGP maybe, I'm not sure I understand the to much of an incline part.

 

The OP stated that he was considering a Cat D6R, i don't know what type of D6 he is considering but a R is larger then a M and most of the D6R's i have moved were Right at the edge or over it, Different areas use different size grousers, the point i was making is a step deck designed to handle the weight condensed on the edge of the trailer like a detachable is designed.
The incline part, he will be going from the ground up the incline to the flat part of the trailer, ground to trailer is aprox 36", i don't know how long the ramps are but he stated he has a beaver tail on the trailer, i previously owned a fixed neck lowboy and loaded off the back with ramps and a beavertail at a similar height, going up the incline, muddy tracks and not seeing the centerline of the trailer until the nose of the dozer starts to go down is a dangerous way to move equipment, i did it for a while until i purchased a detachable, i would never go back to doing it.
Had to add this...LOL
I was in a similar situation when i had the fixed neck hyster lowboy, i didn't want to spend the money for a trailer that i wasn't going to use everyday, probably that is what he is thinking too.

 

They do make step decks that will haul a D6 fine, but your "run of the mill" step deck won't hold up very well with it.

We've actually got a 3 axle 50 ton step that I've hauled a D8K on.

 

Only an LGP would hang over, I agree with the edge not being designed to hold the weight.

 

Only a LGP would hang over?
That is not true, a true LGP is the widest width with that set machine that a manufacturer offers.
Cat, John Deere, Komatsu and others offer many track pad widths over the standard widths while being wider are not considered LGP.
I owned a few JD 750's that were LGP with 34" pads, but one had 28" pads which was not a LGP but the width was 9'1" and it wasn't even branded a wide track, my 850C was close to 10 wide but it had 30" pads and was not a LGP or a wide track.
That is what i meant in my previous post about different areas use different size track pads, Ritchiespecs won't tell you that on there website, purchasing my own equipment and moving others has taught me that,i always have a owner measure the machine because you never know how the machine was optioned out, especially a dozer.

 

By the sounds of it I believe that I would invest in an RGN if I were you. It won't be any more expensive now than after you tear your step up.

 

Wow, an articulated truck on a step would put you awfully tall as well as not having enough trailer to support it. I take the short exhaust stack off of 730s when I haul on our RGN to stay under 14'.