I spoke with Vermonster but sharing my opinions, which are fairly inline with Skibums, here for others considering the same.
As some noted, the most significant limiting factor here is licensing which, for all practical purposes, reduces the maximum combined weight of our vehicle with a trailer to 26000# in every state. It's very difficult to find a consistently implemented exception to this that would be applicable to anyone here who hadn't already purchased their vehicle through a commercial or agricultural entity.
Given that limitation, the maximum trailer weight of each Tremor configuration is as follows:
- F-250 Gas: 16,000#
- F-250 Diesel: 15,200#
- F-350 Gas: 14,700#
- F-350 Diesel: 14,500#
These numbers remain the same no matter whether you're pulling a conventional trailer or a gooseneck.
And, yes, these numbers are counterintuitive in suggesting the 250 Gas has the most towing capacity. Which, from a legal perspective, is correct: if you don't have a commercial drivers license (and if you're not loading so heavy on the tongue/pin as to go over the payload limit on your door jamb.)
Working backwards from this constraint, the math is fairly simple:
14500# (the legal gross combine weight limit of his diesel Tremor) - 12478# (the listed operating weight of a Kubota U55-4) = 2022# (the maximum available weight for a trailer that itself has a GVWR equal to or greater than the weight of the excavator)
And since most trailers that can carry over 12500# themselves weigh well over 2000#, this equation becomes very difficult to resolve positively.
The only possible solution is to pair a U55-4 with an all aluminum bumper pull equipment trailer. There are several on the market with a ~12000# payload capacity and 14000# GVWR that weigh under 2000#. However, I don't know of a specific model that meets the specific constraints and even if one exists (I'd wager one does) this would be cutting it too close for comfort, IMO.
The best solution would be to go for a lower weight excavator. The KX040 (10210#) is, IMO, the best option for our trucks (and most mini-excavator use cases), and this is reflected in the popularity of that model in the market.
In my specific case I resolved this by pairing a Kubota U48-5 (11531#) with a gas F-250, and a conventional 16000# GVW / 4000# equipment trailer.
So modifying the equation above, for my scenario, I get:
16000# - 11531# = 4469# - 4000# = 469# (the amount I'm under the licensed weight limitation.)
Considering that the operating weight of the excavator factors in a 165# operator, this means that I have ~634# of excess capacity: just enough for an excavator bucket or two.
But even this is no panacea as there are additional legal factors to consider. However, I'm personally comfortable with this simple logic (and the accompanying risks) for occasional movement of my machines. Others risk tolerances may vary.