Do I need a bigger tractor?

[oldnslo]

I have a bx1860 with loader and 54mmm(127 trouble free hours). How large a rear finish mower can i handle wanting a 60in or larger.

Since you have a 54" MMM and it works just fine I would expect that it would handle a 60" RFM also. You may have to adjust your travel speed according to the load but that is part of what the HST tranny provides. Only issue with weight is that now you are pulling the load Vs carrying the load so if you have hills this could be a problem.

Side note: JD puts 64" mower decks on their 25HP gas X485 models and my son has 1400+ hours on his with no problems.