I've been using the same old Trek mountain bike that I got back around 1995 era. I use tires that are less knobby (more like on-road) and it supports my weight fine (which is a bit less than yours now, but I started out about the same weight). My rear sprocket set tends to skip under power when in certain gears, so I just keep it in 15th gear all the time; makes for a good leg workout on hills.