About all you can run on R1 (which is a left-over from the early Triang-Hornby days, really), is the tiny 0-4-0 and a few four-wheel wagons. Think of it as a dockyard or factory internal track.
Modern-built large 'express' loco's and especially the new IET (which is longer than usual), prefer R4 as a minimum, although they can be coaxed around R3.
As said above, gradients can be a nightmare, and a gradient on a curve is even worse! You MUST have a gentle sweep up from level to climb, and over to level again at the top, no pointy corners, or the engines will either derail or get stuck. For 20mm, (less than an inch) you will need about 600MM (2 feet) approach, and the same again on the other side - in a straight line, twice that round a curve!