By now I guess most owners of an R class will have worked out their own individual method of getting their loco to pull a decent load on a layout with grades.
Like to share my experience.
I found the hinged plate covering the gap between loco and tender was stopped from moving up past a certain position..........when placed in its normal location on the tender, it was bearing down hard on the front of the tender. This was actually causing the back of the tender to be a little raised, with the back bogie only just being in contact with the rails. At the same time, the back of the loco was being lifted a little, taking the weight off the rear drivers and causing frequent derailment of the loco's rear bogie. Solution was to let the plate hang down on the tender draw bar (initially), and then to remove it altogether, when it fell off while I was trying to get the plug into its socket last time I ran it.
This by itself only marginally increased the pulling power. Wheels still slipped on the grades with very modest loads.
So Bullfrog Snot was applied to the two rear drivers. Performance was improved out of sight. There are no pick-up problems and the loco can pull a more typical load up the grades on our club layout, where before, it slipped to a stand. I feel I dont need to add any weights now.
I know some have aversions to traction tyres. To be honest, I dont know what their beef is. If they get your loco to pull a decent load, what's the problem? I point out that Marklin, Fleischman and Roco have been using traction tyres on their steam locos for decades. And who will argue about the quality of these brands? In this case, these "painted on" traction tyres applied to my R class have turned a "disappointment" into a "very satisfied".
I found my Lima VR B class was a compatible runner with the R class. They ran well together, and I ran a lengthy train with these locos at the head. Looked great. Can show photos if anyone is interested.