The layout has multiple levels. I wanted reasonable sized trains to be able to run without difficulty, so I needed to know that the slopes would be manageable.
To find out what slopes could be used, I conducted some tests using three locos with realistic loads:
- Kato "Eurostar", pulling its 8 carriage rake;
- Farish class 47, pulling 4 carriages + the weight of 4 more;
- Farish 0-6-0 PT, pulling 4 carriages + the weight of 4 more
The conclusions were that in a straight line, these trains would start from standstill on a 1:35 slope and 1:40 was comfortable. I wasn't able to try the effects of a full axle count, or try pulling trains around corners. Consequently I've concluded that I still need to allow some margin.
In practice, my worst case slopes are around 1:60. They were planned to be better than that, but I've kept changes in gradient away from points etc and that resulted in shortening of some of the slopes themselves.