Another comparison would be the Sunset/3rd Rail Erie 2-8-4 Berkshire that I would like to have. The 3 rail engine can negotiate O-54(27"r) while the 2 rail version is listed as 56"r. I understand that the 3rail model has blind center drivers, but man that's a big difference. Especially since many HO 2-8-4 models will negotiate 18"r. If you do the math you see why this puzzles me: 18"r * 87(Ho is 1:87) = 1566" (1:1) / 48 (O is 1:48) = 32.625"r in O scale. I suppose you are right Jim, but this one is puzzling because this is the same model with only the blind drivers and tolerances being different I would think. Perhaps that's all it takes?
I'm still not totally clear on what the missing piece here is. Especially when people tell me that their engines will negotiate much tighter radius than the advertised min. AGHR Matt mentioned that I think most MTH engines up to the 4-6-4s would negotiate 36"r. My own tests with an Atlas F3 coupled to a pair of Atlas gondolas showed that while it doesn't look pretty, they will negotiate 24"r. which I believe is less than what they are listed as.
The whole point of this exercise is to understand what will really run on curves in the 30-48" range that my upcoming layout will have without taking a "Buy it and Try it" approach.
