I’ve been going through a “carpet central” phase, and experimenting with various curves.
First, using tubular track, I’ve been experimenting with O54 and O42 as simple and transition curves, which seems to be a good combination. Greatly reduces cab overhang and also suits my modified Williams Scale Hudson - the 17mm coarse Scale (ie not Hi Rail profile) front pilot wheels manage this easily.
Secondly, Fast Track. I’ve now sourced some O72 to complete the curves. This is definitely the best size for O Gauge! I don’t presently have room for an O72 loop, though. I also have a full circle of O48 and O36. The Hudson will negotiate O48 well enough, although it won’t handle O42 for more than a couple of sections.
I’ve presently got a loop with ends as follows - O72, O72, O36, O36, O72, O72 and that works surprisingly well. The Hudson manages the O36 section, which the large front pilot wheels won’t handle an O36 semicircle (the original wheels handle it without problems, of course). The key seems to be, not to have a full loco length of O42 or smaller.
I had fully expected that I’d need to introduce O48 transitions - something like O72, O48, O48, O36, O48, O72 - but it hasn’t proved necessary. However I think I’ll try it, to see the effects on cab overhang on the middle section.