>>9496025Really depends on a lot of factors but the general rule is if your rolling stock and loco are long you need larger radius.
Passenger sets can be troublesome on a small radius for example. I run the shorter 40’ rolling stock on an inner loop with tight radius with no problems.
If you have turnouts try to stick to the larger ones.
I use the # 6 turnouts with Kato Unitrack.
Here is some info to compare the track sections.
https://www.katousa.com/N/Unitrack/g-single.html 