I know the Porter and Davenport will handle a 13-inch diameter curve. I'm building an On30 pizza box layout myself at the present time, and I'm running an article on one built by another fellow in the Oct. issue of the magazine (O Gauge Railroading magazine) which will be featuring On30 narrow gauge via several different layouts and an interview with the folks at Bachmann. The Oct. issue will be released early in Sept.