How much radius do I need ?

I should add we have 036, 048, 060, and 072 Fastrack

Your 12, 13, and 15 inch cars should work just fine on O36. The 18 and 21 inch will probably need O60 or larger. Some of my 18 inch cars worked just fine in O36. Others did not.

Depends on if the passenger cars are scale, or traditional/027 sized. The trucks on 027 passenger cars are designed to negotiate tight turns.

 

Bruce

There are two things going here -- what works and what looks good. With the above passenger cars, they should all work on O-60, including the 21-inch cars which required O-54 or better. However, cars look better on the widest curve you can fit in your layout room/area.

 

With FasTrack, the largest curve is 42" Radius (O-84); with MTH RealTrax it's 41" Radius (O-82). Every piece of 3-rail equipment produced to date will negotiate 36" radius (O-72), so that should really be your base line. This will ensure that any future equipment will run on your layout, but everything will look better with larger curves. It just comes down to whether you have the space.

Thanks everyone for your input. 

Most of our passenger cars are MTH Railking but we have added quite a few K line cars lately.