3 rail

No simple answer to this one, so let's say maybe.  A lot depends on the type of 3-rail track and/or switches you use, the quality of trucks on the equipment, the flange construction on the wheels, and the minimum diameter of curves you employ.

Chuck

And most 3-rail switches will be difficult to transition with 2-rail scale wheels.  Most 2-rail rolling stock will roll fine on wider curves or straight track, especially if it's a flat-top profile like Atlas track.  I've even run 2-rail rolling stock on Lionel Fastrack, but they come to grief on the switches.

thanks john.i ask because i am eyeballing an atlas 2 rail gunderson set.i use fastrack

I think you better plan on replacing at least the wheelsets and possibly the trucks with 3-rail equivalents.

2 rail stuff runs fine on flat top 3R track, which Fastrack is not.  While it can run ok even on tube rail, it will have absolute fits if there are any switches in the equation.

I just bought an Atlas 2 rail freight car that I intend to convert to 3 rail trucks. Keep in mind I have always had 3 rail O scale stuff. So for me, the deep wheel flanges and giant couplers look great. I was shocked to see how small the coupler and wheel flanges were on this two rail car. It ran fine around the loop of the layout. I didn't take it into any switches so I can't comment on that. I just definitely wouldn't want this car in my consist when I get the need for speed and crank the throttle up. It would almost certainly want to jump the rails.

I'd advise against using 2-rail equipment on FasTrack. I've done it on our O-72 demo layout at the Los Angeles Downtown Winter Festival, but Fastrack isn't true "flat top" rail and I was using shorter equipment and 4-axle diesels. Also, the O-72 is NOT true 36" radius on the curve center line. I'd recommend changing out the trucks for 3-rail which should be a pretty straight-forward swap on Atlas rolling stock. Getting the cover off the coupler box to expose the screws is a little tricky, but not difficult.

I've run two rail equipment on Gargraves and Atlas track.  The wheels bounce through the frogs on the turnouts, but otherwise I have not suffered any major disasters so far.  Depending on car length and the fixed couplers, radius becomes the issue.  Regardless of being 2 or 3 rail, my Kaddee fixed coupler equipped 80' and 85' cars work best starting at 0-80 and up.  O72 does work, but is an absolute minimum.  I know that because the outside loop on my modular home layout is about 071 and some cars and locomotives bounce out of the rails.