TRACK DISTANCE

The minimum spread would depend on the size of the curves and the equipment you are planning to run.

With this info someone on here could help out.

I use Ø108" outer and Ø99" inner curves for my double main, which therefore are 4.5" apart. Where I have four parallel tracks, as in the yard, I use the curves mentioned above, with Ø90" and Ø81". This allows me to run everything I have, including both MTH Premier and Vision Line Big Boys with all my rolling stock and other locomotives. They do come close when I have 18" passenger cars on the outer curves and the Big Boy on the inner curves. 

The only two I cannot run are the MTH DDA40X on the outer curve and the Big Boy on the inner curve; the DDA40X encroaches on the inside of the curve too far because of the long distance between its trucks.

As Scottie said, above, it ultimately depends on the curves you will use and the equipment you will run

Good luck!

Alex 

The 9"/4.5" track center is consistent with Atlas curve track ........ O36, O45, O54, O63, O72, O81, O90, O99, etc...................

Lionel's Fastrack system, which is what the OP is invested in, is designed with concentric curves being 6 inch spacing center to center (excepting O31).

YM96,

   Nothing wrong with FasTrack, and the FTCC Switches are fantastic engineering.  Like Scottie advises it all depends on what you are running or going to run on your tracks.

I do advise using the 072 FTCC Switches, to be able to run many different size engines and lots of different rolling stock.   

If you do have some 036 remember to use 031 RealTrax for your inner most Oval, 031 FasTrack will not fit inside 036 FasTrack with modification.

Have fun building your layout.

PCRR/Dave

FasTrack seriously great track and switches!

I knew I left something out.  I am running 084 curve on the outer most track to accommodate a DDA40X I have, but the rest of the locomotives can handle 060 track on the two inner tracks.  I do have the 072 switch track to accommodate the DD, and only plan to run that one on the outer most track unless I switch it into the inner most track right before I switch it off to it's straight away parking track down the middle.  So 084 and 060.

Caution: 4.5 inches does work with larger curves like 99 & 108, maybe even 81 and 72.  But when you get down to O36 and O45, depending on what equipment you're using, the overhang can be proportionally greater.  So you might want to insert a cut 1" straight in the middle of the O45 curve, to widen the spacing out to 5".  Test it with your largest equipment, as Yardmaster describes above.  Pay special attention to where the inside loop transitions from curved to straight, and how close loco cabs, handrails, etc., get to rolling stock on the outer track.  My $.02.