How exactly are fastback & standard Tubular track curves measured?

Ok found the answer about fastback…

The width of roadbed on a single piece of fastrack is about 4 inches.

The diameter of any circle of fastrack, roadbed edge to roadbed edge, will be whatever its advertised diameter is plus 4 inches. 

So that makes the diameter of a o72 circle 76 inches, from roadbed edge to roadbed edge.

 

 

What about tubular track?  Is O72 tubular measured center rail to center rail?  I guess if it wasn't, then they wouldn't be the same exact radius...

Steam,

 

This out of a Lionel Catalog. 

 

I hope this help you out here.

 

Good luck,

 

John

steam,

yes, center to center rail for O track also. The outside tie to tie is about the same as FasTrack roadbed to roadbed.

 

When adding the four inches to consider the space needed, one must then add the desired clearance to the edge of the deck. For example, having only 3 inches from the track to edge of the table would require twice that for each side or 6 inches.

 

72 diameter plus the estimated 4"=76" plus the desired clearance to table edge of 6" =82" table for an 072 semi circle.

027 type track Lionel tin plate track  is measured from outside of the tie. most other tracks are measured center rail to center rail

FasTrack is center rail to center rail.  My understanding of tin plate track is that it's measured outside rail to outside rail, so it's actually tighter than listed.

Original 027 tubular is measured from outside rails, which results in center rail to center rail of about 25.62. 031 tubular is also measured from outside rails which results in 28.62 from center rails. Atlas measures both 027 and 031 from the outside rails, not center. I believe all Fastrack is measured from center rails.

 

jim r

Just so you don't buy thinking it would work O-31Fastrack curves do NOT fit inside O-36 Fastrack curves however MTH Realtrax O-31 curves do fit. You can mate them by using both the Fastrack Transition 5" piece and the Realtrax 5" Adaptor piece to connect together (I recommend screwing both pieces down or gluing them together as they don't fit tightly together) or just use the one for the track (Fastrack or Realtrax) you're using to mate to tubular track or cut a section of the track straight across and insert track pins. If you have a small layout with tight turns like I do, because of space limitations all my track is Fastrack with O-36 curves except 2 Realtrax sections with O-31 curves on the layout I'm building.

Lionel 027 is measured to the outside of the tie. put a circle together like I have done and measure it. definitely not outer rail.

O-72 tubular is 35.88" center rail radius, 71.76" center rail diameter, for about 74.03" overall diameter including the ties.

Thanks for all the replies!!  So it sounds like O27 is the only one measured different.  That's strange that they do that.

This was discussed in the CTT form a few years back

 

 

http://cs.trains.com/ctt/f/95/t/185721.aspx

Well, they are all measured the same, but FasTrack(& Super O) are really the only consistent ones when it comes to naming their track with center rail diameters(O-72 is close).

 

Even GarGraves sectional track differs between wood tie & plastic tie track dimensions.

 

MTH O-31 for example matches tubular "O" at 28.28" center rail diameter.

I am thinking of putting a loop of track in my closet on some benchwork. So if I have O-36 track then my closet needs a minimum width of 40"? Stupid apartment living, not very train friendly.

Yes, but FasTrack O-31 only needs 35" if nothing overhangs the roadbed.