Measurements of track diameters

[Hydroracer]

I'm totally new to model railroading. I am setting up a "N" scale set which will have many different diameters of track. What I need to know is, how is the diameter measured? I mean is it from the center of the track, or the outer parimeter? Let's say I have a 19" circle, is this measured in the center of the track, or the outside? From the center, it will be much wider than 19" from the outside measurement. I need to know this because I'm making a mountain landscape for this set for Christmas and this set won't arrive until almost Christmas. I want it to be a surprise.

Thanks

Don

[mhampton]

The curve radius is measured to the middle of the track.

[Joe Satnik]

Dear Hydroracer,

The outside diameter is twice radius plus one track bed width. (O.D. = 2R + tbw) 

Bachmann N scale EZ-Track has a track bed width just a hair under 1-1/16". 

Hope this helps.

Sincerely,

Joe Satnik

[jake_iv]

Qucik suggestion Don - visit you friendly hobby shop and pick up a NMRA 'N' standards gage.  It comes with clear instructions and will give you something to check clearances easily.  Generally, you will need about 12 mm of clearance from the outside of the rail head to the closest structure or about 17 mm from the centerline of the track to the closest structure.  In reality you will need more than that on curves because of "overhang" of some model rolling stock and locos.  I would use at least 20 mm minimum clearance everywhere except straight, parallel tracks in the yards.