ho track radius

Model Railroader Layouts and layout building
1

starting to draw up a layout in ho and have a question about fitting a 22in radius curve inside a 24in radius curve, center of track would be 3 inches. this radius will be going along a wall into a corner making almost a full 360 then coming back together. is that possible ,or does the outside radius need to be larger. i also know i will need a car length of straight to prevent a S CURVE. most of rolling stock is shorter wheelbasecars and locos.

2

Anything longer than 50 scale feet is going to be getting real close to each other. Good luck.

3

Eldorado,

If you want to maintain 3" track centers through your curves, either your outer track radii has to increase by 1" (R25"), or your inside track radii has to decrease by 1" (R21").

Tom

4

Elementary, my dear Watson! Elementary!

5

And their centres of arc must be superimposed precisely. [:D]

6

thank you i was having a blond moment at the time on drawing paper. so 25 and 22 will work fine. and give me some car clearance.

7

Don’t forget to allow sufficient clearance on the outside of the outside curve too. We have a tendency to worry about clearances between tracks and forget about the clearance needed on the outside of a curve that may be against a wall or other structure.

According to NMRA Standards (http://www.nmra.org/standards/sandrp/s-8.html) you can probably use 2 1/2 inches between centerlines without problems (see red items in chart below) if it helps you in other areas.

Also don’t forget about easements. Subtracting a quarter or half an inch from your radius for an easement will actually help the operation of the equipment entering the curves - especially with the radii you are talking about.

Good Luck,
-John

This STANDARD lists Track Center Distances and provides for Side Clearances required for various curvatures with three size categories of models.

Curvature Degrees

M(*)

0

5

10

15

20

25

30

35

40

45

Radius - Prototype

Tang.

1146

574

383

288

231

193

166

146

131

‘HO’ Scale

Radius-Inches

Tang.

158

79

53

40

32

26 1/2
8

thanks for more input on this, another thing learned to mrr. hope the weather shapes up when i come down to fort bragg N.C. to welcome my son in law back from afganistan it has been a long wait.

thanks rusty rails