Track and Wheel Standards

Basic Design Dimensions for Standard Gauge

Do not be misled by the large number of decimal places in some dimensions. This does not imply an accuracy that cannot be achieved. The figures have been produced for the purposes of establishing the ScaleSeven Standards and have been calculated to a high degree of accuracy to ensure that the use of the scale ratio does not introduce undesirable distortions.

These standards are for Standard Gauge (4ft 8-1/2in). Use these links for Irish 5ft 3in gauge or GWR Brunel 7ft 0-1/4in broad gauge standards.

Dimension			Prototype	7mm Equivalent		Prototype
			Size (inches)	Exact (mm)	Rounded (mm)	Equivalent (inches)

1	Track Gauge (min)		56.5	32.9583	33.00	56.572
2	Gauge Widening (max)		0.750	0.4375	0.45	0.771
3	Tyre Width	locomotive (nom)	5.500	3.2083	3.21	5.503
3	Tyre Width	wagon and coach (min)	5.00	2.9167	2.90	4.971
4	Back-to-back (max)		53.625	31.2812	31.30	53.657
5	Effective flange		1.125	0.6562	0.68	1.131
6	Back-to-back + effective flange (4+5)		54.750	31.9375	31.98	54.823
7	Check gauge (min)		54.750	31.9375	31.98	54.823
8	Crossing flangeway (min)		1.750	1.0208	1.00	1.714
9	Over check rail faces (max)		53.000	30.9166	31.08	53.280
10	Crossing flangeway – effective flange (8–5)		0.625	0.3646	0.32	0.549
11	Check gauge – (back-to-back+one effective flange) (7–(4+5))		0.000	0.000	0.00	0.000
12	Track gauge – (back-to-back+two effective flanges) (1–(4+(2x5)))		0.625	0.3646	0.34	0.583
13	Back-to-back – over check rail faces (4–9)		0.625	0.3646	0.22	0.377
14	Track gauge + gauge widening – (back-to-back + two effective flanges) ((1+2) – (4+(2x5)))		1.375	0.8021	0.79	1.354

15	Over tyre faces	locomotives	64.625	37.6978	37.67 (min) 37.77 (max)	64.577 (min) 64.745 (max)
15	Over tyre faces	wagon and coach	63.625	37.1145	37.10	63.600

Notes

In the table, the first column of dimensions gives the prototype size, the second shows the exact scale equivalent for a scale of 7mm=1ft (43.5429:1). The third column gives the rounded 7mm scale equivalents which are the basis for the ScaleSeven Standards. These have been set at the values shown after consideration of such matters as the effect of the scale factor and manufacturing tolerances. The fourth column converts the rounded dimensions back to prototype for comparison purposes.

The 7mm scale ratio is 1:43.5429.

Dimension 11 gives the theoretical clearance at crossings.

Dimension 12 gives the clearance on straight track.

Dimension 13 gives the clearance on curved track.

Maximum gauge widening is required at 5-1/2 chains radius, ie 8ft 4in radius in 7mm scale.

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