- Join the NMRA
- About the NMRA
- Education
- Resources
- Community
Search NMRA.org
RP-4.5 Hi-Rail Wheels
NMRA STANDARDS are the primary System for Interchange. For those modelers undergoing transition between Ready-to-Run and Scale Model Railroading according to NMRA STANDARDS these alternate Systems are provided. Wheels and Track made to these specifications will NOT Interchange with those made to conform to NMRA STANDARDS.
See RP-4 for diagram illustrating dimensions, and see RP-3.5 for related TRACK Systems.
Note that these Systems are not developed or controlled by NMRA. For scales where overseas manufacture predominates, applicable NEM/MOROP Standards, modified to agree with observed practice, are shown. For scales where domestic manufacture predominates, dimensions reflecting observed practice in the field are shown. While believed to be reasonably accurate, these dimensions must be followed with reservations, and NMRA cannot be responsible for their accuracy.
Although presented here as standard gauge (4'-8 1/2") Systems, these limits may also serve for appropriate narrow gauge of a larger scale. Thus: "G Gauge", 1 meter (39.37") gauge in 1:22.5 scale, uses No. 1 System dimensions.
| Name of Scale | Scale to Foot | K Check Gauge max | B Back to Back min |
N Tire Width min | D Flange Depth max | T Flange Thickness max |
|---|---|---|---|---|---|---|
| No.1 | 3/8" | 1.652" | 1.567" | .244" | .118" | .087" |
| (42.0 mm) | (39.8mm) | (6.2mm) | (3.0mm) | (2.2mm) | ||
| O | 1/4" | 1.156" | 1.093" | .230" | .094" | .063" |
| (29.4mm) | (27.8mm) | (5.8mm) | (2.4mm) | (1.6mm) | ||
| S | 3/16" | .777" | .705" | .172" | .093" | .065" |
| (19.7mm) | (17.9mm) | (4.4mm) | (2.4mm) | (1.7mm) | ||
| HO | .138" | .604" | .563" | .110" | .047" | .035" |
| (15.3mm) | (14.3mm) | (2.8mm) | (1.2mm) | (0.9mm) | ||
| N | .075" | .320" | .291" | .087" | .035" | .024" |
| (8.1mm) | (7.4mm) | (2.2mm) | (0.9mm) | (0.6mm) | ||
| Z | .055" | .230" | .207" | .061" | .024" | .018" |
| (5.8mm) | (5.3mm) | (1.5mm) | (0.6mm) | (0.5mm) |
NOTES:
1. Truck BOLSTERS (S HI-RAIL only):
Low Bolster: Freight car trucks: 13/32" Passenger car trucks: 1/2"
High Bolster: All Trucks: 5/8"
2. Hi-Rail Wheels do not conform to the contours and dimensions of RP-25, so Flange Thickness T is listed above. Contours typically have no fillet radius between Flange and Tread, and Flange tapers on one or both sides.