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RP-25 Wheel Contour
Designed by Olesen, Mortimer and Bradley
This wheel contour is specified for optimum track holding ability and most prototypical appearance within the Interchange limits of NMRA STANDARD S-4.
- Wheels listed above provide a selection meeting the interchange requirements of STANDARD S-4 and RP-4 in all scales 'O' and smaller.
- N' and D' are Nominal 'design dimensions' providing reasonable tolerance within the limits specified by N and D of STANDARD S-4.
- Dimensions T and W are measured at the Gaging Point P which approximates the point of tangency between R1 and R2.
- Radii at the edge of the flange should be as large as possible within prescribed limits to reduce side friction against the railhead, to protect Frog Points by decreasing effective Wheel Check Gage, and to guide the flange thru flangways and past other obstructions.
- Tread Taper is not required, but 1 degree to 3 degree mold release draft is allowed. Note that NEW prototype wheels include a taper in anticipation of wear. WORN wheels show a reverse taper. Model wheels are often subject to a buildup of track 'dirt' that adds an effective taper.