Proto:87 wheels are set 0.610 to 0.613 inches apart on the track, compared to the minimum of 0.566 inches on the standard HO models. They are 0.064 to 0.069 inches wide, compared to a standard minimum of 0.108 inches, with a flange width range of 0.31 to 0.35 inches and depth range of 0.012 to 0.014 inches. Flanges on standard HO models are generally 0.03 inches wide and 0.028 inches deep.
The Proto:87 track differs from standard HO specifications too, which generally range from 0.649 to 0.672 inches wide on the track gauge, a minimum of 0.605 inch check gauge width and a maximum flangeway width of 1/2 inch. The Proto:87 maxes out at 0.656 inches on the track gauge width, has a minimum check gauge width of 0.625 inches and a flangeway range of 0.022 to 0.023 inches wide.
Proto:87 equipment is not compatible with standard HO deployments. The standard flanges won't fit through the Proto:87 flangeways, and the wheels are too narrow and spaced-apart to pass through either, so you'll have to start a new model project using this type of equipment exclusively or watch your train continuously derail. However, though the minimum radius of the Proto:87 wheel is broader than standard HO, equivalently sized equipment can be used if it is 50 percent greater than the minimum standard HO radius.
