From a question recently received, the recommended allowable wheel size difference on EMD GP type locomotives built up to the early 1970's is:

Wheels on same axle: 1 Tape
Wheels on same truck: 20 Tapes (3/8 inch radius)
Wheels on same locomotive: 32 Tapes (5/8 inch radius)

The reason for these recommended limits is to keep from triggering false wheelslip indications, within the normal operating speed range of the locomotive, due to Wheel Slip System being activated by wheel size differences. This information is generally not shown in the operators manuals and there were no complete locomotive service manuals (LSM) prior to the 1966 product line. The references for this information are EMD Pointers dated 1 June 1971, with corrections in EMD Pointers dated 12 July 1971.

This information tends to be difficult to locate unless you have one of the early 1970's EMD Pointers Article index sheets, thus I am posting it here for general information, both the limits and the specific reference.

PC