From Athearns latest email
Free N Challenger Wheel Set Exchange Program Announced
Based on feedback from customers running the new N scale Challenger loco on code 55 track, Athearn will exchange the non-driver wheel sets for new wheel sets with smaller flanges designed to run on code 55 track. Customers must remove four wheel sets on the loco (two on the lead truck, two on the trailing truck) and all seven wheel sets on the tender, and return them to the following address:
Athearn N Challenger Wheel Set Exchange
1550 Glenn Curtiss Street
Carson, CA 90746
A replacement set of wheels will be send postpaid to replace the wheels returned.
Note: Locomotives should not be returned and drive wheels should not be removed or returned.
The new wheel sets will be available in June, so wheel sets should not be returned until replacements are available.