Training wheelsets are not hard to come by, however high quality training wheelsets are few and far between. Many companies can pack a lot of specs and figures into their wheelsets, but few can touch Shimano's proven quality and reliability.
The Shimano R501-A Wheelset uses a low spoke count, aero-rim profile, and easy to maintain cup and cone bearings. The rims are double wall, and the spokes are stainless steel and bladed. The rear wheel uses a 2x spoke pattern on both sides for optimum power transfer. When you need a wheelset to train on, that you can ride rain or shine without ever worrying about it's durability.
Furthermore the wheels are featured with a rim wear indicator. The asymmetric rim and the high quality angular bearings increase stiffness and provide a long durability. For Shimano 8/9/10-speed.