Go to stimilon.com for details and sign up info. Space is limited to 40 per class ONLY - so sign up today for extra goodies and deeper discounts. MX 338 - The Pro National Track in Southwick, MA. May 26/27, 2012. The Stimilon Motocross Challenge is the event your Mommy warned you about... Check out the videos from past year's events on your right of this page. If they don't scare you or make you feel shame, this is your event! Now go sign up