Kreitler Fly Wheel for Challenger Rollers - Right Side For those who want the absolute closest road feel available indoors, the Kreitler Flywheel combined with the "Killer KOOL Headwind" Fan will provide the ultimate workout. Available right or left specific, they may be used in conjunction with each other for the greatest inertia feel. You can choose left, right, or have both sides with a fly wheel. Both sides are made if you want to have two fly wheels for a longer roll time. For use with Challenger 4.5" rollers Right side Drive