Saris Mag+ Indoor Bike Trainer With Adjustable Magnetic Resistance Control KnobTrainer for All Seasons. Stick to your fitness plan year round with the help of the Saris Mag+ trainer. It is the perfect way to keep your legs warm when it's cold, dry when it's wet, and safe when it's too dark to ride outside. With this turbo trainer, it's easy to turn your bike into your go to calorie burner no matter the season. Simply attach the handlebar mounted shifter to change resistance during your workout without having to leave your bike.