Specifically designed to fit road, tri and gravel bikes and protect them while secured to a vehicle rack. Waterproof exterior that keeps the bike clean, dry, and ready to ride. Protected passthroughs for car rack securing straps . Optional light kit (ZB1301) provides highly visible taillights for driving . Medium size cover tested to fit most 48-54cm road bikes and most 48-52cm gravel and triathlon bikes. Large size cover tested to fit most 55-63 cm road bikes and most 53-63 gravel and triathlon bikes