The L1 front wheel holder is a perfect additional accessory to carry your front wheel on the roof, attached to your rear wheel holder from your bike rack. The L1 comes with one cup, so you have to use your bike rack rear wheel holder vacuum cup, to complete the set. It could carry 9mm quick release front wheel, 12x100mm thru axle, and both 15x100mm and 15x110mm boost thru axle front wheel by secure it with a quick reales to the metal U shape wheel holder.