Ultralight spacer sets come in varying sizes to ensure you get the right bearing seat depth for different size wheel hubs.
If your spacer is too long for the wheel hub, your wheels click, your bearings do not stay seated, and your wheels can come out of alignment. If your spacer is too short, shear load is placed on the bearing raceways, preventing free spin.
Choosing the right spacer can mean fractions of a second between winning and falling short.