[Tom Wells]

Sy,

I've used those spacers on my cars. They're fine if you want a temporary solution but something more durable is needed for the longer term.

The problem was that when I got into a rapid movement situation on a track where they got pinched strongly, they would pop off and get lost. In other words they really can't be used as bump stops.

A completely circular spacer would probably be more likely to stay in place, but the ends of the rack would need disassembly to get them on.

Maybe someone else has found a better solution?

Tom