Yeah ive noticed quite a few of the REALLY light mini lads using motorcycle rear disks on their cars.

Ill probaby just go for a set of alloy radius arms and KAD rear disks for mine, i want it light, but not obsessively so, its mainly a road car at the end of the day and its a full steel body not a space frame too, so subtley different class of vehicle, its never going to be a competition weight wise against something like that!