I remember when rear spoilers were first introduced (may have been Malcolm Simmons?) and they soon became popular (especially those displaying the union jack). I recall Geoff Bouchard using one made out of card and foil that during a race became dislodged. Apparently it was suggested that they helped create "drive" from the rear wheel but Simmo discounted this saying they were another way that riders could display their sponsors. Remember Hans using a front wheel spoiler on one occasion and Tommy Knudsen coming a cropper during a GP when dirt from a rider he was chasing caused the front wheel to wobble alarmingly.