I dropped on some 'old school' (bmx) disc covers on ebay. After much faffing trying to fit 2 discs on each wheel, I gave up and just fitted the outers. The Sturmeys make fitting on the inside problematic to say the least, so I resorted to tie wraps. They came with dodgy graphics http://www.ebay.co.uk/itm/OLD-SCHOO...sure_cycling_bikeparts_SR&hash=item3cca851779 but as I am the high viz maestro, soon remedied. It's as much about visability what with Winter coming as it is to do with aerodynamics. That said, I may gain an extra 1/2 mph......maybe?