I recently bought an Aerojacket Disc wheel cover for my regular training wheel. For the last two years I have used a carbon 101 mm depth rear tubular for long course triathlon races. This has been a definite upgrade from what I train on and I notice the difference. I have always considered using a disc, but because of the cost, I have never made the purchase.
Recently I learned of the wheel cover made by Wheelbulder. The affordable cost made it a no brainier for me. I purchased the wheel cover with the intention of trying it out in one of my races. I placed this on my everyday training wheel and used it in my last two races.
The results: I posted my fastest half ironman bike split. Three weeks later I raced Ironman Arizona and I also posted my fastest ironman bike split. I am definitely sold on the wheeljacket disc covers. I have recommended this to a number of athletes I coach and I will most definitely use this for 2012.
Check out what Wheel Builder has to offer. http://www.wheelbuilder.com/store/