Talkback: Which race wheel type is best for me?
Wheel covers can be just as aero (see 220s own test in the archives) but they far less convenient than a disc as fitting and removing takes ages. They are also fragile and only last a season (the carbon ones may be better). Cheap decent disc wheels (rim brake) are available new on eBay they are normal wheels permanently fitted with a laminate cover. Again the 220 team publish a rubbish incomplete feature. Zipp are probably a lucrative advertiser!