Simulate the sensation of cycling outdoors with the Kreitler Challenger 4. 5 Rollers with Headwind Fan. By bundling the Killer Headwind Fan with Challenger 4. 5 Rollers, you'll experience greater air resistance while training indoors, making the experience both more realistic and challenging, much like riding into a light headwind on the road. The Killer Headwind Fan features an adjustable air inlet that opens and closes to your individual training needs. When open, the resistance is strong enough to challenge the most experienced of cyclists looking to increase their endurance. Conversely, you can close the air inlet for minimal resistance if you're seeking an easier training session. Plus, you'll find the cooling fan provides a nice breeze that works to keep you from sweating profusely, especially if you're training in a poorly ventilated garage or basement. Kreitler's Challenger 4. 5 Rollers provide the smooth-rolling ease of use and quiet operation of their premium Alloy Rollers, except they're constructed with polycarbonate end caps to reduce the overall cost. These polycarbonate end caps are a bit lighter, so they won't carry quite as much momentum as the alloy versions. Despite these differences, the Challenger 4. 5 Rollers roll smoothly without creating a noisy racket, thanks to their concentric alloy drums and ABEC 5 bearings. Since they're the largest rollers available from Kreitler, you'll find they're easiest to use, without the heavy resistance of the smaller 3. 0 and 2. 25 versions.