You’re looking for a new set of race wheels and don’t know where to begin. There are carbon wheels, alloy wheels, wheels with deep profiles, ultra lightweight wheels, disk wheels, tubular and clincher wheels—at times choosing a wheel set might seem harder than actually racing. Keep in mind that next to your fitness, aerodynamics is perhaps one of the most important variables that need to be addressed in cycling.
Contrary to what many might believe, aerodynamic equipment offers slower riders greater return on their investments than the riders who finish out in front of the pack. Partly, this is due to the fact that slower riders are out on the course longer; mostly, slower riders experience more effective crosswind in most instances than their faster competitors (see my article in the April issue of FIRM’s newsletter for a fuller discussion of apparent yaw angles and wind).
It’s important to choose a wheel that matches your average race speed and the wind conditions that you are likely to see in most of your races. A good place to compare the aerodynamics of different wheel designs is Steve Hed's site, which has an interesting interactive tool that will allow you to compare wheels of different configurations:
While this tool is based on Hed's data, it seems relatively consistent with other sources; I'd use it for general comparisons and not worry about specific coefficient values.
Under virtually all situations, a wheel’s aerodynamics is much more important that its weight. If you are interested in competing in multisport or time trial events, then you should get the most aerodynamic wheels possible. A rear disk will be the fastest wheel possible under any conditions; because the rear wheel doesn’t have a steering axis-it only can roll forward—it is largely unaffected by crosswinds. Front wheel selection is more complicated, as they both roll and pivot, and it’s that pivoting that creates handling problems.
While very deep profile rims in the front tend to be the fastest, consider using a moderate profile front wheel if you are worries about handling. Most major manufacturers will offer front wheels in the 50mm-60mm depth range. This depth makes for a good all-around front wheel, and it doesn’t give up much speed to its deeper profiled cousins. Again, it’s important to have a general sense of what your average race speed is and what the average wind conditions are for most of your races.
All aerodynamic wheels are optimized for a relatively narrow range of yaw—that is, for a relative narrow range of apparent cross winds. Most deep profile rims will stall when the wind angle exceeds its optimal yaw range (Hed’s tool, linked above, graphs wheel response to yaw). When a wheel stalls, it effectively loses its aerodynamic advantage. The one main exception to this is Hed’s trispoke wheel, which remains very fast across a wide range of wind angles, though it can be more difficult to handle than a deep profile wheel.
You can make some generalizations. The faster you are, the more that you can be assured that pretty much any aero wheel will work well for you (fast riders experience shallower yaw angles than slow riders); the slower you are, the more you need to match a wheel’s design to your race speed and the likely wind that you’ll encounter. Deeper wheel profiles (80mm or greater) tend to provide more aerodynamic benefits than shallower profiles (60mm or less), though they can be more difficult to handle in very heavy crosswinds. If all of this confuses you and you have funds for only one set of wheels, then go with a wheelset that has a moderate, 50mm-60mm profile. If you only have funds for one wheel, go for a front wheel, as more aerodynamic benefit will be gained here than with a rear wheel, as the rear wheel is drafting the frameset.