Posts Member

are the wheels strickly for racing? or do you want a good all around set of aero wheels? i bought a nice set of alloy Easton Tempest II's that were half price. they are great for racing but not to fragile for training as well.

http://www.pricepoint.com/detail/15310-365_EASTP6-3-Parts-75-Wheelsets/Easton-Tempest-II-700c--Alloy-Wheelset.htm

Posts Member

As has been noted on numerous boards, the MIT research can be a bit misleading because it was all conducted at 0-degrees yaw angle (head on). The benefit of aero wheels is thus understated in their findings.

However, it is also universally recognized that the most important factor in cycling aerodynamics is rider position. So yeah, make sure you've got a good position first! But an aero helmet is definitely a good way to go as well, and quite cheap compared to wheels. But it doesn't have to be either/or -- just get the helmet AND the wheels :-D

Posts Member

It really depends on where you ride. Heavier wheels will have a higher moment of inertia, meaning they resist change in speed. This means they're harder to get up to speed, which is why you would never use them in a crit where acceleration is very important to keep from getting dropped off the peloton, but for non-drafting triathlons, this doesn't matter. In fact, because they resist changes in speed, they won't slow down as fast as lighter wheels, meaning it's easier to hold a higher constant speed on the flats with heavier wheels (crazy, huh?). This is where the location of your riding matters. Tons of hills are harder to climb with heavier wheels (or anything else for that matter), but heavy=steady on the flats.

Another important thing to consider with 100mm wheels is the wind. If it's a gusty day and you have a 100mm rim on your front wheel, you're going to fall. If you ride along the beach at all, I probably would plan on using a different set of wheels on that day. However, the most aero benefit after your body position is your front wheel, so if you can ride a 100mm rim safely, it will make a difference. It all depends on what kind of riding you plan on doing and how comfortable you feel on a wheel that big. I run a sail....I mean disc...on the back of my bike and I feel plenty safe, so don't go thinking that just because you put on a wheel that deep that you're going to suck asphalt. But if you plan on doing the Kitty Hawk Triathlon or climbing Alpe d'Huez anytime soon, I'd stay away.

Posts Member

Most of the 80% comes from the rider (largest profile against the wind). But considering wheels, the main speed benefit from aero wheels is the fact that they reduce the "eggbeater" effect of the spokes in the air. The deeper the rim, the more benefit you get. This is why 808s are faster than 404s and why discs are faster than that. If I remember my physics correctly, comparing a Blackwell wheel and a 404 yields the following:

700mm / 2 = 350mm radius for each.
350 - 100 = 250mm exposed spokes for Blackwell.
350 - 58 = 292mm exposed spokes for 404.

Drag = k*v^2, where k is the drag coeff of the spokes, and v is the linear speed of the spokes at each point, r, along itself (the linear speed increases farther away from the hub). (I'm ignoring fluid density and assuming the spokes are very similar for both wheels)

The linear speed (v) is v = w*r, where w is the angular velocity of the wheel.

So going at the same speed(constant w), the Blackwell and 404 compare thus:

Integrating drag from the hub to 250mm for the Blackwell yeilds:

k * w^2 * 1/3 * r^3|0, 250 = 5208333*kw^2 kg*mm/s^2

For 404s from the hub to 292mm:

k * w^2 * 1/3 * r^3|0, 292 = 8299029*kw^2 kg*mm/s^2

According to this, the 404s have almost 60% more drag. Zipp wheels are the best-built wheels on the market and have that cool dimple stuff, so it's actually less than 60%, but you still get the point.....Blackwells are FAST! As long as you're not going to ride them in the wind and you feel comfortable with them, go ahead and get them. I wanted a set last year, but college budgets don't allow for wheels that cool!

Posts Member

Agreed
:-)

Posts Member

These are kind of true, but when applying them to races they may come across a bit misleading.

Weight matters on a hilly course, but unless it's an all-uphill time trial, the aero benefits outweigh the weight benefits.

Aero wheels don't give any benefit at low speeds, and their benefit DOES increase with speed (drag is a function of the square of speed, so double speed means four times the drag, which is why aero wheels work better at higher speeds), but as long as you're going at least 20 mph or so, there will be a benefit, so it's not like you have to be world-class to benefit from aero wheels.

As far as race distance, the total percentage of time gained will increase with speed, but the total time gained will increase with the distance. Using aero equipment might give a 5% benefit over 40k at about 24 mph (1:02 to :59), but over 112 miles at about 21 mph (slower speed) might only give a 3% benefit (5:20 to 5:10), so it actually helps drop more time even though it's a smaller percentage of time savings due to the lower speed. These numbers are rough estimates and will vary from person-to-person based on speed, positioning, course, etc, but you get the point. 10 minutes savings in an IM is well over a mile saved on the run, while 3 min in an oly is about a half mile on the run.