Saturday, March 28, 2009

Do It Yourself - Aerodynamics

Great article on a few simple steps you can take to make your ride more aero - it's by Bicycling Magazine's Joe Lindsey. I was going to just post the link, but web-articles have a habit of disappearing on me and I'd really like to be able to read this one again, so I'll post it here in it's entirety. Enjoy!

D.I.Y. Aero - by Joe Lindsey

On a flat road, as much as 95 percent of a rider's energy is used to overcome wind resistance, says Todd Carver, who runs Retul, a bike-fitting company in Boulder, Colorado. Just 20 percent of that drag comes from the bike - 80 percent of it is from you. At the same time, Scott Holz, an instructor for Specialized's BG Fit program, says that he sees more mis-fit triathletes than any other group of cyclists. Here's how to tweak your road bike for fit and efficiency.

  1. Attach clip-on aerobars. Don't worry about the position at this point, you'll tweak it later.
  2. Move the saddle forward and/or swap your seatpost. One of the most common conversion fit mistakes: slapping on aerobars but leaving the saddle where it is. If you're effectively moving the handlebar forward, you need to move your body too. Think of it as rotating yourself forward around the bottom bracket, like hands on a clock. Your elbows should be 2 to 3cm behind the rear edge of the aero-bar pads, with a roughly 110-degree angle at the elbow. For road bike fit, a plumb line dropped from the rider's forward knee (with crankarms level) should pass just in front of the pedal spindle. For ideal tri fit, you want your knee farther forward, 1 additional centimeter in front of the pedal spindle for every centimeter of height difference between the saddle and the aero pads. You may need a two-position post, depending on how much adjustment your seat rails offer.
  3. Correct saddle height and angle. Moving a seat forward also effectively lowers it. You want about a 30-degree bend in your knee when the crankarms are perpendicular to the ground. (Note: This is a different measure than the one used for road bike fit.) A normal road position has a level seat, but for a multisport fit, you should rotate the saddle downward one degree for every centimeter of drop between the seat and the aero-bar pads, up to eight degrees. This will allow you to roll your hips forward and open up your hip angle for a more natural pedaling style.
  4. Dial in your back angle. If the aero extensions are too high, move a steerer-tube spacer or two above the stem, or flip a positive-angle stem upside down, or both. Ideally, your back will be flat like Dave Zabriskie's, but spinal flexibility may limit you. If the bars are too low, consider a higher-rise stem.
  5. Tweak your bars. The key here is to decrease frontal area as much as comfortably possible. Align the elbow pads so your elbows sit directly in line with your hands. It's fine to create a wider "stance" on the bar by increasing the distance between the extensions; just keep your forearms pointing straight, not angled inward, which increases drag.

If, after some break-in time, you can't stay in your tuck over the distance of your goal race (cornering, climbing and tricky descents excluded,) then your position is too aggressive, says Specialized's Holz. For sprint tris or time trials that last less than an hour, your position should be as aggressive as you can tolerate. For Olympic-distance events or a 40-kilometer time trial, increase your torso angle five degrees. For a half-Ironman, add five to 10 degrees, and for a full Ironman, 10 or more degrees.

When in doubt, choose comfort over aerodynamics. You'll go faster in a less aerodynamic position if you can reliably produce lots of power over a longer period of time. That said, with any aero position you will probably give up some amount of power compared with your road position, but that's okay. "Cyclists are macho and like to focus on power," says University of Utah researcher Jim Martin, who consults on aerodynamic efficiency with the Australian Institute of Sport. "If you give up a few percentage points in power output, but gain that same amount in aerodynamic efficiency, you'll still go faster."

This article can be found in its original location at http://www.bicycling.com/article/0,6610,s1-1-4-17600-1,00.html

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