Max Wind Speed for Disc Covers
Is there a general rule of thumb on how much maximum wind is ok when using a rear wheel disc cover before it starts causing a handling problem or any other problem? If personal weight matters for stability......I'm about 170lbs. The race is IMAZ. Thanks.
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I've ridden a rear disc in training in winds gusting up to 45mph. Great training for any wacky condition.
Put the wheel cover on for IM AZ. It doesn't get warm enough for temperature gradient winds, and the monsoon season is over. I've been there for all the Nov races, and the worst wind was in the range of 10-15 mph. More likely to be single digits.
I've done two pretty windy races with a wheel cover and both times random strangers told me I needed to take it off or I would end up in the ditch. I had someone come up to me in transition even, and i had no idea who this guy was. Who does that? It wasnt a great way to start my race. I used it anyway, and had no trouble. FWIW, I'm not tiny, 5'10" and I weigh 146-147. The only problem I ever had with handling was when a gust caught the cover as I was cornering. The front wheel is far more difficult for me to handle in gusty winds. Definitely try it out.
The aerodynamics are such that a wheel cover shifts the Center of Pressure closer to the Center of Gravity. So the bike is less 'twitchy' due to the wind. It does increase the surface area of the bike which means there is more of the bike for the wind to push against, so you get races like Kona and Cozumel that don't allow them.
To riff off what Joe already mentioned...
The main determining factor for control is the front wheel and not the rear wheel. The disc stabilizes the bike in the wind. It counters the wind steer on the front of the bike. If the wind increases, it pushes the bike toward the wind, while the front gets pushed away, and vice versa. Think of a weather vane. First, you have forward motion on a bike which is different than if you were just sitting still. To use the weather vane analogy further: a weather vane has an aerodynamic shape (an arrow) in which the front end is obviously thinner than the thick back end of the weather vane (analogous to running a smaller dished front wheel like a 40 or 60mm to the full disc rear wheel). These aerodynamics allow the front to point into the wind. The shallower the front, the easier the aerodynamics are to get it to point into the wind. So a real deep front wheel (like a Zipp 1080 or Hed Jet 9 or arguably a Hed H3) is harder to control than say a Zipp 404 or Hed Jet 6 because it's harder to "pivot" from an aerodynamics standpoint. Therefore, the rider has to compensate for the "extra" pivoting... which is why a deeper front wheel is harder to control.
Personally, I think they ban discs at Kona or Cozumel not because of the disc but because of the stupid choices they know athletes will make when it comes to the depth of the front wheel.
http://www.wheelbuilder.com/aerodisc.html
www.wheelbuilder.com
Right now they are about $100....oftentimes there will be a sale for ~$80. Depending on when your race is, you might want to wait b/c we (EN) will do a mass purchase of wheelcovers along with latex tubes.
Hmmm...I've had good luck with my wheelbuilder cover. Fits the Zipp wheel perfectly. Agree that there is not much to the cover but not much is really needed just something to cover the spokes from the wind. Here is a pic of mine I just glued up the other day.
Hope you get it working for race day.
Heck, on a windy day, my TT/aero frame causes more problems than a rear disc cover EVER will.
Tell them you are an EN member, we get a discount.
Had mine for 3+ tri seasons, dozens of races, always worked well, never had any concerns about the "look" of it. I fail to understand how a disc cover could possible "not work", unless it was cut to the wrong size (ie. you forget to tell them that you've got a PowerTap hub, or give the wrong rim/spoke count inputs).
I've never encountered a race condition I wouldn't put it on for, and I've ridden it in 35+mph gusts.