Aug 1, 2001 1:17 PM
|Hi everyone. I've been looking into aero wheels by HED and ZIPP, and they're all fairly pricey. If I only had enough money to buy one aero wheel, should it be the front, or the rear? Thanks in advance.|
|re: Aero wheels||str8dum|
Aug 2, 2001 8:34 AM
|the point of aero wheels is to reduce drag. you'll get the biggest benefit of reducing drag by going with an aero front wheel, which the winds sees first. the idiot that said get an aero rear wheel 1st apparently never had physics, or rides his bike backwards|
Aug 7, 2001 9:25 AM
|The problem with just a front aero wheel is that general bike handling characteristics are significantly affected by a disc/aero wheel in the front if there is anything but a straight on headwind. Also, the drag coefficient of a wheel is a function of more than the leading profile of it.
Perhaps you, being the rocket scientist that you are, should tell all 180 of the idiots in the Tour de France this year and the engineers that designed their bike setups that they are all wrong and have been for the last 15 years... I'm sure none of them ever had physics...
Aug 7, 2001 10:11 AM
|Aerodynamically speaking, the front wheel is more important the rear, the rear effectively drafts the front wheel and by the time the air reaches the rear it is already somewhat spoiled. Yes, there can be a problem with a side wind. With respect to the Tour..comparing apples and oranges..dont' forget...in the tour they are in a PELOTON, with the exception of the time trials..thus, no need for aero wheels with all the massive drafting going on. Look at the time trials..solid rear discs abound and aero front wheels also....|
Aug 7, 2001 10:13 AM
|want to elaborate on my answer, reason you dont' ride a front solid disc is safety, strong side winds would wreck you. You will see them on enlosed velodrome bikes, but not out on the open road. Oh, my job? I do happen to work in missiles and rockets!|
Aug 7, 2001 10:35 AM
|I was speaking of the tt bikes in the tour since this is a tri messageboard. You will see that most of them used a disc in the rear and some other aero/ultralight configuration on the front. Let's get back to the original post. If you are going to have one Aero wheel it should be in the back... I have never seen anyone with one aero wheel in the front... Anyway, to the original poster, look for a used set of wheels like Ksyriums that will serve several purposes...|
|The Key is Stability||Kudzu Kannibal|
Aug 22, 2001 2:13 PM
|Hmmmm...didn't know triathletes had attitudes (kidding). Yes, the disc is in the rear because of stability. Here is an overview and no I am no aerodynamics genius, but I write software to simulate certain things and here is a synopsis of what I have learned:
Pressure point of air, is a technical term and one your average cyclist doesn't know. To make matters even worse it's very difficult to pinpoint the spot as it's constantly changing. Imagine that your pedaling along into a constant crosswind, you will instinctively have the bike slightly leaned over against the wind, the wind is acting like a large pillow supporting the bike and rider. Then if there's a curve in the road or buildings to interrupt this airflow, your support pillow moves to the front or rear of the bicycle moving the aero steering point. If this happens quickly then your bars go to wobbling and you get unstable.
Ground zero on bicycle aerodynamics is where the rear wheel touches the ground. If the aerodynamic pressure point is at this spot then the bike will be the most stable, but it never is there, it always moves towards the front of the bike. The closer it is to the front of the bike then the less self-centering the bike will be. Generally bikes with standard wheels front and rear are least effected by crosswinds, but they're also the slowest combination to put on a bike. This lack of speed comes through ineffective air management requiring more watts of energy to turn the spokes through the air. You only have a limited number of available watts so you need to use them wisely. To help solve this wattage dilemma some clever wheel manufacturers began making deeper rim sections. This solved the watt problem some but started the instability problems. Now there working on forks and frames to move this "pressure point" back toward the rear of the bike.
Here's some examples of what happens on a standard bike with round tubes using a standard production fork. With the standard 32 spoked wheels the aero steering point is about 12" ahead of the rear axle. By adding a composite or deeper rim section front wheel the aero steering point moves to about 30" ahead of the rear wheel. The reason for this is that a standard front wheel has approximately 110 square inches of surface area and the composite Deep V and 3 / 4 spoke wheels have 200 to 245 square inches of surface area. Then if you add a solid disc front wheel with over 550 square inches of area, the aero steering point moves to about 45" ahead of the rear wheel, this is a bad situation because it eliminates all self-centering effects on the bike. Unfortunately it also adds the most speed to your bike by reducing your pedaling wattage by some 20%-30%. Well, as racers, we all want that speed so.... what are we gonna do?
By adding more area to the rear of the bike, and specifically in the rear wheel area and behind the axle point, a lot of stability will be regained. When you're using deep section front wheels, you need to balance the aero pressure point with more square inches of surface area in the rear. By adding properly designed fork mass or trailing edges we can regain steering input, and by having your aero bars set correctly to balance the weight distribution, you can regain control of your bike. Of course there are still issues on the frame, but that is another topic, however this is why you are seeing some frame designers add surface area to the rear of their bikes.
So now you know why you don't see many, if any, cyclists putting discs on the front as well as the rear. If money is no issue check out Nimble, because there are other factors such as rolling resistance, weight, and intertia that come into play - ESPECIALLY on hilly courses, right?
Have a good one folks.
|The Key is Stability||Kudzu Kannibal|
Aug 22, 2001 2:28 PM
Most of this information was courtesy of BicycleSports, but I knew a lot of it myself. They just seemed to put it together better. Also, remember that your aerodynamics improve as you get cyclists lining up behind you. Yes even for the front runner...watch auto racing. It creates a push affect on the front rider and so on. And thus the Peloton, but you guys knew that already.
Have a great day.
Tri harder, Tri faster, Tri again next week!