There hasn't been anything that can prove whether or not the dimples actually provide any aero dynamic benefit.

For the record, Flashpoints are not undimpled 404's but they are good wheels at a nice price point. I don't remember exactly what all the differences are but 404's are made of many pieces of carbon, FPs are made of like four. The hubs are different, made off shore with different bearings, the spokes are different. etc. etc. etc. They were made to compete with lower priced wheels in the market.

Bottom line, if you can afford the Zipps, have to have the Zipps, think the Zipps will be faster or are missing podium by seconds, by the Zipps. Otherwise, there are plenty of other wheels that will give you nearly the same if not the same benefit.

Chrissie Wellington won on Hed Jets. $1000 less than Zipps.

I am a mechanical engineer, and while I am not an expert, I know a little bit about aerodynamics. In perfect conditions, the dimpled rotating surface creates a boundary layer of air that the wind you slice through can go over a little easier. How much easier? I have heard a savings of about 10% on wheel drag. Note I say wheel drag, not total drag. The rider contributes much more to overall drag than bike frame or wheels.

The key is that it is a rotating surface. The owner of my local bike shop told me of some wind tunnel testing he was involved with on dimpled helmets and clothing, and dimples did not help there.

If you wallet can support it, and you must have it, go for it. But I agree with tsilcyc, and I will take it a step further. In my humble opinion, the vast majority of us are not winning or losing races because of a few extra watts that could be saved with dimples. The strongest athletes are winning races because of their ability, not their equipment.

The Zipp web site has some technical info about the dimples written in non engineering language if you are interested.

I have never used this site, but here is a thought...http://www.racedaywheels.com/home.html allows you to rent wheels...Try a set of Zipp dimpled, and a comparable non dimpled set on the same course and see what happens.

Just out of curiosity, which Zipps and we're you psyched to be riding Zipps instead of the Mavics? Also, what distance was the race?

It is no more or less quantifiable than your anecdotal sprint wheel test.

I disagree with that sentiment. If the wheels really do make a difference, who cares if it's the difference from 18->19mph or 25->26mph. It may be a little "silly" to spend the money for that advantage if it's not going to help you win races, but I also say budget issues are a personal choice unrelated to race placing.

Anyways, I have looked a lot at Zipps -vs- Flashpoint and decided if I couldn't get the Zipps, I would go with something other than the Flashpoints (I chose Reynolds - just picked up a used Stratus DV w/powertap - decision largely made on the Reynolds' astonishingly low weight). They are, as a previous poster stated, a little bit more different from 404's than Flashpoint would have you believe. I feel like you're still paying too much for the Zipp name. One thing the Flashpoints do have going for them, though, is they look hot.

-Grant-

This is twice today that I went back to my folder of links and couldn't find what I was looking for, but I read an article with either Steve Hed or John Cobb that said the tipping point between rolling resistance and aerodynamics was somewhere around 12mph. A lot of people quote 20mph, but I've never seen anything to support that and I suspect people just like to say it because it's a nice round number.

Also, the equation for power required to overcome aerodynamic drag is:
P=1/2 * d * v^3 * A * Cd
(d=air density, v=velocity, A=frontal area, Cd=Coefficient of Drag)
So as speed increases, more power is required according to a cubic factor. However, Cd is a first order factor. That means that scaling Cd will scale Power proportionally. In other words, a 10% reduction in Cd will result in 10% less power being used to go the same speed, or at the same power a 10% reduction in Cd will result in (1/(0.9^(1/3))) more speed (103.6% for 10%) regardless of what that speed is.

So in essence, you're correct that a faster rider will benefit more (103.6% of 23.0mph is 23.83mph, a change of 0.83mph; whereas 103.6% of 18.0mph is 18.65mph, a change of 0.65mph) but in both cases it's the same 103.6% factor for the same aero improvement (say, deep wheels).

What's shocking, however, is that because the age grouper has more to gain, they will actually close the gap between themselves and the pro for the same aero change!

Take, for example, an 18mph AG'er and a 23mph Pro on a 56 mile course.
The AG'er at 18.0mph would normally finish in 3:06:40.00
Improve to 18.65mph and they will finish in 3:00:9.65
Difference of 0:06:30.35

The Pro at 23mph would normally finish in 2:26:05.22
Improve to 23.83mph and they will finish in 2:20:59.92
Difference of 0:05:05.29

If the pro would have beat the AG'er by 40:34.78 before improvements
If they both make the same aero improvement for 10% reduction in Cd but both maintain the same power as before, the Pro beats the AG'er by only 39:09.73

And they both lay the smack down on their previous equal competitors by over 5 minutes.

Now I don't have any articles to cite to corroborate my calculations or any enginerds to consult, but I've reasoned this out pretty significantly because I'm a gear nerd and I want the coolest stuff I can possibly afford even if I'm an 18mph middle-of-the-pack'er.

-Grant-

P.S. If there are miscalculations above or if my reasoning is flawed, I will gladly eat my humble pie, eBay my aerobars and take my steel fixed gear for a 150mi intervals ride in the mountains ;)

^That's some good stuff, man! I'm sure a lot of people appreciate all the work you did. You did miss one thing, though :)

As you decrease Cd and the aerodynamic drag decreases, the speed increases (this is pretty intuitive and you already said it anyway). Because drag is proportional to the cube of velocity while directly proportional to frontal area, the pro will have an exponentially larger resulting increase in drag because of his larger speed difference, so a 10% decrease in Cd yields a decrease in drag of slightly less than 10% with the AGer being slightly closer to 10% than the pro.

23.83^3 - 23^3 = 1365.32 increase in drag (I have no idea what units this is in!)
vs.
18.65^3 - 18^3 = 654.89 increase in drag

These are just estimates since the speeds with the aero improvements should be slightly slower, but it illustrates the point if you use your imagination :)

I don't want to take the time to figure how these numbers will change the times of each athlete, but I'd guess that it would give the AGer another several seconds advantage over the pro. I know this only validates your point further, but fixie intervals in the mountains are good for you! ;-)~

TROLL!

But, onto the dimples. I don't really understand the gain with dimples on wheels. The reason dimples help with a golf ball is they make the flow over the ball become more turbulent, and this causes the flow to break away from the surface of the ball later than with purely laminar flow.

I can't see how this would benefit a wheel as much. The wheel cuts through the air, but the spinning motion is much faster, so they flow doesn't necessarily break away from the surface in the same way, especially since half of the air will break over the tire, which may or may not be smooth.

Just my $0.02, but I think the dimples might have been adopted from golf balls, or maybe another application where they give a large change in performance, and I don't think it carries over to wheels.

BTW... if you all want to know why zipps have dimples... why not ask Josh Poertner (zipps head carbon designer) yourselves...
http://www.zipp.com/Support/AskJosh/tabid/183/Default.aspx

So what happens if you can't afford the wheels or the power Meter? :>

Thankyou for your replies. I guees what i am getting at is that if I ride around a 22mph to 23mph on a flat course how much more of an advantage am i getting if i buy the upper end zipps wheels (or any other high end wheel) compared to the flashpoints.

I know from riding my friends Bontrager's 5.0's in some of my races last year, that it seemed once you got those wheels up to speed, it took less effort on my part to keep them at speed. Of course i am only comparing this effect to my training wheels (Fulcrum 7's). The race wheel i choose, i want to have the same perceived effect.

If the Zipp's(or any other high end wheel) keep there speed much more effectivley than say the Flashpoints then it would seem like a no brainer to me to buy the higher end wheel. Though, if the difference is small than would it just be smarter to buy the Flashpoints and spend the extra money on say a Aero Bar?

My bad. I'm pretty new here.

If I had some extra money to invest in stuff, though, I think it would go into power well before I got new wheels though. I completely agree that you get more bang for your buck, from what I've heard. Plus, you're actually becoming a better athlete, and not just riding nicer stuff. Anyways, I agree, and I rescind my troll comment.