Zipp has just started to release a new line of aero wheels with a new shape they call “Firecrest”. This new design was created when Zipp was trying to create a carbon clincher and just happened upon this new super-aero shape. This wheel is supposed to be more aero (faster) and more stable against side winds.
I got the chance to test ride as set of the 808 carbon clinchers. The 404 carbon clinchers have just been realized and you can actually find a set at PowerTri, but for now the 808s are rare… very rare! The only set in Utah is on my bike! This is only temporary as I have to return them to our Zipp Rep next week. I had a chance to go for a ride them today and will race with them at Lake Powell this weekend. Here I’ll try to give an objective review of the wheels.
Lets start by quickly explaining why these wheels are supposed to be so much better. I wont go into as much detail as I’d like to for the sake of time, space, and that there are other sites with that information. I was able to attend a 2 hour seminar at Interbike about them, so I do feel like I know a lot. Come into PowerTri sometime and I can explain in more detail. You are also welcome to comment and I’ll answer any questions you have.
In creating a carbon clincher they had to widen the rim to make the carbon strong enough to hold the bead of clincher tire. After creating this shape they went to the wind tunnel to find that the 404 was much more aero than their 808 (and just about all other wheels). They recalibrated the wind tunnel a few times thinking that it was an error. It was not. With this new shape that was faster than the 808, they realized they had to do the same thing to the 808. They found that the 808 Firecrest has, at most yaws (effective wind angle), similar time savings as a disc. Below is a diagram with the shapes of more traditional aero wheels, Zipp’s previous wheel shape, and now their new Firecrest shape.
On the right is a traditional shape that many companies use. The second to the right is Zipp’s old shape that was considering one of the fastest in the industry. The left most shapes are the new Firecrest shape (tubular and carbon clincher).
As you can see, the Firecrest shape is actually widest at its closest point to the spokes (in this picture it is the bottom of the shape). This is more effective as this wide area is the first part it hit the air when looking at the airflow over the rear part of the wheel (many times people only look at the air flow needing to flow well on the front half, meaning as the air flows over the tire, then the rim, and then into the spokes). This shapes ends up making it more aero and thus, faster. Well, how much faster? The new Firecrest 808 Tubular is 15 seconds faster over a 40k than its predecessor, the toroidal 808. The 404’s improvement is 9 seconds. I could not find the time improvement of the clincher (from alloy clincher to carbon clincher). My assumption would actually be that there is a bigger improvement because before, the tubular was slightly more aero than the alloy clincher (and lighter), but now they are the same shape, so the advantage of the tubular is narrowed to just being lighter. In other words, I think the change in shape for the clincher is more dramatic than that of the tubular, so I wouldn’t be surprised if there is a bigger time savings for the new Firecrest 808 carbon clincher over the old clincher.
That is not all though! The new shape is also more stable than previous versions. When testing the wheels the Zipp engineers were able to track the center of pressure on wheel. Think of this as how you would find the center of mass of an object, but has to do with how pressure is put on a wheel (by air/wind). The noticed that while making adjustments to the wheel that this center of pressure actually changed. They had no idea they could control it! The next question was, well, if they could control it, where did they want it to be? They centered this pressure on the hub with makes the wheel extremely stable in cross-winds! This means that people who normally feel they can only ride a 404 because they are worried about being pushed around, can now ride the 808.
My Test Ride
So, now that I’ve explained all the technology and changes to the wheel, I’ll tell you how my ride went and if all this stands true.
Aero/Speed: To tell you the truth it was so windy that I couldn’t tell if I was any faster with the wheels. I went down a hill that was somewhat protected from the wind and it was extremely smooth and fast. Remember that it would be hard as a rider to notice a 15 second difference over an hour ride. I will follow-up with this after the race on Saturday though to give more feedback on speed.
Stability: This is where I think some of the biggest benefits are. I was actually glad that it was very windy on my ride, so I could get good feedback on the stability. Honest opinion – Awesome! It was great in the wind. This is not to say that you don’t feel any of it or that there isn’t any tugging from the wind, but it hands very well. It seems to just find its way through the wind. When most wheels start to get squirrelly this wheel may waver once and then finds it’s true again. On the hand it did not handle the turbulence very well created by passing cars. It’s not worse than previous wheels, I just didn’t feel that is was any better. The car turbulence thing is usually a training issue and isn’t a problem during racing.
Other: I really like the look of the new hub design and especially the skewers. These are lighter than previous titanium skewers and very aero (you can still buy new titanium skewers for extra weight loss). The one thing I don’t like is the new rear hub makes a clicking noise when you are coasting (I know, most do), but this was is pretty annoying. It’s definitely not worth the worry, but it’s there.