After reading the ‘Fastest aero wheel’ thread earlier it hit me that there are so many misconceptions about not only the aero efficiency of wheels, but of the handling characteristics. This was probably most highlighted by the one poster claiming that a rider was sure to have the front end of the bike ‘washed out’ by any cross wind. Fortunately the half a dozen pros at Kona on full 808 setups didn’t seem to have those problems this year, including
This shows that the 808 has roughly 30% less side load than the Dupont/Specialized/Hed3 wheel for the same wind and wind angle. This is almost purely a result of surface area, and partly due to the patented 808 shape which uses curvature to reduce the loading further. Having said this, we’ve also tested the Hed Deep and found it to have less side load and torque than the H3 as well, so I’m not sure where this misinformation about deep rims being more unstable comes from, but it sure seems to be wrong according to all the data we’ve ever seen, as well as all of the rider feedback we have seen and heard from people who are actually riding these wheels.
The thing that is rarely mentioned in these debates is the effect of wheel rotation within the fork on stability. The benefit of a deep or very deep rim over a composite spoked wheel is that as the wheel rotates the surface area visible to a crosswind only changes by the amount of spoke surface area shielded by the fork leg, whereas a composite 3, 4, or 5 spoke wheel has it’s surface area change dramatically as nearly one entire spoke can be shielded in the draft of the fork leg (and deep legged aero forks only accentuate this), creating a state where in certain cross winds the wheel’s surface area can change by nearly 30% when ever a spoke is between fork legs. In testing, we have found this variable surface area and variable side load can contribute to perceived instability by the rider (Zipp built the first 3 spoke wheels back in 1990 so we have have studied this for a long time) far more than a constant side load situation as seen with a deep rim. I’m certainly not just trying to say that this is something specific to Zipp either, our experience and data shows that this is true for any deep rim vs. any composite spoked wheel. My advice to people looking at deep and very deep rims is that if you’ve ever riden a 3, 4, or 5 spoke wheel then you should have no problem with any deep or very deep rimmed wheel.
For more aero data and info you can check here for data on things ranging from spoke shape to spoke count as it affects aero performance: http://www.zipp.com/tech/aero.shtml
The thing that is rarely mentioned in these debates is the effect of wheel rotation within the fork on stability. The benefit of a deep or very deep rim over a composite spoked wheel is that as the wheel rotates the surface area visible to a crosswind only changes by the amount of spoke surface area shielded by the fork leg, whereas a composite 3, 4, or 5 spoke wheel has it’s surface area change dramatically as nearly one entire spoke can be shielded in the draft of the fork leg (and deep legged aero forks only accentuate this), creating a state where in certain cross winds the wheel’s surface area can change by nearly 30% when ever a spoke is between fork legs. In testing, we have found this variable surface area and variable side load can contribute to perceived instability by the rider (Zipp built the first 3 spoke wheels back in 1990 so we have have studied this for a long time) far more than a constant side load situation as seen with a deep rim. I’m certainly not just trying to say that this is something specific to Zipp either, our experience and data shows that this is true for any deep rim vs. any composite spoked wheel. My advice to people looking at deep and very deep rims is that if you’ve ever riden a 3, 4, or 5 spoke wheel then you should have no problem with any deep or very deep rimmed wheel.
Let’s say the rider has an H3 up front, and is riding at a cadence of 100 in a 53/17 gear. That means that his front wheel is rotating >300 times per minute, which means that a spoke crosses the fork >900 times per minute, or >15 times per second. Can this lead to instability, either perceived or real? Hard to imagine, but I’m not very bright.
This was probably most highlighted by the one poster claiming that a rider was sure to have the front end of the bike ‘washed out’ by any cross wind. Fortunately the half a dozen pros at Kona on full 808 setups didn’t seem to have those problems this year, including
No fair posting data. This only confuses things. In fairness to the poster the winds were apparently nothing this year compared to previous years. Living here in Floriduh I contend with gusty 20+mph winds all the time, and even ride in the occasional hurricane or tropical storm. I can guarantee that a deep section like the Jet60 is a handful in heavy gusts, and I’ve had the front end get dangerously light on more than a few occasions riding in an area about 2 miles from my house. With wind heavy enough to push me into a pretty significant lean, this could be a serious issue for someone less than my 160lb. I recall the nun being “washed out” and thrown off the road a couple of years ago…there’s a reason discs are banned.
For winds 20mph and less I’d have no problem riding a superdeep front. The max 0.05lb decrease in drag from 404 to 808 (riding 25mph vs 25.2mph) is only really at 10 and 15 degrees. I can’t personally see the advantage in an 808 versus the 50% increase in side force at 15 degrees to save at most 2 minutes on an IM. Personal opinion though, as I have to deal with those kinds of winds on a regular basis.
Those data are great at demonstrating the aerodynamic efficacy going into the wind (or at least up to a 30 degree angle). My concern isn’t front wheel handling going into a 30 degree angled headwind, my concern are the 20+ mph crosswinds at 90 degrees (or even 60) that one encounters in the midwest (KS, OK, TX). Certainly Kona is windy (although fairly calm this year), but I’d like to see some more data. If we’re on the issue of wheel handling, I think it’s pertinent to describe cross wind forces for 808 vs. 404 vs. HED3. Do you have any of these data? I’d be very interested in seeing how they pan out.
…a spoke crosses the fork >900 times per minute, or >15 times per second. Can this lead to instability, either perceived or real? Hard to imagine, but I’m not very bright.
If you do more squats you will have enough leg mass to counter any increase in side force. It also helps your brainpower, we all know lifters are smart.
Warning: non-lab-tested second-hand rumour data follows:
I have a friend that says at certain speeds the thrumming can actually vibrate the front end noticeably. Granted these speeds are >40mph down hills with particular angles of crosswind, but a 30Hz vibration in the front end could be a wee bit distracting.
Keep in mind I suspect Josh is referring to apparent wind which is function of actual wind angle and speed. If you are heading due north and wind is from the west, the apparent might be more like a northwestly.
Good point, but 30 still seems a bit shallow, even when correcting for this. I’d like to see 45 degrees apparent (true crosswind if 20mph crosswind and traveling 20mph). I think that would be true? Could be wrong.
