Buying an Aerodynamic Front Wheel

One of my closest friends is a very gifted road cyclist that races prominently and may be working towards a career as a pro. He recently wrote to me about purchasing an aerodynamic wheelset and asked me my opinion about the products available. Below is my response to him, slightly modified to be a more fitting blog entry.

-----------------------

In regards to wheels, here's my synopsis of the available options.

Aero wheels can, for all intensive purposes, be divided into two categories: toroidal and non-toroidal. The toroidal cross-sectional shape, a special kind of bulge, is protected by a patent shared by Zipp and HED. Zipp in turn shares it with its Flashpoint subsidiary and SRAM affiliate, while HED produces rims for Bontrager. It's widely accepted now that the toroidal cross section is the most optimal shape for an aero wheel, and it basically operates by filling the low pressure gap formed by the air splashing around the leading edge of the tire. This generally leaves wheels like Mavic, Shimano, and Reynolds, which have a standard V-shape trailing edge, behind in terms of aero performance. Reynolds has made some strong claims about achieving comparable performance with their new rims, basically by making them extremely narrow, but there claims to my knowledge have not yet been independently affirmed, and to me would seem to only really apply to very low yaw angles (like when riding into a headwind). This high-performance at low yaw-angles could correspond to a loss of performance in cross-winds. Check out this image showing results from an independent lab comparing a wide range of wheels in the wind tunnel. 

Aero Wheel Drag Data circa 2007. Click to enlarge. 

For more information regarding cross-sectional shape and aerodynamic wheel performance, check out this article.

The venerated Zipp 404 clincher uses Zipp's 505 rim. Though it's 58mm depth puts it in the same range as the wheels yet to be discussed, its $945 retail price puts it in another, much higher price point


So if we look at toroidal wheels, we have Zipp, HED, Flashpoint, and SRAM. Zipp is the 'no-holds-barred-top-of-the-line performance' brand, but doesn't really (since 2007) offer a tangible performance benefit over HED or Flashpoint worth the markup. So we look at HED and Flashpoint. Both companies offer an excellent product and I know of innumerable tales of HED's excellent customer service. Given the comparable price points and performance, I would consider it a wash between these two. A review from testrider.com (now Peleton Magazine) is no longer available but spoke very favorably of the Flashpoint 60 wheelset. 

The Flash Point 60

And check out HED's website to read about their wheels, specifically the HED Jet 6 C2. HED's website is extremely informative and I love this page, Aerodynamics , where you can compare the aero performance of their wheels at different yaw angles (for readers not up to date on yaw angles, here's an example, although HED's website has an interactive yaw angle tool as well. 0 deg yaw would correspond, say, to riding directly into a headwind. Riding at, let's say, 25mph into a light cross wind would be 5 deg, stronger cross wind would result in 10 or 15 deg, etc...)

The HED Jet 6 C2

The SRAM wheels are slightly different. Whereas the HED Jet C2s are basically an aluminum clincher with a carbon fairing, the SRAM wheels are a carbon wheel with an aluminum rim affixed to it. I personally like the HED system, as, for me, there's a lot more ease of mind in case you hit a pothole, but the SRAM system could offer some performance advantages (like stiffness or vibration dampening) that carbon fiber is touted as having. Slowtwitch has a huge forum and aero wheels are often discussed. By looking them up I found nothing but good things about people's experiences with SRAM wheels. The basic synopsis is that they're heavier than HED, with lower quality but still quite nice bearings, hubs, and spokes. 

SRAM S60, also available in an attractive gray/black color scheme

Along with Flashpoint, SRAM wheels were reviewed favorably in all of the independent analyses that I found on-line (eg. the previously mentioned testrider.com reviewed them and were impressed). 

The toroidal shape of the SRAM S40

'Aero trumps weight' is a die-hard mantra of triathletes (especially considering our mostly flat or gentle courses at a constant tempo). Weight among wheels at comparable price points can still be a valid consideration, however. Whereas the front HED Jet 6 C2 comes in at 774g, and the front Flash Point 60 at 854g, the front wheel of the SRAM S60 runs 835g. This puts it well in the same range as the more expensive wheels, but almost 10% heavier than the HEDs. There are two perspectives on wheel weight. One contends that, since it is rotational, not translational, weight, a 60g reduction in wheel weight will mean a lot more than a 60g reduction in static frame weight. It could mean, some contend, that slight bit of extra energy to make the last wheel after a split or break in the race, or allow you the extra energy after an hour long crit to pull off the win in the final sprint. I wouldn't be able to tell you whether or not it's worth ~$200, though, to jump from the SRAM S60 to the HED Jet 6 C2 or FP60.


The opposing view on wheel weight, however, is that the weight of aerodynamic wheels is not a significant metric for consideration. Given the exponential nature of drag increasing with speed, the greater aerodynamics of a wheel made heavier by it's slippery shape more than compensates for the added mass. There's some very valid math to back it up, as well. Check out this editorial from Slowtwitch on the subject, Why Wheel Aerodynamics Can Outweigh Wheel Weight and Inertia.

Finally, regarding comparing the above options, the one reference I can make is to groupsets. SRAM wheels are like Rival- they offer pretty much the same performance as Red at a fraction of the cost, they're just heavier and by far the best value. HED is like Ultegra SL, which I consider to be the best combination of value and high-performance, and Zipp is like Record, which may be the very best but is also obscenely expensive.

If it were me, I would buy the SRAM S60 or S80 front wheel and keep my wheelcover over my Ksyrium Elite rear wheel. But I won't be penalized by the extra weight the way you may be.

The best option? Don't buy an aero wheel and instead buy a powertap hub on a handbuilt box rim wheel, like this $660 option from excelsports.com

A Powertap hub and monitor/computer

That would probably be of greater benefit to your cycling than any aero wheel (same for me), but it's not as sexy. 


------------------
And there we have it. The synopsis regarding buying an aero front wheel concludes, rather abruptly, with the answer of 'don't' and instead buy a handbuilt wheel with a powertap hub. Should you already be training with power, or are disinterested in putting the effort into using a powermeter to its best effect, then by all means grab one of these excellent wheels. 


Quick Disclaimer:

1) It seems redundant to say, given that it's on a blog, but the above entry is just my opinion, 2) Any information or phenomena presented as facts are up to the reader to verify rather than blatantly accept as truth, 3) Prominent brands, like Bontrager, Easton, EDGE Composites, and Shimano, in addition to less well-known brands like Gray or Neuvation, aren't thoroughly considered purely due to my lack of familiarity with them, 4) Since he's a road cyclist, this entry is purely a consideration of appropriate aero wheels in the 50mm-60mm range of rim depth. These are all also the most versatile front wheel for the triathlete as well so the conversation is quite relevant to the time trial and triathlon cyclist.  I could greatly expand on many of the above subjects, and likely will in future entries, but will keep this entry as a synopsis for someone new to aero wheel purchasing.