In the pits: Time trial bikes in California
By James Huang, technical editor | Monday, February 18, 2008 11.00pm
The Felt DA of Slipstream rider Dave Zabriskie is ready to go just prior to his start. James Huang, technical editor
The Tour of California prologue was just 3.4km (2.1mi) long, but its relatively flat course meant that teams and riders paid special attention to aerodynamics.
Wind tunnel testing has long been an integral part of the early season preparations, but as teams and riders have become better at cheating the wind, little details are beginning to make more of a difference.
Cables, cables, go away
As it turns out, poor cable housing placement apparently has a more detrimental effect than was once thought and teams are being more mindful of cable routing than in years past. Housing has a relatively small frontal area but its round cross-section creates turbulent airflow at the front end of the bike that can affect the performance of the more aerodynamically shaped surfaces behind it.
The Slipstream/Chipotle riders left the start house aboard Felt's latest DA frames which were designed using computational fluid dynamics software and wind tunnel testing. As a result, Felt engineers routed the derailleur and rear brake housings into the frame right behind the stem where the air was already ‘dirty' from the rider's hands and arms, thus leaving clean air around critical frame regions.
According to Slipstream team physiologist Allen Lim, sheltered housing consistently saves about 1-2 watts in the wind tunnel without the rider aboard. Lim said that adding the rider does wash that result out a bit, but, "it still matters."
The concept isn't new (Zipp incorporated the feature in its radical 2001 frame from the early 90's) but other makers have followed suit, such as Trek with its Equinox TTX used by Astana, and previously Discovery. On frames not designed with internal cable housing, team mechanics made use of zip ties, electrical tape and whatever else would work to tuck the lines around the stem.
That small detail probably didn't make that much of a difference during the short prologue, where the fastest times were under four minutes, but could very well have an impact on Friday's longer time trial stage in Solvang.
Zipp and PowerTap get together
Power meters have always been a critical part of Slipstream's training and racing equipment but in the past, riders have either had to ride deep-section rims built around PowerTap hubs during time trial events or simply go without if they opted for discs. But we spotted a couple of Slipstream riders at the prologue with new Zipp discs, both of which were co-developed with PowerTap to incorporate the power measuring technology inside a new hub.
One of the wheels is based on the flat-sided Zipp 900 for riders that prefer a stiffer wheel while the other incorporates the company's latest Sub9 shape. Zipp claims its Sub9 is not only the first wheel to yield negative drag (otherwise known as lift) under certain wind tunnel conditions but also delivers a more comfortable ride as well.
The Zipp-designed hubs include PowerTap's latest 2.4GHz wireless hardware but use Zipp axles, bearings, and freehub internals. According to Zipp marketing manager Andy Paskins, the PowerTap-equipped wheels add only 120g to the standard versions and hubs will be available with ceramic bearings as an upgrade.
Rock Racing goes against the clock with an amalgamation of equipment
Rock Racing has been awash with controversy lately and not even its relationships with bicycle and equipment sponsors past and present has been spared. DeRosa emerged as the team's bicycle supplier earlier this season and we expected to see the team's abbreviated roster aboard the Italian company's TT model, the carbon fibre Kron.
Instead, we spotted no fewer than three different makes of bikes in the pits prior to the start of the prologue. Half-hearted camouflage efforts did little to hide the distinctive shapes of Scott's Plasma TT and Look's 496 frames and there were no Kron framesets to be seen at all (although they may have pulled them out when we weren't watching). At least one rider took off on an aluminium DeRosa Protos road model fitted with clip-on aero bars.
Team boss Michael Ball has managed to strike a wheel sponsorship deal with Cole Products, though, and most team bikes we spotted were equipped as such, along with big green "ROCK RACING" decals, naturally. Still, the team pit area was littered with a wide range of other models from manufacturers such as Mavic, Zipp, Lightweight, and Lew Racing.
You can follow BikeRadar on Twitter at twitter.com/bikeradar and on
Facebook at facebook.com/BikeRadar.
can also improve your fitness and train with us on training.bikeradar.com.