Trek's new Time trial bike – currently named the Speed Concept – has been much in the spotlight over the first week of the Tour de France, with three Astana riders (Armstrong, Contador and Leipheimer) piloting the machine in the Kazakh Team's TTT victory. But there's more to this bike than simply a refinement of the current TTX.
The Speed concept is based on aerodynamic research that's been doing the rounds in automotive circles for over 70 years. We spoke to Tyler Pilger, road product manager at Trek and one of the men closest to the design, and he gave us the lowdown.
The problem with the 3:1 tube profile is that it has a very blunt font end, so we've used technology that's more often seen on high performance and efficiency cars. The Speed Concept is based around a profile known as the Kammtail Virtual Airfoil", Pilger tells us. The Kamm profile (named after the research Wunibald Kamm) uses a much narrower profile but the tail of the airfoil is chopped off after the widest point of the tube.
This creates a virtual wake which mimics the aerodynamic effect of an longer, narrower wing. While true high-speed airfoils use an 8:1 profile The Trek KVH (Kammtail Virtual Foil) is actually derived from a ratio of a little over 4:1 before the truncating of the rear of the foil. "We found this to give the best low speed performance and it allows us to still design a bike that's fully UCI legal", says Pilger. "We're confident it's UCI compliant in every aspect: frame, handlebars, seatpost. Everything".
The concept may be a new one in cycling but it has a 70 year legacy in automotive design. Kamm's research in the 1930s was quickly taken up by motor manufacturers looking to produce shorter vehicles with good aerodynamics. The Wikipedia entry (http://en.wikipedia.org/wiki/Kammback) lists the 1940 BMW 328 "Mille Miglia" Kamm coupé as the first car to use the shape, and there are plenty of other notable machines in the list, including Ford's GT40 and the Citroen CX.
The frontal aerodynamics aren't the main bonus though: the Kamm profile is particularly good in yaw situations (crosswinds), and Pilger is keen to point out that for a bike, that's nearly all of the time. "At 20mph with a 10mph sidewind you're already at 26° of yaw", he explains, "and a bike runs at 10° of yaw or more for most of the time it's being ridden. The benchmark numbers for head-on drag are interesting for comparison, but in the real world it's the yaw numbers that matter: in a yaw situation the Kamm Tail design just gets better and better".
Trek are confident that out on the road, with a rider and crosswinds, the Speed Concept is the slipperiest bike there is. "We started out running the tube shapes through CFD (Computational Fluid Dynamics) on the computers and then progressed to the wind tunnel", says Pilger. "Just the difference in drag in the downtube alone is phenomenal".
The frame design is the main innovation but there's plenty of other touches to shave tiny amounts of drag. The cabling is entirely internal: the only visible cable is the one that feeds the rear mech. The front brake is also completely integrated, forming part of the fork structure, and the DuoTap sensor port in the chainstay (the same as the new Madone) completely hides the computer sensor from view - and wind. On top of all the aerodynamic benefits the new frame is also 200g lighter and 17% stiffer than the TTX, both significant numbers.
And if you want one, will you be able to buy one? Well, yes. But not yet. "It will go into production", Pilger assures us, "but it's not a 2010 bike. We couldn't get the new Madone and the Speed Concept through the whole cycle, there's just not enough time. we will be getting the bike to market as quickly as possible but we're not publishing a date yet". Hopefully we'll see it in the 2011 range, but it may well be later. By then, of course, we'll no doubt be seeing the Pros on something even faster...
Dave is a founding father of road.cc, having previously worked on Cycling Plus and What Mountain Bike magazines back in the day. He also writes about e-bikes for our sister publication ebiketips. He's won three mountain bike bog snorkelling World Championships, and races at the back of the third cats.