AERO SPEED WITH ROAD BIKE EFFICIENCY AND COMFORT
The TTi is our third generation triathlon specific design and our fastest yet. Company founder, Bob Parlee, spent two decades focusing on the hydrodynamics of high-performance boat design before turning his attention to racing bikes in the 1990’s. Bicycle aerodynamics and boat hydrodynamics have a lot in common and his background in boats is a huge asset to our development processes. We also now depend on complex computer-based simulations, 3D modeling, rapid prototyping and robust wind tunnel test sessions at a world-class university in Cambridge, MA to validate our designs prior to road-testing with world-class athletes.
Bob found early on that standard high lift (“wing”) sections, that are popular in the bicycle industry, rarely work well. We use a combination of low-drag NACA sections, as well as our own custom, low-speed aero sections, that optimize a bike’s aerodynamic performance without sacrificing ride quality. Bob’s experience with boats taught him how to create his own foil or “wing” sections optimized for complex performance requirements. High lift sections are efficient at low angles of attack (head-on wind conditions) whereas our sections have greater efficiency at greater angles of attack (cross-wind conditions).
Unlike the foils on a sailboat, or airplane wings, the sections on a bicycle are static and cannot be adjusted as wind conditions on the road change. Variations in terrain, and large objects like trees, buildings, and hills influence wind speed and direction requiring the use of aero sections that excel “off the wind”, also described as efficient across a wide range of yaw angles. The results from our wind tunnel testing demonstrate that our TTi is as, and often more, efficient than our competitors in a greater range of wind conditions (fig2.1).
At around 3 degrees of yaw angle (the angle of attack) the Parlee TTi begins to get more efficient, and continues out past 15 degrees (fig 2.1). Many other bikes start to lose efficiency at 3 degrees. In a wind tunnel, everything except the variable being tested (the change in yaw angle of the bicycle) is constant. On the road, where conditions are constantly changing, efficiency at greater yaw angles is of great advantage to a rider. As can be seen from the wind tunnel results our TTi has less drag over a much wider range of yaw angles. These results validate the design goals: make a fast bike in a wide range of real-world conditions.
Much of the improvement from last years TT to the 2013 TTi can be attributed to our new fork. This fork is our own design for this bike, and its key innovation is in the approach to air flow around the fork crown and wheel interface. The industry trend is to close the gap between the fork and wheel forcing air flow to the outside surfaces. We’ve taken the opposite approach in opening up this gap (fig. 2.2).
Having a generous spacing between the crotch of the fork and the wheel smoothes the air flow, allowing it to split and pass through with fewer disturbances. We’ve always believed the front 1/3 of the bicycle is the most critical to the overall aerodynamic performance of the whole bicycle. And as it turns out, the addition of our new fork design to the TTi has created a faster bike while retaining the road feel, handling, light weight and comfort that all PARLEE designs are known for.
Aero properties are worthless without a bicycle that fits. 10 years of working with bike fitters and athletes of all levels building custom bikes have given PARLEE one of the best baselines to build functional race bikes that fit perfectly. The TTi features our ground-breaking Flex-Fit geometry. Flex-Fit geometry features two head tube heights for each given frame size. This effectively doubles the number of athletes who can fit the bike without compromise. The TT features the broadest range of stack and reach positions (fig 3.1) and is not limited by a proprietary bar/stem system that restricts adjustment of the elbow or hand positions.
Further improving rider positioning is our proprietary seat post design. First featured on our TT model, it features a modular rail system which creates an effective seat tube angle range of over 5 degrees. All adjustments to saddle position are set independently with an Allen key. Setup and minor adjustments could not be easier.
The TTi has been designed to be the most usable triathlon bike in the world. The TTi supports mechanical shifting systems from Shimano, Campagnolo and SRAM, and electronic shifting systems from Shimano (Di2) and Campagnolo (EPS). It features industry standard front and rear integrated brakes by TRP.