Ben Meir
REAP Vekta: Aerodynamics Explained
- June 25, 2021
- , 3:57 pm
The Vekta is an incredibly aero road bike. Here we explain why it’s so fast and how our very small team made it that way.
Why it’s so fast
The Vekta is one of the very fastest aero-road bikes in the world. During development, the Vekta delivered results in both wind tunnel and velodrome testing that put it on par with top time trial bikes, never mind its own category. Reducing drag to this extent requires every element of the bike to be honed.
One of the most important ways in which the Vekta achieves its incredible speed is the precision with which we can mould the crisp edges to the frame shapes. Like many bikes, the Vekta uses truncated airfoils (think of a D shape that’s smaller at the straight edge) which make the airflow behave as if it were following a long, traditional airfoil (like a stretched out teardrop with a point). The air continues to flow smoothly once it has passed the frame and it meets again as if it had followed a complete airfoil. Turbulence, and therefore drag, is minimised.
The reasons for choosing truncated airfoils in place of complete ones are to do with how these shapes perform when part of a bike frame; they are lighter, more compliant to bump forces, and stiffer laterally against pedalling forces. They also allow designers to simulate airfoils that are beyond the UCI’s limits and as a downtube they better envelop bottles. Simply, they’re a win all round.
However, the performance of truncated airfoils (also called Kamm-tails) hinges on how sharply the shape is cut off. If the rear corners are too round, the air follows around them and becomes turbulent, and the effect is lost. A sharper radius greatly improves the aerodynamic benefit, but is very difficult to mould, generally too difficult for mass production. That’s where our specialism and composite (rather than alloy) moulds give us the edge, if you’ll forgive the pun.
The Vekta’s downtube also features a ‘trip’, a sharp crease that’s precisely placed and angled to influence the airflow to follow the virtual airfoil shape.
Several other features contribute to the Vekta’s speed:
- Reduced frontal area is achieved by the flat toptube and the dropped seatstays.
- Turbulence and pressure spots are reduced by the wide stand fork and the dropped seatstays, both of which allow air moving past the bike to be less disrupted by the forward moving upper part of the wheel (spokes, rim and tyre) and the air dragged with it.
- Smoother airflow is achieved by the wheel-hugging downtube and seat-tube which transition the air more cleanly between the wheels and frame.
- The frame’s tube profiles have been optimised for the latest wider aero wheels with tyre widths of 25-28mm.
The Development Process
The Vekta was born from REAP’s first bike, the searingly quick Gen1 tri machine. The shaping of the Gen1 was done by the same team of computational fluid dynamics (CFD) experts as designed the UK Sport bikes which dominated the London Olympics on the track and was ridden to gold in the TT by Bradley Wiggins.
The Vekta frame was designed in CAD based on the Gen1’s profiles, then turned into a foam prototype. This model was sanded into shape by hand to adapt the structures to a double-triangle frame, scanned back into CAD, and then machined again in foam. This second rapid prototype was tested at the R J Mitchell wind tunnel at the University of Southampton and was immediately super-fast, on par with a TT/tri bike from one of the most respected aero brands.
The first rideable carbon fibre prototype was then produced and this was tested at Derby Velodrome by Dan Bigham of WattShop, with REAP pro triathlete Tom Bishop riding. Using a road helmet, bars and wheels (ENVE 7.8s), regular rather than aero brakes and a basic tri suit, the CDA figure was 0.19, a number that would be very good for a time triallist and is off the scale for a road bike. Dan was amazed at the outcome and that gave us the confidence to tool up for production.
As a very small and new brand, we didn’t have the budget to go around the R&D loop of iterate-test-revise half a dozen times, so we had to rely on expertise to get it right quickly. We were very happy when the data told us that we had
