For exarnple, when you go at 40km/h, your wheels spin with double speed at 80km/h and from 15krn/h the air resistance is a big factor to overcome.
The force we have to invest to go against the air or wind. The aerodynamics in tires or wheels is quite complex and requires a thorough study as many components influence. First we explain some basic parameters.
The resistance to move a bike forward is divided into
The air resistance is divided into
...that in conditions with a fully frontal wind angle of 90%. If we change this angle everything will change and that is where an aerodynamic design can be beneficial or not.
In aerodynamics of bikes we talk a lot about the "sail effect". (nautical boat) We all know that a sailboat to go against a wind direction has to cross in a zig zag way. Although there are very small winds angles that act on sail, they also push the object forward.
We call this effect in Progress TURBO, it greatly reduces air resistance according to height - rim profile, angle and wind strength.
How the side wind or sailing effect affects a cyclist:
Most of the manufacturers and we make the design of wheels and all the tests with a wind simulation of 45km/h is where the sailing effect is very considerable. A rim with good aerodynamic efficiency can reduce your tirne over long distances in a matter of minutes. But if the design of the rim and the shape is not well achieved, the sail effect can be zero or even the opposite can cause turbulence and a lot of air friction - DRAG.
Computer simulation rear side rim
The secret is to design rims where the wind slides without turbulence at different angles from the top of the tire over the curvature of the rim on both sides. When the wind is better coupled laterally to the walls of the tire more turbo and thrust effect.
We measure this flow in the wind tunnel by turning the wheel between 2 angles - 20 ° to +20 °. Thus we see exactly when and at what angle we have maximum efficiency and at what time the flow breaks or takes off from the rim.
It is very important that it is well integrated into the rim. Our AIR + PLUS rims are very wide with a 21 mm interior and 30mrn exterior that open the tire walls enough to form a stepless line.
Not all tires are recommended for time trail since they offer up to 4 extra watts of air resistance. (Direct advice in Progress or through the tire manufacturers)
Who have passed through the tunnel can offer accurate data such as
The average of all these results indicates the resistance in (W) watts. In Progress we offer this data on our website or catalog shortly. Data offered by the GST wind tunnel that measures 4.000 data per second.
Any deep section rim influences the handling of the bike and the control. Side winds with strong gusts are able to pull you off the road. Thus it is important to know how to choose the right wheel for the type of track and profile of the rim.
It is very difficult to establish some parameters since each brand is different. It also depends how much you want to take advantage of the turbo - sail effect. In our new AIR + PLUS we use an easy-to-use and safe profile with a completely round U-type design that reduces lateral wind resistance to the maximum and is more predictable. Even so, we recommend our SPACE model with 88m not to be used in peloton races or only used as a rear wheel. In TT and Triathlons the SPACE according to data is one of the fastest wheels on the market. Our rims up to 50mm profile are totally recommended for any type of route or wind.
WIND TUNNEL TEST 2019-11-28
AIRBUS, GST Windkanal, Immerstaad