A BRIGHT AND BREEZY FUTURE

How much more aerodynamic can a wheel get? Chief aerodynamicist Jim Farmer explains

‘There are two main factors at play that make a wheel fast – drag and lift. Put an aero wheel straight into the wind and there’s minimal drag and no side lift. But turn that wheel into the wind and increase the angle of attack – or yaw angle – from 0° to 12° and you get lift, which is when the wheel wants to move forward like a boat sail. As the wind angle changes the wheel will eventually stall, and there’ll be no lift. With a boat that means it stops, with a plane that means someone isn’t coming home for dinner, and with a bike wheel it means you’re going to go slower.

‘Lift offsets drag – although because of you and the rest of the bike it will never overcome drag – so the ideal scenario is a low-drag, high-lift wheel. The problem is such wheels would tend to handle badly in crosswinds as they’re so deep [increased wheel depth is related to high lift]. The other problem is drag and lift change depending on wind angle, making manufacturers’ claims to having the fastest wheel very difficult to qualify. Fastest when?

‘What we’re looking to make is a wheel that is consistently good, if not necessarily ever the best, across a variety of conditions. To do this we’re investing a lot in CFD. At the moment we can model the airflow over a wheel and tyre, but in a year’s time it will hopefully be the entire front end of the bike including spokes.

‘Then the next problem is what to do with the numbers the computer spits out. For that I’m currently working with Stanford University to develop code that says, OK, these are your parameters – wind speed, air pressure, etc – and here are some geometric tweaks to your wheel that will optimise the wheel for your chosen conditions. They do it in the aerospace industry already, and I want to bring it to bicycles.’