Formula One and aerodynamics expert JP Ballard believes that wheels with tubercles, or bumps on the rim profile don't offer an advantage
Last month Zipp launched its new NSW 454 wheel, with a rim shape inspired by the fins of a hump back whale.
Speaking at the launch of the new DT-Swiss ERC 1100 Dicut wheelset, JP Ballard the technical director of Swiss Side, explained why the new wheel didn’t have the bumps (tubercles) found on the new Zipp NSW 454.
Ballard, who worked previously as technical director in Formula One, described how aerodynamicists have long studied and known about the ‘tubercles’ (bumps in layman’s terms) on the fins of humpback whales.
These nodules are said to help humpback whales be very manoeuvrable despite their large size.
The theory is, that a bike wheel can behave in a similar way to the wing of a plane and like the wing of a plane, a wheel can stall.
By including the bumps/nodules you can avoid the wheel stalling at high yaw angles because “vortecies form between the tubercles and these re-energise the flow,” said Ballard.
Ballard added “we did this in F1 first and in air they don’t work because of Reynolds numbers – the density of air is much less than water.”
Perhaps then, wheels that feature tubercles/bumps on the rim will be excellent when ridden underwater, or at the very least through very deep puddles?!
As proof of this, Ballard displayed pictures of prototype Formula One cars, that featured tubercles at various locations on the wings.
He also showed a selection of prototype wheels that DT-Swiss and Swiss Side had worked on that featured ‘tubercles’ similar to those on the Zipp 454 NSW.
When integrated into a wheel rim, Ballard explained “tubercles don’t work because they create more drag. They create more high pressure, low pressure areas on the surface of a wheel resulting in a net drag increase.”
Video – How much faster are aero wheels?
The price to the consumer should not be overlooked either, with the incorporation of tubercles into the wheel rim shape significantly increasing the cost of manufacture using current methods.
Zipp’s 454 NSW costs an eye watering £3500 a pair. Conversely, by not including tubercles, DT-Swiss was able to make its new wheels comparatively more affordable.
Ballard, clearly has a vested interest in saying that DT-Swiss wheels with no tubercles are superior to Zipp’s wheels with tubercles, however his argument is compelling when you factor in that they explored the concept and dropped it.
Whether the inclusion of the tubercles into a wheel rim design is cutting edge aerodynamics or a marketing gimmick is hard to say, but it is possible to question why the likes of Formula One and Aerospace hasn’t adopted them.
Why do we not see aeroplanes or helicopters with them? Perhaps we will.