Moto3 Aerodynamics: How The Law Of Unexpected Consequences Produced Closed Rear Wheels

There was some consternation in Austria in August when KTM rolled out a wheel cover for the rear wheel of the KTM RC4 on the Red Bull KTM Ajo bikes of Pedro Acosta and Jaume Masia. Despite the strict technical rules in Moto3, the specter of aerodynamics has reared its ugly head.

Naturally, this advance could not go unanswered by KTM's only technical rival in Moto3. At Aragon, the Hondas of the Leopard squad – the most technically advanced of the Honda Moto3 teams – also sprouted a closed wheel cover, almost identical in design to that of the KTM.

This goes against everything the technical regulations for the Moto3 class have been designed to do, and yet it is simultaneously the natural end result of it. Despite the explicit ban on aerodynamic appendages such as are seen in MotoGP.

The section on aerodynamics reads:

"Devices or shapes protruding from the fairing or bodywork and not integrated in the body streamlining (eg. wings, fins, bulges, etc.) that may provide an aerodynamic effect (eg. providing downforce, disrupting aerodynamic wake, etc.) are not allowed.

The Technical Director will be the sole judge of whether a device or fairing design falls into the above definition."

What this means in practice is the bodywork has to look like a 'traditional' fairing, with smooth sides except for the vents to allow the air which builds up behind the fairing after it passes through the radiator and oil cooler to escape. The only bulges allowed are the flared sections in front of the clipons and the windscreen, keeping the wind off the rider's hands and head. But no wings, spoilers, or ducts as seen in MotoGP are allowed.

It is an immutable law of nature, however, that banning something in the technical regulations merely stimulates the ingenuity of engineers, and encourages them to find a way around the rules as written. The rule makers for Moto3 did their best to limit the use of aerodynamics, but that doesn't mean that the manufacturers will not explore what is not explicitly banned.

In a recent video on the MotoGP.com website, which takes a surprisingly deep dive into aerodynamics, Ducati Corse boss and chief engineer Gigi Dall'Igna explains that aerodynamics is an underused and underexplored area of motorcycle engineering. "Motorcycle aerodynamics has always been too often neglected. Only in the last few years has significant progress been made," he told MotoGP.com's Steve Day.

One thing which Dall'Igna did not mention was the reason he and his team at Ducati Corse started to explore aerodynamics so extensively. During the transition to the era of spec electronics, a lot of the tools engineers used to manage the behavior of the bike, such as wheelie on corner exit, were removed.

The art of the possible

No longer could the engineers write ever more sophisticated electronics algorithms to monitor and calculate the precise moment the front wheel would lift off the ground, and manage torque output to maximize acceleration while keeping the front wheel just above the surface of the tarmac. Instead, Dall'Igna and his engineers turned to aerodynamic wings to keep the front wheel on the ground, maximizing drive onto the straight. Where Ducati led, others soon followed.

Fearing a spending war, MotoGP's rule makes – the Grand Prix Commission – clamped down on what was permissible in MotoGP, and imposed much stricter rules on the Moto2 and Moto3 classes. The MotoGP manufacturers – once again led by Ducati – have turned their attention to bike attitude, using ride-height devices to manage the rear of the bike and extend anti-wheelie even further.

With less competition in Moto3 – just KTM and Honda – the stakes were lower. The fact that there are so many parts of the bike capped by cost – engine and chassis packages, for example – means there is little room for exploring new technology. But the very tightness of the regulations, and the nature of the class, keeping bikes close together, means it is inevitable that the loopholes which were open would be explored.

What is the purpose of those rear disc wheels? By enclosing the wheel, airflow around the rear wheel is smoothed out, which reduces drag. The spokes of the wheel, spinning at high speed, churn up the air and produce turbulence, and turbulence in turn produces drag. By covering the rear wheel, you eliminate that turbulence, and reduce the amount of drag.

Of course, these gains can't compare with the benefits to be had from the kind of aero seen at the front of MotoGP bikes. They only provide marginal gains, and even then, can be sensitive to side winds.

But the way the technical regulations are written leaves few places to explore. And the nature of the bikes created by the technical regulations can make marginal gains extremely valuable.

Locked down tight

Under the Moto3 technical regulations, engines are homologated for a season, with each manufacturer committed to supplying identical engines to every rider who uses them. Teams are explicitly banned from touching the engines – they are a sealed unit, which may only be maintained and worked on by the manufacturer, and have to be returned to the manufacturer after use. The teams can do nothing beyond a change of exhaust to try to find more performance.

Gear ratios are locked down too, the teams forced to choose a maximum of two different ratios for each of the six gears the gearboxes use. Furthermore, they are only allowed three different ratios for the final drive. There is very little to be gained from gearing.

The electronics are also locked down tight, the teams all restricted to using the Dell'Orto spec ECU and software. Despite the electronics being limited, this is one point where teams have been known to pursue gains in the past, with engineers playing around with quickshifter timing and other engine parameters to extract the very last ounce of performance.

The chassis of the bike also has to be homologated, and so-called performance parts (basically, chassis updates) made available to everyone. Here, too, it is hard to make a difference compared to your rivals.

Wiggle room

And so the value of even those marginal gains from enclosing wheels becomes inflated. With next to no other avenues to explore in search of performance, factories and teams are left to try things which provide even the smallest benefit compared to their rivals. The law of unexpected consequences strikes again.

Does this mean we can expect to see an all-out aerodynamic war in Moto3 between KTM and Honda? That is vanishingly unlikely. The marketing value (and hence the economic value) of Moto3 is not high enough to make it worth throwing a metric tonne of R&D cash at the class. Furthermore, the technical rules are locked down enough to prevent the very worst excesses.

But the closeness of the class, and the closeness of the bikes does mean that teams will continue to spend what they can to try to make the difference. The aerodynamics cat is out of the motorcycle racing bag, and it won't be put back in again. Not even in Moto3.


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year: 
2021

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Comments

If motogp was not welded to tradition so firmly we would have seen long ago seen bikes evolve to far more streamlining. It started to develop in motorcycle racing in previous years (in the form of dustbin fairings) but after some nasty accidents it got banned. I pretty sure we could get some relatively low capacity high speed bikes with increased performance and safety by allowing more innovation. Like I said welded to tradition. Despite the bullshit, racing does not contribute as much as it's claimed to innovation in vehicles. 

When i first spotted the wheel covers my initial guess was that they would make a draft harder to pick up for a following rider, of the utmost importance in moto3.

When thinking about getting a tow and not down force or the like, aerodynamics in general are less about just streamlining up front than they are about putting the air back together behind you which is why the wheel cover makes such a huge difference. the hole in the air behind is tidier and should therefore be harder to sniff out and latch on to as it's a smaller target.

If you want to see a world where aero has gone bonkers, look at road bicycles where you are the engine and the selling points are how many fewer watts (typically in single digits) the rider has to put out to achieve the same speed over distance.