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Aerodynamics: Go with the flow
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Aerodynamics: Go with the flow

Team Fast Bikes

Back when I was learning to ride, there was some properly mad stuff going on with aerodynamics. It was the late 1980s – bikes had only recently started having full fairings – and the bike firms were going crackers trying loads of different stuff. To be fair, they were trying just about anything back in those days – two-stroke engines, four-stroke engines, water-cooling, oil-cooling, 16in front wheels, anti-dive forks. It’s almost like they didn’t really know what would work, so just got busy trying everything they could. And aerodynamics promised a lot in terms of performance. When even the biggest engines were only making about 100bhp, it seemed like a smart plan to make the most of what you had. And so covering the bike in slippery, smooth plastic panels that would slice through the air much easier became fashionable. Early designs like Kawasaki’s GPZ900R showed the way, and soon we had the likes of Honda’s CBR1000F and Suzuki’s GSX1100F – enormous, bulbous, plastic whales on two wheels.

Space and all that

It was Kawasaki that hit the peaks of aerodynamic design back in the 1990s. The Japanese firm famously also made spaceships and aeroplanes, so were perfectly equipped with all the wind tunnels and supercomputers they needed to explore the bleeding edge of aero design. And in 1990, they launched the ZZ-R600 and ZZ-R1100, which were far more aerodynamic than anything else out there. From their huge front mudguards, which cut through the air then channelled it back onto the wide, smooth, curved flanks of the main fairing, back to the broad, sleek tail unit, the ZZ-Rs looked more like fighter jets than sporty-tourers.

“It’s about controlling how a vehicle moves through the air, at speed, and altering the vehicle’s form to optimise that process”

And the results were impressive – not only did the 275-odd kmph 1100 take the ‘fastest roadbike’ crown it would hold for most of the 1990s, the 600 only went and won the British Supersport 600 title under John Reynolds. But what is aerodynamic design all about? Well, to be fair, it’s an enormous topic, which we could fill most of the magazine with for the next six months, and still not dent the surface. But in essence, it’s about controlling how a vehicle moves through the air, at speed, and altering the vehicle’s form to optimise that process. Now, the obvious thing to consider is speed – a sleek, smooth, streamlined shape like an arrow will be able to go much faster than a blunt, squared-off shape like a brick, for the same force going through it.

But there’s a lot more to it than speed, especially in modern bike design. Martin Lambert, Kawasaki’s European PR boss, told us about some of the aerodynamic considerations the firm have to think about on a modern bike. “We have a wind tunnel and aerodynamics plays a huge part in performance. For example, remember those tiny winglets on the lower fork of the ZX-12R? But ‘aero management’ is just as big an issue – you have to manage air into the fairing, and air out again, for cooling. There’s also noise to consider, and even things like pedestrian safety – we have special kapok dummies to test for any sharp edges on fairings.”

Life can be a drag

So, the ideal aerodynamic design has to think about performance in terms of speed – but also efficiency. A well-designed fairing will reduce the effort needed to move through the air, and thus, can reduce fuel consumption. That can mean a smaller fuel tank will do the job, so you can make the bike smaller – further improving aerodynamic performance, in a ‘virtuous circle’. Engineers will want air intakes cut into the front parts of the fairing, to get air into the air box for the engine, and also to feed cooling air to water and oil radiators. That air then has to be exhausted – the engine intake air obviously coming out via the exhaust system, and the cooling air generally comes out of cutouts in the main fairing side panels.

Even here, though, there’s more optimisation taking place: Kawasaki in particular has made a big deal out of its ‘Ram-Air’ intake systems, from the ‘Hoover’ hoses on ZXR750s, through the chin-mounted scoops on the ZZ-R1100 and now the big ducts on the supercharged H2. Collecting the engine’s intake charge from the high-pressure zone at the front of the fairing ensures plenty of cool, dense, fresh air, which will give maximum power and efficiency. And at higher speeds, there’s the chance for a gentle ‘forced induction’ effect here – although the pressure gains even at three-figure speeds won’t make too much difference to the power output overall.

“Even a small half-fairing can make a massive difference here if it’s well-designed, directing the wind blast up and over your body and letting you cruise at high motorway speeds for hours”

After drag considerations, perhaps the next most important job is to protect the rider – both from the wind blast at high speeds, and exposure to the weather. As you’ll know if you’ve ever ridden a mega-bhp naked bike, just hanging on in a 160kmph wind puts a load of strain through your neck, shoulders and back muscles. Even a small half-fairing can make a massive difference here if it’s well-designed, directing the wind blast up and over your body and letting you cruise at high motorway speeds for hours without snapping your vertebrae and exploding your wrists with arm pump.

Protection from the weather is a tricky job, and you’ll need to have a fairly serious fairing if you’re wanting to keep real bad conditions at bay. In the past, that meant enormous plastic barn-door jobs, using brute-force and ignorance to keep you dry and warm. But computer-aided design, and loads of time with wind tunnels and the like have let designers do a much better job with much less. Look at something like the new Triumph Tiger adventure bikes, Ducati’s Multistrada or BMW’s R1200 GS. They’re all essentially touring bikes of course, so they need to keep wind and weather off the rider and pillion. Rather than just bolting on a massive screen though, they have smaller, adjustable windscreens, with wind deflectors round the fuel tank area, complex hand guards and big ‘beaky’ front mudguards.

With less weight, reduced drag – and better looks – than the old-school fairing designs, these bikes still do a good job of protecting you from both windblast and the weather though, by working smarter rather than harder. And wind protection isn’t just about riders being pussies and wanting a cosy, easy life. Cristian Gasparri is the project leader at Ducati for the new V4 Panigale. He told us at the V4 launch that rider comfort is also a safety matter. “For a long ride, you need comfort – not just for comfort itself, but also so your body is less stressed, and to be more able to react to the events of the road.”

Know how to flow

The final thing to consider is what the MotoGP guys were aiming for with all their aeromalarkey last year – handling. Before we look at them though, let’s have a look at one area where aero is crucial for handling – cars. Managing airflow properly can improve so-called ‘downforce’ at speed, while also cutting drag to the minimum, all the while cooling the enormously powerful engines and brakes. Take a look at an F1 car – that giant aerofoil at the back acts a bit like the wing on a Boeing 737, generating lift. But they’ve bolted the bugger on upside down, shoving the rear wheels into the tarmac, to give lashings more grip. Huge ducts on either side feed water and oil radiators with cool air. Meanwhile, up front, a smorgasbord of small aerofoils, blades, spoilers and ducts take the 320kmph breeze, and direct it in the most efficient way under, around, over and through the car. Channelling high-speed air under a smooth underbody section on a car reduces air pressure actually under the car – ‘sucking’ it hard onto the ground.

The result? Stunning levels of grip from aerodynamic downforce, while also giving the minimal levels of drag possible, and keeping 800bhp motors and carbon brakes cool. The big problem with bikes here is that they’re not a very stable platform. At all. The four wheels of a car, and the relatively small amounts of suspension travel mean engineers can control the spacing between the car and the road very closely. Cars don’t wheelie or stoppie, unless you’re doing something very wrong (or very right…). That means that downforce works well while cornering, and the underneath of the car can be useful too.

Bikes lean while cornering of course, and that, plus the relatively large suspension movements under braking and acceleration in particular makes it far harder to make much use of aerodynamics. In addition, a setup which worked when you were hard on the brakes, would be no use at all on the way out of a bend, when the bike’s wheelie-ing. On the brakes, you’d perhaps want aero to be trying to keep the back end of the bike down for a little longer, to give more braking force at high speeds when you first hit the brakes and before the rear wheel lifts. But then on the gas, you want the opposite: some way of holding the front end down.

We asked Cristian Gasparri about this too, and he told us about the problems with optimising aerodynamics for handling on a bike. “Aerodynamics and handling? Yes, it is important for bikes, but there is not one unique answer. Every bike is different and each solution has a different impact – it is good in one direction, but has a bad impact in another. That’s why tests in the windtunnel are so complicated to manage, we have so many with the Ducati Corse guys, they have to test a lot of time, every kind of solution.”

Gasparri says even the most obvious answers don’t always work out the way you’d think they will. “You might test something that you think will work well, from a theoretical point of view – but it doesn’t always work out this way. Also, the size of the rider, their position on the bike, it changes completely the result. Everything has to be worked out in detail with lots of calculations, then simulated in software. Then, finally we go into the wind tunnel with a lot of options, in order to manage carefully this kind of solution.” It might be hard, but the bike firms have still been trying. Last year’s MotoGP series saw enclosed aero ‘wing’ sections on the front fairing of several bikes – Ducati’s factory bikes in particular. They were able to optimise one area – trying to keep the front end down under acceleration, and controlling wheelies while still putting down power.

Will we see that appearing on road bikes any time soon? You’d have to say yes – nothing is cooler than MotoGP tech of course, and the first bike with wings will be snapped up by all the cool guys. But we’d expect it to be in a rather watered-down form. Having a bike ridden by Andrea Dovizioso on a track, in controlled conditions, with slicks, is one thing. Having your mate Dozy Andy trying to break his own lap record of the local ring road on his be-winged ZX-10R, at rush hour, in a howling gale, is quite another. The potential for aero on bikes to go wrong is pretty clear – if you’ve ever been caught on a big suspension bridge in a storm, you’ll know how nasty things can get. So any aerodynamic parts will have to cope with all the vagaries of road riding, and probably end up far less effective as a result.

Words by Alan Dowds