Sportsbike designers have been trying to optimise motorcycle aerodynamics for the last few decades, with varying degrees of success. The Hayabusa, with its 300kph top speed, gets it right, but earlier bikes like the Ducati Paso and the Honda CBR1000F also took major strides forward in terms of design and optimised aerodynamics
What
are the things that matter most when it comes to increasing a motorcycle’s
overall performance and efficiency? Power and weight, right? Yes, certainly,
more power and less weight are a good thing. But there’s also one more factor,
which is especially relevant for bigger, faster, very powerful bikes –
aerodynamics. As speeds increase, most of the engine’s power is spent in
overcoming wind resistance. So, with improved aerodynamics, motorcycles can
deliver higher performance levels as well as better fuel efficiency.
How it Works
In the context of motorcycles, the objective of optimising a bike’s aerodynamics is minimising wind resistance at higher speeds. This is accomplished by adding a full or a partial fairing that optimises air flow around the vehicle and its mechanical components, thereby reducing drag. However, in addition to achieving reduction in drag, designers must also pay attention to the styling – the bike must also look good – as well as the ergonomics, so that the machine remains easy and comfortable to operate.
Most motorcycles, but especially ‘naked’ bikes (which do not have any sort of fairing), have pretty poor aerodynamics since the engine, all components and of course the rider himself are all fully exposed and hence create ‘drag.’ Scooters, which have full bodywork that covers the engine and other mechanicals, can have better aerodynamics but these often do not travel fast enough for aerodynamics to become a very big factor in their overall performance. Also, unlike cars (which have a fixed coefficient of drag), two-wheelers have another factor that affect their aerodynamics – the rider. How the rider sits on a motorcycle and the ways in which his/her body position and posture keep changing during acceleration, braking, cornering and other manoeuvres, means that a motorcycle’s aerodynamics keep changing all the time.
If you thought that might be challenging enough for two-wheeler designers, wait, there’s more. A motorcycle’s bodywork/fairing (key elements that dictate how its aerodynamics work) must not only reduce drag and look good doing it, it must also not negatively impact the vehicle’s handling. Wind pressure, and how it acts on a bike’s fairing and bodywork, can affect stability and must be designed in a way so that it can deal with wind turbulence without causing the rider to lose control of the machine. The early-1990s Honda CBR900RR even had holes drilled into its fairing, at the front, purportedly to minimise the effect of crosswinds on the bike’s stability.
How it Works
In the context of motorcycles, the objective of optimising a bike’s aerodynamics is minimising wind resistance at higher speeds. This is accomplished by adding a full or a partial fairing that optimises air flow around the vehicle and its mechanical components, thereby reducing drag. However, in addition to achieving reduction in drag, designers must also pay attention to the styling – the bike must also look good – as well as the ergonomics, so that the machine remains easy and comfortable to operate.
Most motorcycles, but especially ‘naked’ bikes (which do not have any sort of fairing), have pretty poor aerodynamics since the engine, all components and of course the rider himself are all fully exposed and hence create ‘drag.’ Scooters, which have full bodywork that covers the engine and other mechanicals, can have better aerodynamics but these often do not travel fast enough for aerodynamics to become a very big factor in their overall performance. Also, unlike cars (which have a fixed coefficient of drag), two-wheelers have another factor that affect their aerodynamics – the rider. How the rider sits on a motorcycle and the ways in which his/her body position and posture keep changing during acceleration, braking, cornering and other manoeuvres, means that a motorcycle’s aerodynamics keep changing all the time.
If you thought that might be challenging enough for two-wheeler designers, wait, there’s more. A motorcycle’s bodywork/fairing (key elements that dictate how its aerodynamics work) must not only reduce drag and look good doing it, it must also not negatively impact the vehicle’s handling. Wind pressure, and how it acts on a bike’s fairing and bodywork, can affect stability and must be designed in a way so that it can deal with wind turbulence without causing the rider to lose control of the machine. The early-1990s Honda CBR900RR even had holes drilled into its fairing, at the front, purportedly to minimise the effect of crosswinds on the bike’s stability.
Motorcycle aerodynamics must work and the bikes must also look good. That's the challenge for designers
Major
Challenges
The rules of physics dictate that air pressure rises to the cube of speed. So, for every 1kph, the corresponding air resistance increases by a multiple of three. What that means is, at 100kph, around 80% of a motorcycle engine’s power output goes towards overcoming air resistance. Hence, while designing a motorcycle and figuring out its aerodynamic properties, a key objective for engineers is to reduce drag – the obstructive force generated because of the difference in air pressure between the front and rear of the vehicle. Drag acts on the frontal area of a two-wheeler (usually, the larger the frontal area, the greater the drag), slowing it down. Also, drag increases at an exponential rate as speeds increase, so the faster you go, the harder the engine has to work to overcome drag.
When air comes into contact with a two-wheeler and its rider, at and near the surface, air speed becomes the same as that of the moving man and machine. However, friction pulls adjacent layers of air (in addition to the thin surface that’s in contact with the moving bike) along for the ride, and that’s where the problems begin. The difference in air speeds keeps increasing as we move outwards from the surface layer that’s in contact with the moving motorcycle, with the outer layers of air moving at a much slower pace. The faster the bike goes, the bigger those differences in air speeds become, increasing drag exponentially and building up what is referred to as the ‘velocity gradient.’ As the velocity gradient increases, air flow becomes more unruly and turbulence increases.
The designers’ objective is to create a shape that reduces turbulence as much as possible, ensuring smooth air flow, allowing the vehicle to ‘slip through’ air with as little disruption as possible. While designing a motorcycle’s bodywork, engineers try to keep the separation point (the point where the layer of air that’s in contact with the moving vehicle detaches from the bodywork) as close as possible to the rearmost point on the vehicle, and with the smallest cross-section possible, so as to minimise wake. Think about it for a minute and you’ll realise why the classic ‘teardrop’ works best for aerodynamics. Though it’s not particularly well suited to most two-wheeler applications, the Suzuki Hayabusa is just about the closest that any production motorcycle has gotten to that shape, which is perhaps why it has a top speed of around 300 kph.
Different Solutions
So, theoretically, the most aerodynamic motorcycle would be one that’s shaped liked a teardrop. However, that shape often doesn’t work in the real world. To overcome that, designers have tried various work-around methods, including all-enveloping ‘dustbin’ fairings that were tried in the 1950s. Back then, manufacturers like Gilera, Moto Guzzi and Norton were using all-enveloping fairings – which earned the dubious nickname of ‘dustbin fairings’ due to their bulbous shapes – on their racebikes. While these may or may not have provided some benefits in terms of aerodynamic efficiency, they also made bikes unstable at high speeds and were consequently banned by the FIM in 1957. All-enveloping bodywork has still been used on sportsbikes in the 1980s and the 1990s (for example, on the Ducati Paso and the Honda CBR1000F), and the current Suzuki Hayabusa and Kawasaki ZX-14R use it to this day, but all these bikes a much leaner, slimmer form than the dustbin fairings of yore.
At the other end of the spectrum was the revolutionary Britten V1000 of the early-1990s, which despite its minimalist design and hardly any bodywork to speak of, proved to be faster than any other superbike of its time. Indeed, while all-enveloping bodywork continues to be useful for two- and three-wheeled streamliners used for land speed record attempts, that’s perhaps because those vehicles only have to travel in a straight line at extremely high speeds, and their riders do not have to deal with bends or corners.
Indeed, covering a motorcycle in flowing bodywork is only part of the equation and while this does lower the coefficient of drag, there’s still the rider himself, who disrupts the airflow efficiency envisioned by the aerodynamics engineers. Hence, managing airflow over and around the rider may be the key to achieving ideal aerodynamics on a bike. MotoGP engineers, who work at the very cutting edge of aerodynamics technology, may have some answers. In recent years, MotoGP bikes have used winglets or ‘air-blades’ mounted on their fairings to create downforce for added grip and stability, along with strategically placed strakes and ducts to manage air pressure and high-speed turbulence. These winglets/air-blades are aerodynamic aids that come from the world of aerospace engineering and are designed to cause small amounts of controlled turbulence, which ultimately helps create a virtual ‘wall’ of air around the rider and smoothing air flow over the entire moving vehicle. These winglets, also referred to as ‘vortex generators,’ have been used by bike manufacturers for the last few years and their use has become more commonplace these days as engineers’ understanding of how these work – and how they affect a motorcycle’s high-speed handling – has improved.
The rules of physics dictate that air pressure rises to the cube of speed. So, for every 1kph, the corresponding air resistance increases by a multiple of three. What that means is, at 100kph, around 80% of a motorcycle engine’s power output goes towards overcoming air resistance. Hence, while designing a motorcycle and figuring out its aerodynamic properties, a key objective for engineers is to reduce drag – the obstructive force generated because of the difference in air pressure between the front and rear of the vehicle. Drag acts on the frontal area of a two-wheeler (usually, the larger the frontal area, the greater the drag), slowing it down. Also, drag increases at an exponential rate as speeds increase, so the faster you go, the harder the engine has to work to overcome drag.
When air comes into contact with a two-wheeler and its rider, at and near the surface, air speed becomes the same as that of the moving man and machine. However, friction pulls adjacent layers of air (in addition to the thin surface that’s in contact with the moving bike) along for the ride, and that’s where the problems begin. The difference in air speeds keeps increasing as we move outwards from the surface layer that’s in contact with the moving motorcycle, with the outer layers of air moving at a much slower pace. The faster the bike goes, the bigger those differences in air speeds become, increasing drag exponentially and building up what is referred to as the ‘velocity gradient.’ As the velocity gradient increases, air flow becomes more unruly and turbulence increases.
The designers’ objective is to create a shape that reduces turbulence as much as possible, ensuring smooth air flow, allowing the vehicle to ‘slip through’ air with as little disruption as possible. While designing a motorcycle’s bodywork, engineers try to keep the separation point (the point where the layer of air that’s in contact with the moving vehicle detaches from the bodywork) as close as possible to the rearmost point on the vehicle, and with the smallest cross-section possible, so as to minimise wake. Think about it for a minute and you’ll realise why the classic ‘teardrop’ works best for aerodynamics. Though it’s not particularly well suited to most two-wheeler applications, the Suzuki Hayabusa is just about the closest that any production motorcycle has gotten to that shape, which is perhaps why it has a top speed of around 300 kph.
Different Solutions
So, theoretically, the most aerodynamic motorcycle would be one that’s shaped liked a teardrop. However, that shape often doesn’t work in the real world. To overcome that, designers have tried various work-around methods, including all-enveloping ‘dustbin’ fairings that were tried in the 1950s. Back then, manufacturers like Gilera, Moto Guzzi and Norton were using all-enveloping fairings – which earned the dubious nickname of ‘dustbin fairings’ due to their bulbous shapes – on their racebikes. While these may or may not have provided some benefits in terms of aerodynamic efficiency, they also made bikes unstable at high speeds and were consequently banned by the FIM in 1957. All-enveloping bodywork has still been used on sportsbikes in the 1980s and the 1990s (for example, on the Ducati Paso and the Honda CBR1000F), and the current Suzuki Hayabusa and Kawasaki ZX-14R use it to this day, but all these bikes a much leaner, slimmer form than the dustbin fairings of yore.
At the other end of the spectrum was the revolutionary Britten V1000 of the early-1990s, which despite its minimalist design and hardly any bodywork to speak of, proved to be faster than any other superbike of its time. Indeed, while all-enveloping bodywork continues to be useful for two- and three-wheeled streamliners used for land speed record attempts, that’s perhaps because those vehicles only have to travel in a straight line at extremely high speeds, and their riders do not have to deal with bends or corners.
Indeed, covering a motorcycle in flowing bodywork is only part of the equation and while this does lower the coefficient of drag, there’s still the rider himself, who disrupts the airflow efficiency envisioned by the aerodynamics engineers. Hence, managing airflow over and around the rider may be the key to achieving ideal aerodynamics on a bike. MotoGP engineers, who work at the very cutting edge of aerodynamics technology, may have some answers. In recent years, MotoGP bikes have used winglets or ‘air-blades’ mounted on their fairings to create downforce for added grip and stability, along with strategically placed strakes and ducts to manage air pressure and high-speed turbulence. These winglets/air-blades are aerodynamic aids that come from the world of aerospace engineering and are designed to cause small amounts of controlled turbulence, which ultimately helps create a virtual ‘wall’ of air around the rider and smoothing air flow over the entire moving vehicle. These winglets, also referred to as ‘vortex generators,’ have been used by bike manufacturers for the last few years and their use has become more commonplace these days as engineers’ understanding of how these work – and how they affect a motorcycle’s high-speed handling – has improved.
As the Yamaha Frog 750 concept bike (on top) and older bikes from Gilera, Moto Guzzi and NSU show, manufacturers have been experimenting with fairing design for a long, long time and some of these have worked really well
Future
Directions
Over the next few years, new electric powerplants, which will ultimately
replace the IC engine on many (most?) motorcycles, will bring further
disruption to motorcycle design. Electric motors and controllers can inherently
be simpler and more compact than IC engines, with fewer moving parts. However,
electric bikes will also need big, heavy battery packs and their placement
within the bike’s frame and bodywork will create its own set of challenges,
also in terms of aerodynamics, which engineers will have to solve. Another
major factor that may affect motorcycle aerodynamics could be safety. With
increasingly stringent safety requirements, manufacturers will need to pay
attention not just to style, ergonomics and high-speed stability, but also how
elements of a motorcycle’s bodywork – the fairing and windshield, for example –
behave in the event of a crash. Newer materials, the need for vehicle
lightweighting, increasing engine output and the never-ending quest for higher
speeds will, in the foreseeable future, continue to push the evolution of
two-wheeler aerodynamics.
Note: I first wrote this article for Auto Tech Review magazine, when I was working
with that publication as its executive editor, sometime in 2016-2017. Due to
some difficult circumstances, the magazine shut down just before the Covid
pandemic hit India.
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