Aerodynamic tweaks

Air is a strange thing. On one hand it can’t stop a feather falling, but on the other it can lift a jumbo jet off the ground. It’s also the thing that caps a bike’s performance. If bikes could be speed-tested in a vacuum they’d be much, much faster. So it’s no wonder aerodynamics are taken so seriously.

Manufacturers have teams of engineers dedicated to getting this black art to work for us.

In most cases, we don’t notice the changes to new models unless someone in the marketing department decides to make a big deal out of it. So we’ve put together a list of 10 common aerodynamic tweaks you can find on your bike.

Width: The smaller something is, the more easily it passes through the air. You only have to ride along sat upright, then tuck behind the screen to prove this.

An in-line-with-the-frame V-twin engine is a very good aerodynamic design. Better than, say, an in-line four, since it minimises a bike’s frontal area.

But slap a radiator in front of the lead cylinder and the benefit is reduced. So V-twin manufacturers slot them in at the sides, where they are better aerodynamically and more efficient, too.

Benelli’s Tornado triple has radiators tucked up in the tail unit, allowing the bodywork to fit snugly against the engine.

Fins: Until the threat of legislation put them off the idea, manufacturers pursued the title of " world’s fastest bike " with unbridled enthusiasm.

For their attempt at a bike capable of 200mph, Kawasaki drew on the expertise of its plane-makers to combat the problem of airflow slowing its ZX-12R at high speeds. The idea of Kawasaki’s winglets is to keep the dirty, turbulent airflow separate from the clean airflow above it, thereby reducing drag.

Subtle fins on a bellypan reduce drag by diverting air from the rear tyre.

Mudguards: Look back to the bikes of 15 years ago and you’ll find mudguards have got bigger. And that’s not because roads were cleaner back then.

Mudguards are normally the leading piece of bodywork and they have several jobs to do. Not only do they deflect road crud, they channel air around the front tyre and into the radiator.

Wheels create a massive amount of turbulence. Mudguards help pass the air around the bike, deflecting it on to the fairing. To see how much they affect things, take your mudguard off and see how much cooler the engine runs. And how much dirtier it gets.

Mirrors: Anything protruding from the main body increases drag, and that means mirrors. So not only are they mostly useless at high speeds, they’re also slowing you down. Suzuki’s Hayabusa is the exception. Its mirrors are an integral part of the aerodynamics.

When testing at MCN, we typically do some top-speed runs with the mirrors folded back. When we tried this with a Hayabusa it actually went 3mph slower.

Suzuki claims that " the mirrors are longer at the bottom than at the top for a smoother effect, and to reduce lift. " It’s right.

Fairing panels: Big, smooth bodywork panels are aerodynamically best. But it’s difficult to fit large panels to bikes. Because of their shape, several joins are normally required and this means fasteners and lips, which create drag.

Ducati has solved this on the new 998, choosing to use one large panel either side. This also removes the need for bolt heads to fit the panels together, which further reduces wind resistance.

They’ve also done away with the large vents that featured on previous 916/996 models, too. If you need another excuse to clean your bike, a polished surface cuts drag.

Deflectors: Look at Gilera’s new Supersport 600 and you might notice the extra bodywork to the side of the headlights. These small extras are there to smooth and deflect the airflow around the rider’s hands. You can see a similar design on the front of Aprilia’s RSVs.

The reason for the deflectors is simple. We need wide bars to steer, but a narrow bar angle would be better from an aerodynamic point of view. By adding the deflectors, the bike can pass more cleanly through the air, with the benefits of easy leverage without drag.

Seat humps: In 1996, Suzuki launched the GSX-R750 WT. It had a mental engine, great chassis and a funny, duck-tailed seat hump. While most bikes were still relatively square at the tail, the GSX-R was criticised for its unconventional look.

What we probably didn’t appreciate at the time was that aerodynamics at the back are just as important those at the front.

It’s a fallacy that pointy shapes cut the air and so are quicker. For instance, did you know bullets would be more aerodynamic fired backwards? The faster and more smoothly an object can get the air to flow off it is more important that the hole it initially punches through the air.

Indicators: Mirrors can cause unnecessary drag and indicators are guilty of the same charge. But BMW produced an innovative solution to this back in 1983, when they launched the K100 RS, by combining the two-into-one unit.

While this is largely a styling exercise on such a relatively slow bike, other manufacturers have been quick to adopt it on their faster bikes, notably Honda’s 176mph Super Blackbird. It has the effect of reducing the frontal area of the bike as well as smoothing the airflow over the bike’s body panels.