It’s interesting to see how ‘superbikes’ have evolved over the years. The first mass produced four-cylinder bike from Japan, the late-1960s Honda CB750 weighed 240 kilos, had less than 70 horsepower on tap and on a good day, would do about 200 km/h. The 2006 Yamaha R6 weighs 160 kilos, has 133 horsepower and does more than 250 km/h without breaking a sweat. Comparing the old CB750 and the newest R6 in terms of acceleration and handling would probably be akin to comparing your living room sofa with a Greyhound. One is big, soft and gentle. The other is lean, quick and vicious.
So how is it that modern day motorcycles are able to offer performance that’s so hugely in excess of their 1960s/1970s brethren? What exactly has changed? Well, everything really. Engines, to begin with. In the old CB750’s time, two-valve cylinder heads were the norm, unlike the double overhead camshafts and four-valve cylinder heads that are popular today. And given carburetors and their float chambers (which only allow certain mounting angles), inlet/exhaust ports were often restricted from offering their best. Today, four-valve cylinder heads allow the combustion chamber to be more effectively shaped and also allow higher compression ratios.
Carbs have made way for fuel-injection, which means far more precise fuel metering. Clever, electronically-controlled throttle valves allow much bigger air/fuel intakes than what was possible back then. Intakes are partially restricted at lower engine speeds (thereby ensuring adequately high air velocity in the intake tracts and preventing fuel from dropping out), but are opened up fully at higher speeds for The Full Monty. EFI systems can also be mounted at much more extreme angles than carburetors would allow, usually giving the air/fuel mixture as straight a run at the combustion chamber as possible. Again, the result is more efficient combustion and more power.
Modern engines are ‘oversquare,’ where the bore is bigger than the stroke. The pistons in such an engine have shorter distances to travel, compared with the pistons in an ‘undersquare’ engine of the same capacity, which allows for much higher rev limits. Witness the new Yam R6 again, where the four-cylinder 600cc engine is redlined at 17,500rpm – stratospheric when you compare it with the old CB, whose four-pot 750cc unit would not go beyond 8,500 revs. Credit must also be given to advances in materials technology, which allows for lighter, stronger and more durable pistons, cams and con-rods.
If power outputs have skyrocketed, braking, handling and grip have also kept up. First, the brakes. In the 1960s/1970s, you were lucky to have disc brakes at all – most bikes were making do with drums. Bikes which did have disc brakes at the front were fitted with one small disc and a small, single-piston caliper. Modern superbikes have huge discs – two of them – at the front, gripped by four- or six-piston calipers. Stoppies, anyone?
Motorcycle suspension has become far more sophisticated too. USD forks reduce unsprung weight at the front and given their stout dimensions, just refuse to flex. Some manufacturers also apply special coatings to the stanchions, to reduce stiction. At the rear, shock absorbers often use rising rate springs and are adjustable for preload. Suspension on the more expensive bikes is also adjustable for compression and rebound damping so that owners can tailor the handling of their bikes to their own tastes.
Also in the interests of handling, lightweight and strong aluminium beam frames are used, which keep the centre of gravity low and which are largely free of flex – giving riders the confidence to push ever harder. Rake and trail figures are also much lower now than they used to be, which has made even big bikes more ‘flickable’ then before. And finally, wide, sticky and low-profile radial tyres make sure that in high-speed cornering, riders usually run out of courage before they run out of grip.
Lighter, more powerful and ever faster – that’s the mantra for sportsbikes. And thankfully, there’s no looking back.