The Power of Balance

MotoGP racers talk about it, road bike engineers strive for it and, if your bike’s got it, riding really, really quickly is easy. But what the hell is balance?

INSTRUMENT OF DIVINE BALANCE 1: SUZUKI GSX-R750 K9

Perfect power 132bhp instead of the 1000’s 165bhp means quicker steering, less weight and less fear. GSX-R600 chassis. Compact and shrink-wrapped around the tiny engine, the small chassis swells confidence.
Underslung exhaust
. Not original but crucial to centralising the mass, something many balanced bikes share.

The original GSX-R750F was the child of two parents; Suzuki's World Endurance programme (which went from reliable, fast but weighty GS1000-powered prototypes in 1980 to the honed XR41 works racer and the title in 1983) and European market research that concluded road riders might well buy a road-going XR41 of their own should one be made available.

Combining a then innovative aluminium frame, a uniquely lightweight and high performance oil cooled motor and styling that was pure endurance racer (the first GSX-R750 prototype, unveiled at the 1984 Cologne motorcycle show, was pure XR41, just as two generations of Fireblade (2004-2007) were pure RC211V MotoGP racer) the GSX-R750F was truly original in a way few new sportsbikes have been since. And, unlike those Fireblades, Suzuki's race-replication went deeper than plastic. With absurdly lively geometry (steep head angle, short wheelbase), a peaky but competitive engine and, most importantly of all, a refreshing lack of weight (Honda's VF750 Interceptor and Yamaha's FZ750, both of which were liquid-cooled, made similar power but weighed between 25kg and 50kg more), the GSXR750 was a balanced rapier of a machine, one that asked questions of the general public's riding ability and, in many cases, found it wanting. For a modern equivalent imagine one of the Japanese big four coming out with a carbon-framed 1000 that made a class-average 165bhp but that weighed some 140kg and flirted with instability so shamelessly the aftermarket grew fat off the back of a steering damper gold mine.

Now imagine also that a couple of win-hungry individuals got hold of said carbon-framed work of fiction and, with little more than a race cylinder head and an exhaust, turned up at a superbike meeting to kick ass, perhaps with an unknown American racer by the name of Kevin Schwantz in the saddle. For proof of the GSX-R750F's balance of strengths and fundamental rightness you need only consider the 1986 Trans-Atlantic races. Kevin Schwantz flew in to race at Donington with nothing more than his riding kit; he had no bike. By contrast fellow American Fred Merkel had a Honda worth half a million dollars.

Suzuki's Martyn Ogbourne left a rubber cheque for a GSX-R750, hastily threw a few Yoshimura parts and some lightweight wheels at it and Schwantz, having grown up on America's counter-clockwise tracks, promptly hopped on and turned right out of Donington's pitlane. But despite the inauspicious start Schwantz would leave the UK a legend, having diced with Merkel, pulled off the mother of all saves and shown the cream of British racing talent the meaning of bravery. Sure he was Kevin Schwantz, but the bike played no small part. "I wasn't that impressed when I first saw the motorcycle but when I got to ride the thing it was actually quite the machine," says Schwantz. "It was real fast and real light." The GSX-R750's form has waxed and waned ever since, Suzuki spoiling its balance some years only to restore its status as the complete road sportsbike the next. Fortunately Suzuki have stuck with the capacity though, and the GSX-R750 K9 is a good one. Try it. Feel the power of balance.

After a test involving the Suzuki GSX-R750, chances are you're already sick of the B word; balance...

...well, sorry, but it’s difficult to dismiss the “best of both worlds" cliche when it's coming from riders of James Whitham's calibre. And when a bike with a pretty unique blend of power and chassis geometry (the GSX-R is the sole surviving sports 750) wins so emphatically ahead of two machines as talented as the Ducati 848 and Triumph Daytona 675, something must be afoot; perhaps there's something to this balance thing?

If you're a race fan, chances are you've been hearing the B word a fair bit recently, usually in reference to a Yamaha, be it the 800cc M1s of Valentino Rossi and Jorge Lorenzo or the superbikes of Ben Spies or, in the British domestic series, Leon Camier and James Ellison. In each case the story is, according to our esteemed commentators, the same; no power advantage and, given that control tyres are mandatory and most machines close to their series’ weight limit, no weight or grip advantage either. Instead balance is apparently the winning difference they have in common.

And it would seem this balance stuff is pretty potent. Camier is 113.5 points ahead of team-mate Ellison and a scarcely believable 156.5 points ahead of the nearest non-Yamaha, Stuart Easton's Fireblade. Together Rossi and Lorenzo have pushed Yamaha 66 points clear of Honda in the 2009 MotoGP constructor's championship; 230 points to 164.

"When people talk about balance with regard racing motorcycles they're talking about a balance of qualities," explains MotoGP technical journalist Neil Spalding. "At the end of the day a bike's just a heap of bits which, when put together, has a certain character, certain strengths and weaknesses. A balanced bike is one that allows a rider to use all of its performance. So for example there's no point having the bike with the most grip if it makes so little power it can't make use of all that grip, just as there's no point building the most powerful bike if the rider hardly ever gets to use all of that power [the latter is a common trap in racing circles. Mick Doohan famously fell out with Honda when HRC's engineers went blindly chasing horsepower and built an inferior NSR as a result]. In superbike racing at the moment it's pretty common to tune the engines for more power and torque, only to then have the electronics piss away a fair bit of that torque because it's counter-productive. A more balanced bike wouldn't make the additional torque in the first place."

All of which rings true with the GSX-R750 test. Even a standard GSX-R1000 has so much power most riders struggle to deploy it on a racetrack, let alone on the public road. And yet the GSX-R1000 is compromised a little by its additional power, being a shade heavier, a little slower to change direction thanks to its wider rear tyre (190/50 compared to the 750's 180/55) and a whole lot more intimidating given its huge grunt. As a result the 750 is the better-balanced option for most riders, with the confidence building feel of a 600 but a more versatile engine. Th e 750 isn't the lightest or the most powerful of the GSX-Rs but it is the most balanced.

It's the same story with Yamaha's M1 MotoGP racer, which has helped set the 2009 season on fi re by being, well, not great at any one thing. "The M1 is widely regarded as being a balanced motorcycle," continues Spalding. "It's not the highest revving 800, nor the most powerful, but it

is the best combination of compromises for a given racetrack on a given day. It's also easy to set-up within the limited amount of practice time available to the teams this year, which has changed the game. It's no good having the best bike out there if it needs hours of work to reach its full potential. The Yamaha can be on the pace very quickly.

“At the end of the 990cc MotoGP era I'd argue the Ducati was as good as the 800 Desmosedici is now, it's just that it took hours to set-up properly. Th e best race bike is the most balanced bike; it's not the best at any one thing but it is the least worst at all of them."

While Neil hints at user-friendliness with regard the M1's easily sorted chassis, James Whitham believes that trait – user-friendliness – goes hand-in-hand with balance. "When you talk about a balanced race bike it means you get a nice feeling from it," says James. "Th ere may not be one thing that stands out about it – chances are it's not aggressive, really powerful or very front-heavy – but that means there's nothing to stop you going quick on it. Balance is a word that covers everything and doesn't really apply to much, but in essence it means a bike you can get on and be happy with; a bike that gives you feedback.

Spencer's Honda NS500

INSTRUMENT OF DIVINE BALANCE 2: HONDA NS5001982-1984

Sharp geometry Based on contemporary 250 geometry, the NS was flighty. Wobbles were Spencer’s problem
Ultra-compact engine
Three-cylinder where everything else used four, the NS’s tiny engine was key to the bike’s unique remit
Aluminium frame
Nothing new in GP racing in 1982 but, thanks to the NS’s modest power, it didn’t snap...
16-inch composite wheels
Ultra-light wheels helped everywhere, from agility to acceleration

After Honda's brave but ultimately futile attempt to return to the top of Grand Prix racing with the four-stroke NR500 in 1979, the firm acknowledged the insurmountable nature of the challenge and deployed its light and simple two-stroke NS500. After years of relative technical stability in the long and glorious reign of MV Agusta's four-strokes, the class was once again plunged into a furious development war, one that pitched a new generation of riders against soaring power outputs, hopeless tyres and chassis engineering that struggled desperately to get on terms with a marked escalation in the forces involved. These bikes were nasty.

But against this backdrop of cracking frame tubes, delaminating rubber and fierce powerbands, for once Honda kept things simple. To take on bikes like Suzuki's RG500, a powerful square-four monster screaming out 130bhp (just five years earlier less than 100bhp had been enough to win championships), Honda's Shinichi Miyakoshi, Erv Kanemoto and Freddie Spencer developed the 100bhp 250, a concept based on the undeniable truth that, despite the power deficit, lap times in the 250 and 350 classes weren't far off those of the 500s, particularly on tight tracks.

The resulting V3 NS (the central cylinder pointed forwards, the outer pair vertically upwards) used cylinders based on Miyakoshi's motocross singles, complete with reed valve induction (the opposition were exclusively discvalved at the time; more powerful but harder to pushstart), and mounted the engine in a simple twin-loop aluminium frame on lightweight 16" composite wheels. Every effort was made to remain true to the 100bhp 250 brief, with specially designed short sparkplugs to keep the engine small and a fairing with no greater frontal area than a 350. 20bhp down on the opposition the NS nevertheless won races by virtue of being 15kg lighter, more agile thanks to its short wheelbase and, crucially, kinder to its tyres, then the biggest limiting factor. The first race win came in the 1982 Belgian GP, the first championship win the following year. Spencer pushed the little NS to improbable corner speeds, his high apex and subsequent exit speeds giving the illusion of awesome acceleration. To this end he employed dirt track machine control, pushing the front tyre past its limit on corner entries before “saving” it with the throttle. By tapping on the gas the bike’s weight was transferred rearward, averting a crash.

"They're a really nice bike; I've ridden a couple of NSs," says James Whitham. "For me the three-cylinder Honda was the next generation of two-stroke 500s well ahead of its time. It was twenty years ahead of the flippin' RG500. I've ridden absolutely mint 1981/1982 RG500s and they're nowhere near as nice as the Honda; nothing like as sweet."

"The Yamaha M1 is a rider's bike, and by that I mean it's on your side," continues Whitham. "90% of road racing is in your head, no matter what people say. If you don't have a feeling for what's going on, it's really difficult to push hard and get results. The Fast Orange YZF750 I raced wasn't the fastest or the most powerful thing out there, and it probably wasn't the best-steering either, but it did tell you exactly where the limit was. And because it gave you that feedback you could push to the limit all the time. Other bikes I’ve ridden, particularly 500 GP bikes, gripped better than that YZF, they steered better and they had more power but you just didn't know where the limit was. After you'd crashed it three or four times you ended up riding miles from the limit because you weren't really sure where it was. Racing's all about confidence, and a balanced bike breeds confidence."

Ah, the YZF, another 750 shot-through with delicious balance. Overshadowed by the more powerful Fireblade, the YZF was a bike in which the engine and chassis worked together to virtually disappear, leaving the rider to get on with the hard bit, the riding. In the hands of our own Niall Mackenzie the YZF managed three back-to-back British Superbike titles in the mid-1990s.

The GSX-R750 is similarly blessed now, as it has been at several key points in its 24-year history, not least the 2000 BSB season, when unchecked brawling broke out around the country as Neil Hodgson on the GSE Ducati and Chris Walker on the Crescent GSX-R750 went to war. On paper the struggle was an unequal one – certainly the GSX-R750 didn't have anything like the 996's race pedigree at that point (few bikes did) – but to judge the protagonists on paper would be miss one key point, namely Walker's towering confidence in the under-powered 750.

"'With race bikes you know within a few hours whether you're going to be competitive or not, and with the Suzuki I knew straight away we were going to be strong that year," remembers Walker. "My confidence was sky-high on that Suzuki. I could get away with anything on it; sliding it wet or dry, backing it in. It was a little underpowered compared to the Ducati but I think that helped, and it was just so nimble." Of course Neil Hodgson and the Ducati prevailed but, bar that heartbreaking engine failure at Donington, that season would have been a triumph of balance over brute force.

For road riders the same principles apply. Designing a new bike is about laying down a marker somewhere on countless sliding scales, from stability and agility to power and drag, stiff ness and weight (see right). "A bike needs well balanced chassis stiff ness, a suitable steering head angle (generally speaking the more raked the forks, the more stable a bike is) carefully considered aerodynamics (this is particularly important for high-speed stability), careful weight distribution and well-balanced spring rates front and rear," says Karl-Maria Grugl, a chassis engineer at KTM. BMW's development guru Stephan Fischer agrees: "You must compromise between many things; agility and stability for example. If you imagine a chart with an X and Y axis, these two qualities are on opposite sides. If you mark all the conflicting qualities of handling on this chart, the area within this area is constant. So if you increase stability to 10%, you have to reduce agility 10% unless you come up with a new technology." And while there is undoubtedly science involved – few if any beautifully balanced bikes were created by accident – there's more to it too, an X-factor that can turn up unexpectedly and, more frustratingly, remain conspicuously absent where all the sums look good.

"Who knows what it is? On paper a bike can look absolutely fantastic but then it gets finished and it isn't," ponders James Whitham. "It's a complex mix of things that makes a bike balanced. It's not just where the centre of gravity is or how the weight's distributed; it's about everything, from power delivery to geometry. And for me it's always been something Yamaha have been good at [history, at least in GP racing, would tend to concur, from the YZR500s of the late 1980s and early 1990s through generations of super-sweet TZ250s to the current MotoGP M1]. Maybe they just suit the way I ride but Yamaha have always tended to build rider-friendly bikes, albeit not all of them. I get on my 350LC and compared to modern bikes it's rubbish, but there's something about the way it all works together that makes it a lovely, funny, balanced enjoyable thing to ride."

HOW WOULD YOU DO IT?

Just some of the myriad factors a motorcycle engineer must balance – how would you do it?

Power

More power brings more speed, up to a point. From there on more power simply places additional demands on the chassis. For example the frame will be need to be stronger and heavier to cope. More power has other drawbacks. Bigcapacity engines are physically larger and heavier, increasing the amount of aerodynamic drag a bike develops thanks to a larger frontal area. Bigger radiators will also be required, further increasing drag. However, not enough power is bad news, particularly on a race bike.

Chassis geometry

A sharp rake angle and short trail and wheelbase will create a quick-steering bike that can change direction like a firefly. On the downside it’ll wheelie if you so much as look at the throttle and flap its bars wildly should it encounter anything resembling a bump. Stability or agility?

Aerodynamics

After all the hassle of teasing power from your engine, free speed in the form of low-drag aerodynamics is a tempting proposition. But nothing’s free. Smooth, all-enveloping fairings cut through the air easily but can make a bike prone to instability, particularly in crosswinds, and may create heat dissipation problems.

Brakes

Huge discs (330mm on the Blade) do a great job of stopping a bike thanks to their large surface area and useful leverage, but they’re heavy and they slow a bike’s steering thanks to their gyroscopic effect. CBR is more agile.

Chassis stiffness

A bike with poor torsional or longitudinal stiffness is a bad thing, giving the rider confusing feedback and compromising both suspension performance and steering accuracy. But stiffness brings weight, at least unless you introduce a new technology, hence Ducati’s carbon frame in MotoGP. Lateral stiffness is a trickier one to balance; too much and the bike will suffer a lack of grip at extreme lean angles. RSV4 frame has more lateral flex than the RSV-R for this reason.

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