Cycle News - Archive Issues - 1990's

FEATURE Changing the face of GP racing By John Keogh ~, II, \: .... .I-< 0... < 24 hile taking a browse through a copy of the FIM's Road Racing Technical Rules, as you so often do, it might occur to you that there are a number of areas that cou'ld use some more liberal interpretation - interpretati<:>n that might just make racing motorcycles look quite a bit different from how they do at the moment - and it might make them faster, too. Rules regarding engine and tun'ing for the various classes, even at Grand Pri~ level, are very specific in what they will and will not allow, but those for body'work are notably less stringent. Since changes in bodywork might lead to improvements aerodynamically, it might well be worth experimentation and coming up with alternative shapes to those seen on the current Honda, Suzuki, Yamaha and Aprilia machinery. The question is, are current race bikes' fairings particularly aerodynamic or are there an'y loopholes in the rules tha t might allow different bodywork for increased top speed? Let's have a look. The main rules concerning bodywork or streamliiting are Articles 45.01 and 45.03, which state that you can't cover the wheels or extend fairings beyond the front and rear wheefs, and also Article 45.06, which states that you can't cover up the rider in' wind-cheating bod ywork. So that's the streamlined top-speedrecord-breaker appearance out the window! Not that you'd want such enclosed bodywork anyway, because of the modern way of riding that sees the rider hanging off in cornen. and generally shifting all around the bike. However, it may be possible to get a significant advantage from detail design. And, of course, a small advantage can make a big difference when there are worldwide teputations of the big factory teams - and the major advertisers sponsoring them - resting on getting results. So, if we can change a little bit of fiberglass bodywork and gain 10 mph on a long straight or even 0.3 of a second per lap, it would be well worth it. lf we start at the front of the bike, we will already see some areas that a]]ow bodywork different from that seen on current bikes. In recent years, as designers have put sleeker noses on bikes to better cut through the air, the front-bodywork rule has changed to its current condition of no fairing allowed further than lOOmm ahead of the front-wheel spindle. Looking at bikes like the Honda NSR500 or Suzuki's RGv, we can see quite a sharpangled profile right up to this 100mm limit - or, in Suzuld's case, beyond it and having to be cropped bac!< a little. But are these shapes really as wind-cheating as they could be? Do airliners have sharp noses? Well, no, not unless they're designed to go supersonic. For lowspeed aerodynamics, it might be preferable to have a softer, bulbous shape more like the Yamaha's 500cc Grand Prix .bike or Aprilia's 250. This year, in fact, Aprilia has changed last year's slimmer road-version fairing of the RS250 to the more bulbous, more aerodynamic race version of Tetsuya Harada and Loris Capriossi's bike - I wonder why? - At least as significan t, however, is that moving vertically downward we find that it is not the upper fairing that hits the air first but, of course, the front tire, which is spinning, and therefore completely disturbing the airflow from there on. What would be useful is a fully shrouded front wheel, which is of course what the '50s Grand Pri·x bikes did with their "dustbin" fairings. But the rule that bann~ these fairings is stilJ with us in Article 45.01, which states that we must be able to see the front wheel. However, 45. 01 also states, "with the exception of the part hidden by the mudguard." Therefore there is nothing preventing us from having a large mudguard and shrouding the wheel in at least this area. But how large? Article 43.02 states: "The front mudguard must cover at least 100 degrees of the circumference of the wheel. In this area the wheel may be covered, respecting the angles mentioned below. The angle formed by one line drawn from the front edge of the mudguard to the center of the wheel and one drawn hori.zontally through the center of the wheel must be between 45 and 60 degrees. The angle formed by one line drawn from the rear edge of the mudguard to the center of the wheel and one drawn horizontally through tne center of the wheel shall not exceed 20 degrees." Got that? The key thing in this rule, as with many rules, is what it does not say. In this case, it is ·not made clear if the 20-degree angle for the rear edge is above or below the horizontal line. This means we could be liberal in our interpretatiOll of the rule and take it below. We might further shroud the whole wh~el area, including the brake discs and nasty, very unaerodynamic forks, but stilJ be within the letter of the rules. If the scrutineers complain, you can say that it is still possible to see the front wheel rim except for "the part hidden behind the mudguard"! At this point you might get banned for not respecting the spirit of the rules, but let us not be deterred. Shrouding the wheel in this way would probably cause heat buildup in the brakes, So vents would be needed, particularly for steel brake rotors. Covering -much of the spinning components and the uneven front forks that so disturb the airflow for the rest of the bike should considerably help the aerodynamics as we go further bac!< and might offset any problems. Once off the front wheel and sleek fender it would then be usefu-I to extend the lower bodywork forward as close as possible to the tire while still allowing for suspension and steering movement. This should help allow continuation of a hopefully laminar (good!) airstream. Most modern fairings already do this to a degree, partially covering the front wheel by exploiting the rule that says it is the wheel rim that must be visible from the side, not the whole tire. However, these are usually much wider currently than might be possible The complete aero package might look something like this. The enclosed fron wheel minimizes turbulence created by the spinning hoop, and a rear-mounted radiator helps keep the frontal area to a mini'!'um. The suit helps keep the contour created by the front fairing intact all the way to the large tallsectlon - producing better laminar flow and therefore less drag. here if we have already shrouded the majority of the wheel with our superfender. In this case we might as we]] bring the fairing width as close as possible to tha t of the tire and fender. If we can also incorporate an' exit area just behind the front tire for the disturbed air pclJed around its lower, stilJ-exposed portion, then all the better. Every motorcyclist knows tha t a good racing tuck is more aerodynamic than sitting bolt upright. The front screen can be made to maximize the benefits of this tuck, and you will often see production racers using different screens than stock to better clear the flow around their helmets when crouching. Scott Russell currently uses a higher "aero" screen on his Daytona-winning Yamaha rather than the standard YZF model's. There are two schools of thought here: 0) that you use a high screen and deflect air around the helmet, or (2) use a much smaller screen (such as on the Ducatis) and let the rider's nicely rounded helmet do the job of cutting through the air instead. The latter may not be as comfortable as the first option, but number two proved almost as effective with Anthony Gobert being just edged for pole by Russell at Daytona. (Or could

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