Cycle News - Archive Issues - 1990's

·IN ID S ELOOK . Honda Racing Corporation ake no mistake on th is point: At HRC, the 500cc Gra nd Prix class is, an d always will be, the highest level of mo torcycle racing. At H RC, the a rgument over w hich class is be tter 500cc GP or World Superbike - simply does not exist. "These races are completely differen t," explained Kanazawa. "The 500cc Grand Prix are like the Formula 1 car race. We mu st win in this one. Superbikes are like a tour ing car race. Of course, we expect to w in, bu t it's only a tou ring car race in the end. "We must keep racing in the 500cc Gra nd Prix. Unfortunat el y, th is typ e o f machine is very expe nsive. The H arri s and the ROC machin es have eng ines man ufactu red by Yamaha. I think this machine is still expe nsive for privateers. Some ma nu facturers mu st make a cheaper machine ." On tha t no te I was told that I could go d own to the first floor of HRC, and have a private look at the all-new SRSOOV. I was surprised tha t they allowe d me to look at the all-black test bike that various Japanese magazines have taken spy shots of d uring tests at Suzuka Circuit, rather th an the NSR500V "show bike" that w as ph otographed in NSR livery for the pu blicity photos. The mos t not iceable diffe rence between the tw o versions is a revised front fairing, wi th a fresh-ai r d u ct beneath the front nu mber-plate pa ne l runni ng to a sealed airbox. The sealed a ir box is loca te d beh in d the cylinders and above the gea rbox, as on the NSR250 race bikes. Conceptua lly, there is nothing new abo ut th e NSR500V ot her than it is a 500cc V-twin. It is verv similar to the NSR25B, but in a mirror image; that is, the 500V' s s wi ngarm is on the left (looks to be taken straight off the RC45), the 250's is on th e right. The u pp er cylinder on the 500V is on the left, while on the 250 it is on the right. With the fairing mou nt ed , there is precious little that can be see n of the engine. , The big q uestio n is: Can th e NSR500V be a w inner? Ho nda has cited tha t the difference in lap times between the 500 and 250cc classes has shrunk over the past few seasons, and to this there is no argument. 111.1995, the average speed of the pole position qualifiers was 98.84 mph in the 500cc class, and 97.04 mph in the 250cc class, for a difference of 1.80 m ph. In 1990. the speeds were 100.92 and 96.50, respectively, for a difference of 4.42 mph. From their spec sheets, the difference in average lap speed between the 250 and SOOcc classes should be greater than the 1.8 percent that ex ists. Honda's NSRSOO is rated at 190 horsepower at 12,750 rpm, while the NSR250 is only half that. with 95 horsepower at 12,750. The NSRSOO has a 15-percent speed advantage over the NSR25 0, with claimed top speeds of 195 mph and 170 mph, respectivel y. The NSR250 makes up for the horsepow er disad vantage through smaller frontal area and low er weight. Th e smaller size of the 250 also endow s it with an aerodyn amic ad vantage. Assuming that ro lling resistance is negligible, the 95-hp 250 must have a (coefficient of drag)(frontal area ) value of around 3 squa re feet to ach ieve a 170-mph top speed. For the 500. with a rated horsep ower of 190 and a top speed of 195 mph. the value must be ve ry close to 4· square feet. Thus , the 250 h as abou t 75 percent the aerody namic drag of the 500. Assum ing a rider weight of 70.ki lograms, and a fulltank fuel weight of 24 kilograms on the NSR500 and 16 kilograms on the NSR250, the sma ller NSR would weigh approximately 181 kilograms at the.start of a GP, whereas the larger NSR would weigh approximately 224 kilograms. In other words, the 250 weighs about 81 percent of the 500 at the start of a Grand Prix. M \D 0\ 0\ ...... c:')' ....... ... ;..; 0.. ~ 34 e uture an t e The NSR250 and the NSR500 can run the same size fron t tire (a 12/60-17 Michel in radial), thus the 250's lower weight provides a significant advantage on breaking (224/181=1.283, or 24-percent better). The SR500 uses a bigger rear tire than the NSR250 (18/ 67-17 vs. 13/61-17, respectively), thus a comparison of theoretical cornering po tential requires assuming both rear tires can provide equal amounts of lateral grip. Given th is assumption, the lower weight of the 250 will im p rove its cornering speed to the square roo t of the weight ratio, which works ou t to an l l-percent advantage (sqrt(224 /181)=1.113, or Ll-percent better). Where the 250 rea lly su ffers against the 500 is in accelera tion. At low speeds the 250 has roughly half the acceleration capability of the 500 (assu ming the 500 can find tra ction!), and at higher speeds the 500 s imply p u lls away. No w the question is: How will the NS R500V compa re? First, Honda claims a horsepower figure of 135 for the big V-twi n, and this seems reasonable. Assuming identical brake mean effective pressures, component stresses, combustion toughness, and so on, the theo retical predict- we ig h ts a nd so on, so me b as ic engi nee ring can be employed to estimate acceleration potenti al between the three bikes. Ho w this is done is a tech sto ry in itself, so to make a long story sho rt, here are th e traction-available figures, stated in units of g's, as a function of speed, in mph . NSRSO NSR250 NSR500V O Speed 2.84 1.41 2.01 50 2.33 1.15 1.65 60 0.96 70 1.38 1.97 1.17 0.81 80 1.68 1.00 0.68 1.44 90 100 1.25 0.85 0.57 110 0.72 0.48 1.08 120 0.61 0.39 0.92 0.50 0.31 0.78 130 0.65 140 0.39 0.23 150 0.30 0.15 0.52 160 0.07 0.40 0.20 . 170 0.10 0.00 0.29 180 0.01 0.17 n/a n/a 190 0.06 n/a ed horsepower of the twin should be tha t of the V-four, Clearly, the NSR500V is down on acceleration by a wide margin to the NSR500. By the same token, the NSR250 su ffers even worse in this regard. H ow is it that th e m odest bra king and cornering ad vanta ge of th e NSR250 can m ak e up for the hu ge acceleration disadvantage? The answer lies in the fact that wide-open-throttle acceleration is a relatively rare event over one lap of a Grand Prix track. For examp le, take Donington circuit. Computer traces from the Division 1 factory GP bikes ind icate that wideope n throttle is used only 23 percen t of the time during a la p. Braking makes lip anoth er 17 percent, and midthrottle maneu vering m akes up the remaining 60 percent. In 1995, the pole posi tion qualifying speed at Donington for the 500cc class was 96.05 mph, and 94.61 mph for the 250cc class. At these speeds, the NSR500 acceleration po tential is 1.35 g, the NSR 250 is 0.63, and the NSR500V is 0.93. Now, if the NSR500 can lap Donington at a 96-mph divided bv root two. This works out to within one horsepower of 135; thus, Honda's claimed hor epower for the NSRSOOV is consistent with their other Grand Prix bikes. With respect to aerody namics, let's assume that th e effective fro n tal area of th e NSR500V w ill be between th at of the NSR250 (3 sq u are feet) and the NSR500 (4 squa re feet), or in othe r words, 3.5 square feet. Now the weigh t factor. Honda claims a weight for the NSRSOOV of 110 kilograms, but the rules allow 100 kilograms. Let's assume tha t Honda finds a way of brin gin g the factory bikes in righ t at the limi t. For a fue l load, let' s average that of the 500 (24 kilogram s) and the 250 (16 kilograms), for an estima ted fuel weig ht of 20 kilog rams. Ad d 70 kilograms for the rider, and at the start of the Gra nd Prix the NSR500V comes in at 190 kilogra ms. This weight advantage lends the NSRSOOV an IS-percent gain in braking over the NSRSOO (224/190=1.179), and a nine-percent advantage in cornering speed (sqrt (224/190)=1.086). With these claimed horsepower figures, drag figures,

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