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Driving report Derbi 125

Dwarf uprising

Derbi factory rider Yoichi Ui made the established Honda and Aprilia teams legs and dashed just past the world title with the Spanish 125cc. MOTORRAD tried the red racer.

"You don’t become world champion with six zeros, it’s that simple." Harald Bartol, designer of the lightning-fast 125cc Derbi, takes stock of the 2000 season in an objective and uncomfortable way. The daredevil Youichi Ui fell in five of the six grand prix races without any points, only once the technology went crazy in the form of a defective battery. The fact that Ui secured the runner-up title with only 13 points behind despite the crashes is primarily thanks to his fiery red Derbi. A package of ingenious two-stroke power and consistent optimization of the chassis, brakes and aerodynamics.

Goal before we curiously dive into the depths of the technology, I force myself into the leather, knot the links to the jackknife and thread myself into the fast GP course in Barcelona.
Actually, it rarely happens that a height of 171 centimeters can only be stowed behind the panel with difficulty. But on the 125cc Derbi everything is two sizes smaller, shorter, narrower. And lighter.
The 70 kg motorcycle completely redefines the word handling. It wobbles and wobbles, the GP-Flea reacts to tight steering commands with a completely exaggerated change of direction. No, the Derbi cannot and does not want to drive slowly. She loves the tightly tensioned gas rope, not twitching and hesitating, just flipping it, not with force, but with soft impulses, the lying upper body bent over the delicate tank, that’s how it works. Let it roll smoothly, sail along in soft curves, the engine at speed Keeping them happy, just don’t spread hectic.
The Derbi single quickly comes out of the quark at over 10,000 rpm and kicks off a lot, at 13500 rpm it’s shift, but that doesn’t bother us. Simply leave the accelerator, a quick step on the gear lever, and the electronic gearshift does the rest. Tea white power spring elements with their 95 and 100 millimeter shorts spring travel bump through the fast, undulating curves, it trembles and shakes, the horizon blurs. Anyway, let it stand, the Dunlop rubbers will fix it. Lose everything ?? just not the momentum. Because with the momentum comes the fun, rider and bike find the rhythm and the ideal line. Braking points are gaining in importance, with brilliant feedback and metering the cute little Nissin brake calipers bite. And just when you’re in the right mood, it’s over, it’s over. Friendly mechanics steal the Derbi from under my bum after eight laps, fingering the electronics of the data memory with a mischievous grin. I suspected it: all embarrassments are recorded. Every hook, every twitch, every slack in the speed range. And there are a ridiculous 20 seconds short of pole position. 2.13.03 ?? that’s not enough to be in the forehead row even when it rains.
To put it the other way round: How does the 125cc Derbi achieve 1.52 lap times? With the 52 HP, for example, which Harald Bartol presses out of the single cylinder with precision work. In the club with the best aerodynamics and the petite Japanese Ui in the saddle, the Derbi runs an incredible 225 km / h at the end of the long home straight.
As a basis for the stable performance, the ex-GP driver Bartol favors a stable crankcase, which ?? manufactured using the sand casting process ?? Retains its shape even under maximum load, which prevents performance-inhibiting tension in the crank mechanism.
Bartol made a conscious decision not to use a water-washed crankcase, as is used at Aprilia. "Firstly, the required stability suffers, and secondly, the cooling effect from the engine circuit is too low to have a positive effect on engine performance," he explains his design.
Another step towards efficient power output is gear lubrication with a small oil pump. The six-speed cassette gearbox is supplied with only 340 cm³ of lubricant, which means that the balance shaft and primary gears do not rotate in an oil bath, but only in the oil mist, which minimizes slipping losses.
When it comes to the actual power components, i.e. the cylinder, head, carburetor and exhaust, the Austrian designer is more conventional. Five transfer channels transport the mixture into the combustion chamber, which is monitored by a knock sensor. If the electronic detection announces the destructive self-ignition, known in technical jargon as detonation, the ignition timing and mixture composition on the 39 Keihin carburetor adjust themselves in fractions of a second so that the engine runs cooler, ie the pre-ignition is reduced , the mixture via a Enriched power jet nozzle.
On the inlet side, the air sucked in on the cladding front flows through a huge airbox and the wide-open carburettor air funnel to the membrane control. The two membrane tongues regulate the gas flow to the crankcase, not divided into individual segments, but rather designed as uniform carbon fiber plates. The dynamic pressure generated in the airbox by the airflow increases the maximum engine output from around 200 km / h by around one hp. But only if the carburetor and ignition are electronically trimmed for the additional air volume.
F.In terms of the movement, Derbi goes its own way with the two tiny brake discs on the front wheel. Overall, the two brake calipers are 100 grams heavier than the four-piston system of the competition, but the rotating masses are reduced. This is a decisive factor for handling, the difference between the 200 mm panes and the 320 mm panes that are usually installed is considerable. At the same time, the telescopic fork is spared twisting thanks to the even load on the symmetrically mounted brake system, which benefits steering precision and controllability when turning. Forged magnesium wheels from Formula 1 supplier BBS and a fairing that has been optimized in the wind tunnel are further pluses of the Derbi 125. However, technology boss Bartol is certain that some of the competitors will take over them in the next season. Or better: copied. But the arrows that Derbi has in his quiver should be enough to stand up to the established factory teams in the 2001 season.

Technical data Derbi 125

Engine: water-cooled single-cylinder two-stroke engine, displacement 124.8 cm³, bore x stroke 54 x 54.5 mm, no exhaust control, membrane control in the crankcase, mixture lubrication, a Keihin flat slide carburetor with electronically controlled power jet, 0 39 mm, Ramair system with electronically controlled mixture enrichment, CDI map ignition, detonation sensor on the cylinder head, a gear-driven balance shaft. Power transmission: multi-plate dry clutch, six-speed cassette transmission with oil pump. Secondary drive via roller chain without O-rings. Power: 52 HP at 12500 / min Chassis: aluminum bridge frame, load-bearing motor, white power upside-down fork, fully adjustable, two-arm swing arm made of aluminum profiles, swing arm pivot point adjustable, white power central spring strut , full adjustable, operated via lever, spring travel front / rear 95/100 mm, double disc brake front, 0 200 mm, Nissin two-piston calipers, disc brake rear, 0 190 mm, forged BBS magnesium wheels, Dunlop slicks front 9 / 78-17 inches, rear 12 / 59-17 inches, chassis data: wheelbase 1215 mm, steering head angle 68 degrees, (plus / minus 0.5 degrees variable ) caster k. AT., weight 70 kg. Contact: Derbi Nacional Motor, S.A. Mollet de Valles, E-08107 Martorelles (B). Internet: www.derbi.com

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