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Driving report Aprilia RSX 550

Do-it-yourself supersport

After the discontinued 250cc two-stroke and lively 400cc four-stroke, there is a gap in the supersport segment. Editor Werner "Mini" Koch has built a racer based on the Aprilia SXV 550 Supermoto with a weight of 134 kilograms and 71 hp, which could serve as a rapid gap filler. Here is his report on the history of its origins.

The supersport scene has quietly said goodbye to the little thugs. Ten years ago, the 250/400 amateur racing classes were bursting at the seams, but the manufacturers pressed on the tube and only pressed the outrageously expensive 600 cc in addition to the high-priced 1000 cc. If you want to drive a super sports car, you have to look deep into your grandma’s eyes and dig deeper into your budget? Nothing works below 10,000 euros.

The question arises: Didn’t we have fun with the little racers and their almost 70 hp? Goal. And how! Sailed past the GSX-R muscle man on the outside, mixed up the whole field in the rain and brushed everything in the way in the tricky infield of Hockenheim with the 70 hp racing flea. Great fun for little money.

So the call came at just the right time. Tommy Bayer, press spokesman for Aprilia Germany and an avowed RS 250 fan, couldn’t take it any longer. "There you go, build me a feather-light 70 hp racer with 130 kilos by next spring." No sooner said than done. The original idea of ​​lowering a 550 Aprilia Supermoto just by shortening the suspension travel and packing it in a racing fairing was discarded after the first inventory. Why? Because too many technical compromises can permanently spoil the driving behavior.

It was just before Christmas S.XV 550 Supermoto in the workshop, two days later the standard front frame mesh was flexed off and the torso was ready to mutate into a street racer by means of a newly designed tubular space frame. A simple but rigid frame structure made of 30-millimeter precision steel tubing, which is rigid thanks to stable triangular connections, establishes the connection between the glued, standard cast aluminum parts and the new control head, which is around 100 millimeters lower. Compared to a voluminous aluminum frame, the airy tubular space frame leaves enough space to accommodate the necessary electrical components in a compact yet easily accessible manner.

Bilski

The lightweight construction is fun even when standing still – to look at it.

The remaining elements should, if at all possible, be used for reasons of design and cost. As a result, the beautiful aluminum swingarm was retained, as was the shock absorber, only trimmed to 120 millimeters of travel with a harder 140 kg / cm spring and adapted damping. At the front there was nothing to be done with the long cross fork, which is why a used and weight-adapted Showa fork of the Aprilia RSV 1000 has the 3.50 inch wire-spoke wheel. The front wheel brakes with the 320 mm brake disc from the Supermoto, which is completely sufficient thanks to its low weight and a maximum top speed of 220 km / h for the RSX 550. Every other component, regardless of whether it was notches, tanks , shift linkages, footrests or exhaust manifolds, had to be painstakingly made and adapted by hand. And the rear frame including the silence is lowered, the GRP parts of the Aprilia RS 125 are reshaped and, finally, the engine oil for the dry sump lubrication is bunkered in a new oil tank.

For the time being, it should stay with a study without road approval. With TÜV-compliant standard equipment, a rule of thumb should add another eight kilograms. Makes a ready-to-drive sports motorcycle weighing 142 kilograms, which, in series production, should be available for well under 9,000 euros.

After a good 220 working hours, the freshly painted prototype rolls onto the handling line for the first roll-out at Baden-Airpark. As always on maiden voyages, all possible and impossible scenarios run through your head: Will the weld seam hold on to the steering head? Are the frame beams really as stable as planned? Or the engine plops out of the chassis with the first wheelie?

cook

Ready to jump – a lot can be extracted from the engine at a high speed.

You can hardly see on the film how easy it is to turn such a little rascal around the corner. Aim for the curve, flip it, and whoosh, the 134-kilo racer follows the mere thought as if pulled on a string. Because the brute acceleration does not naturally occur with 71 PS, the quick line is required when riding the RSX 550. Turn with a lot of momentum, do not waste time due to the steep incline and balance with even more momentum on the last centimeter of asphalt. The throttle hand, spoiled by the GSX-R 1000 and the like, needs a few laps before you dare to turn the tap to the stop before the apex of the curve and fly in generous arcs through the labyrinth.

But this is all the more important because the Aprilia V two-cylinder, which revs up at lightning speed and acts rather rudely when the load changes, still requires some fine-tuning of the mapping of the injection. For this, the engine grabs a lot from medium speeds and clicks violently into the speed limiter, which locks at 11500 revs. The six gears are typed through in no time under the eerily beautiful two-cylinder blasts from the short exhaust stubs? and the fun takes its course.

The machine

Bilski

Real lightweight: only 134 kg with a full tank.

Engine: water-cooled two-cylinder V-engine, four valves per cylinder, 52 kW (71 HP) at 10900 / min, 53 Nm at 8800 / min, 553 cm³, bore x stroke: 80.0 x 55.0 mm, compression: 12.5: 1, ignition / injection system, 40 mm throttle valves, multi-disc oil bath clutch, six-speed gearbox.
Frame: tubular steel frame with glued aluminum cast parts. Upside-down fork, Ø 43 mm, aluminum swing arm with Sachs suspension strut.
Dimensions and weights: wheelbase 1380 mm, steering head angle 67 degrees, caster 98 mm, wire-spoke wheels 3.50 x 17 and 5.50 x 17, front tires 120/70 ZR 17, rear 180/50 ZR 17, spring travel front / rear 120/120 mm, single disc brake front, Ø 320 mm, rear single-disc brake, Ø 240 mm, weight with a full tank of 134 kg, weight distribution f / r 54/46%. Conversion price: around 12,000 euros.

Tea heart of the Aprilia RSX 550

cook

The engine comes from the Supermoto SXV 550.

The Supermoto SXV 550, which has been built for almost two years, serves as the basis for the prototype. Two 40 millimeter intake manifolds with electronic injection and four titanium valves take over the gas control of the light and with a 77 degree cylinder angle extremely compact drive. The stiff engine housing with integrated cylinder bores and cast-in swing arm pivot point, as a load-bearing element, ensures a large go of the chassis stability of the new tubular space frame, which is open at the bottom.

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