for Vespa 90 R/ SS/ 125/ PV/ ET3/ PK50 XL/ XL2/ PK125/ ETS/ N/ S/ XL/ XL2
39,8 mm
straight teeth
for primary 24/72

Grade AA – first-class repair and for tuned engines
Product description
Stefano BENELLI has been passionate about all possible petrol-driven vehicles, either two or four stroke, since the 1980’s. His love of the two-stroke is strong and especially for the Vespa. This is where he could gather his first experience in motor tuning and many of his developments have seen successful use in scooter sprint racing. He found that the original Vespa gearbox was unable to cope with the extra power. Back in the days when the only aftermarket gearbox component available here in Germany was a shorter 4th gear for the smallframe engine, the BENELLI range of gearbox parts were already being included in scooters racing in the Italian national racing series. In more recent times gearbox parts from a number of manufacturers have become available. Outside of his home country of Italy, parts produced by BENELLI were very hard to obtain and only a small exclusive circle of racers and tuners were even aware of their excellent reputation and existence. During product comparisons conducted in Germany his gear cogs were rated better than those from other component manufacturers. Nowadays the BENELLI enterprise has become a small-scale producer of high-end gearbox components using the finest materials suited for a wide spectrum of potential employment. They have proven successful for use in off-road, circuit and sprint racing machines. The most simple and effective method of overall gear ratio adjustment is to replace the primary drive cog on the crankshaft. A basis for this conversion is provided by a primary drive with straight-cut cog teeth. The fine adjustment of the smaller of the cogs in the primary drive enables the gearbox to be set up precisely, to suit every stage of tuning. The BENELLI gears are very high quality processed, tempered and made of special steel. The choice of the correct primary drive ratio depends on a number of factors: Nominal motor speed, gear ratios, area of use, and the circumference of the rear tyre. The primary drive gear ratio is determined by the number of cog teeth on both of its cogs. A 72/24 primary drive provides a 3.00 gear ratio and the greater this value (or quotient), the shorter the ratio. The BENELLI produced Vespa smallframe primary drive cogs are suitable for use with the existing gear ratio and are also compatible with primary drives made by other producers. BENELLI offer a variety of possibilities for combination with the 24/72 and the 27/69 primary drive cog sets.
Conclusion: Once the primary drive has been installed in the gearbox it can be further fine tuned by replacing individual gear cogs.
Do not forget to order the suitable primary drive cog by either RMS, Surflex, Crimaz or DRT!