The gear cog attached to the clutch assembly drives the primary gear cog attached to the input shaft in the large frame VESPA motor. Through varying the size or number of teeth on this cog, you can change the primary gear ratio of your motor. Changing the clutch cog is the quickest and easiest way to change the overall gear ratio of your motor. The more teeth the clutch gear cog has, the higher the gearing.
All clutch gear cogs that fit the VESPA 125 GTR/ TS/ 150 Sprint/ Super/ PX80-150/PE/EFL till '94 with the clutch basket outer diameter of 96mm are interchangeable without having to change the primary driven gear cog. The 200cc clutches with 20 and 21 teeth on their respective cogs also fit, but due to the increased diameter of the clutch basket (115mm) either the clutch cover must be modified, a clutch gasket surface area spacer used or, last but not least, a 200cc clutch cover being used. If the 200cc clutch with a 23 toothed cog is to be included, the primary driven gear cog with 65 teeth, also from the 200cc motor, should also be used. When the 108mm outer diameter clutch is used in a 125-150cc motor the primary driven gear cogs with 67 and 68 teeth have proved effective in combination with the clutch gear cogs with either 20, 21 or 22 teeth.
The primary driven gear cog in the 200cc motor with 65 teeth can be combined with 21 or 22 toothed cogs, along with the original item with 23 teeth. The most popular clutch gear conversion cog is the version with 22 teeth, so enabling an improved acceleration through the gears, without expensive tuning measures, especially between 3rd and 4th gears. For VESPA T5 motors equipped with the MALOSSI 172cc cylinder kit, a clutch gear cog with 21 or 22 teeth has proved suitable.
If you change the respective primary driven gear cogs, other combinations are, of course, possible. More original clutch gear cogs are available in the online catalogue underneath CLUTCH-Spare parts. Even more transmission ratios are made possible with the extensive range of high quality clutch gear cogs produced by DRT.
SIP-TIP: Do not forget to order a new castle nut, safety washer, thrust plate and a pushrod. New clutch friction plates are also recommended when doing this job. With differing sizes of gear cogs on the input and output shafts even more experimentation with gear ratio is possible. Wider section tyres are also a popular way of raising the gearing of your motor.
SIP community user “LaRocca” on Art.-Nr.13082300: “The solution to enable 87km/h on a PX80 with a DR135cc kit, without having to rev it to death!”