Gearbox 21/60, (2.86) teeth,
for 102-155cc cylinder, DRT
COBRA, for Vespa 50-125/PV/ET3
The latest technical coup from Denis at DRT is the COBRA primary drive gear kit. The cog around the clutch basket has 60 teeth, so enabling gear ratios ideally suitable for motors with a cubic capacity of between 75 and 155cc. Once installed this kit allows quick and easy adjustment of the overall gear ratio of your motor to suit road or track conditions.
The DRT COBRA clutch basket has strengthened aluminium spring retainer plates and reinforced primary drive shock absorber springs. The cogs themselves are made of a special grade of steel, tempered and precisely finished. The cog teeth are straight cut, CNC machined and have had metal removed to lower the overall weight. The initial primary drive gear ratio of the kit is 22/66 but the cog around the clutch basket with 60 teeth can be combined with smaller cogs that have 19, 20, 21 or 23 teeth. This results in overall gear ratios of between 2.61 and 3.16 being possible, all with the use of one single primary/clutch basket.
Conclusion: The Swiss army pocket knife of the primary gear conversion kits.
SIP-TIP: Do not forget to order a new fixing nut for the input shaft, a safety washer, new bearing and fresh gearbox oil for safe and enduring use of your motor.
SIP community user “Salvatore Randazzo” ESC rider on Art.-No. 1544000: “I can cover a large range of gear ratios with the COBRA kit by just changing the 'shaft' cog. In other words it offers a suitable gear ratio for go-kart tracks (3.16) through to endurance races (2.61) without having to split the crankcases every time.”
Gear recommendations with primary drive gear CORBA:
75cc: COBRA 19/60 teeth + DRT input shaft Runner 40430313
80cc: COBRA 19/60 teeth + DRT shortened 4th gear 40442400
100cc: COBRA 21/60 teeth + DRT shortened 4th gear 40442400
130cc: COBRA 22/60 teeth + DRT shortened 4th gear 40442400
135cc: COBRA 21/60 teeth + DRT shortened 4th gear 40442400
COBRA 22/60 teeth + DRT input shaft Runner 40430313
OEM Numbers (for the purpose of comparison)
pr S100 311.rz60-21k (2.86-RINF) (DRT)
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