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- Vespa Classic
- Primary Sprocket - POLINI 2.56→2.46 - Vespa Small Frame - 28 teeth (straight cut), for Polini Primary 27/69
POLINI 28-tooth primary sprocket for the straight-toothed POLINI Primary 27/69 – extends the gear ratio from 2.56 to 2.46.
The POLINI 28-tooth primary sprocket allows you to specifically increase the straight-toothed POLINI 27/69 primary gear ratio. This 28-tooth sprocket is installed in place of the stock 27-tooth sprocket.
This changes the gear ratio from 27/69 = 2.56 to 28/69 = 2.46. The numerical primary gear ratio thus decreases by approximately 3.6%. The distance traveled per engine revolution increases, theoretically, by about 3.7%.
28 teeth for POLINI 27/69 2.56 → 2.46 approx. 3.6% longer straight-toothed
The stock POLINI primary drive features a 27-tooth pinion and a 69-tooth primary sprocket. This results in:
| Stock gear ratio | 69 ÷ 27 = 2.56 |
|---|---|
| With a 28-tooth sprocket | 69 ÷ 28 = 2.46 |
| Change in gear ratio | approx. 3.6% lower |
| More travel per motor rotation | approx. 3.7% |
A lower gear ratio results in a longer gear ratio. At the same engine speed, the vehicle therefore covers approximately 3.7% more distance. At the same time, the engine requires correspondingly more torque to smoothly accelerate through the longer gear ratio.
This sprocket is particularly useful when a high-torque small-frame engine with the 27/69 primary gear set revs out too early or revs unnecessarily high at cruising speeds.
The 28-tooth sprocket is matched to the tooth geometry of the corresponding straight-toothed POLINI 27/69 primary. It is therefore not intended as a universal 28-tooth sprocket for any 72-tooth primary sprockets.
Before installation, verify that the correct POLINI 27/69 primary sprocket is actually installed. The number of teeth alone is not sufficient to determine compatibility; the tooth profile must also match the primary sprocket.
| Manufacturer | POLINI |
|---|---|
| Component | Primary Sprocket |
| Teeth | 25 |
| Tooth Profile | Straight-toothed |
| Matching primary | POLINI 27/69 |
| Stock gear ratio | 27/69 = 2.56 |
| New gear ratio | 28/69 = 2.46 |
| Change in gear ratio | approx. 3.6% lower |
| More travel per engine revolution | approx. 3.7% |
| Vehicle range | Vespa Smallframe |
The POLINI 28-tooth primary pinion is a simple way to moderately extend the standard 27/69 primary gear ratio. The ratio changes from 2.56 to 2.46—a change of approximately 3.6%.
This makes the sprocket particularly suitable for high-torque small-frame engines where the stock 27/69 ratio is slightly too short, without having to change the entire primary gear ratio.
