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- Vespa Classic
- Primary Sprocket - POLINI 2.56→2.65 - Vespa Small Frame - 26 teeth (straight cut), for Polini Primary 27/69
POLINI 26-tooth primary sprocket for the straight-cut POLINI Primary 27/69—shortens the gear ratio from 2.56 to 2.65.
The POLINI 26-tooth primary sprocket allows you to specifically increase the POLINI 27/69 straight-cut primary gear ratio. This 26-tooth sprocket is installed in place of the stock 27-tooth sprocket.
This changes the gear ratio from 27/69 = 2.56 to 26/69 = 2.65. The numerical primary gear ratio thus increases by approximately 3.7%. The distance traveled per engine revolution decreases, theoretically, by about 3.5%.
26 teeth for POLINI 27/69 2.56 → 2.65 approx. 3.7% shorter straight-toothed
The stock POLINI primary drive features a 27-tooth sprocket and a 69-tooth primary sprocket. This results in:
| Stock gear ratio | 69 ÷ 27 = 2.56 |
|---|---|
| With a 26-tooth sprocket | 69 ÷ 26 = 2.65 |
| Change in gear ratio | approx. 3.7% higher |
| Less travel per engine revolution | approx. 3.5% |
A higher gear ratio means a shorter gear ratio. At the same engine speed, the vehicle therefore travels approximately 3.5% less distance. In return, more traction is available at the rear wheel, and the engine reaches a slightly higher RPM at the same driving speed.
This sprocket is particularly useful when the 27/69 primary ratio is slightly too long for the existing engine configuration. The shorter gear ratio improves traction and can help the engine rev out better in top gear, even under load.
The 26-tooth sprocket is matched to the tooth geometry of the corresponding straight-toothed POLINI 27/69 primary sprocket. It is therefore not intended as a universal 26-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 gear tooth geometry must also match the primary sprocket.
| Manufacturer | POLINI |
|---|---|
| Component | Primary Sprocket |
| Teeth | 25 |
| Toothing | Straight-toothed |
| Matching primary | POLINI 27/69 |
| Stock gear ratio | 27/69 = 2.56 |
| New gear ratio | 26/69 = 2.65 |
| Change in gear ratio | approx. 3.7% higher |
| Less travel per engine revolution | approx. 3.5% |
| Vehicle range | Vespa Smallframe |
The POLINI 26-tooth primary pinion is a simple way to moderately shorten the straight-toothed 27/69 primary. The gear ratio changes from 2.56 to 2.65—an increase of approximately 3.7%.
This makes the sprocket particularly suitable for small-frame engines, where the 27/69 ratio is slightly too long. The shorter gear ratio improves traction and can be achieved without completely replacing the primary drive.
