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- Vespa Classic
- Primary Sprocket - POLINI 3.00→2.88 - Vespa Small Frame - 25 teeth (straight cut), for Polini Primary 24/72
POLINI 25-tooth primary sprocket for the straight-toothed POLINI Primary 24/72 – reduces the gear ratio from 3.00 to 2.88.
The POLINI 25-tooth primary sprocket allows you to specifically increase the POLINI 24/72 straight-toothed primary gear ratio. This 25-tooth sprocket is installed in place of the standard 24-tooth sprocket.
This changes the gear ratio from 24/72 = 3.00 to 25/72 = 2.88. This corresponds to an increase of approximately 4.2%.
25 teeth for POLINI 24/72 3.00 → 2.88 approx. 4.2% longer straight-toothed
The stock POLINI primary drive has 24 teeth on the pinion and 72 teeth on the primary sprocket. This results in:
| Stock gear ratio | 72 ÷ 24 = 3.00 |
|---|---|
| With a 25-tooth sprocket | 72 ÷ 25 = 2.88 |
| Ratio increase | approx. 4.2% |
A lower gear ratio results in a longer gear ratio. At the same engine speed, the vehicle therefore covers a greater distance in theoretical terms. 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 24/72 primary gear reaches redline too early or revs unnecessarily high at cruising speeds.
The 25-tooth sprocket is matched to the tooth geometry of the corresponding straight-toothed POLINI 24/72 primary sprocket. It is therefore not intended as a universal 25-tooth sprocket for any 72-tooth primary sprockets.
Before installation, verify that the correct POLINI 24/72 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 |
|---|---|
| Part | Primary Sprocket |
| Teeth | 25 |
| Tooth Profile | Straight-toothed |
| Matching primary | POLINI 24/72 |
| Standard gear ratio | 24/72 = 3.00 |
| New gear ratio | 25/72 = 2.88 |
| Change | Approx. 4.2% longer gear ratio |
| Vehicle range | Vespa Smallframe |
The POLINI 25-tooth primary sprocket is a simple way to moderately extend the standard 24/72 primary gear ratio. The ratio changes from 3.00 to 2.88—a change of approximately 4.2%.
This makes the sprocket particularly suitable for high-torque small-frame engines where the stock 24/72 ratio is slightly too short, without having to change the entire primary gear ratio.
