Short fourth gear for Vespa PX and PX EFL

Better gear ratio with a short 4th gear

Kurzer vierter Gang Vespa PX

Why should your Vespa have a short 4th gear installed?

You install a short fourth gear to improve the gear ratio from third to fourth, which works perfectly fine with a short fourth gear with 36 teeth.
A short fourth gear makes sense for all Vespa PX engines, no matter if you are a daily, tour or race driver.
This drive wheel has 36 teeth, which is one more than the original fourth gear cog of a Vespa PX200.

PRO – Premium Tuning Parts

The material used for BGM PRO gear boxes are extremely solid. The gear cogs are made from high alloyed Ni-Cr-Mo case hardened steel (20NiCrMo2-2/ AISI8620) to suit highest load levels.
The base material is of very high quality and suitable for highest levels of engine performance. Surface hardening is precisely defined to HRC 58-60 making the sprockets extremely wear resistant. Always high quality. No compromises.

BGM PRO short fourth gear
Advantages of a short fourth gear:

  • more relaxed driving
  • closer gear step
  • higher gear ratio and optimisation of the gear box

Gear wheel 4 -BGM PRO- Vespa PX EFL T5 125cc, PX200 EFL (short) – 36 teeth

Short fourth gear Vespa PX EFL Suitable for all gearboxes with flat . How to recognise these gearboxes? The driveshaft has a locking ring fitted in front of the gear cogs.

Gear wheel 4 -BGM PRO- Vespa PX (-1984), PX200 (short) – 36 teeth

Short fourth gear Vespa PX (-1984) Suitable for all gearboxes with bended cruciform. How to recognise these gearboxes? The driveshaft has a locking ring fitted in front of and behind the gear cogs.

The middle part lies on the cruciform. Measures:

  • PX old type (until 1984, bended cruciform): 5mm
  • EFL (since 1984, flat cruciform): 6,5mm

Middle parts of BGM gear cogs are larger (approx. 1/10mm) and therefore the contact surface for the cruciform is larger.

Scooter Center technology TIP:

A short fourth gear can be perfectly combined with the 64 teeth primary drive wheel by BGM Pro, which has a longer reduction. Using a 24 teeth clutch sprocket significantly increases the total gear ratio, but decreases the gear step from third to fourth, turning the entire engine performance into top speed.

BGM PRO short fourth gear
Advantages of a short fourth gear:

  • more relaxed driving
  • closer gear step
  • higher gear ratio and optimisation of the gear box

When working on a gearbox, don’t forget:

Especially interesting

So far, Malossi sports and Polini 221 engines, which are high in torque, have proven their quality in combination with a 24/64 gear ratio and a short fourth gear. BGM6536L

A short fourth gear reduces the gear step between third and fourth, in order to grant a sufficient torque and smooth gear ratio and nice acceleration when changing to fourth.

The table and graphs** below show the difference. Higher reduction leads to nice cruising speed in towns and on large roads at lower gears with very low revs. This combinations offers rather quick driving and a higher top speed with lower revs when driving in fourth. 24_64 graph

24_64 tab

**(We would like to take this opportunity to thank GSF member Motorhead for the Gear Calc!)

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