Better gear ratio with a short 4th gear
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.
BGM 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 the 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.
- more relaxed driving
- closer gear step
- higher gear ratio and optimization 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 cruciform. How to recognize these gearboxes? The driveshaft has a locking ring fitted in the 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 gear boxes with bended cruciform. How to recognize these gearboxes? The driveshaft has a locking ring fitted in the front of and behind the gear cogs.
The middle part lies on the cruciform. Measurements:
- PX old type (until 1984, bent 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 the total gear ratio, but decreases the gear step from third to fourth, turning the entire engine performance into speed.
- more relaxed driving
- closer gear step
- higher gear ratio and optimization of the gear box
When working on a gearbox, don't forget:
- Gear selector cruciform for Vespa
- Vespa gearbox oil
- Gasket Vespa
- Liquid gasket
- Transmission shimming
- Shoulder rings and gearbox shims for Vespa
Particularly 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 to short fourth gear. 
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. 
** (We would like to take this opportunity to thank GSF member Motorhead for the Gear Calc!)
