Scooter Gears Explained! Primary & Secondary Kits - Which To Buy?

Summary

In this video, Brad from Scooter Street explains the function of gear up kits and how to calculate final drive ratios for scooters. He dissects a 50cc Piagio factory diff, illustrating primary and secondary gears' roles in reducing engine load. Brad teaches viewers how to determine their scooter's current ratio and suggests gear up kits based on scooter setup, emphasizing the balance between top speed and acceleration. He advises against overly aggressive gearing that could hinder acceleration and offers tips for different scooter configurations.

Takeaways

• 🔧 Gear up kits are designed to modify the final drive ratio of scooters to improve performance.
• 🛠️ Understanding how factory differentials work is crucial before discussing gear up kits.
• 📏 The primary and secondary gears in a differential work together to reduce engine load and allow for higher engine RPMs.
• 🔄 The final drive ratio is calculated by multiplying the reduction ratios of the primary and secondary gears.
• 📐 To calculate the final drive ratio, count the teeth on the gears and use the formula: (large number/small number) for each set of gears.
• 🚲 Different scooter models with the same engine may have different factory gear ratios due to varying wheel sizes.
• 🔄 Gear up kits alter the reduction ratio, which can affect acceleration and top speed.
• 🛍️ When choosing a gear up kit, consider the scooter's current setup and the desired performance outcome.
• 📉 A more aggressive gear up kit can result in a higher top speed but may negatively impact acceleration.
• 🔄 For a stock scooter or one with a performance exhaust, a 10-15% reduction in gearing is recommended.
• 🏎️ For more aggressive setups, like a 70cc kit, a 25-30% reduction might be suitable, but it can be challenging for the engine to handle.

Q & A

What is the main topic of the video?

The main topic of the video is explaining gear up kits for scooters, specifically how differential gears work and how to calculate the final drive ratio.

What is a gear up kit?

A gear up kit is a set of gears designed to alter the final drive ratio of a scooter, typically to increase top speed by reducing the engine load.

How does the factory differential work?

The factory differential contains primary and secondary gears that work together to reduce the rotation from the rear pulley of the transmission to the wheel, allowing the engine to rev more freely.

What is the purpose of the idler gear assembly?

The idler gear assembly is part of the secondary gear set and works together with the primary and secondary gears to reduce the speed of the wheel compared to the engine.

How is the final drive ratio calculated?

The final drive ratio is calculated by dividing the number of teeth on the larger gear by the number of teeth on the smaller gear for both the primary and secondary sets, then multiplying those two results together.

Why do different Piaggio models have different rear gears?

Different Piaggio models have different rear gears because the size of the wheel affects the reduction needed; larger wheels require more aggressive reduction to cover more ground per rotation.

What factors should be considered when choosing a gear up kit?

When choosing a gear up kit, consider the scooter's current setup, such as whether it's stock or has performance modifications, as this affects how much gearing the scooter can handle.

What is the recommended percentage increase for a gear up kit on a stock scooter?

For a stock scooter or one with a performance exhaust, a gear up kit with a 10-15% increase is recommended.

What is the potential downside of using a gear up kit with too aggressive a reduction?

Using a gear up kit with too aggressive a reduction can cause the engine to struggle to rev properly, negatively affecting acceleration and potentially preventing the scooter from reaching its top speed.

What is the role of the variator in relation to gear up kits?

The variator plays a role in gearing as well, and for very aggressive gear up kits, a race-oriented variator or lightened rollers might be necessary to compensate for the increased gearing.

What is the Meloy overrange transmission and when would it be used?

The Meloy overrange transmission provides additional lower gearing on the variator, which is useful for scooters with race kits or very aggressive final drive or diff gear setups.