The clutch is a crucial component that allows controlled power delivery from the engine to the drivetrain. Coleman mini bikes use an automatic centrifugal clutch paired with a continuously variable transmission (CVT) to provide smooth, seamless acceleration without manual shifting. In this article, we’ll take a deep dive into how the clutch and CVT operate on our 212cc and 196cc mini bikes.
Centrifugal Clutch Operation
Instead of a manual clutch lever, Coleman mini bikes have an automatic centrifugal clutch that engages based on engine rpm. Inside the clutch housing sits a set of weights, shoes, and springs.
At low rpm, the clutch springs hold the shoes away from the inner drum. No power is transferred, so you can start the engine without immediately moving forward.
Once rpm reaches around 2,800, centrifugal force causes the weights to swing outward, overcoming the spring tension. This forces the shoes to press against the drum inner surface, clutch engaged.
The clutch engagement is progressive, starting from the bottom of the shoes then gradually moving upward as rpm increases. This allows a smooth, controlled engagement instead of an abrupt on/off.
With the clutch engaged, the drum is now locked to the input shaft and can transfer power to the transmission and rear wheel. Adjusting clutch engagement rpm affects the stall speed and launch characteristics.
Continuously Variable Transmission (CVT)
The centrifugal clutch transfers power to a CVT, providing seamless acceleration without shifting gears manually. This automatic transmission uses a drive belt connecting two variable diameter pulleys.
The drive pulley is attached to the clutch drum input shaft, while the driven pulley is on the rear wheel output shaft. Each pulley has a fixed half and a sliding half that moves via centrifugal force.
At low speeds, the belt rides higher on the drive pulley and lower on the driven pulley. This provides high torque but low rpm, great for acceleration from a stop.
As speed increases, the driven pulley halves move together, increasing diameter. At the same time, the drive pulley halves separate, reducing diameter. This keeps the belt tight as the gear ratio changes.
The CVT tuning provides optimal rpm and torque throughout the speed range. Top speed is reached when the belt is at the very bottom of the drive pulley and top of the driven pulley.
Shifting is unnecessary since the CVT dynamically adjusts based on riding conditions. The system is low-maintenance and enclosed to prevent dirt or debris interference.
Clutch Maintenance Tips
To keep your Coleman mini bike clutch performing optimally, here are some key maintenance tips:
- Check clutch shoe thickness periodically. Replace shoes when worn to 3mm or less.
- Lubricate the clutch drum with quality molybdenum grease. This reduces friction and heat.
- Inspect clutch springs for proper tension. Weak springs cause premature engagement.
- Check clutch cable adjustment so engagement point is in the ideal rpm range.
- Remove clutch cover and clean any debris or dirt buildup around shoes and drum.
- Replace worn belt with exact OEM part number to maintain proper CVT tuning.
Signs of clutch issues include loss of acceleration, belt slipping, burning smell, and abnormal engagement rpm. Address any problems promptly to avoid damage.
Upgrading the Clutch and CVT System
One exciting advantage of Coleman mini bikes is the huge selection of aftermarket parts allowing customization and performance upgrades. Here are some popular options related to the clutch and CVT system:
- Heavy duty clutch springs – Stronger springs raise clutch engagement rpm for a higher stall speed. Great for drag racing.
- Clutch ramps – Ramps modify centrifugal force on weights for faster or slower engagement. More launch control.
- Lockup clutch kits – Locks the clutch for direct engine-to-wheel power transfer. Eliminates belt slippage at launch.
- CVT kits – Upgraded drive and driven pulleys plus belt provide higher torque capacity and new gear ratio options.
- Billet clutch bells – Lighter billet aluminum clutch components reduce rotating mass for quicker rpm jumps.
- Speed limiters – Limits max rpm to control top speed when upgraded clutches raise shift points.
With a huge aftermarket selection, you can customize clutch engagement, launch, top speed and belt life to match your riding style and terrain.
Conclusion
We hope this overview gives you a better understanding of how the centrifugal clutch and CVT operate on Coleman mini bikes. While an automatic transmission lacks the direct mechanical feel of a manual, it provides easy operation and low maintenance.
The clutch engages smoothly to avoid stalling, while the CVT provides seamless acceleration without shifting. Together, they make our mini bikes fun and easy for kids and adults to operate. Experienced riders can still enjoy tuning the clutch and transmission for optimized performance.
Check back on our blog for more technical guides covering engine, suspension, wheel and tire upgrades. At Coleman Powersports, we want to fuel your passion for modifying and personalizing your very own mini bike. With the right aftermarket parts, you can build a machine as unique as you are. Just don’t forget to take safety precautions whenever pushing the limits.
