Joe,
I didn't mean to mislead you. The 19 tooth metal gear is driven by a larger drive gear. They are not inter-changeable. All the drive gears are metal and usually don't get damaged with a plastic gear. You could probably use the yellow - 24 tooth gear without the adapter and be pretty close. Another possibility is the green gear with 22 teeth. Other factors could be in play here also such as tire size and actual speedometer calibration.
Fred
