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The transmission might seem complex – but it doesn’t have to be. Once you understand why you need it, it’s actually not as complicated as it might seem.

Just like how the concept of gear ratios isn’t all that complex.

Tune in to learn:

  • The basic principles of a motorcycle transmission
  • Why you need a transmission in the first place
  • What gear ratios are


Hello, and welcome to another episode of 30-minute motorcycling – a podcast for those riders who are at the beginning of their own Dual Wheel Journey, where you’ll discover something new about how your motorcycle, moped, or scooter works – in less than 30 minutes.


If you’ve listened to Episode 26 of this podcast about what the drivetrain is, you probably remember that I said that the transmission was worthy of its own podcast?


Well, it’s finally time to dive deeper into the motorcycle transmission – arguably one of the most complicated areas.


And to complicate things even further, there’s the whole concept of “gear ratios.” 


But don’t worry, in this episode, we’re going to explain them both – we’re going to talk about what the transmission does, why you need gears in the first place, and as promised, we’re finally going to demystify the concept of “gear ratios.”


But first, let’s start with what the transmission does.


The motorcycle transmission is largely a box that contains a series of gears – hence why it’s sometimes called “the gearbox.”


The lower the gear is, the faster it will rotate, which in turn gives you more power. Compare the amount of power you’ll get in first gear with the power in fourth gear.


Anyway, each gear actually consists of two gears – one is fitted to the “input shaft,” and the other one is fitted to the “output shaft.” 


The input shaft is attached to the engine, while the output shaft transfers the power through to the rear wheel.


When you select a gear with the gearshift, the gears are locked in place to their corresponding shaft.


I’ve mentioned “gears” a lot, but why do you even need these gears? 


The answer to that is simple – if there was no gearbox, much less any gears, all power from the engine would be delivered nearly instantly.


In some situations, like when you’re pulling away from a stop, this would be fine. However, when you’re doing 80 km/h on the motorway, an instant power boost might cause you to lose control of the bike and get into some serious trouble. 


That’s why you have gearboxes. Think of each gear as a switch for a different road scenario.


When you want to pull away from a stop, you switch to first gear so you can get away quickly.


When you’re up to speed (no pun intended), you’ll switch to a higher gear to maintain the speed and avoid sudden power boosts.


Now, the transmission is beginning to make more sense, doesn’t it?


But there’s still the topic of gear ratios, which we’ll cover now.


Remember – each gear consists of a pair of gears – one for the input shaft and one for the output shaft.


But now is a good time to mention that the gear for the input shaft is smaller than the one for the output shaft, and even though they’re linked together, they don’t turn at the same speed.


The gear on the input shaft actually turns faster than the one on the output shaft. 


This is what the gear ratio refers to – it refers to how many rotations the gear input shaft has to rotate to make the corresponding gear on the output shaft complete a full cycle.


For example, let’s say that we have a gear ratio of 3:1. This means two things:


1: The input shaft rotates 3 times faster than the output shaft

2: The output shaft has 3 times more gear teeth than the input shaft 


And there we have it – we’ve now demystified not only the motorcycle transmission but also gear ratios. 


But there’s still a lot to cover, so if you’d like to know more, including what a “constant mesh gearbox” is, and how you can calculate your gear ratio easily, I’ve included a link in the show notes to a blog post on The Dual Wheel Journey that goes into more detail.


I hope you enjoyed listening, and above all, that you learned something new. 


But wait a minute – perhaps you’re wondering why I didn’t talk more about the clutch? That’s because it’s the topic of the next podcast episode.


Until then, keep your helmet on and your eyes on the road. Bye!