Grinding questions about motorcycle gears and transmissions
When you think of a motorcycle, you usually picture cruising down the highway, leaning into corners, and hammering through the gears as you accelerate.
In this article, I will answer some of the more common questions about motorcycles and gears.
Why do motorcycles have gears?
Motorcycles have gears to keep the engine RPM (Revolutions per Minute) in a usable range when transferring power to the rear wheel.
Motorcycle engines make their power in a specific RPM range. If the RPM is too low the engine won’t have enough power to turn the rear wheel.
Similarly, if the RPM is too high the power of the engine is used up and won’t be able to transfer any additional power to the rear wheel.
In general, the faster a motorcycle is going the less power is needed to keep the rear wheel turning.
Therefore motorcycles use gears to deliver the appropriate amount of power to the rear in order to drive at different speeds and various terrain.
Most use a dog gearset that is mounted inside the engine case to achieve this.
What is a motorcycle gear?
This one is very confusing because the industry also refers to items such as helmets, gloves, coats, and boots as motorcycle gear.
A gear also refers to a circular piece of metal with the edges cut in a straight or helical pattern, usually made to mesh with another gear or shaft.
To add to that gear can be associated with what configuration these gears are arranged at a specific moment for example first gear, second gear, and so on.
It all comes down to context, if someone says check out my new gear they are probably talking about the stuff a rider wears.
On the other hand, if someone says I pulled a wheelie in second gear, that refers to the specific configuration of gears inside the transmission.
When a gear is referred to as a physical piece it is usually something like this gear is broken or worn out.
What is a straight-cut gear on a motorcycle?
A straight-cut gear on a motorcycle is a gear that is cut so that it can be placed in line with another gear to transfer power.
This allows a smaller gear to operate a larger one or vise versa. Straight-cut gears can also be used to turn a belt or chain.
It does this by allowing the cut portions or teeth to mesh with the rollers on a chain or grooves on a belt.
This chain or belt can be attached to yet another straight-cut gear allowing you to transfer power over relatively long distances.
This is how most motorcycles deliver power from the transmission to the rear wheel.
What is a helical-cut gear on a motorcycle?
A helical-cut gear on a motorcycle is a gear that has a spiral pattern that allows it to mesh with another gear at an angle.
Unlike straight-cut gears which are placed in line with each other, helical gears are usually placed at a 90-degree angle from each other.
This allows power to be transferred at an angle which can be beneficial in some applications. For example, this can allow a motorcycle to turn a drive shaft which can then turn the rear wheel without using a chain or a belt.
Helical-cut gears allow a motorcycle to place these items inside housings so they are not exposed to the elements.
It also makes the power transfer between the transmission and tire smoother than the traditional chain or belt drive.
What is a dog gear set on a motorcycle?
A dog gearset on a motorcycle is a special collection of gears and shafts, that have bumps or dogs on one side and hollow spots for them to fit onto another gear.
This is accomplished by a fork controlled by the rider and a shift drum moving gears along a shaft.
This allows a motorcycle to be driven on a wide range of terrains and at a variety of speeds.
What is a fork in a motorcycle dog gear set?
A fork in a motorcycle dog gear set is a somewhat C-shaped piece of metal that sits in a grove connected to a gear and allows it to slide across a shaft.
The other end is round and has a small protrusion on the end that sits inside a shift drum.
When the shift drum is rotated it moves the fork which in turn slides a gear or a set of gears along a shaft meshing them with other gears.
What is a shift drum in a motorcycle dog gear set?
A shift drum in a motorcycle dog gear set is a cylindrical piece of metal with slots in a pattern grooved into it that help guide the shift fork along a shaft when the rider depresses or raises the shift selection lever.
This allows the motorcycle to shift gears to keep the engine at a usable RPM range.
Why are motorcycles manual?
Most motorcycles are manual because of ever-unpredictable conditions and terrain faced by motorcycle riders, especially off-road motorcycles.
Using a manual transmission gives the rider control of which gear a motorcycle is in so they can keep the engine in that usable RPM range.
That and there is a certain amount of fun in shifting through the gears as the motorcycle accelerates.
What is a manual motorcycle?
A manual motorcycle is one where you manually depress and raise a pedal or use electronic buttons, in concert, with manual clutch engagement to change gears.
This is especially helpful for off-road motorcycles as the terrain they face may force them to down-shift quickly to keep the engine in the usable RPM range, something automatic transmissions struggle with.
What is an automatic motorcycle?
An automatic motorcycle is one that does not need rider input to shift gears or accelerate. This frees the rider from the need to manually keep the engine operating in the optimal RPM range.
The most common type used today is a continuously variable transmission (CVT) and only really shows up in street motorcycles.
Why are there no automatic motorcycles?
The truth is there are automatic motorcycles they just are not that common, especially compared to their manual counterparts.
Because of ever-unpredictable conditions and terrain faced by motorcycle riders, especially off-road motorcycles, a manual motorcycle allows more control in unpredictable situations.
Gears will always be a part of motorcycles, whether a 2-stroke, 4-stoke, and even electric you will always need to transfer power to the rear wheel. The trick will always be how to do this as efficiently as possible.
Hopefully, after reading this you have an idea of why gears are needed and how they work to keep the rear wheel turning.
As always feel free to contact me with any questions, concerns, or topics you want to be covered.