why use transmission?

[Cozmik Mezzenger]

Please elaborate ,
What does it do to gearing?

In order for your engine to output enough torque to power your bicycle, you will need a significant gear reduction. We will be using a jackshaft for 2-stage gear reduction in order to avoid having to use gigantic sprockets.

For a 2-stage reduction, the overall gear ratio is the product of the individual stages. So if you have a gear ratio of (a:b) for the first stage, and (x:y) for the second stage, your overall ratio would be (ax:by). For example, let's say we have the 11t driving the 36t from before, but then the second stage is a 9t driving a 36t. First we multiply 11 x 9 = 99 and 36 x 36 = 1,296. Then you write them as a ratio 99:1,296. Then, we simplify that ratio by dividing both sides by 99 (divide the left side by itself, and the right side by the left side). So 99 / 99 = 1, and 1296 / 99 = 13.09. So the final ratio is 1:13.09. In case that's too complicated for you, here's a link to a Gear Ratio Calculator.

From 79cc Motorized Bicycle From Scratch by TheNecromancer13.

 

[the13bats]

No gee wizz not too complicated for me, (big grin )
Thanks, its what i was wanting to know...

 

[Cozmik Mezzenger]

No gee wizz not too complicated for me, (big grin )
Thanks, its what i was wanting to know...

Glad I could help.

 

[MotorBicycleRacing]

I am assuming these so called "transmissions" i see used on 212s and some 79s are gear deduction units,

But my confusion comes in with i see some same/similar builds run trans and some dont but both "seem" to work,

So how about giving me a 101 on these trans and where and why they are desirable or a down right must

Many thanks,
Cheers
b

As already stated by Cozmik chain alignment from the motor to the rear wheel also requires a jackshaft.

If you run a chain or belt straight from the engines shaft to the back wheel you will have to offset the
engine to the right by an impractical amount aside from looking goofy.
Four stroke motors like the 79cc and 212cc are already very wide even as centered in the frame.

Wheel size also changes gearing so small wheels can have direct single chain lines especially when
you use small pitch sprockets like 3/8" and less that make the sprocket diameter smaller than 1/2"
You see this on minibikes where the sprocket can be close to the same size as the wheel.