Sprocket size for casual riding

[darkhawk22]

Hey Guys,

I'm new to the 4-stroke world and I'm wondering what the best size sprocket would be for a build. I have a bike that has a 44 tooth sprocket on it now but haven't really had a chance to ride it around much due to the fact that it needs some brakes. In general it's pretty hilly around the neighborhood. Thoughts appreciated.

 

[Agreen]

Which engine and gearbox?

I use a 50t sprocket on mine, but it's a Honda 196cc with a cvt. A huasheng 49 will need a different sprocket, even more so depending on the transmission.

 

[darkhawk22]

This bike has the Huasheng 49 with the 4T transmission I believe

 

[Agreen]

Being not too familiar with that one, I'm not the best to give a good answer. From what I've heard, the 4G transmission can be either a 5:1 or 4:1 ratio. The output sprocket can be a few different sizes too. Really, the best way to determine is by simple calculations.
Usually, you do a (driven/drive) x (driven/drive) calculation to get the overall ratio. If the 4g you have is a 4:1, then it's (4/1)x(wheel sprocket teeth/trans output sprocket teeth). So with a 10t output, and a 44t wheel sprocket, (4/1)*(44/10)=17.6:1 reduction ratio. Now you need the engine speed and size of your wheel. So if you want to cruise at 5000 rpm with a 26" tire (figure out the distance one tire revolution gets you), then you divide 5000 rpm by the reduction ratio to get the rear wheel revolutions per minute= 284 rpm. Multiply that by 60 to get rotations per hour=17045.5. 26x2.125" tire has a circumference of about 6.791339 feet, so multiply that by the RPH=115761.429. That gives you feet/hour, divide it by 5280ft/mile and you get approximately 22 mph at 5000 rpm.

Note that it's theoretical, and that's with a lot of assumptions. The max rpm is also said to be 6800. Substitute your numbers from your transmission (should just be able to count the teeth) and do some plug/chug calculations to get your ideal gear combination.