Sprocket size for casual riding

darkhawk22

New Member
Aug 17, 2010
733
0
0
Acworth, GA
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

Member
Feb 10, 2013
792
11
18
Southeastern GA
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.
 

Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
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.