Gear Ratio Question?

carl_baron123

New Member
Jan 12, 2009
12
0
0
Australia
I am going to hook up my offroad scooter to a 48cc ww motor but I have a quick question about gear ratios... I am still a little confused about it all. People have told me that I need a ratio of 18.75:1. Is that right? I am guessing i need a jackshaft. The thing is, if i use too high a ratio, it will not reach the speeds that I intend it too but if I could go too low, then i risk burning the clutch. I am running 16"x2" tyres so that if probebly my problem. I have come to the obvious conclusion that bigger wheels means faster speeds but with my frame, there is no way of getting these sizes unless i mod the frame, which i dont really intend to do unless necesarry. What other options do I have?
 

comfortableshoes

New Member
Jul 22, 2008
606
0
0
Beverly, MA USA
there is a sticky post at the top of the forum- there is a download for a gear calc. you enter in gear sizes and tire size and engine rpm and you get a very accurate speed.

Other than that I don't have an answer for you.

I do have a question though, what braqnd and model is the 48cc WW? Cause I'd love me some more WW power!

.dd.
 

carl_baron123

New Member
Jan 12, 2009
12
0
0
Australia
there is a sticky post at the top of the forum- there is a download for a gear calc. you enter in gear sizes and tire size and engine rpm and you get a very accurate speed.

Other than that I don't have an answer for you.

I do have a question though, what braqnd and model is the 48cc WW? Cause I'd love me some more WW power!

.dd.
I am looking at getting a Stihl FS48 ww which i presume is 48cc. I may be (and most probably am) wrong but that is just what I am guessing it means. I am buying it off ebay if everything goes to plan.
 

Andyinchville1

Manufacturer/Dealer
Dec 26, 2007
502
1
18
Scottsville, VA
HI,

Custom sprockets can change gearing without necessarily resorting to jackshafts and all BUT really depends on you install (the rear tire being as small as it is may be the limiting factor if you need to gear lower wiithout a primary gear reduction)....

On the other hand, since your rear tire is so small, maybe you don't need to gear so low after all.....

Off hand, I can't recall what the HT type engines run as far as reduction (the primary reduction I think is about 4:1 (under the clutch cover), then the approximately 4:1 reduction from engine drive sprocket to standard rear sprocket (44T) yields about 16:1 overall reduction but that is typically for a 26" rear wheel AND most people gear UP anyways (smaller rear sprocket)....

Of course you'd need to gear to get your engine into its power band....which varies from engine to engine...

Sounds like experimentation is in order ;-)

Hope this helps.

Andrew