4G 100 tooth to 80 tooth. Speed change??

Velodrome

Velodrome

Well-Known Member
So I just finished a build with a 49cc HS and 4G with a 100 tooth. Its converted to belt final drive. The thing could climb a tree with even my fat but on it. :) but top speed is only about 15 mph with the 2.5 in output pulley and whizzer scheve. ( sp?) I have limited room to change the output pulley but think I can squeeze a 3" in there. I have ordered an 80 tooth pulley from Bicycle-engines.com and am wondering if my thinking is correct. 20% less teeth should result in a 20% gain in top speed correct? That; if the final drive ratio remains unchanged? PS: Heres the build. http://motorbicycling.com/showthread.php?t=47095&page=6
 
well hmmm um well ok....I think you are correct on the 80t but wouldn't you want smaller than 2 1/2 on the gearbox?? or not because you are so large on the rear (the sheave..)
 
I've never been good at ratios and stuff. I guess my real question is. ? Is the ratio chainge linear? Being its an 20% change in the primary section; all other variables unchanged ( top engine RPM, final gearing and tire circumfrence) does a 20% change in the primary reduction give more, less or the same 20% change in top speed??? IF (if ) the ratio is linear my 15 MPH top speed raised by a 20% change in the primeary would be ( 15X1.2=18 ) only a 3 MPH + delta. Not much gain. Somboty check my thinking and math. cuz I anint great at this stuff.
 
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