Howdy Fellas.WOW nice to see all the interest.
Dr. J
stock gearing on these 49cc' s is 6/68. they also come in other sizes such as 7 tooth ,64 tooth etc.
When i finallystarted getting the gearing close .I coulda kicked myself for missing the obvious.
The problem was i was trying to turn a much larger tire than it was designed for.
Now I am not the sharpest tool in the shop and have no mechanical background of anykind so my formula might sound a little (simplestupid) to some of you fellas.
i realized right away that to turn a tire 4 or 5 times larger , i would need a sprocket 4 or 5 times llarger which meant a sprocket not much smaller than the 26 inch bicycle tire i was mounting it to which is why i had to step it down twice .
after tryiing the hit and miss approach for awhile which consisted of different pulleys, belts to match , trying to work different sprockets into the equation to fine tune the ratio and then 1 day , like a vision bursting across the sky(arlo guthrie line)lol,i realized how simple it was.
Take the circumference of the original tire, the circumference of the new drive tire,calculate the ratio(2.5 to 1, 3 to 1 or whatever it is,and apply that ratio to your pulleys.
i Believe the original tire was 32 inches and the 26 inch bicycle tire was approx 80 inches in circ.
i assumed that if 32 goes into 80 excactly 2.5 times, i should be dead on if i use a 2.5 to 1 ratio if i ran it in conjunction with original gearing.
so if i throw a 5 inch pulley running to a 12 inch pulley which is approx. 2.5 to1 , i should in theory bee getting the same travel distance per engine revolution.
Hope yer following so far?? I'm about as good at explaining things as I am at ratios and Algebra'
T%he reason i mention algebra is because even though a 12inch pulley aoppears to be 2and2/5th's times larger than the 5 inch pulley, the diameters are 15 and 35 respectively which is a 2 and a third to 1 ratio.a 10 inch pulley is 28inches circ.`which would give you just under a 2 to 1 ratio which would gear me a little higher than the pocket bike.
Now heres where your bike is going to go ok or it's gona go like a raped ape because the difference between 2.5 , 2and 2/5th's and 2 and a third will make it or break it
If its geared a touch to low ,you'll be revving to high and running hot which will decrease your power and if its geared a touch too high,it'll start lugging toward the high rpm range and it wont get maximum revs out of it which will cost you speed`
I geared it down about 5% and got an extra 5 mph out of it so the ratio you use is highly dependent on the motor your using,
I am currently using a 5and a half inch pulley running down to a twelve inch with the stock 6 to 68 tooth gears. i used the 5 and a half with a 10 inch sprocket and was ok but this game me a little mire bottom end and didnt cost me neo top speed as i can wind it up a little more .
sorry for rambling and hope this helps more than it confuses.
will gladly try to answer any other questiosns
~Haggard~
OH built a full suspension using basically the same design with same type of motor . got some chrome running boards for free so cut out some full fenders for front and back ,bent and shaped by hand and with a vise. turned out exc. get comments all day long on them. even nicer than the chrome ones on my schwinn cruiser.
`i kept them square cut and flat at the back with an oversized flareout and rounded and arched the fronts. got enough material to make 1 more set which have already been sold for $150 to the same fella that gave me the running boards lol I amaze myself sometimes ??!!!?? lol will post picks if anyone wants to see or try it also they really make the bike as i used the same running boards to make my gas tank supports etc.