This is a 8 year old thread about sprockets.
More ppl will see and be able to help if you start your own thread.

 

Hi, sorry about posting on an old thread but I found this through a google search and it helped me so I wanted to post a bit more info that may help others.

I bought a used 2007 Gio 50cc for my 3 year old son this summer. I would ride it with him and combined we were about 180lbs, rated for 160lbs. The problem we would run into is the same problem most have. The thing goes 30mph but won't move from a stand still. With both of us on there if we weren't on a hard surface or pointed down hill I would need to push with my feet to get going. The problem was worse when I limited the throttle travel. I have a 2 year old son as well who will use this quad when my older son out grows it so I wanted to gear it down as low as possible using the same chain. I found out later chains are cheap so I shouldn't have worried about that but I only wanted to buy two components to save money.

It had a ratio of 2.85 with a 13t on the front and a 37t on the back. I believe this is the same as lots of 110 and 125s come with. Way to high for a 50cc. I googled and found as small as 9t for the front so then I wanted a 42t for the rear to keep the same chain. Unfortunately no one in N. America had a 9t but they had 10t so I figured good enough I'll go with a 41 in the back, but nope, they are special production = expensive. So I ordered the 9t of of aliexpress, and it came with one snap ring to hold it on since the factory clip wouldn't fit anymore. Then I looked at ordering a JTR801.42 online but my local Honda was within dollars and it came in a day so I did that. I think I had maybe 20-25 CAD into the sprockets. They both fit perfect and the chain was only slightly tighter, maybe backed the bolts off 1/4". This gave me a ratio of 4.67 and about 65% more bottom end torque.

After installing it I am very happy with how it turned out. With the 180lbs on the 50cc quad we can get going from a stop in a somewhat soft stubble field. I left the throttle limit screw where it was before the mod and now the quad will reach top speed/top rpm before the stop. But top speed is maybe 10mph now. If I limit the throttle anymore it makes it harder to start. Also I can stop right before the atv ramps into the box of my truck and the quad has lots of power to make it up them. I searched for hours trying to figure out what ratio would be good so I wanted to post this for others.