anderkart
Moderator
Ander the sprocket is a 70 tooth split sprocket and the lug pattern seems to be roughly 2" apart. Hope that helps
If your current gear ratio is working good on your track with your old rear tires,
you could exsperiment using this calculator: http://www.diygokarts.com/speed-calculator.html to discover what sprocket changes would be needed to give simalar top speed results with your new rear tires, compaired to your old tire hight.
Chances are your axle sprocket is the type commonly used on most all racekarts. They have 6 mounting bolts on a 5-1/4" bolt-circle pattern, like all the sprockets your find listed at this link: http://www.out2win.com/catalog/sprkt_axle.html
PS: If your chain measures 3/8" from pin to pin, you'd need the #35 -pitch sprockets