Lower gear ratio

[No Limit RC of Ohio]

I'm running a 13 tooth CB and a 52 tooth spear gear and I want to go LOWER for my Savage Puller, does any one make a "say 12 tooth CB and say a 56 tooth spear gear"? I want to go as LOW as possible for wheel speed all I'm doing now is slipping the clutch at 3/4 track with 50 lbs on the sled. Any idea's? I know I may have to mod the engine plate but I still think lowering the gear ratio with help. Thanks
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[Bankrupter]

I know there is 12's 56 IDK... what clutch ?

http://www.rc-tires.com/Parts-Clutc...t_info.html?osCsid=5k5u9ji1g9ngieddbi8f940vm6