It say's "4x4"
nice looking kart/Jeep!!!
I think the axle sprocket from what I can see of it is plenty big or couldn't be increased very much due to ground clearance- the sprocket on the jack shaft could be MUCH smaller to get any torque. I agree with T3beatz about the 7" driven but there's very little room right now. If the jackshaft sprocket was decreased it may allow enough space for the 7" driven assuming that it's not already a 7" now. What size sprocket is on the jackshaft? I think with the size of those tires if they're running on low air pressure you might have a semi-soft ride in the trails- but a continous beating on rough terrain will cause a frame failure.