11 tooth will fit, but.... the chain is real close to and rubs on the the counter shaft nut. Not good... Plus the 11 tooth sprocket will not last very long. We tried it for 6 hrs of riding and the teeth were already wearing, plus the heat build up during high speed runs was higher (we could tell by the burned chain lube stuck to the 11 tooth sproket). Rule of thumb from many quad racers I have known is no smaller than a 12 tooth... It will work... but you decide if you like it..

-Brad D-