no. I did this to my cat you go bigger on one and smaller on the other. this keeps the number of teeth the same and you can keep the chain the same. when I bought my sled the guy befor me changed one gear only and it chewed up the chain. I when to buy a used gear the proper size but he didn't have one but he had the match for the other gear. he said I would lose about 5 MPH off the top end but gain bottom end. He was right and I love it, hugh difference in bottom end snap. Now I dont remember what I did but I think you make the small gear smaller and the big gear bigger. but better double check that.