If you use high-performance spark plugs in your motorcycle, you should not have to worry about a decrease in gas mileage. In fact, the opposite should be true. Most high-performance spark plugs boast that you will experience more power as well as higher gas mileage. This occurs because the spark plugs actually increase the efficiency at which the fuel in your tank is burned. When this occurs, the recess in the electrode in the center will be charged with fuel. This helps break down the fuel more efficiently and provides you with better gas mileage.