Burning in the knees could also result from spinning too low a cadence. If i remember correctly you are riding a SS so this is not as adjustable--the harder you must push to turn the pedal means more pressure on your knees. Higher cadence both puts less pressure on your knees and allows you to use slower muscle fibers (less force per revolution required) creating less muscle fatigue (burn). Read Sheldon Brown's article on cadence as a supplement to seat height for the described knee issues.