I have a 2 stroke 70 cc with no modifications , 26" tires , and a 36t sprocket and run about 30 to 35 mph. little slow on the takeoff , I have to help pedal a little but on the top end I 'am moving pretty fast for a bicycle! I imagine if you installed a 27t sprocket , just a guesstimate maybe 40 to 45 mph , which should be plenty fast! the real question would be after successfully adapting a 27t , how am I going to stop?