I'm a little confused. How did you know how fast you were going?
The taller tires effectively change the ratio, but unless you've adjusted the speedometer for that change you are really going quite a bit faster than the indicated speed (provided the speedometer was right before).
The improvement noise wise might be quieter tires instead of the motor going slower. It may be that new tires all around might be all you really need.
What kind of tires did you take off?
