I was running 2.25 cruisers and went down to 26 X 1.75- big difference! In rolling resistence and weight and VIBRATION- Only $10 tire. In fact of all the things I did, that made the biggest difference in vibration. Then, I even put a 27 X 1 1/4 wheel and tire on the front with a road brake. Even better roll.
Heres some tires on ebay- 1.5 inch, very smooth tread Not a bad deal.
Bicycle 26 x 1.5 Slick Bike 2 TIRE 2TUBE/RIMSTRIP+VIDEO - eBay (item 270448303085 end time Dec-25-09 06:56:01 PST)