I changed to the Avons AM41 and AM42 as well as an 18T sprocket from newspeedmaster.com.
My impressions is that the Avon tyres make a big difference in handling although I didnt press them since I've only put on 50 miles.
The sprocket is nice at highway speeds but in city driving downshifting is more frequent.
Also the stock sprocket had a rubber ring attachement on both sides. The replacement I bought from newspeedmaster doesnt. I dont know if it matters. Maybe someone can comment on this.
No, the rubber seems to be some engineer's attempt to lessen chain/sprocket noise. It has no real value. Too bad they didn't spend the extra time/effort instead to make the speedometer accurate
Speaking of speedo, I forgot to mention (I m on a roll with depleting my savings on this bike). I bought the handheld Garmin Legend C GPS and checked the speeds. Its off by 10% at any speed. At 70MPH its true 63MPH.