SpeedDog830: What's wrong with 6100 rpm at 85 mph? My engine doesn't seem to vibrate at higher cruising revs, and the rpm is not an issue as the S4 is a 10,000 rpm engine (10,700 is actually the limiter cutoff if you fit the Corsa kit that includes the Corsa cams - mine has ony the pipes / airbox / injection kit whose limiter is factory set at about 10,000).
6100 rpm gives me about 73 hp on tap at 85 mph in top gear, versus the 57 hp I'd have available with stock gearing.
And at 3500 rpm at 60mph with the stock gearing, I'd have only 36 hp versus the 47 I have with my 14/42 gearing, plus if the guy in front of me slows down, I'd need to downshift because an S4 is pretty unhappy below 4000 rpm.
I try to avoid using my bike in heavy traffic because of the obvious high potential for injury in a collision with ANY 4 wheeled vehicle, but if I have to be there, I want the bike to respond RIGHT NOW without downshifting when I see a need to move away from where I am.
By the way, this gearing does not reduce my top speed at all over stock, because the stock gearing is too numerically low to meet noise and emissions requirements.
Oh, and by the way, the gearing chnage described above, from 15/37 to 14/42, is enough to lower the quarter mile time by a full half second, because the stock gearing is WAY out of line for 1/4 mile use.
Jim G