The calculations are straight forward. If you change from 4.11 to 3.55, your RPM will be reduced by about 16% (at the same MPH).
Someone will post the address/link for an RPM calculator, but let's say your RPM at 60 mph is 3200 with a 4.11 rear; the RPM would be about 2750 with the 3.55 rear. 450 RPM reduction
Or, say your RPM is about 2700 at 55 mph (4.11 rear); at 2700 RPM with a 3.55 rear, you'd go about 64 mph. 10 mph improvement
http://www.csgnetwork.com/multirpmcalc.html(I hope my quick calculations are close to being correct)
Tim
