I believe I have a Michelin HydroEdge 215/60R15 on my RT. Speedometer is now never more than 1 MPH different than my GPS & often reads the same speed. Slightly taller overall, but never a Nanny problem.
I'm with you. I have 4,000 miles on a Firestone Touring Elite 215/60R15 purchased and mounted locally. Speedometer is now spot on with the mile markers and no problems with the Nanny. Still have the stock tires on front of my 2010 RS