Have just purchased a 2015 RX350. Because we wanted the Navigation system, we were told we had to get the 19 inch tires. Asked if we could get the 18 inches put on and told no....Since driving we have noticed a rougher ride. Went back to the dealer and asked if we could possibly do a switch to the 18 inch, since we are unhappy with the ride....Dealer has not been very co-operative... Anyone else notice the difference in the ride between the 19 and 18 inch....