I have 205/70R15 Goodyear Integrity tires on my 64 with knock offs. I also have the Integrity's on my 56 vette and my Buick LeSabre. They are "S" rated tires and like tens of millions of other drivers, have had no problems with driving with "S" rated tires. My life and any passenger's life's are not any more valuable when I'm driving a Corvette then when I'm driving a Buick, in fact, I drive the Buick faster with higher loads( I can carry 4 additional passengers and more junk in the trunk in the Buick) on the interstate for longer periods of time then either of my Vintage Vettes. I purchased my tires from Wal-mart( they will special order any Goodyear tire for you). I checked the speedometer on the 64, with 205/70's against the speedometer on my C5 and at 60 MPH it was within 1 MPH of the C5's. There is plenty of room to run the 215/70's on the KO's and it won't affect the speedo that much. Unless you are planning to be a major law breaker on our public steets and highways, don't worry about having to have "performance" tires.