I have a 1992 Saab 900 convertible turbo. Is it Ok to have 195/60/R15 tires on the back, and 195/65/R15 tires on the front? I have a chance toget four new Pirelli tires, but they don't match. I assume it's not a big deal, that the 60 to 65 won't make a difference in driving or performance. But thought I'd ask. First-time Saab buyer.