Okay, on the front of my car, I have 2 tires of the same brand (Cyclone Touring A/S 98s) with even wear and good tread right now (approx 8/32). Now in the back I have one National XT 4000 97s and the other one is Multi-mile Grand Tour Tr 98t, with similar, but not exact, tread patterns. At one point I had 2 National tires on the back but one if them developed a leak. I was looking around at junkyards and I found a good tire on a aluminum rim for $40. Those two back tires will not be rotated (but I will always have matching ones in front). I put this tire on myself, so currently no mechanic had the chance to tell me anything about this. I have been driving around for weeks like this and I don't notice anything. How will those two tires wear out? Is it not safe to mix and match speed ratings (I don't drive much over 70mph anyway) as well as tread patterns? I have these on a 2004 Impala base.