i have an '04 mazda3 sport GT with 47 000km. i've noticed that the car is a bit unstable at highway speeds (steer wheel shudders), so i took it to the dealer and he said i need new tires. NEW TIRES AT 47K???? he says they wear quickly cuz they're performance grade. it sounds a bit insane to me. any opinions on this or advice would be great.

 

Michael,

If you don't believe your dealer, than test the tires yourself. Most modern street tires have wear marks. If your threads are even with this mark, its time for you to change your tire.
Its for your safety as when it gets that low, your stopping distance extends.

Also, sounds like your wheels/tires are out of balance. If you drive your car extended period like that, tires will form uneven wear and its nearly impossible to balance. That might be the case why they asked you to replace it.

 

Performance tires (even all-season ones) are made of softer compounds for better grip and handling. They will wear much faster than a standard "All-Season" tire.
47k sounds about average, maybe a little better than average, even.

 

The 04 3's back tires have been known to cup alot faster than the front, this is what happend to my car, although I did not have the performace set up. Fortunatly my rear tires were under warenty, once the dealership replace them the shaking stopped.