Using different tread patterns means the way the tire is grabbing the road is different. For instance, take Diamaris on the X5. If you mount the tire incorrectly without taking into account tread direction, then mount them there will be excessive noise and worsened handling characteristics. I'm not saying running different tires will lead to absolute death, but you'll make better times 'generally' by running the same tires front and rear. IMO.

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