Run Xi with different size tires on front? on 2004 BMW 325xi

Would you harm a 2004 325xi if one tire is 205/55/16 and the other tire is 225/40R/18? Tire circumfrence is only a difference of .66 inches? I am worried about the x drive and I need to drive the car in an emergency for 400 miles.

Asked by for the 2004 BMW 325xi
Your 2004 325xi has front and rear open differentials. What this means for you is yes, you can drive it for a short time in this condition. BMW anti-lock brakes and traction control electronics can be very sensitive. All wheels and tires should be the same size as well as the same brand on each axle. Two different manufacturers may sell the same size tire but the circumference may be off enough to set a fault in the vehicle.
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The general rule of thumb with all wheel drive is the tires need to be the same. If the different size is on the rear, and it has a limited slip, that could be bad for the limited slip. Maybe a call to the dealer service department could help you? I don't blame you for being apprehensive because I would be too.
If you need a car right away, you might consider renting some economy or mid-size car. When my car was at the body shop, the rental was about $20-25/day (on the insurance's dime).
yea it would big time. dont do it