[Kathleencary]

Is it true you can't replace only one tire if you should ruin it, but instead must replace all four?

 

[pleiad7]

Depends on the amount of wear... if the difference is more than 1/32 you should replace all four.

 

[adc]

You can measure the circumference..should be no more than 1/4" difference in all tires.

 

[lwerring]

In vehicles with all-wheel-drive systems, including Subarus, Audis and Lamborghinis, the differential and the computer work together to send the right amount of torque to each wheel to minimize slippage and maximize control. If one of the tires is a different size than the others -- because three tires are worn and one is brand new -- the computer will take an incorrect reading and the differential will work too hard. Drive this way long enough and you'll burn out the drivetrain. From How Stuff Works

 

[dave5358]

Is it true you can't replace only one tire if you should ruin it, but instead must replace all four?

Other users have given you the reason why and suggested the permissible limits of difference in tire size.

If you look around your local area, you may find a tire shop or service that can grind some tread off a new tire to make it match the tread on your remaining tires.