1) Refer it to your liability insurerer--they should defend and indemnify you.2) If you need to defend the matter yourself (for some reason, an insurer is unable or unwilling to defend you), then you focus on the fact that the tire popping was not your fault--you are only liable to the extent you were at fault for an accident. You should seek documentation showing that you performed maintenance; showing that you used the appropriate tires for the vehicle; if you had the tire recently rotated or replaced, you may need to get the mechanic, etc. to testify that it was done properly and the right tire was on the truck; etc. If you an show that you did nothing wrong and there was no reason to think the tire posed a risk or hazard, you should be able to defend against liability.