I have a cut in the sidewall of my passenger side rear tire. I would rather not relive the stupidity as to how this happened. Suffice it to say that I had my head somewhere it should not be when driving.

So on to my question. I know and AWD car is picky about tire sizes being the same. My question is this: How much tire wear on the three good tires is enough to cause issues with this.

Next question: How do i measure tread depth other than with an actual gauge of some sort.

Thanks in advance.