How do you measure tread depth?

Answer 1

The Liberty Mutual Solutions site has a really helpful article, with step-by-step instructions, on car maintenance. You can find the full article in the related links below.

Here's how to check a tire tread, which is also in this article:

1. Examine your tire treads at least monthly.
2. First, look for bubbles, cracks, worn spots and splits.
3. Then, check your tread wear either by examining the tire tread wear indicators or by inserting a penny upside down into the grooves on each tire.
4. If you see the top of Lincoln's head, it's time for new tires.

Although these instructions apply to almost every make and model of a car, we your should still read your owner's manual for your car's specific maintenance requirements. And if something doesn't seem right, it never hurts to seek a second-or even third-opinion!
Inspect them very carefully all around the perimeter and across the tread. Tread should be even all the way across. Worn tread on one side means a mechanical problem in the main ball joint or suspension. Tread can go down to about 1/8 inch in dry weather, however that may be too thin for safety in rainy weather.

Tires have wear bars that go across the tread, if the tread is down to the bars, the tires need replacing. The old way is to use a penny and if the head of lincoln is covered the tires need replacing.
Insert a penny upside down into the groove. If some of Lincoln's head is buried,

you have roughly 3/32s of an inch of remaining tread which is legal in most states.

However, a tire with that much wear isn't safe in the rain, where you need deep channels to carry away water to avoid hydroplaning.

New tires generally start out at a tread depth of 10 to 11/32s of an inch.