Not sure if you need new tires yet? A tread depth gauge is the most accurate tool to see the actual measurement, but for an easy pass/fail test all you need is some spare change. Here's a guide for the quarter tire test, and why SimpleTire believes that using a quarter is better than the traditional penny tire test.
How the Quarter Test for Tires Works
Tires need to be replaced when the tread-the part with all the grooves-wears down. A tire's tread is measured in 32nds of an inch, but most of us don't have a tread depth gauge handy (and using a ruler isn't all that practical either). Luckily, if you turn a quarter upside down, the distance from the edge of the quarter to the top of Washington's head is about 4/32". So, all you have to do for a tire quarter test is to put a quarter head-first into the grooves of a tire. If the tire's worn enough that it doesn't cover Washington's head, it's about time to replace it.
Quarter Tire Test versus Penny Tire Test
For a while, the penny was the go-to coin for people wanting to use spare change to know when to change their tires. But the trouble with the penny tire test is that it tells you if your tires are completely worn, meaning you'll see if you're already late in replacing your worn tires.
The penny test for tires and the quarter test for tires both work the same way; you take the coin, stick it into your tire's tread head-first, and if you can see the top of the president's head then you need new tires. A penny is obviously smaller than a quarter though, and so is the distance from the edge of the coin to the top of the head. On a quarter, it's about 4/32nds of an inch but on a penny, it's 2/32nds, which happens to be the minimum legal tread depth in most states.
If you're doing a tread depth penny test, you're basically finding out when your tires are already illegal. And considering how important tires are to your safety out on the road, why would you wait to find out if you're already at risk?
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