When it's raining…a quarter will get you home, a penny might not.

Friday, July 2, 2010 by Luke Pavlick

The "penny test" tread depth check doesn't hold water.

Yes, U.S. coins can be substituted as a tire tread depth gauge to measure the critical, final few 32nds of an inch of remaining tread depth.
tread depth penny



Place a penny into several tread grooves across the tire. If part of Lincoln's head is always covered by the tread, you have more than 2/32" of tread depth remaining – the minimum legal amount of tread required.

tread depth quarter


Place a quarter into several tread grooves across the tire. If part of Washington's head is always covered by the tread, you have more than 4/32" of tread depth remaining.



Tire Rack has tested the effects of tread depth on wet stopping distances. Using a BMW 325i and a Ford F-150 Supercab 4x2 with three sets of tires for each vehicle (Michelin for the BMW and BFGoodrich for the truck): ): a brand-new set, a set shaved to 4/32-inch, and a set shaved to 2/32-inch. The test track was then dampened to simulate moderate rain conditions. After repeated stops from 70 mph were conducted with both vehicles on all three sets of tires, average stopping distances were calculated.

The test showed that for both vehicles, braking distances from 70 mph to a standstill were nearly doubled with the 2/32-inch tire set over the brand-new set -- from 195.2 feet to 378.8 feet in the BMW sedan and from 255.9 feet to 499.5 feet in the Ford truck. With the 4/32-inch set, distances were nearly split between the previous two sets, resulting in a 290.0-foot stop in the BMW and a 377.8-foot stop in the Ford.

When your tires are worn to 2/32-inch of tread depth there's not enough area for water to be evacuated by a tire, which causes an increased stopping length due to hydroplaning. In wet conditions, it's fairly clear that the more tread depth available, the easier it is for a tire to do its job.

Don't let this be you next time it rains!

 My name is Luke Pavlick and I am a Car Guy
and yes, if you ask my wife it is a sickness



Comments on When it's raining…a quarter will get you home, a penny might not.

Leave a comment





Captcha