Tread-depth test should defer to quarter, not penny

We've always found that our tires get squirrely in the wet before they fail the old penny test for tread depth. The Tire Rack, supplier of black round things and other accessories, are suggesting that the price of your safety has appreciated by 24 cents. For years, the penny test has been a quick way to turn a common item of pocket detritus into a tread-depth gauge. Hold Abe upside down, and if the tread clears the top of his noggin, you've got at least 2/32nds of an inch of tread. When tread gets down that low, however, things start to get hairy. 2/32nds is the minimum depth that warranties on the tires will be honored, but that doesn't make it wise to cruise around on rubber that tired. We were once treated to a nasty little bit of unexpected oversteer when taking an off-camber turn downhill during a rainstorm with tires that barely passed the penny test.
The Tire Rack is encouraging drivers to use a quarter instead of a penny. Using George's melon as a guide in the same way as the penny, the minimum tread is 4/32nds, double the penny test. It could be argued that there's a lot of miles to be had during that 2/32nds delta, but your life, and that of your passengers, is far more valuable than a few miles on a set of tires. In Tire Rack tests, the "quartered" tires had significantly better grip and shorter stopping distances in the wet. The hope is that awareness will increase and lives will be saved. There's no need to wear your tires so low – it's not like they're slicks – and it's one of the cheapest measures you can take to ensure the safety of you and your cargo.

[Source: Tire Rack]

UPDATE: The Tire Rack also offers up this video to show the difference in stopping distances between new tires, tires worn down to a quarter's measurement (4/32"), and tires worn down to a penny's measurement (2/32"). The difference between all three is pretty dramatic, especially the "quartered" and "pennied" that are separated by only 2/32" of tread life.


Tire Rack experts seek change in tread-depth limits

SOUTH BEND, Ind., JULY 23 /PRNewswire/ -- Quarters are safer than
pennies when it comes to checking your tires, according to new tests
conducted by The Tire Rack, the country's largest independent tire tester.
With much of the summer travel season remaining and a change of season
looming, now is especially important for drivers to be aware of their
tires' condition.
(Photo: )
For decades the tire industry has taught drivers to use the so-called
Penny Test as a simple way to tell when tires were worn out. But experts at
The Tire Rack say that popular lesson is outdated, compromises safety, and
should give way to the Quarter Test.
In the old Penny Test, seeing the top of Lincoln's head while holding a
penny upside down in a tire tread groove indicated a tread depth of
2/32-inch (1.6mm) or less, and that the tire needed replacing. Instructions
on how to properly check tire tread depth can be found at
In driving tests conducted by The Tire Rack, a late-model pickup truck
riding on tires that passed the Penny Test -- legal in most states --
averaged 499.5 feet to stop from 70 miles per hour on wet pavement. That's
equal to about 12.5 school busses, or nearly a tenth of a mile.
However, the same vehicle riding on tires that passed Tire Rack's
proposed Quarter Test stopped almost 122 feet (24%) shorter. These tires
had treads measuring 4/32-inch (3.2mm) deep, as measured from the edge of a
quarter to the top of Washington's head. Not only were braking distances
significantly reduced, overall grip noticeably improved. Dramatic footage
comparing Penny- and Quarter-Tested tires is available online at
"The Penny Test was an indirect result of tire warranties," explained
John Rastetter, director of tire information at The Tire Rack. "It is to
that depth (2/32") that most warranties remain valid, encouraging drivers
to drive longer on tires that don't provide enough wet-weather traction."
Tire Rack tests showed that doubling the tread depth at which warranties
are voided will improve safety by cutting braking distances and improving
traction in the wet. "We know these changes won't happen overnight so we're
encouraging drivers to pay more attention to their tires now," he said.
Wet/Snowy roads + Worn tires = A real problem
In 2005 584,000 car crashes occurred in the rain, causing 169,000
injuries and 2,914 fatalities, according to the most current data from the
National Traffic Highway Safety Administration (NHTSA). Another 264,000
crashes occurred in snow and sleet, accounting for another 53,773 injuries
and deaths.
Rastetter and his team feel many of these incidents were likely related
to worn tires since NHTSA data also show some 20 million vehicles have at
least one bald tire. In addition, less than one in three (31%) drivers
doesn't know how to tell if their tires are bald, according to the Rubber
Manufacturers Association, a tire industry trade group. A bald tire is one
with less than 2/32-inch of tread depth.
Tire companies spend millions of dollars developing tread patterns that
channel water away from under a rolling tire. This channeling allows the
tire to stay in contact with road surfaces, especially at highway speeds.
As tires wear, their ability to displace water and grip snow is
diminished, increasing the chance of hydroplaning. Hydroplaning occurs when
tires are forced up off the pavement by water trapped under the tire. The
result is a complete loss of traction that leaves drivers helpless to
control their vehicles. By the time a tire is near the end of its service
life it can displace a tiny fraction of the water, and grip little of the
snow, it could when new.
"Riding on worn or bald tires in rain and snow is like trying to ice
skate in dress shoes," said Rastetter, "you're going to lose control."
About The Tire Rack
Founded in 1979, the family-owned Tire Rack has become America's
largest independent tire tester and consumer direct source for tires,
wheels and performance accessories. A team of more than 80 test drivers
test tires from every major tire manufacturer on a state-of-the-art,
10-acre test facility at the company's headquarters in South Bend, Indiana.
Findings are posted free on the company's website,,
where consumers can thoroughly research a purchase. The Tire Rack also
posts data collected from more than 119,000 consumer surveys representing
more than two- billion miles of real-world tire information; the largest
known cache of such information anywhere.

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