This is all relative. In most areas the legal limit for tread wear is
2/32". At this depth, if you're driving through standing water or
snow, you're going to have difficulty. In wet weather, you'll need to
If I'm going to be doing driving in snow, I want 5/32" minimum on the
drive wheels. But as we don't get very much snow here, I tend to ride
my tires out and deal with making alternate plans if it snows and
Ultimately, it's up to you. Did they tell you what the measurements
Within my long life, I've sometimes had to gird my loins when
dealing with tire shops. I noted that some of these guys didn't
check tire pressure at all, while others didn't have accurate
So, a while back, I decided to buy my own tread depth gauge.
Well, not so fast: none of the chain stores had any. In my area,
we still have one, and only one, _real_ car parts store. You know
what I mean: the sort of place where they have good products and
the guys behind the counter are seasoned and know their stuff.
They have a substantial business delivering parts to independent
repair shops and have branches in other cities in the region.
They didn't have a depth gauge in the shop, but they did have a
few in their warehouse a few blocks away. The gauge was cheap and
it hangs in my garage. It can be handy for seeing how the tire's
wearing. Using a coin is good for a near-death condition, but I
like having the gauge, which is well-designed and has a few
different scales on it.
Tires have wear indicators molded into the tread. If you can see them, they
are no longer legal and tires should be replaced. If they are not visible,
they are probably safe for normal driving. The wear indicator is a strip of
rubber across the tread that is recessed in the tread and shows when the
tread is worn.
If you drive in snow or carry heavy loads, that should be considered also.
If the tires are the originals at 10 years old, they may be getting brittle
from age. I'm not sure, but the tire makers are saying something like 4
years or so as maximum.
Tire manufacturers want to sell tires. In my opinion-- and I have no
empirical backing to support this, of course-- is that they'll last
much longer than four years in many cases. Some tire industry
knucklehead told me it was the law that tires had to be replaced after
they were five years old. My tires typically never make four years
old (that'd be about 100,000 miles), but if they did, I'd judge their
age-condition on the amount of cracking in the tread and sidewalls. I
think that's a much better indicator than any hard-and-fast time rule.
I buy and have my tires maintained at Sears and a complicating factor is the
tread warranty. Sears will prorate the tires if they wear out before they
reached the stated mileage. In other words if you buy a tire rated at 65k
miles and it wears out at 40k you get money back toward the purchase of a
new tire. The money back part is good, however Sears considers a tire "worn
out" when the wear indicators are flush with the tread, which is at or below
2/32nd" I was in this situation recently where I was feeling concerned
about the minimal tread, but I had to wait longer to get them prorated.
Fortunately the weather is generally dry where I am. otherwise it would have
been a dubious choice to wait.
The wear indicators were put where they are after a lot of research and
testing by tire makers and by safety people in the government. Without
them, people would use tires until bald, like some of us did when teenagers.
If you don't feel confident, just buy new tires.
Tread design channels the water so the tire can make contact with the road.
The amount of water, the road surface, speed, and contaminants on the road,
all affect how well that works. Only you can put a price on peace of mind.
Safe for what?
For dry pavement, tires are safe until bald as long as no cords are
For lightly wet pavement, 2/32" is plenty.
For 1" of standing water, 1/2" of tread isn't enough.
There is no absolute standard for "safety."
I run my tires down to the wear bars and even a little beyond if I don't
have an inspection coming up. I rotate and maintain my own tires
(weekly or so pressure and tread checks) so I am aware at all times of
the status of my tires. I adjust my driving accordingly. If it is
pouring rain, I take a difference vehicle that has more tread on the
tires. If dry, I drive the worn tire vehicle. If I get caught in the
rain, I either wait it out or drive much more slowly being conscious of
the risk of hydroplaning.
I also run tire pressures at the upper limit for the tire as this also
reduces hyrdoplaning. While there is no formula for cars to predict
hydroplane speed, it IS a function of tire pressure and more pressure is
better as the NASA formula shows. However, this is for aircraft tires
which are more alike than are car tires and runways are a more
consistent surface than are roads so don't take the speed from this
formula as being applicable to cars. However the RELATIONSHIP between
tire pressure and onset of hydroplaning is applicable.
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