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Sumitomo Tire Replacement
When should I replace my tires?
According to most states' laws, tires are legally worn out when they have worn
down to 2/32" of remaining tread depth. To help warn drivers that their tires
have reached that point, tires sold in North America are required to have molded
indicators called "wear bars" across their tread pattern from their outside
shoulder to inside shoulder. Wear bars are designed to visually connect the
elements of the tire's tread pattern & warn drivers when their tires no longer
meet minimum tread depth requirements.
However, as a tire wears it is important to realize that while its dry traction
& handling will improve…its ability to perform in rain & snow will diminish.
At 2/32" of remaining tread depth, resistance to hydroplaning in the rain at
highway speeds has been significantly reduced & traction in heavy snow has
been virtually eliminated.
If rain & wet roads are a concern, you should consider replacing your tires
when they reach approximately 4/32" of remaining tread depth. Since water can't
be compressed, you need enough tread depth to allow it to escape through the
tire's grooves. If the water can't escape fast enough your vehicle's tires will
be forced to hydroplane (actually float) on top of the water, losing traction.
If snow covered roads are of concern, you should consider replacing your tires
when they reach approximately 6/32" of remaining tread depth to maintain good
mobility. The reason that you need more tread depth in snow is because your
tires need to compress the snow in their grooves & release it as they roll. If
there isn't enough tread depth, the "bites" of snow your tires can take on each
revolution will be so small that your traction will be reduced. Because tread
depth is an important element for snow traction, winter tires start with deeper
tread depths than standard all-season or summer tires. Some winter tires even
have a series of wear bars molded in their tread pattern indicating
approximately 6/32" remaining tread depth.
What is the right size for my vehicle?
A tire's first requirement is that it must be able to carry the weight of your
vehicle. No matter how good a tire you select, if its capabilities are
"overworked" just carrying the load, it will have little reserve capacity to
help your vehicle respond to quick emergency. So when you are in the selection
process, make certain that your new tire's size is designed to carry the weight
of your vehicle! Don't undersize.
The other size consideration is overall tire diameter. Since many of the
functions of today's vehicles are highly computerized, maintaining accurate
speed data going into the computer assures accurate instructions coming out. And
an important part of the speed equation is your tire's overall tire diameter.
For cars & vans, staying within a ±2% diameter change is desirable.
Some plus sizing on pick-ups & sport utility vehicles (SUVs) has traditionally
utilized sizing outside of this ±2% diameter allowance. The critical factors of
concern when changing from the Original Equipment size are: 1. to ensure the
tires carry the load (& potential load) for the vehicle; 2. to ensure the
vehicle stability has not been compromised; 3. the acceleration & braking have
not been compromised by the change; & 4. there is no interference of the tires
with the body, suspension, or chassis of the vehicle.
Most tire dimensions can be calculated. See the section on
