| Why should I
rotate my tires?If you never rotate your
tires, the fronts will last about 10,000 to 20,000 miles and the rears
will last 50,000 to 80,000 miles. The reason we rotate tires is to even
out the wear and properly done, all the tires will be worn out at the same
time. It's also a great excuse to inspect your brakes on a regular
basis.
When and how should
I rotate my tires?
It is very important
to rotate your tires every 6,000 to 7,500 miles. Three things should occur
during a tire rotation. First, all the tires should be properly inflated.
Second, the tires should be rotated. Third, a physical inspection of the
brakes should be made while the tires are off. It make no sense to pay to
have your brakes checked, then 3 months later pay to have your tires
rotated.
A lot has been written
about the proper way to rotate tires. The biggest portion of the
discussion is whether or not it is OK to change the direction of the
rotation of the tire. If a tire is moved to the other side of the car, the
direction of rotation has been changed. Years ago that was a no-no but now
many tire makers recommend the crisscross way.
Different tire
manufacturers may suggest different ways and if you want to be entirely
correct, check with the maker of your tires.
In my opinion, you may
rotate straight forward and straight back or you can crisscross the fronts
and\or the backs before you rotate. At our shop we rotate our customers
tires a variety of ways depending on the wear pattern on their tires.
If the tire is
scalloped and causing a whine or hum at higher speeds, we will change the
direction of rotation to help even out the wear.
Scalloped tires are
often used as a reason to sell shocks or struts. It is my opinion that the
tire itself is the cause more times than not. The tires we see scalloped
seem to be the same all season brands over and over again. It's been a
month of Sundays since I've seen a highway tread pattern tire
scalloped.
Don't forget this one
important point. Once a tire begins a wear pattern, it will continue with
that pattern until you throw the tire away or it wears out. So if you
install new tires and one of the front tires starts an abnormal pattern
because of an alignment problem, having an alignment done fixes the cause
but not the tire.
Make sure to check
your spare at least once a year.
BALANCING YOUR TIRES
The technical definition of balance is the uniform distribution of mass
about an axis of rotation, where the center of gravity is in the same
location as the center of rotation. A balanced tire is one where mass
of the tire—when mounted on its wheel and the car's axle—is uniformly
distributed around the axle (its center of rotation). Balanced tires
can spell the difference between a positive and negative driving experience.
Drivers of high performance vehicles will be more sensitive to imbalance
problems, but no driver is happy with an annoying vibration. |
| AN OUT OF BALANCE TIRE AND WHEEL ASSEMBLY:
Degrades ride quality and driver comfort.
Shortens the life of tires, bearings, shock absorbers and other
suspension components. Vibration is the most noticeable effect of imbalance.
It is dependent on vehicle speed.
It often first becomes apparent between 40 and 45 mph and increases
in magnitude with greater speeds. |
| SOURCES OF IMBALANCE
Two sources of imbalance occur in tires: heavy or light spots in the tire
and radial or lateral run-out. Imbalance also can be caused by:
Variations within the wheel, such as thickness and welds.
Rotor and axle imbalances. |
Heavy or Light Spot Imbalance
There are two types of imbalance caused by heavy or light spots:
static and dynamic.
Static imbalance: Occurs when there is a heavy or
light spot in the tire so that the tire won't roll evenly and the tire/wheel
assembly undergoes an up-and-down movement.
Dynamic imbalance: Occurs when there is unequal weight
on both sides of the tire/wheel assembly's circumferential centerline. The
tire/wheel assembly has a side-to-side movement. |
Heavy or Light Spot Balancing
Achieved either statically or dynamically, depending on the type of imbalance
that has occurred.
Static balance: Achieved with a bubble balancer but does not correct
for dynamic imbalance.
Dynamic balance: Achieved with a spin balancer where the tire/wheel
assembly is balanced both statically and dynamically. |
Radial or Lateral Run-out Imbalance
This results from poor bead seating on the rim or the placement of components.
Poor bead seating is usually the result of improper mounting or the use of
improperly made wheels. A small degree of this imbalance is acceptable, but
too great a run-out causes vibration and excessive tire wear. |
| Radial Run-out: An "out-of-round" situation where vibrations are
produced as the wheel spindle moves up and down.
Lateral Run-out: A side-to-side or wobbling movement of the tire and
wheel. It is less common than radial run-out. Sensitivity of a vehicle to vibration from radial run-out is four to eight times that of wobble from lateral run-out. |
Run-out Balancing
Depends on whether it is radial or lateral run-out.
Radial run-out balancing: Achieved by rotating the wheel and tire
assembly two stud positions on the hub, or by rotating the tire 180°
on the wheel. If run-out is still over specification, check wheel run-out
and mark the low point. Rotate to match the high point of the assembly
run-out with the wheel low point. If the assembly run-out is still too
high and the wheel is within specification, replace the tire.
Lateral run-out: Achieved by using a run-out gauge to check both the
tire and wheel. Chalk-mark the highest point of run-out on both the wheel
and tire. Replace whichever (wheel, tire, or both) is out of specification. |
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