The Tire Doctor
Those spots before your eyes can mean many different things. Some of those dots can even
help you minimize ride disturbances and irregular wear.
|What Do These Marks Stand For?
In a perfect world, you'd have perfectly
round, perfectly balanced tires, mounted on perfectly round, perfectly balanced wheels,
attached to perfectly straight, perfectly true-running axles.
But in the real world, nothing is perfect. No matter how hard
manufacturers work to eliminate them, there are always variations in tires, wheels, hubs,
bolts, axles, and every other part of a wheel end assembly.
And even if they come out of the factory in near-perfect
condition, wear, damage, improper installation or poor maintenance can negate the
These variations can create what are called radial and lateral
force fluctuations. Those are fancy words, but the result of either one can be ride
disturbance, rapid wear, irregular wear or all three.
Careful tire mounting using these marks can help you minimize these
My Tires Have Red Dots. What Are They For?
When a tire spins, the amount of force
it exerts against the road varies. In severe cases, the result can be a rough ride
and wear problems. One reason the force can vary may be that the tire isn't perfectly
round. It has "high" spots and "low" spots. (There are also lots of
other reasons, which we'll explore in future issues of Real Answers.)
The difference between the high and the low is called radial
runout. Using sophisticated computer analysis, Bridgestone engineers have found that a
graph of the force variations looks a bit like a wave, as does a graph of the runout
By simplifying the graphs to what is called their "first
harmonic," it's possible to find the place on the tire where, on average, the
force variation is greatest. That's where the first harmonic curve hits its high point.
And, it turns out that the first harmonic high point for the
radial runout coincides pretty well with the first harmonic high point for radial force
Now, wheels, especially steel wheels, tend to have the same kind
of high and low spots as tires. In fact, many steel wheels are marked with a dimple that
indicates their low spot.
So, if you could match the high point on the tire to the low
point on the wheel, these forces would, to some extent at least, cancel each other, and
you'd expect to get a smoother ride and maybe improved wear.
Some original equipment manufacturers are doing this kind of
match mounting when they mount tires and wheels on new trucks. The tire is marked with a
red dot at the high point, and this is matched with the low point dimple on steel wheels.
On steel wheels without a low point dimple, and on aluminum wheels, the red dot is matched
to the valve stem.
For a slight improvement in uniformity on steering tires, with
hub-mount wheels, you can torque wheel nuts with the red dot at the "12 o'clock"
Carefully tighten one nut with a hand wrench before using the air
wrench. Be sure the air wrench does not reposition the wheel.
||What Are The Yellow Dots For?
Just as it's very hard to make a tire or
wheel that's perfectly round, it is also very difficult to make tires and wheels that are
perfectly in balance.
You can help minimize the amount of weight needed to balance a
tire and wheel assembly by mounting the tire so that its light balance point is matched up
with the wheel's heavy balance point.
All new Bridgestone truck and bus radials are factory- marked
with a yellow dot at the light balance point. Generally, the heavy balance point of a
wheel is at the location of the valve stem. This is true regardless of whether the wheel
is steel or aluminum.
For best initial balance, match yellow dots to valve stems.
Which Dot Takes Precedence?
If a Bridgestone tire you're mounting
has both red and yellow dots, the red dot has priority. Match it to the wheel low point
dimple or valve stem. Ignore the yellow dot. Remember, "red rules."
Do I Have To Do Anything
Special On Duals?
On dual assemblies, the best idea is to
"clock" the two wheels so that their valve stems are 180 degrees apart. There
are several advantages to this:
1. It makes air pressure maintenance easier.
2. Match-mounting tires and wheels puts the high points or
balance points opposite each other, which helps counteract remaining imbalance or force
What About Marks And
Dots Of Other Colors?
On Bridgestone radials, only red or
yellow dots are used in match-mounting. Ignore any other colors.
Does Every Tire
Manufacturer Use The Same Marks?
Unfortunately, no. Some
manufacturers do not mark their tires at all, and some use different colors. If you're not
using Bridgestone radials, you'll need to consult your tire supplier for more information.
How Will I Remember All
Call us, at 1-800-847-3272, and ask for
a copy of our step-by-step video, Truck Tire Mounting for Customer Satisfaction, and a
free mounting procedure wall chart for your shop.
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