What Are These Red and Yellow Dots On My Tires?

March 19th, 2010

The dots actually serve a very important purpose in ensuring accurate installation. The red and yellow dots help installers find a tire’s high spot, low spot and light point for consistent balancing.

According to Bridgestone, “The difference between the high and the low is called radial runout. Using sophisticated computer analysis, engineers have found that a graph of the force variations looks a bit like a wave, as does a graph of the runout variations.

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 variation.

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.”

A yellow dot indicates the light balance point on the tire. In order to minimize the amount of weight needed to balance a tire and wheel assembly, match the light balance point to the wheels heavy balance point, which is normally located at the valve stem.

In a situation where a tire has both a red and yellow dot, the red dot takes precedence and should be mounted to the wheel low point dimple or valve stem.

To view the full article from Bridgestone, visit http://www.bridgestonetrucktires.com/us_eng/real/magazines/97V1Issue2/Doctor.asp.

What Are These Red and Yellow Dots On My Tires? was written by of TireTeam
Tags: Bridgestone
Posted in: about Tires
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