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Tire Dots: What Are They For?
by Larry Carley copyright 2023 AA1Car.com
If you have purchased a new set of tires recently, or bought a new vehicle, you may have noticed some small RED andYELLOW ink dots on the sidewall of the tires. These dots are obviously some kind of marking applied by the tire manufacturer, but what are they for?
The colored dots are there for the purpose of positioning the tires when the tires are mounted on the wheels. These dots are alignment marks that are intended to improve wheel balance, ride smoothness and tire life.
The RED dot on a tire’s sidewall indicates the HIGH POINT on the tire. This is the point of MAXIMUM LATERAL RUNOUT when measured around the outer circumference of the tire.
Tire manufacturers try to make their tires as round as possible. The rounder the tire, the smoother it rolls. But all tires are hand built so there will always be some slight variations in roundness when a tire reaches the end of the assembly and curing process.
There are no official industry standards in the U.S. as to how round a tire should be, but as a rule a new tire should usually have less than 0.030 inches of runout (less is better). Runout that exceeds only .050 inches (the thickness of a dime) is enough to cause a noticeable vibration at highway speeds on many passenger car or small SUV tires. Lower profile performance tires with stiffer sidewalls are more prone to experience this type of vibration than tires with larger aspect ratios and diameters.
A tire that is out-of-round by .030 inches will generate an imbalance of nearly 30 pounds at 50 mph. This is the equivalent of the tire being out-of-balance by about 1.5 ounces. And the faster you go, the worse the tire shakes.
The larger the tire and the taller the sidewalls, the more runout the tire can tolerate before vibration becomes a problem. A relatively large heavy-duty truck tire, for example, may tolerate runout of up to .060 to .080 inches before it causes a noticeable vibration.
So back to the RED dot. By locating and marking the high point on a new tire with a RED ink dot, the tire manufacturer provides an indicator or index mark that tells you where the tire is most out-of-round. The dot does not tell you how much it is out-of-round, but hopefully the out-of-roundness will be no more than .030 inches or whatever standard the tire manufacturer sets for its products based on size and application.
Wheel manufacturers do the same thing when they check the roundness of their wheels except that they find and mark the LOW spot on the rim. With steel wheels, there may be a WHITE dot to indicate the low spot. On aluminum alloy wheels, there may be a small dimple on the rim that indicates the low spot. Or, they might not be any marks depending on the wheel manufacturer. There are no industry requirements for marking wheels so it is hit or miss.
By aligning the RED dot on the tire with the White dot or dimple on the wheel when the tire is mounted on the rim, the total runout of the tire and wheel assembly will be minimized (maybe even eliminated) resulting in a smoother rolling tire/wheel assembly with less vibration and wear. This is called “match mounting” and it is typically used on performance cars and race cars to minimize high speed vibrations. It also makes the balancing process easier because there will be less vibration to compensate with offsetting wheel weights.
For everyday driving applications, match mounting can improve both ride smoothness and tread life for highway driving. The force of the vibrations produced by runout and imbalance increase exponentially with speed. You may not feel a thing driving around town at 30 to 40 mph, but when you’re on the open road going 70 to 80 mph or more with a tire that is out-of-round or imbalanced, it can really shake.
In spite of the benefits of match mounting, few tire stores take the time to match mount tires and wheels. They may only consider match mounting if repeated wheel balances fail to eliminate a high speed vibration problem.
And what if there is no runout mark on a wheel to indicate its low spot? Then you have to use a dial indicator on the wheel to find its low spot. The bare rim (no tire) can be mounted on a spin balancer or on an axle on the vehicle, then rotated slowly 360 degrees while using the tip of the dial indicator to find the low spot. Once the low spot has been found, mark the wheel then match mount the tire on the wheel aligning the red dot on the tire to the low spot on the wheel. Yes, match mounting takes time. But if you want to minimize runout for a smoother ride and reduced tire wear, it is worth the extra effort.
Tire manufacturers say if there is no runout mark on a wheel, you can simply align the RED dot with the valve stem when mounting the tire on the wheel. This may or may not affect overall runout, but it will put the maximum runout of the tire in the same location as the heaviest part of the rim, which is where the valve stem is located. This, in turn, should make it easier to spin balance the tire/wheel assembly by positioning maximum tire run and wheel imbalance in one general area.
The YELLOW dot tells you where the LIGHTEST point is on the tire. The tire manufacturer spins the tire to find the lightest point I terms of overall balance and marks it with the YELLOW dot. The dot does not tell you how much the tire may be out-of-balance, only that there is an imbalance and this is the point where the tire is lightest.
Tire manufacturers who spin their tires and mark the light spot with a YELLOW dot say the YELLOW dot should be aligned with the VALVE STEM when the tire is mounted on the wheel. Why? Because the valve stem is usually the HEAVIEST spot on the wheel due to the added weight of the valve stem and Tire Pressure Monitor Sensor (TPMS) on the end of the valve stem inside the wheel.
A typical TPMS sensor that is used inside a wheel on the end of a valve stem only weighs about 1 to 1.5 ounces. That may not seem like much weight, but it can generate the equivalent force imbalance of about 10 to 15 pounds at highway speeds.
Aligning the lightest spot on the tire with the heaviest spot on the wheel should reduce the overall imbalance of the tire and wheel assembly, allowing the wheel to be balanced with few weights. Fewer wheel weights stuck to the inside of the rim (or on the lip of the rim in the case of a steel wheels) means less chance of losing a wheel weight that would upset balance, and less chance of balance changing significantly as the tire wears from normal use.
From what I have observed, it seems that few if any tire installers are using the RED and YELLOW tire dots when mounting new tires on wheels. I've examined tires on new car lots and tires on vehicles that have just come out of tire stores. In almost every case, the RED and YELLOW dots are randomly located with respect to the valve stem or runout marks on the wheel. Apparently nobody is taking the time to align either the RED or YELLOW tire dots to the wheels. Tire installers are just throwing the tires on the rim, letting the wheel balancer figure it out and getting the job out the door as quickly as possible with the least amount of labor.
So my question is, if the RED and YELLOW dots on new tires are being ignored, why should tire manufacturers take the time and effort to mark their tires?
I think tire manufacturers are doing the right thing in trying to help installers figure out the best way of mounting a tire on a wheel. But if the people who are installing tires are not being trained to use the dots, or are too busy to align the marks when mounting tires, the dots essentially serve no purpose.
If a tire is mounted on a wheel with no attention to the location of the RED or YELLOW dots to the wheel or valve stem, it may create a potential problem for the customer who is having new tires installed on their vehicle.
In most instances, a wheel balancer will cover up for sloppy installation practices as long as the amount of runout or initial imbalance is not too great. But in cases where tire and/or wheel runout and/or initial imbalance is excessive, it may result in a high speed vibration problem even after the tire/wheel has been spun balanced.
An indication that there may be a runout and/or imbalance problem is when a spin balancer indicates a LOT of weight is required to achieve overall balance. That often means there is too much runout in the tire and/or rim, or there is excessive imbalance in the tire and/or wheel, or a wheel is bent.
Match mounting the tire and wheel should reduce the amount of weight required to achieve proper balance. Or using the RED or YELLOW dot to position the tire on the rim may reduce the problem.
Wheel balance is achieved by attaching adhesive stick-on weights to the inside surface of alloy wheels, or mounting clip-on zinc, steel or lead weights on the rim lip of steel wheels. As a rule, it should not take more than about 6 to 8 ounces of correction weights to balance a typical passenger car or small SUV wheel. Larger heavier tires and wheels wheels may require more correction weights.