Originally Posted by Bluepill
It's correct. The dot indicates the light spot in the tire. By matching it with the valve stem (the heavy spot in the wheel) the combination should require less added weight to balance.
This is basically true, with a caveat. It depends on what color the dot is (yellow or red) as to what it dictates (light spot or runout/radial force variation). This article from tire business may help explain it better. This article states that the red dot takes priority, but I have seen TSB's from some manufacturers that don't say the same. Also I have seen white dots in place of yellow ones:
Dots, dots everywhere. There are lots of dots in our lives, whether or not we recognize them. There are techie dots called pixels that make up the images on our computer monitors and television screens. There are those voluptuous dots on that little ``itsy, bitsy, teeny, weenie, yellow polka dot bikini'' that you stared at near the pool or on the beach last weekend.
And there are those paint dots that you see almost every work day on the lower sidewall of new tires. While you may understand the importance of the pixels on your screen and the effect that polka dots on that bikini can have on you, do you know what those dots on new tires mean and how they can impact you?
If you guessed that these paint dots are supposed to be used when mounting tires, you would be right. But these dots can be very confusing since some manufacturers use them while others don't, and some dots are different colors than others. The question you have probably is, ``What do they mean on the tire I am mounting?!'' And that is an excellent question.
A question of balance
If you are staring at paint dots on truck tires, you should know that they were installed to assist you in correcting tire balance and radial runout conditions.
Manufacturers of commercial truck radial tires may apply a variety of colored dots on the lower sidewall for customer or factory purposes. Not all tires have markings and even the paint dots on those tires that do are temporary and can be scuffed off during normal shipping, handling and use. That's why you don't usually see them on used tires.
The dots on new tires that have them are not critical but are intended to guide technicians when positioning the tire on the rim during the mounting process.
Since it is very hard to make a tire that is perfectly balanced, some tire manufacturers apply yellow dots that indicate the tire's light balance point and serve to help you balance the assembly while mounting the tire. The yellow dots should be aligned with the valve stem on both steel and aluminum wheels since this is the wheel's heavy balance point. This will help minimize the amount of weight needed to balance a tire and wheel assembly. So usually, whenever you see a yellow dot, match it up with the valve stem.
This is always true except in cases where a red dot also appears in the lower sidewall. The red dot indicates the high point for both radial runout and radial force variation. As I'm sure you know, not only is it hard for tire manufacturers to make a perfectly balanced tire, it also is very difficult to make a perfectly round tire.
Tires tend to have high spots and low spots. The difference between the high and the low is called radial runout. Radial runout changes the radius of the rotating assembly, causing it to raise and lower the vehicle as it rolls along. That gives the perception that the tire is ``hopping'' or ``bouncing'' down the road and ends up delivering a rough ride to the driver and irregular wear to the tread.
Radial force variation is similar to radial runout and is a result of a heavy or thicker area being manufactured into the tire due to variations in component thickness, placement and overlapping. Radial force variation applies more force against the road at the tire's thicker spot as the tire runs, which causes one sidewall to flex differently than the other. The result is tire/wheel assembly vibration and irregular tread wear.
To avoid or minimize these problems, whenever you see a red spot, match this up with the valve stem-unless you happen to have a steel wheel that has a dimple on the exterior side of the rim area. The dimple indicates the wheels' low spot and is spec'ed by some original equipment manufacturers so that they can match mount tires and wheels installed on new trucks at the factory.
If you see both a red as well as a yellow dot on the tire, the red dot takes priority. An easy way to remember this is the phrase ``Red Rules.'' Ignore the yellow dot and match the red dot to the wheel low point dimple as some vehicle manufacturers do or, if no dimple is marked on the wheel, align the red dot with the valve stem.
Other colors/no colors
When you are installing dual tire assemblies on a vehicle, always ``clock'' the two wheels so that their valve stems are 180 degrees apart. This is done for two reasons.
The biggest one is so you can access the valve stems and take and adjust inflation pressures while the tires are on the vehicle. However, a secondary reason is that it also puts the balance points opposite each other and counteracts any of the remaining imbalance, radial runout or radial force variation.
If you see any blue, green, purple, white, pink or orange dots, just ignore them. They are ``mystery'' dots and are there for factory purposes. Once the tire leaves the manufacturing plant, dots of those colors have no use.
Some manufacturers do not put any dots on their tires.
A tire with no dots does not indicate a lack of tire uniformity or factory inspection. It simply means that those tire companies didn't want to put any dots on their tires. So you are on your own. If you find imbalance to be a problem after mounting the tire, rotate the tire 180 degrees on the rim and then recheck the balance.
Since all the tire companies seem to have their own policies regarding mounting dots and there was no one source to find this information, the Technology and Maintenance Council (TMC) asked each company to advise it of its mounting markings and what they are to be used for. It then produced RP243 Tire and Wheel Match Mounting Markings.