On the sidewall of most new tyres are red and yellow painted dots. These are markers or guides to be aligned with particular points on the wheel. The alignment matters for the balancing of the wheel: If these dots on the tyres are properly aligned with certain points on the wheel, minimal weights will be used for balancing.
When tyres are made, they are almost never perfectly balanced. Most manufacturers will place a yellow dot on the section of the tyre where there is least weight. The technician is then supposed to line up this yellow dot to where the valve stem is located. Where the valve stem is located is the heaviest point of the wheel. By aligning the lightest spot on the tyre with the heaviest point on the wheel, the tyre/wheel balance is as close to optimal as can be. As such, you won’t be using as many lead weights around the wheel to balance out the tyre and wheel. Using fewer weights means you get a more balanced wheel, which then means a quieter, more comfortable ride, and a longer-lasting tyre. All these add up to significant savings for the user.
Tyres are never perfectly round, either, even when new. They have high and low points because of where the belts are joined, and these points can cause vibrations when a tyre is rolling. The red dot indicates the tyre’s high point. Most of the time, a wheel will also have a dot—either a drilled dot or a sticker to indicate its low point. If you have these marks, you should align the red dot with the mark on the wheel. By doing this, you minimize the vibration caused by the high point of the tyre.