As well as the normal side wall markings like brand name and size, aviation tires feature a number of other curious markings. The red blobs and green spots which appear around the sidewall of the aviation tire are explained in this article.
The Red Blob:
This mark shows the balance mark. The concept of balance for an aviation tire is just the same as the concept of balance for the wheel and tire assemblies on a car. Think of balancing scales and you will be in the right place.
The act of balancing ensures that the weight of the tire is even around the axle. This means that the tire will cause no sensation of shudder or wobble when it is rotating and its wear will be even.
During the balancing operation the tire is placed on special and very accurate scales. A display highlights the light spot to an operator. Balance is achieved by fixing a weight to the inner liner at the light spot of the tire. It is the extra weight, applied in the right place, which brings the aviation tire into acceptable balance.
The tire and the wheel are balanced separately. The heavy spot of the wheel is aligned with the light spot of the tire during assembly which results in a balanced wheel and tire.
The light spot will move during aircraft operation and throughout the lifecycle of the aviation tire.
The Green Spots:
Repeating green spots appear towards the rim area of aviation tires and are called awl (pronounced all) vents. These vents are tiny holes which are made with a tool called an awl. The holes allow air, which might remain inside the aviation casing after the manufacturing process and which might permeate the aviation tire during operation, to escape.
Awl vents are of a defined diameter and are made to a defined depth at defined points around the tire. An amount of green ink is deposited by the tool on the sidewall as the hole is made. This green spot indicates the location of vents around the tire and shows the venting process was completed.
Damage such as bulges, ply separations, and blisters might result if the awl vent procedure is not completed.