Tire Mold Folds: What They Are, Why They Happen, and When to Be Concerned
Note: This article is intended for general tire education. Visual appearance alone may not always be sufficient to determine the condition of a tire. Any questionable tire condition should be evaluated by a qualified tire professional.
A mold fold is a visible surface irregularity that can sometimes appear on a tire as a result of the molding and curing process.
It may look like a small wrinkle, fold, ridge, flap or uneven area in the rubber. In many cases, these marks are cosmetic and do not affect the tire’s structural integrity or performance.
Because mold folds can vary in appearance, however, it is important to understand what causes them and how to distinguish a harmless surface condition from something that may require further inspection.
How Mold Folds Can Occur
During tire production, an uncured tire is placed into a mold where heat and pressure are used to cure the rubber and form the final tread pattern, sidewall design and other exterior features.
As the tire expands into the mold, the rubber must flow evenly across a complex surface containing tread blocks, lettering, mold sections, vents and other details.
Occasionally, a small amount of surface rubber may:
- Fold over itself
- Become slightly displaced
- Collect near a mold joint
- Form a small flap or raised ridge
- Cure with a minor wrinkle or uneven surface
The result can be what is commonly described as a mold fold.
A shallow mold fold that involves only the tire’s outer rubber surface is generally a cosmetic manufacturing characteristic rather than a structural defect.
What Does a Mold Fold Look Like?
Mold folds can have several different appearances.
They may look like:
- A thin flap of rubber
- A small raised wrinkle
- A folded-looking section of surface rubber
- An uneven ridge
- A shallow crease
- A small area of excess rubber near a mold line
They are usually localized and affect only the outer rubber surface.
Depending on their location, some minor molding marks may become less noticeable as the tire is used.
Mold Folds vs. Mold Flash
Mold folds are sometimes confused with mold flash.
Mold flash occurs when a small amount of rubber is forced into the joint between sections of the tire mold during curing.
This can leave behind a thin raised line or very small flap of excess rubber.
Both mold flash and shallow mold folds are generally cosmetic when they involve only the outer rubber surface.
Mold Folds vs. Vent Spews
The small rubber hairs or nubs commonly seen on new tires are another normal result of the molding process.
These are known as vent spews.
Tire molds contain small vents that allow trapped air to escape during curing. A tiny amount of rubber can enter those vent openings under pressure, creating the familiar rubber hairs seen on many new tires.
Vent spews are not mold folds, but both are examples of visible characteristics that can result from the tire manufacturing process.
When Is a Mold Fold Considered Cosmetic?
A mold fold is generally considered cosmetic when it is:
- Shallow
- Limited to the outer rubber surface
- Not cracked or separating
- Not exposing reinforcing material
- Not associated with a sidewall bulge or bubble
- Not increasing in size during use
A superficial molding irregularity does not necessarily indicate a problem with the tire’s internal construction.
When a Tire Should Be Inspected
Not every unusual-looking area on a tire should automatically be classified as a mold fold.
A tire should be professionally inspected if the area:
- Appears unusually deep
- Is cracked or opening
- Shows signs of separation
- Exposes fabric, cords or other reinforcement material
- Changes in appearance after the tire is placed into service
- Is associated with air loss
- Produces an outward bulge or bubble
These conditions may indicate something other than a cosmetic molding characteristic.
Mold Fold or Sidewall Bulge?
This is one of the most important distinctions to make.
A mold fold typically involves the surface rubber and may appear as a wrinkle, flap, ridge or shallow crease.
A sidewall bulge or bubble, on the other hand, pushes outward from the tire.
An outward bulge can indicate damage to the tire’s internal reinforcing structure and should not be dismissed as a molding mark.
If a tire has a localized outward bulge or bubble, it should be removed from service and inspected by a qualified tire professional.
What About Sidewall Indentations?
Radial tires may also display slight inward vertical indentations in the sidewall.
These are sometimes mistaken for mold folds.
Radial tire construction uses reinforcing cords that overlap during assembly. When the tire is inflated, the overlapping area may stretch slightly less than the surrounding sidewall, producing a visible inward indentation.
A normal radial sidewall indentation is a construction characteristic and is different from both a mold fold and an outward sidewall bulge.
The Bottom Line
Mold folds are generally minor surface irregularities created during the tire molding and curing process.
When a mold fold is shallow and limited to the outer rubber surface, it is typically cosmetic and does not affect the tire’s structural integrity or performance.
However, the term mold fold should not be used to describe every unusual-looking area on a tire.
Deep folds, cracks, separation, exposed reinforcement material, air loss or outward sidewall bulges require further inspection.
When there is any doubt about the condition of a tire, the safest course is to have it examined by a qualified tire professional before continued use.
Disclaimer
This article is provided by Interco Tire Corporation as a general educational resource and courtesy to customers, dealers, and tire owners. It is not intended to replace an in-person inspection or professional evaluation of any tire.
Photos, descriptions, and general information cannot always accurately determine the condition, safety, or serviceability of a tire. Tire damage, manufacturing conditions, impact damage, improper inflation, overloading, age, installation, and other factors may not be visible without a physical inspection.
If there is any question or concern regarding the condition of a tire, Interco strongly recommends that the tire be removed from service until it can be inspected in person by a qualified tire professional.
Do not continue operating a vehicle on a tire that shows signs of a bulge, separation, exposed cord or reinforcement, cracking, air loss, impact damage, or any other condition that may affect tire integrity.
Interco Tire Corporation assumes no responsibility for decisions made solely on the basis of the information or photographs contained in this article. When in doubt, have the tire professionally inspected before further use.