Tire Inspection
Tire Bulge Inspection
A bulge on a tire — sidewall, shoulder, or tread face — means internal structural damage has already occurred. The visible bulge is the outer rubber moving away from the structure beneath it. The tire cannot be repaired and should not stay in service.
Bulges are easy to miss on a casual walk-around. Finding them requires deliberately looking, running a hand along the sidewall, and checking the inside of dual assemblies with adequate light.
What a bulge is and what it means
A bulge forms when internal cords, belts, or plies break or separate, and the remaining rubber and air pressure push the outer surface outward at that point. The visible protrusion is the tire's outer surface unsupported by the structure beneath it. That area can fail suddenly when the reduced-structure zone is stressed by a road impact, pressure change, or load shift.
Where to look for bulges
| Location | How to inspect | Cause |
|---|---|---|
| Outer sidewall | Walk around the tire; look from low angle; run a hand along the sidewall | Road impact, curb strike, pothole hit, prior underinflation fatigue |
| Inner sidewall | Use a flashlight to inspect the inner side of every tire, especially inside duals | Same causes — hidden from casual inspection |
| Shoulder area | Check where tread meets sidewall; feel for any step or protrusion | Impact damage, heat separation at tread-to-sidewall zone |
| Tread face | Look for any raised area or irregular surface in the tread; tap to check for hollow sound | Belt separation under the tread — less visible but serious |
When you find a bulge
- Remove the tire from service. A bulge is not a repair candidate.
- Do not simply reduce pressure and observe. The structural damage is already done.
- Note the position and document for maintenance records.
- Inspect the wheel for damage that may have caused or contributed to the bulge — curb strikes can damage both the tire and the rim.
- Check the mate tire in a dual set — a severe impact that caused a bulge may have affected the mate as well.
Bulge vs. bead area swelling
A bulge in the sidewall is structurally significant. Some apparent bulges near the bead area are related to mounting issues rather than structural failure — for example, a tire not fully seated on the bead. If uncertain about what is being seen, the conservative approach is to have the tire inspected by a professional before the next trip. Do not assume any outward bulge is cosmetic.
Step-by-Step Checklist
- Check both sidewalls — outer and inner.
- Use a flashlight on inside duals.
- Run a hand along each sidewall to feel for protrusions.
- Remove any tire with a confirmed bulge before the next dispatch.
FAQ
Can a truck tire with a bulge be repaired?
No. A bulge in the sidewall or shoulder of a truck tire indicates internal structural damage — broken cords or separated plies. This damage cannot be repaired to restore the tire's structural integrity. Industry-standard repair limits (as defined by bodies such as the Tire Industry Association) do not permit repairs in the sidewall area that would address a structural failure. The tire should be removed from service and replaced. Running on a bulging tire risks sudden failure.
What causes a sidewall bulge on a truck tire?
The most common cause is impact damage — striking a curb, pothole, or road debris with enough force to break or separate internal cords at the impact point. The cords may break without tearing the outer rubber, so the tire looks intact from outside until the bulge becomes visible. Prior underinflation fatigue weakens the casing and makes impact bulging more likely. Some bulges develop slowly from casing fatigue over mileage, particularly in applications with frequent tight turns or road hazards.
Can a bulge be on the inside sidewall where I cannot easily see it?
Yes, and this is why inside dual inspection requires deliberate effort and adequate light. Impact damage to the inner sidewall — from road debris striking the inside of a dual assembly, or from the inside tire contacting the outside tire in a severely mismatched dual — may only be visible from inside the assembly. A casual walk-around at highway rest stops will not find an inner sidewall bulge. Use a flashlight and check the inner sidewall at each scheduled inspection.
Source Notes
- Government 49 CFR 393.75 - Tires
- Government TireWise Tire Safety
- Industry U.S. Tire Manufacturers Association Tire Safety
- Site note TruckTireGuide.com editorial notes