Tire Sidewall Bulge Study: 28 km/h Pothole Impact at 35° Can Cause Damage, Not Factory Defects

Tire "Bulges" Aren't Always Factory Faults: Road Impact Angle & Speed Test Results

A new impact study led by TireLink Lab shows that more than one in four sidewall bulges returned under warranty were caused not by material defects but by acute curb or pothole strikes. Using a 315/80R22.5 drive-axle tire on a 6×2 tractor, engineers reproduced the damage at only 28 km/h when the wheel hit a 120 mm pothole edge at a 35° approach angle. Peak sidewall compression reached 4.8 kN, enough to fracture the inner liner and trap air under the outer ply.

Key Findings

• Impact speed ≥ 25 km/h + angle ≥ 30° = 85 % probability of internal ply damage

• Speed < 20 km/h or angle < 20° = zero visible deformation after 50 hits

• Inflation 10 % below placard raises fracture risk 40 %; 10 % above reduces it 25 %

• RFID loggers recorded a 3 ms pressure spike of +0.9 bar during compression, proving instantaneous overload

Commercial Meaning

For fleets, the difference between a warrantable defect and driver-induced trauma is measurable. Installing in-vehicle vertical-accelerometers (±5 g threshold) cut false claims 32 % in a 200-truck Brazilian trial. Likewise, dash-camera footage showing approach angle >30° is now accepted by three major Asian manufacturers as grounds for claim rejection, saving distributors an average US$1.9 million per year.

Bottom Line

A sidewall bulge can look identical whether born on the production line or on a pothole at 28 km/h. Angle and speed data give importers the evidence to separate road trauma from true factory faults—protecting margins and keeping genuine quality issues in focus.