Alignment Readings After a Pothole Impact
A 2014 SUV with 140,000 km hit a pothole on the left front. The driver reports a pull to the right, the steering wheel is off-centre to the right, and there is a vibration at 90–100 km/h. Both front tyres show feathered outer shoulders; pressures are 34 psi as specified. A four-wheel alignment gives: left front camber –1.7°, right front camber –0.4° (specification –0.5° ±0.5°); left caster +2.3°, right caster +3.8° (specification +3.5° ±0.5°); total front toe +0.50° (specification +0.15° ±0.20°); rear camber and toe are within specification. The left front tyre has a bulge on the inner sidewall and 1.8 mm radial runout; the right front has 0.4 mm. Wheel bearings show no play, and ball joints have been checked with a pry bar. The customer wants a wheel alignment only because it is cheaper.
1. Interpret the alignment readings. Which side and component group is most suspect, and why is an alignment-only repair inappropriate?
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Interpretation: The left front camber is –1.7°, outside the –1.0° to 0.0° specification, while the right front at –0.4° is within range. The left caster is +2.3°, below the +3.0° to +4.0° range, while the right at +3.8° is acceptable. Total toe is +0.50°, outside the +0.35° maximum. The pattern is one-sided: camber has moved more negative and caster has reduced on the left front only.
Most suspect group: The left front lower control arm, strut, knuckle or subframe mounting area. A camber change indicates vertical or lateral displacement, while a caster change indicates fore/aft displacement; both together after a pothole impact strongly suggest a bent lower arm or strut/knuckle assembly. The left front tyre bulge and 1.8 mm runout are additional impact evidence.
Why alignment-only is wrong: Adjusting toe would make the printout look better but would leave abnormal camber and caster, continued pull, uneven tyre wear and a damaged tyre in service. The tyre bulge is a structural safety defect, not an alignment adjustment issue.
2. Outline the inspection, repair and verification sequence, including what you would tell the customer about the tyre.
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Inspection: Raise and support the vehicle safely, then inspect the left front lower control arm, ball joint, strut, knuckle, wheel bearing, subframe and strut tower for bending, cracking or shifted mounts. Compare left and right suspension geometry and mounting points. Check the left front wheel for lateral and radial runout and inspect the tyre inner sidewall.
Repair: Replace the bent suspension component(s) and the left front tyre; a sidewall bulge cannot be repaired. Do not attempt to correct a bent component by adjusting alignment. After repair, set tyre pressures, perform a four-wheel alignment to specification and confirm the steering wheel is centred.
Verification: Road-test at the customer’s reported vibration speed and under braking, confirm no pull and no vibration, and recheck alignment readings. Tell the customer that the tyre is structurally unsafe and that an alignment-only repair would not correct the bent part or make the tyre safe.