New tyres and a pull that alignment cannot explain
A 2023 hatchback with 9,000 km has four new tyres of the correct size and specification fitted. The owner says the car has pulled right from the day of fitting and the steering wheel sits about 4° off-centre. Alignment has been done twice at another shop: total toe and individual toe within specification, camber left −0.5° and right −0.4°, caster left +3.1° and right +3.0°, thrust angle 0.02°, all inside the manufacturer's tolerance. Cold tyre pressures are 33 psi on all four. After a 5 km drive the front brake temperatures are 55 °C left and 57 °C right, so no caliper is dragging. The tyres are asymmetric, not directional, so a cross-swap is permitted. You swap the two front wheels left to right and the pull reverses to the left, with the same steering-wheel offset.
1. Work through the evidence and explain the cause of the pull.
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The alignment readings are consistent side to side and the thrust angle is effectively zero, so geometry is not generating a lateral force. Brake temperatures within 2 °C rule out a dragging caliper, and equal cold pressures rule out a pressure split. The decisive test is the cross-swap: a pull that changes direction when the front wheels are exchanged is a tyre-generated force, not an alignment fault. The usual mechanism is conicity - the tyre is effectively a truncated cone and rolls along a curve, pushing the car to one side - with ply steer, belt offset or uneven stiffness as related causes. The car has covered only 9,000 km, so worn suspension bushes or a bent component are unlikely, though a quick check of ball joints and control arm bushes is cheap insurance. The steering-wheel offset of 4° is separate: toe was almost certainly set with the wheel held off-centre, which is a workmanship issue and does not by itself cause a pull.
2. What is your repair plan, and what would you refuse to do?
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First document the swap test, then identify which tyre is responsible. Swap the two front tyres on their rims, rotate each tyre 180° on the wheel and refit, because match-mounting often cancels a conicity high spot; if a road-force balancer is available, use it to measure radial force variation and confirm the offender objectively. Refit and road test on a known flat, straight section with the steering centred, not on a cambered road. If the pull persists with the same tyre in the same position, that tyre is defective and should be replaced under warranty, not compensated for elsewhere. Refuse to disguise the symptom by loading camber or caster asymmetrically, and refuse to release the car with the steering wheel off-centre. After the tyre is resolved, reset toe with the wheel held straight on a level pad and recheck the alignment printout.
3. What records would you keep, and how would you explain the outcome to the customer?
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Keep the alignment printout from before and after, the tyre serial numbers and DOT date codes, the swap-test result in writing, brake temperature readings, radial force or match-mounting data if measured, and the final road-test note. Photograph the steering-wheel position before correction. Explain in plain terms that the tyres were fitted correctly in size and pressure and the suspension geometry is sound, but one tyre rolls as if it were slightly conical, which pushes the car sideways; the swap test proves it because the pull followed the tyre. Note that this is a manufacturing variation, that it is not caused by the customer's driving, and that it is covered by the tyre warranty. Explain also that the steering-wheel offset was a separate setting error and has been corrected, and ask the customer to return after 500 km so the toe and the wheel position can be rechecked.