The shimmy that outlasted the pothole
Mara hit a pothole outside Stirling, split a front tyre, and had a replacement fitted at the roadside. The new tyre held pressure, but the steering wheel still shivered at 55 mph. The problem was not a bad tyre. The wheel had lost dynamic balance, and the fitting had only solved half the job.
A tyre can be round, correctly inflated and still out of balance because weight is unevenly distributed around the rim and sidewall. That matters most at speed, where a small imbalance becomes a vibration. The takeaway is simple: after a pothole or a roadside tyre change, a road test and a balance check are part of the repair, not extras.
Why impact shifts more than tread
A pothole strike can move a clip-on weight, disturb the tyre’s seating on the rim, or change the relationship between wheel and hub. None of those faults shows up in a pressure gauge. A balancer spins the wheel and measures the heavy spots, then calculates correction weights for the inner and outer planes. The story’s cause was a weight that had shifted about 20 grams; the symptom was a steering wheel that felt loose at motorway speed.
The result can be misleading if a fitter only balances the new tyre. The opposite wheel may carry an older imbalance, and the vibration can feel like it comes from the new corner. A four-wheel check gives a cleaner diagnosis.
What a spinboss check adds to the story
When the fitter ran a spinboss balance check, the machine separated wheel imbalance from tyre runout and confirmed the rim was true. The correction was a small weight and a re-seat of the bead. The shimmy disappeared on the next road test. That is the practical value of a spin check: it turns a vague complaint into a measurable correction.
The takeaway is to ask for before-and-after balance readings. Numbers make the work visible, and they help a driver decide whether to recheck the wheel after another hard impact.
Questions to ask before a mobile fitting
- Will you spin-balance every wheel you remove, or only the replacement?
- Can you show the before-and-after imbalance weights?
- Will you re-seat the tyre and check rim runout before adding weights?
- Do you road-test at a safe speed where the vibration appeared?
Mara’s case ended with a quiet steering wheel, but the useful lesson was procedural. A roadside tyre repair is not finished when the tyre holds air. It is finished when the wheel spins true, the weights are documented, and the driver knows what to feel for next time.
