Begin with the driver’s complaint, not the equipment
A steering wheel that shakes only between 55 and 65 mph usually points to a wheel-and-tyre assembly issue, not a brake fault or worn suspension. On a 2018 Ford Focus, the owner noticed the shimmy after clipping a pothole; below 50 mph the car felt normal, and braking did not change the vibration. That narrow speed band is useful evidence: it suggests imbalance, runout, or a shifted tyre belt rather than a warped disc. The takeaway is to record the exact speed window before anyone lifts the car.
Step 1: Capture the conditions that trigger the vibration
Write down the speed range, whether the shake is felt through the seat or the steering wheel, and whether it changes with load or direction. The Focus driver reported a steering-wheel shake, not a floor-pan shudder, which points toward the front axle. Check tyre pressures cold and inspect each tyre for bulges, cuts, or missing wheel weights. A missing 20g weight on a front wheel can produce a noticeable shimmy at motorway speeds. This step turns a vague complaint into a repeatable test.
Step 2: Use a spinboss check to measure, not guess
The next move is a dynamic balance check. A mobile fitter using a spinboss balancer can spin the wheel assembly and log imbalance, radial runout, and lateral runout in one pass. The machine does not “fix” anything by itself; it gives the operator a map. On the Focus, the first spin showed 35g of imbalance on the front-left wheel and visible lateral runout at the tyre bead. That combination explained both the speed-specific shake and why a simple stick-on weight might not have cured it.
Step 3: Separate wheel, tyre, and hub causes
Before adding weights, the fitter should clean the hub face and re-seat the wheel, because rust or debris can tilt the assembly and create false runout. If the spinboss reading changes after re-seating, the hub interface was the cause. If it stays high, move the tyre 180 degrees on the rim and recheck; a belt shift or stiff sidewall will often reveal itself as a runout pattern that follows the tyre. A bent rim from the pothole is the third possibility, and it usually shows as a concentrated lateral runout at the flange.
Step 4: Rebalance, road-test, and recheck at the original speed
In the Focus case, re-seating the wheel and rebalancing removed 30g of the imbalance, but 5g remained; the tyre was rotated on the rim, and the final spin fell within 5g per side. A road test at 60 mph confirmed the shimmy was gone. The practical lesson: use the spinboss reading to choose the next action, then repeat the same road test. If the shake returns, recheck the report rather than adding weights blindly.