The car is bouncing on a smooth road – could it be the tyres?

Why does the car bounce on a flat road?

The most common sources of vibration are the wheels, tyres or rims; less commonly, the suspension or brakes.
The body of the car shakes when a wheel does not rotate perfectly smoothly or has an incorrect weight distribution. This can be caused by an imbalance, a warped rim, a bulging tyre or debris in the rim. Bouncing can also occur due to worn shock absorbers, warped brake discs and play in the suspension components. Sometimes the culprit is ice or mud trapped inside the rim, or tyre pressure that is too low. After a long period of inactivity, a tyre can become ‘flat-spotted’ and cause a wobbling effect for a few kilometres.

Is it the wheels, the tyres or the rims that are to blame?

Very often, yes, because they directly transmit vibrations to the bodywork and the steering wheel.
Common causes include lost balance weights, a bent rim following a knock from a pothole, a worn or ‘bulging’ tyre, and a dirty hub. TPMS sensors and inserts, if damaged or fitted incorrectly, can also cause a balance issue. The problems become more pronounced at certain speeds. Vibrations from the front wheels are more often felt on the steering wheel. Vibrations from the rear wheels are transmitted to the seat and the floor.

How can you rule out problems with the suspension and shock absorbers?

You need to check that the shock absorbers are not leaking, inspect the condition of the springs and bushings, and carry out a test drive.
Worn shock absorbers cause the wheel to ‘bounce’ over bumps, which is visible as a wobble in the bodywork. Traces of oil on the shock absorber, uneven ‘serrated’ tyre wear and the car rocking when you press down on the mudguard are warning signs. Loose bushings and pins cause knocking noises and pulling to one side when braking. At a garage, you can have the shock absorbers tested on a test bench and the wheel alignment checked. If the components are leak-free, have no play and the car handles confidently, look further into the wheels for the source of the problem.

Can an imbalance cause the bodywork to vibrate?

Yes, this is one of the most common causes of vibrations occurring at a specific speed.
An imbalance means that one part of the wheel is heavier. As the wheel turns, a centrifugal force is generated, causing the car to vibrate. The symptoms usually become more pronounced as speed increases. After changing tyres, hitting a kerb or driving over potholes, the balance often changes. Mud, snow and small stones inside the rim can also have an effect. If it is mainly the steering wheel that is shaking, it is usually the front. If the seat is vibrating, it is often the rear.

How do you check wheel balance and runout in practice?

It is best to use a wheel balancer with proper centring and measure the radial and lateral runout; if necessary, carry out a road test on the wheel.
Practical procedure for the inspection:

• Clean the contact surfaces between the wheel and the hub, and remove any rust and dirt.
• Check the centring rings and cones. Incorrect centring will produce a false result.
• Check the tyre pressure, the condition of the tread and whether there are any bulges in the tyre.
• Balance the wheel dynamically and position the weights in the correct places.
• Check the run-out of the wheel rim and tyre. If it is outside the manufacturer’s tolerance limits, consider having the rim straightened or replacing the tyre.
• Use ‘match mounting’, i.e. rotate the tyre on the rim to minimise the radial force.
• Carry out wheel balancing with a road test. Such a test reveals problems that are not apparent in a standard measurement.
• After fitting, tighten the wheels in the correct order and to the correct torque, and finally take the vehicle for a short test drive.

Which steering system faults produce similar symptoms?

Play in the tie-rod ends, control arm pins, wheel bearings and the steering gearbox.
If there is a knocking noise over bumps or the car ‘floats’ in potholes, this is often down to play in the suspension. Vibrations in the steering wheel when braking usually indicate a problem with the brake discs and their runout. Worn wheel bearings, as well as causing vibrations, produce a constant hum that increases with speed. Wear and tear on the tie-rod end can also occur, which manifests as a grinding noise and intermittent resistance when turning the steering wheel. After repairs, the mechanic usually recommends checking and adjusting the wheel alignment.

When do such symptoms pose a risk on the road?

When the vibrations build up rapidly, the steering wheel jerks out of your hands and the tyre shows visible deformation or a leak.
Tumours on the sidewall of the tyre, cracks in the wire cord and a warped rim following a collision with a pothole are particularly dangerous. If the rim becomes very hot or you can smell burnt rubber, you should stop driving. The TPMS warning light indicating a drop in pressure is another warning sign. After recently removing the wheels, it is always worth checking that they are securely fitted. Driving with a loose wheel carries the risk of losing control of the car.

What can you do straight away if your car starts to shake?

First, it’s a good idea to slow down and pull over to a safe spot, and then check the basics.
Walking briskly along the roadside or in a car park:

• Inspect the tyres. Check for bulges, cracks, foreign objects and localised tread wear.
• Check the tyre pressure when the tyres are cold. Incorrect pressure can increase vibration.
• Remove mud, stones and ice from the inside of the wheel rim.
• Visually check that the bolts are tight and, if in doubt, stop and seek professional assistance.
• In the event of serious damage to a wheel, fit a spare or a temporary spare.

Next, it’s worth having your wheels checked at a garage. This includes dynamic balancing, balancing with a road test, wheel straightening, tyre repair or replacement, and, if necessary, a check of the suspension and wheel alignment. A mobile tyre service is also available to resolve the issue on the spot. In Warsaw, there is a tyre repair workshop serving private motorists and businesses, including delivery vans and vehicles fitted with TPMS.

Whatever the cause, vibrations are a warning sign. A prompt diagnosis helps to preserve your tyres, wheels and suspension, and, above all, restores peace of mind whilst driving. It is worth treating this as an investment in safety and comfort.

Book a wheel alignment or mobile tyre service, to safely eliminate vibrations!