The road is smooth but the car feels bumpy

Reasons why the road is smooth but the car feels bumpy:

1. Suspension system malfunction causing a bumpy ride on smooth roads.

Even the smoothest roads have minor imperfections, which the suspension system is designed to absorb or minimise. The springs in the suspension system primarily handle bump absorption, while the hydraulic shock absorbers reduce the number of spring oscillations, significantly improving vehicle stability.

When shock absorbers fail, the springs' oscillations become uncontrolled, causing the car to bounce and creating a bumpy sensation. Common causes include oil leaks leading to loss of pressure, accumulated dirt increasing resistance, or deformed shock absorber rods.

Solution: Visit a garage or dealership to replace the suspension system.

1. Unbalanced tyres causing a bumpy ride on smooth roads.

A tyre consists of a wheel rim and rubber tyre, and due to material and manufacturing variations, their weight distribution is never perfectly even. At high speeds, this imbalance causes noticeable vibrations. Therefore, new tyres require balancing after fitting, typically to within 5g.

However, as tyres wear with use, they gradually lose balance, leading to vibrations during operation.

Solution: Have tyres rebalanced every 40,000 miles. During balancing, remove all old weights and rebalance, especially when fitting new tyres.

1. Incorrect wheel alignment causing a bumpy ride on smooth roads.

Wheel alignment refers to the toe angle, camber angle, caster angle, and kingpin inclination. These angles are precisely set when new, but gradually change with mileage as suspension components flex. When these angles alter, the tyre contact patch and vehicle thrust line may shift, creating a bumpy sensation.

Solution: Toe angle can be adjusted via tie rods or links, while camber and kingpin angles are generally fixed unless aftermarket suspension is fitted. Wheel alignment adjustment may help.

Normally, only toe angle is adjustable via tie rods or links, with camber and kingpin angles being fixed unless aftermarket suspension is installed. Sometimes, minor suspension deformation (as little as 1cm) from accidents - invisible to the eye - can change wheel and kingpin angles by over ten degrees.

1. Abnormal tyre pressure.

Incorrect tyre pressure can also cause a bumpy ride.

Solution: Adjust tyre pressures to manufacturer specifications.