A flat spot is a slightly flattened section of a tyre where it has rested under the car's weight, and it causes a vibration when you first drive off. After a car has stood for a while, this is common and usually temporary, easing as the tyres warm and regain their round shape. Permanent flat spots from long storage or a deflated tyre, though, need replacement.
What causes flat spots
When a car sits in one position, the weight presses the tyres against the ground at a single point. Over days or weeks, especially in cold weather or with low pressure, the tyre can take a temporary set there. The result is a thump or vibration as you pull away, fading as the tyres flex back into shape on the move. The longer and colder the stand, the more pronounced it is.
Temporary vs permanent
Most flat spots are temporary: a few minutes of driving warms the tyres and the vibration disappears. Permanent flat spots form when a car stands for many months, when tyres are badly under-inflated, or when a tyre has been driven on while flat, see driving on a flat. If the vibration doesn't clear after a good drive, the damage is likely permanent.
How to prevent them
Prevention is simple. Keep tyres at the correct pressure (or slightly higher for long storage), and move the car occasionally so it doesn't rest on the same spot for months. For seasonal or stored vehicles, the same care that protects against ageing applies, and it's worth a pre-trip check, especially on a caravan or trailer that stands a lot.
Flat spots from hard braking
There's a second kind of flat spot: one worn into the tread by an emergency stop that locks a wheel, scrubbing rubber off in one place. Modern ABS makes this rare, but it can happen. Unlike a standing flat spot, this one is physical wear and won't recover, so the tyre usually needs replacing if it causes vibration.
When to replace
If a flat spot won't drive out, or the tyre is visibly worn in one spot, replace it. We can inspect and replace flat-spotted tyres at your home or work across the UK. Book a check.
