Do you ever notice a vibration or a steering shimmy during the first few kilometres of driving after your car has been parked overnight or longer?
The vibration (or shimmy) is apparent for a while, then goes away. This condition is called flatspotting, it is used to describe the flatspots in the tread that form when the vehicle is parked. Flatspotting can be temporary (the “flat” portion of the tread will “round-out” as the tyre warms up) or (in severe cases) may be permanent.
How does flatspotting occur and how can it be minimised ?
As a tyre rolls along the road, it will go from an unloaded state to a loaded state about 500 times a kilometre (or 8 times a second) when driving at 60km/h. This load/unload cycle causes deflection in the tyre carcass which generates internal friction and heat in the tyre. When the vehicle s parked, the tyre is warm and will gradually cool.
Flatspotting occurs when the portion of the warm tread in contact with the ground (which is flat) “sets” to adopt the shape of the ground. The flatspot that forms during this time is what causes the vibration when the is next driven. As the tyre “warms-up” when it is next driven, the tread deformation (or flatspot) is “ironed-out” and the vibration abates and disappears.
The factors that can affect the “level” of flatspotting can include:
- Low Ambient Temperature
- Heavy Loads
- Low Tyre Inflation
- Length of time that the vehicle is stationary