Scuttle shake (sometimes called cowl shake in the US) is the term used for the phenomenon experienced in many convertible or open top

automobile A car or automobile is a motor vehicle with Wheel, wheels. Most definitions of ''cars'' say that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, pe ...

s where, due to lower structural rigidity caused by the lack of a roof, the middle section of the

chassis A chassis (, ; plural ''chassis'' from French châssis ) is the load-bearing framework of an artificial object, which structurally supports the object in its construction and function. An example of a chassis is a vehicle frame, the underpart ...

flexes, causing the bulkhead in front of the passenger compartment to move and vibrate when the vehicle is subject to uneven road surfaces.The Knowledge: Scuttle shake
Times Online Passengers feel it as a noticeable vibration and shudder.

References

{{automotive-part-stub Vehicle technology