A seat wedge for a car is not always a good idea if you have a bad back

[olddriver]

I believed that vibrations in my Corolla at motorway speeds were giving me a back ache and hence I bought a 11 deg Coccyx wedge cushion:-

http://www.kozeekomforts.co.uk/department/comfort-and-heat-therapy/coccyx-wedge-cushion.php

At motorway speeds with the wedge cushion in place, the seat back appeared to move up and down considerably with the unevenness in the road surface.  In desperation, I pulled out the cushion from under me, and a huge relief came over me and I felt comfortable, it was unbelievable the difference that it made without the wedge cushion.  Consequently, use caution when using these type of cushions at motorway speeds.

Note: unknowingly at the time, the vibration problems had been resolved prior to that journey by rebalancing all the wheels:-