What are those knobs on the sides of the seats for??

[Robert1994]

They do in fact pump up the lumbar support in
the lower seat back. They work just like the doctor's.
Open the valve to let air out, close it and squeeze the
bulb to inflate the bladder in seat back.
If it's not working, check to make sure the hose doesn't
have a crack in it.

 

[Nadine UK GTS]

Squeeze the bulb part in the palm of your hand several times to firm up the lumber support in your seat, it just pumps air into a rubber cushion with in the seat. Value must be off to pump it up though, turn the valve clockwise to lock it, anticlockwise to release it / deflate the lumber cushion.

Alternatively, use it as a stress reliever, when stuck in traffic! Or use it to tone the muscles in your forearm, toned arms are useful when applying the parkbrake!

 

[Roland L-Ocala FL]

The rubber bulb hangs down from the seat, and it takes a bit of pumping to inflate the air bag for the lumbar support, but it does work quite well on longer trips to inflate it or deflate it. It changes your back support and makes the trip a bit more comfortable.

 

[phiebert]

On mine, the bulb and the valve are the same piece. The valve is at one end of the bulb and the hose to the bladder is at the other end of the bulb, hanging by your right foot on driver's side.

Never used it though!