Right conditions almost to save energy, primarily engineering a car feature (5,8)
I believe the answer is:
power steering
But I can't explain it at all! Could you help me understand?
(Other definitions for power steering that I've seen before include "It gives strength to a driver's elbow" , "Driver's aid" , "help in driving" , "Grit sweeper on? (anag) -- it makes driving easier" .)