Varies - but I would say when the driver thinks it's a pain (pig) to drive in traffic. -> unrelated to kws/power <-
driver, clutch, gear box, gear ratio's, steering, suspension/set-up, brakes, tyres
but to provide some general indication due to the subject 100 to 400. (so I spose that's saying I think over 400 )
Depending on the driver, vehicle and the destinations frequently travelled.