JT wrote:
I've read a fair bit about the new "adaptive" steering that BMW are fitting to some of their newer cars. This varies the ratio of the steering so that at low speed a small amount of wheel movement will give a large amount of lock for easy maneuvring, whereas at high speed the steering "gears down" to give greater sensitivity. Clearly this variable rate can only be achieved by using some sort of "drive by wire" steering system.
Not true. It's more like (well this is how it was described to me) a variable length lever system. The speed sensing servo adjust the length of the "lever" and so varies the steering ratio. There's a permanent mechanical connection from wheel to wheels as required under EU type approval regulations. A variable ratio servo system failure leaves you with fixed ratio steering rather than no steering at all.
JT wrote:
The practical benefit is that this more or less does away with the need to change grips on the wheel - eg a low speed U turn can be made without moving the hands away from the "quarter to three" position. So if we're all agreed that fixed input yields the best control, then that's a clear benefit of "drive by wire" steering!
And it all scares the hell out of me. I *know* the level of available grip by steering feedback. I find straight ahead in a skid by the steering wheel tug from the castor angle. I know if a front wheel locks up under braking because of the steering tugs. I don't want them to take these vital messages away. Neither do I want synthetic messages.
As far as the BMW variable ratio thing goes, folk are commenting that you never know how much lock to wind on - I'd much rather know, turn and then adjust if necessary - the idea of not knowing with certainty, in advance, what the effect of turning the wheel is... well, er... complete crap.