75's on ice
 

I have put the Spitfire away for the winter and have been driving my 75 again. The FBH is working beautifully! none of this de-icing nonsence for me! I have noticed that whilst driving over ice patches the 75's rear wheels will push out which feels odd at the controls.

Anyone else experiance this? I'm sure there is nothing wrong with the car. I think it's caused by the passive rear steer Z-axle getting out of shape.

The Spitfire has some element of passive rear steer in the way the rear suspension works but doesn't do this because it's rear wheels can't move outward, only up&down and slightly forward and back.

I've never driven a rear wheel drive Z-axle equipped car so I don't know if phenonemon effects V8's or B*Ws. I just think it may be a disadvantage in icy conditions but an advantage in most other driving conditions.

Have you had the 4 way tracking done recently? It is recommended to do so.....

On the whole I find the car quite good in icy conditions, esp in Snow mode ;)

Does the 75 have passive rear wheel steering? I can't say I have noticed any such effect on my car? :shrug:

Now my Citroen ZX deff does have it! and it is very noticeable even on gentle corners. .. :D
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Advantages of Z axle as I see them
 

Makes motorway lane changing at speed sweeter. You also notice it on roundabout at slow moderate speeds it gives more grip.

When owners jack up the rear of their cars maybe to change a wheel have they not noticed the outward motion of the wheel when the friction of the road surface no longer holds the wheel in. I'm sure mine does that on both sides at the back, I'm guessing they all do.

I'm not questioning the workings of a Z axle (whatever that is) What I am asking is - does the 75 have passive rear wheel steering? Or even this Z axle thingy? :shrug:

My ZX corners 10 times better than my 75 (A) because it's shorter and lighter, and (B) because it does have passive rear wheel steering.. :D
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z-axle
 

Yeah I think it does. It's a sort of complicated double wishbone system on the 75 with lots of rubber links that give movement.

On a Peugoet 306 or Rover 25 the rear steer is very pronouced. They use trailing arms with wobbly mountings to achieve this. My Rover 200 has no rear steer and is very different to R25's that do.

I had a Golf Gti Mk1 and an Austin Meastro (Meastro layout drives like a wide Mk1) and they had regular trailing arms with solid mounts. They drive without the artic truck type bend in the middle sensation you get with modern cars.

hmmm, never noticed this on my 25.... the only thing i noticed was its tendancy to lift off oversteer at times when it really shouldnt let go! in fact, saying that, the 75 seemed to have a tendancy to oversteer once the back had let go or looses grip...

also never noticed the movement on the rear wheel but generally when the car was jacked up it was something to so with the front.

if this is the case, this may explain the (what seems like) excessive play in the handbrake. many people have noticed when the handbraje is applied, there is a slight movement before the handbrake seems to 'bite'. if the car has got passive rear steering, this could be the explaination. just the 'slack' being taken up on the rear end...

I was under my car with my local mechanic this afternoon,and could see no sign of any type of rear wheel steering, passive or otherwise. :shrug:

So Joe.. It would seem your car may have a problem with it's rear suspension.. :o
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I think there is some confusion here about what the BMW Z-axle is and what design constitutes a form of rear wheel steering. The Z-axle doesn't have any steering function. If you compare it with the German Weissach system used by Porsche, you'll see the difference.

For example: http://www.autozine.org/technical_sc...spension21.htm

TC

The z axle is a modified version taken from the 5 series adapted for a front wheel drive car,it's design allows a small degree of rear wheel steer

That's what they say:shrug: