75's on ice

-Joe · 7th December 2010, 00:17

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.

Dragrad · 7th December 2010, 00:24

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

James.uk · 7th December 2010, 00:35

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

Now my Citroen ZX deff does have it! and it is very noticeable even on gentle corners. ..

...

-Joe · 7th December 2010, 01:01

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.

James.uk · 7th December 2010, 01:11

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?

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..

...

-Joe · 7th December 2010, 01:23

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.

peelaaa · 8th December 2010, 18:48

Quote:

Originally Posted by -Joe

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.

My cdti tourer does exactly the same, it feels as if the back is about to lose traction then gains traction.

Villa Villan · 8th December 2010, 23:13

http://www.autozine.org/Graveyard/html/Rover/75.html

Note the updates.

Cheers
Tony

-Joe · 11th December 2010, 01:04

The passive rear steer function is controlled by the "give" in the rubber bushes used to connect the wishbones. It will allow a small forward and back motion of the rear wheels.

In the Spitfire this maybe 1/2 centimeter at maximum. In the 75 it might be 1cm or so I guess.

With modern small cars they use trailing arms mounted solidly to the wheels center axle but with a rubbery mount to the body well forward of the center of the wheel. Which I feel is a bit uncivilised and takes getting used to but it does make these hot hatches handle really well.

The pivot point on 75 is closer to the center of the wheels so that the small rear steer characteristic is harder to detect.

The outward push is to do with the wishbones design for up and down suspension movement.

I guess the garage guy just doesnt understand suspension geometry in the same way as a car designer. If the rear wheels can independantly move back and forward even a little bit, that will help steer the car.

7th December 2010, 00:17	#1
-Joe Avid contributor Rover 75 Classic SE 1.8T Join Date: Dec 2008 Location: wink Posts: 135 Thanks: 0 Thanked 20 Times in 15 Posts	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.

7th December 2010, 00:24	#2
Dragrad This is my second home *None DROWNED** Join Date: Aug 2007 Location: Cardigan Posts: 33,339 Thanks: 1,257 Thanked 1,664 Times in 1,081 Posts	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 __________________ Andrew Ich Dien Problem solving is... lateral thinking SEARCH FIRST ...ASK LATER...

7th December 2010, 01:01	#4
-Joe Avid contributor Rover 75 Classic SE 1.8T Join Date: Dec 2008 Location: wink Posts: 135 Thanks: 0 Thanked 20 Times in 15 Posts	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.

7th December 2010, 01:11	#5
James.uk Passed Away 2002 Pale Blue. Rover 75 CDTi Connoisseur auto. 170K miles Join Date: Dec 2008 Location: Near the M67. Posts: 14,509 Thanks: 199 Thanked 585 Times in 397 Posts	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? 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.. ... Last edited by James.uk; 7th December 2010 at 01:47..

7th December 2010, 01:23	#6
-Joe Avid contributor Rover 75 Classic SE 1.8T Join Date: Dec 2008 Location: wink Posts: 135 Thanks: 0 Thanked 20 Times in 15 Posts	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. Last edited by -Joe; 7th December 2010 at 01:29..

7th December 2010, 00:35	#3
James.uk Passed Away 2002 Pale Blue. Rover 75 CDTi Connoisseur auto. 170K miles Join Date: Dec 2008 Location: Near the M67. Posts: 14,509 Thanks: 199 Thanked 585 Times in 397 Posts	Does the 75 have passive rear wheel steering? I can't say I have noticed any such effect on my car? Now my Citroen ZX deff does have it! and it is very noticeable even on gentle corners. .. ...

8th December 2010, 23:13	#8
Villa Villan I really should get out more....... ZT-T 160 1.8T Join Date: Jan 2008 Location: West Sussex Posts: 2,664 Thanks: 46 Thanked 64 Times in 42 Posts	http://www.autozine.org/Graveyard/html/Rover/75.html Note the updates. Cheers Tony __________________ [SIGPIC][/SIGPIC] Last edited by Villa Villan; 8th December 2010 at 23:18..

11th December 2010, 01:04	#9
-Joe Avid contributor Rover 75 Classic SE 1.8T Join Date: Dec 2008 Location: wink Posts: 135 Thanks: 0 Thanked 20 Times in 15 Posts	rear suspension The passive rear steer function is controlled by the "give" in the rubber bushes used to connect the wishbones. It will allow a small forward and back motion of the rear wheels. In the Spitfire this maybe 1/2 centimeter at maximum. In the 75 it might be 1cm or so I guess. With modern small cars they use trailing arms mounted solidly to the wheels center axle but with a rubbery mount to the body well forward of the center of the wheel. Which I feel is a bit uncivilised and takes getting used to but it does make these hot hatches handle really well. The pivot point on 75 is closer to the center of the wheels so that the small rear steer characteristic is harder to detect. The outward push is to do with the wishbones design for up and down suspension movement. I guess the garage guy just doesnt understand suspension geometry in the same way as a car designer. If the rear wheels can independantly move back and forward even a little bit, that will help steer the car. Last edited by -Joe; 11th December 2010 at 01:06..