Unequal Rear Suspension Settings?

Kearton · 28th March 2024, 10:06

(ZT-T)
I recently thought that my left-hand rear spring might have broken as the wheel seemed to be sitting closer to the wing than on the other side. The springs aren't that old, but one of them had had to be replaced after only 10,000 miles (a presumed manufacturing flaw), so I thought that the other side might now have gone.

I drove it to my garage cautiously to be checked. I was pleased when they reported that both springs were fine, and in fact in very good condition. The culprit had been low tyre pressures - way lower than I'd expected. (I hadn't used it much since Xmas, so the monthly checks had been missed.)

I asked about the apparent difference in wing clearance between left and right sides, which I didn't think could have been caused by low tyre pressures alone. They said that BMWs - with which they were more familiar - have their rear suspensions set slightly lower on one side to offset the weight of the driver, in order to improve handling. Since MGR used a variation of the BMW rear suspension, the garage thought that they might have done that too.

Has anyone else heard of this and/or know whether that is the case?

SD1too · 28th March 2024, 11:41

I'd check your shock absorbers if I were you.

Simon

bsafly · 28th March 2024, 12:11

Quote:

Originally Posted by SD1too

I'd check your shock absorbers if I were you.

Simon

And the condition of your upper arms!

xsport · 28th March 2024, 13:36

and the spring thickness and lengths. I think the garage are playing silly billies !!

Kearton · 28th March 2024, 22:58

Quote:

Originally Posted by SD1too

I'd check your shock absorbers if I were you.
Simon

Quote:

Originally Posted by bsafly

And the condition of your upper arms!

Quote:

Originally Posted by xsport

and the spring thickness and lengths. I think the garage are playing silly billies !!

Thanks all for the suggestions.

The shock absorbers were replaced about 15-20,000 miles ago, along with the upper suspension arms. The garage said that both these and the springs were in good condition.

Ride height is controlled primarlly by the springs, so i don't think it can be due to the shock absorbers. I didn't ask the garage whether they had checked the spring lengths, so that might be a possibility.

I think my next step will be to recheck the clearances with the car on level ground. My drive has a bit of a slope.

Has anyone heard of those differences being the norm on BMWs?

SD1too · 29th March 2024, 06:33

Quote:

Originally Posted by Kearton

Ride height is controlled primarlly by the springs, so i don't think it can be due to the shock absorbers.

Have you ever fitted shock absorbers yourself Kearton?

Simon

Kearton · 29th March 2024, 07:10

Quote:

Originally Posted by SD1too

Have you ever fitted shock absorbers yourself Kearton?

Simon

Not on a car.
If you need to do, it I think it will be easier on the rear than the front as the springs are housed separately, so there is no need to remove them.

KWIL · 29th March 2024, 08:09

Springs should be replaced in pairs to ensure equal performance. Shocks do not set ride height.

SD1too · 29th March 2024, 09:12

Quote:

Originally Posted by KWIL

Shocks do not set ride height.

I see that you are a professional engineer Ken so can you help me with this please?

Whenever I fit a shock absorber I have to raise the car body very high, beyond spring-determined height, in order to insert them. When the body is subsequently lowered the spring partially compresses but so does the shock absorber. A point of equilibrium appears to be reached. Surely this would depend upon the ability of both the spring and the pressurised shock absorber to compress, wouldn't it?

If I removed my shock absorbers completely, would you say that the car's body height would be identical to that with the spring/shock absorber combination fitted?

I'd be grateful if you could explain where I am going wrong with this.

Simon

dave lincs · 29th March 2024, 12:32

Quote:

Originally Posted by SD1too

I see that you are a professional engineer Ken so can you help me with this please?

Whenever I fit a shock absorber I have to raise the car body very high, beyond spring-determined height, in order to insert them. When the body is subsequently lowered the spring partially compresses but so does the shock absorber. A point of equilibrium appears to be reached. Surely this would depend upon the ability of both the spring and the pressurised shock absorber to compress, wouldn't it?

If I removed my shock absorbers completely, would you say that the car's body height would be identical to that with the spring/shock absorber combination fitted?

I'd be grateful if you could explain where I am going wrong with this.

Simon

I would think the answer is obvious but as the clubs technical advisor why don't you make it Simple Simon and remove your shock absorber and try it then you can let us all know

28th March 2024, 10:06	#1
Kearton Gets stuck in MG ZT-T CDTi Join Date: Jul 2007 Location: Sunny Suffolk Posts: 617 Thanks: 1 Thanked 16 Times in 13 Posts	Unequal Rear Suspension Settings? (ZT-T) I recently thought that my left-hand rear spring might have broken as the wheel seemed to be sitting closer to the wing than on the other side. The springs aren't that old, but one of them had had to be replaced after only 10,000 miles (a presumed manufacturing flaw), so I thought that the other side might now have gone. I drove it to my garage cautiously to be checked. I was pleased when they reported that both springs were fine, and in fact in very good condition. The culprit had been low tyre pressures - way lower than I'd expected. (I hadn't used it much since Xmas, so the monthly checks had been missed.) I asked about the apparent difference in wing clearance between left and right sides, which I didn't think could have been caused by low tyre pressures alone. They said that BMWs - with which they were more familiar - have their rear suspensions set slightly lower on one side to offset the weight of the driver, in order to improve handling. Since MGR used a variation of the BMW rear suspension, the garage thought that they might have done that too. Has anyone else heard of this and/or know whether that is the case?

28th March 2024, 11:41	#2
SD1too Doesn't do things by halves Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model. Join Date: Mar 2007 Location: Former Middlesex Posts: 20,382 Thanks: 1,587 Thanked 3,749 Times in 3,181 Posts	I'd check your shock absorbers if I were you. Simon __________________ "Whatever is rightly done, however humble, is noble." Sir Henry Royce.

28th March 2024, 13:36	#4
xsport Posted a thing or two rover 75 club se Join Date: Apr 2011 Location: Leicester Posts: 1,660 Thanks: 358 Thanked 419 Times in 310 Posts	and the spring thickness and lengths. I think the garage are playing silly billies !!

29th March 2024, 08:09	#8
KWIL Precise Rover 75 Tourer 2.5KV6 Connoisseur SE Join Date: Mar 2013 Location: Fleet Posts: 2,954 Thanks: 630 Thanked 617 Times in 480 Posts	Springs should be replaced in pairs to ensure equal performance. Shocks do not set ride height.