Is300 - rear end unstable in higher speed bends

[Iceboy]

Hi All,

I'm going through my car to make it mechanically sound and although I'm still new to her, I feel the back end is not right.

On fast motorway slip roads, the ones that curve to the left or right, the car feels very unstable at the back if there are any bumps in the road surface.

I have also notice when carrying passengers in the back on the motorway, over smooth tarmac at 70mph, when the motorway carriageway dips up and down, the car again feels a little unsettled at the back.

The car has done 124k, has a full history and the previous owner has fitted Eibach lowering springs, which makes the ride height perfect. In fact the suspension feels excellent at everything except the high-speed undulations in the road surface.

Is it time to change the shocks?

IceBoy

[NemesisUK]

If they weren't changed when the lowering springs were fitted then, yes and try and get shocks with a shorter stroke to go with the springs.

Also check all the suspension and sub-frame bushes for deterioration. 

[steve2006]

Agreed, shocks in the first instance...how you checked them for leaks visually and done the bounce test?

Also check ARB bushes for wear and diff mountings.

[Iceboy]

Thanks all,

Done the bounce check and it moves up and down a couple of times before it settles. So I've order new KYB shocks.

IceBoy

[lexus22]

Check the tyres! Are they the same make, groove pattern?

[Chrisgixer1]

On 6/14/2021 at 2:32 PM, Iceboy said:

Hi All,

I'm going through my car to make it mechanically sound and although I'm still new to her, I feel the back end is not right.

On fast motorway slip roads, the ones that curve to the left or right, the car feels very unstable at the back if there are any bumps in the road surface.

I have also notice when carrying passengers in the back on the motorway, over smooth tarmac at 70mph, when the motorway carriageway dips up and down, the car again feels a little unsettled at the back.

The car has done 124k, has a full history and the previous owner has fitted Eibach lowering springs, which makes the ride height perfect. In fact the suspension feels excellent at everything except the high-speed undulations in the road surface.

Is it time to change the shocks?

IceBoy

I have the sportcross and I’d probably describe the rear the same way. It’s like there is lateral as well as vertical movement for me? The rear does not remain still but combined with vertical movement and lateral movement the end result is diagonal 45 degree travel in response to wumps and large bumps (not small rattle bumps) 

in relation to my other new post I’d also suspect bush play either in rear control arm or subframe bushes but I’m told they are fine structurally and the car has always had the issue so I  have assumed it’s normal, in an abnormal that’s how they are sort of way. 
 

id presume after market poly or some other less comfortable bush option would be the fix but assumption is the mother of all…. well you know the saying 

 

certainly in other cars high speed cornering has LED to various instability issues and poly bushings have fixed it at the expense of some small amount of ride comfort all other times. 
 

so the world of compromise for the masses is possibly the culprit I guess