Overly bouncy suspension

Overly bouncy suspension

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RB Will

Original Poster:

7,115 posts

207 months

Wednesday 26th May
quotequote all
Hi All

Just after any info. A friend that I do trackdays with has recently "upgraded" his mk5 Astra VXR from standard suspension to a full Gaz Gold setup, as per the link. For use on road and track.
(https://gazcoilovers.com/vauxhall-astra-mk5-vxr-gaz-gold-coilover-suspension-kit-154-p.asp)
Just to clarify the kit was not bought or fitted by the company associated with the website so dont go badmouthing them lol.

Anyway, the new kit has rendered the car pretty unpleasant on the road. I don't know enough about suspension to know quite what is wrong, neither does he and the 2 garages (the supplier, and a local specialist) he has been talking to about it have been giving opposing views.

Ive just been out for a ride with him to experience it myself. It takes in small/ sharp bumps, like potholes, drain covers etc really well, not crashing through them or bouncing off etc. It just can not cope with bigger or more flowing undulations like uneven road or slightly subsided etc and anything from 50mph up is almost enough to launch you out of your seat. It feels like the whole car, possibly more the rear, is just being thrown up in the air.

It doesnt ever come to a hard stop compression wise and there is no obvious damage to bump stops or compression contact on the springs.It is not set to a low ride height. The front has arch clearance and the rear is even higher as he was advised to set up the rear high to give it some rake due to being a beam at the rear.

I think the supplier has told him to stiffen it up but the local specialist is telling him to wind it to its softest setting. Ive just been out in it with it set on 2 of 10 stiffness and behaving as above.

The only car Im familiar with that is not on oem suspension is my Cerbera on Nitrons and it doesnt do anything like this, quite the opposite.
So don't know if this is just how track race suspension is when used on the road or if there is something wrong.

Apparently the rear springs are 425lb (specified by the supplier).
Car weight is 840kg up front and 440kg at the rear.

Scrump

14,688 posts

125 months

Wednesday 26th May
quotequote all
If the damping is on 2 out of 10 then I would set it to 5 and try the car then set it to 8 and try the car.
Play with the settings on what you have and get a feel for what difference this makes before trying anything else.

It does sound like it is already too hard though. If you try the other damping settings and it is just as bad, or worse, then the spring rates would be my next thing to look at.

rustednut

591 posts

14 months

Wednesday 26th May
quotequote all
What was it like on the original setup?

Has he spoken to the supplier for their comments?

Did he compare overall measurements etc before fitting ?

RB Will

Original Poster:

7,115 posts

207 months

Wednesday 26th May
quotequote all
Scrump said:
If the damping is on 2 out of 10 then I would set it to 5 and try the car then set it to 8 and try the car.
Play with the settings on what you have and get a feel for what difference this makes before trying anything else.

It does sound like it is already too hard though. If you try the other damping settings and it is just as bad, or worse, then the spring rates would be my next thing to look at.
I have told him to find a piece of road, drive it a few times, then turn them up to full hardness and see if it makes it better or worse.

rustednut said:
What was it like on the original setup?

Has he spoken to the supplier for their comments?

Did he compare overall measurements etc before fitting ?
Original setup was absolutely fine on the road. The car has been owned by our friends or family for about the last 10 years.

He has spoken with the supplier, they told him to try winding it up a bit, this is where the disagreement is as the local specialist who looks after the car and loads of other track cars round here has told him to put it softest.

what do you mean by comparing measurements? weight distribution? In which case no. He only had the car weighed as the supplier had asked him to give them the weight when he said he was having problems with it.


Its not what I would describe as a fidgety ride its less harsh than that.
My i30N is really stiff in its hardest setting but it deals with bumps completly differently more skipping overthem than amplifying them.

DaveyBoyWonder

1,250 posts

141 months

Wednesday 26th May
quotequote all
Gaz stuff has adjustable damping doesn't it (the custom rear Gaz shocks on my van do anyway) so surely its just a case of dialling the damping in? Anyone on an Astra forum with the same suspension setup who can help? Maybe find someone who preps track cars properly to get them to do it / help?

Kawasicki

9,585 posts

202 months

Wednesday 26th May
quotequote all
Can you see how much gap there is between the jounce bumper/spring aid/bump stop and the top of the dampers?

Have you done a simple bounce test? Sometimes it shows up whether ou have too little or too much damping.

rustednut

591 posts

14 months

Wednesday 26th May
quotequote all
RB Will said:
Scrump said:
If the damping is on 2 out of 10 then I would set it to 5 and try the car then set it to 8 and try the car.
Play with the settings on what you have and get a feel for what difference this makes before trying anything else.

It does sound like it is already too hard though. If you try the other damping settings and it is just as bad, or worse, then the spring rates would be my next thing to look at.
I have told him to find a piece of road, drive it a few times, then turn them up to full hardness and see if it makes it better or worse.

rustednut said:
What was it like on the original setup?

Has he spoken to the supplier for their comments?

Did he compare overall measurements etc before fitting ?
Original setup was absolutely fine on the road. The car has been owned by our friends or family for about the last 10 years.

He has spoken with the supplier, they told him to try winding it up a bit, this is where the disagreement is as the local specialist who looks after the car and loads of other track cars round here has told him to put it softest.

what do you mean by comparing measurements? weight distribution? In which case no. He only had the car weighed as the supplier had asked him to give them the weight when he said he was having problems with it.


Its not what I would describe as a fidgety ride its less harsh than that.
My i30N is really stiff in its hardest setting but it deals with bumps completly differently more skipping overthem than amplifying them.
I would have more faith in the supplier in this instance.

But experiment with the settings and use the same roads to test/compare.

I have a feeling they might not be right for the car though, but you need info to go back with.