Setting up a correct coilovers height

[detch]

I have an E85 Z4 that’s currently lowered on cheap Racing Line (Chinese) coilovers:
http://bit.ly/432Ja9q

It’s also running on 19" wheels, and the ride quality is really bad—super crashy and harsh over bumps. I suspect the car is lowered too much and riding on the bump stops.

Do you have any advice on:

• How to properly measure ride height?

• What a good target height is for these cars?

• Any tips on setting up coilovers in general?

I’m having trouble finding a mechanic who understands how much to lower, not just how to adjust the height. Any help or references (especially for Z4s) would be massively appreciated!

 

[brillomaster]

Well measuring is straightforward- car on flat, level ground, measure wheel arch to centre of wheel. Someone will tell you what the standard ride height is, I'd go for 20-30mm drop from there.

As for a proper set up, you'd need a racecar set up or wheel alignment place. Whereabouts are you, might get some recommendations...

Also... cheap coilovers and 19s won't help. Do they have any adjustment other than spring perch height?

As a starter for 10 I'd just take the wheels off and go 30mm up all round, might be a bit better, certainly won't be any worse...

 

[Mr Tidy]

My car came with H & R coil-overs fitted - to the extent that the floor grounded when I went over a speed bump for the first time.
It also had 19s and spacers.

I took it to Ross at RBM and he wound the ride height up a few turns on both sides and removed the spacers, but it wasn't much better so I went back and got them wound as high as possible and after that it didn't ground out even if it is still considerably lower than standard.

But the ride quality was the same whatever height it was running at. My conclusion was that to allow for more than a 30mm drop the springs would have to be stiffer or it would be bottoming out.

If yours don't have any compression/rebound adjustment I don't think you can do much about ride quality other than fit smaller wheels with more tyre sidewall, and obviously not run-flats.

 

[Jollygiant]

This is what i used to set up the Max'peedo' rods that are on my E85 when I bought it and it improved things no end.
https://www.youtube.com/watch?v=W1maEWgDz3c

I also played around with the adjusters on the top to fine tune it. I also have 17 inch wheels on mine and it handles and feels pretty good, like a little sports car should firm and responsive without being crashy and harsh.

I'm no expert but the rear looks to be sitting a bit low on yours.