BC or Spax coilovers?

[mike46]

Firstly, sorry to start another thread on coilovers!

I just have a few question, and also welcome any suggestions people have!

I think I have narrowed my choice down to the BC or Spax coilovers.

I am swinging towards the BC as I have used these before on a 350Z, but has anyone else on the forum used these for the Z4?.. Any opinions would be great! Not sure on the max lowering distance.

I would also like to know what other parts people generally replace/upgrade when fitting coilovers? I was going to buy a new nut/bolt for all the ones I will have to undo, partly just incase I have to sheer any off!

 

[GuidoK]

Any opinions would be great! Not sure on the max lowering distance.

What is the goal your trying to reach?

lowering your car to the max, or get better performance on road&track?

If it's the first, lowering the car, BC will do fine, just as D2 and Ksport (they have dual screw capabilities.
If you want to upgrade the performance, get something from a specialized and proven brand like Bilstein, KW, H&r, AST etc.
If you're upgrading because of performance: get new (thicker) anti rollbars.

When installing coilovers: get new rear shock mounts. They are maybe included in the coiloverset.
When lowering extreme: get a set with camberplates (included in sets like BC/D2 etc)
Also look at your arb connecting rods. First they are a wear item, but secondly with some coilovers you need shorter ones. Sometimes they are included, sometimes not. There are adjustable ones on the market. Be sure that when the suspension is in full droop (wheels completely hanging down when on a ramp), the arb doesn't touch the front lower suspension arms.

 

[mike46]

I am mainly interested in lowering the car, I don't want to ruin it but I don't intend on going on track.

I know the BC have camber plates, but I am unsure if they come with rear top mounts. Is a new set of OEM ones adequate, or is there an alternative?

Sorry to be a noob, but is this what you mean by arb connecting rods?.... http://www.eeuroparts.com/Parts/48807/Sway-Bar-Link-Front-31356780847/
I wasn't aware adjustable ones were available, how do I know if this will be necessary?

 

[GuidoK]

with arb connecting rods I mean those sway bar links. They're also called drop links.

You don't know on forehand if you need adjustable (shorter) ones untill you install them.
When you install the coilovers (car is on ramp/lift, with both wheels free!)), and you've set the coilovers in the lowest position that you will use them, It may be that you cannot put on those drop links because they're too long. The arb touches the lower control arm (arb sits above the control arm, and the drop links want to push the arb further down than possible).
When you lower the car, the control arms rise less than the drop link mounting hole on the coilover, so the drop links will fit. But when your suspension comes to a full droop (wheels completely down, like when taking a speed bump fast (when leaving the bump), you can get the situation that the arb touches the control arm and put excessive force on the coilover.
This can happen:


By pushing hard on the drop link lug on the coilover, it rotates in the screw threads and lashes the tyre. (the picture above is not from my car, but some e46 with that specific problem presumably).

I had to shorten my droplinks, but I use an M3 ARB in the front that has a slightly different geometry. So that is a bit of an experimental setup.

It's a problem that you may not even encounter, but things like this can happen.

This is a pic from my car when fitting kw V3, the lug sits about 10mm too low for the mounting bolt from the droplink if you look carefully.

So I shortened them myself.

But I think that BC coilovers come with special shortened droplinks and rear upper shock mounts.

If you do a lot of miles, the camberplates may wear (the balljoint/pillowball inside the camberplate) and that can cause rattle.