Spring specs and strut tower reinforcement

[ionofchios]

Hi guys,

I’ve just got hold of a 12/2006 3.0si Coupe (e86). I’m going to replace the front suspension and wishbones, and add BMW strut tower reinforcement plates between the underside of the tower and the strut. The car has the M suspension option.

I was thinking it might be a good idea to add some extra rust prevention between the tower and the reinforcement plate, since I guess water might get up in their. Any recommendations for what to use?

What, actually, are the BMW part numbers for front and rear springs, given that my car has the M Sport suspension option? RealOEM is missing these for some reason. What are the springs specs, meaning length and whatever else is important? I understand that the M suspension is 15 mm lower than standard, and I want to keep it like that, as BMW intended, and I certainly don’t want it lower. Anyone know any good aftermarket springs that are a direct replacement for the originals?

I’ve come across 2 potential part numbers for the front springs which some sites think are correct: 31336760622 and 31336760623. Are either of these correct, and if both are okay, what’s the difference?

Will be adding Bilstein B6s all round - but I don’t yet have any questions about those ... except maybe whether bump stops are, or are not, needed

 

[z4pilot]

I'm sure someone will be along shortly with the relevant part numbers, but any reason why you are wanting to reinforce the strut towers when you're not uprating the suspension? Under normal usage, I don't believe that these car suffer from issues in that area?

 

[rally-chris]

Suplex are the brand that people often use when replacing Z4 springs ‘like for like’. 06231 is the part number for M sport spec rear springs, which are a regular failure on our Z4s now they’ve reached a certain age (from £30 each on eBay). I’ve not heard of common front spring problems though?

Chris

 

[Magicarcher]

For rust protection I tend to use Bilt Hamber UB on external surfaces. It is impossible to say how good it is without controlled experiments, but it is generally well respected and easy to use.

 

[ionofchios]

Thanks for the input, guys. Suplex looks good - I’ll try and find those.

Actually, I don’t have any reason to replace the front springs, only the wishbones and struts. I just thought if I was doing everything else on the front, I should do those too. Could reuse the old ones, of course.

The reason for the strut tower reinforcement is that I can see a bit of doming, at least it looks like the bolts are not all quite straight (not very pronounced, though).