Z4-forum.com

GuidoK wrote: ↑Fri Nov 10, 2017 4:42 pm I think the main risk is that there is no real userexperience regarding if the chassis can hold a coilover or not without severely stiffening up the suspension.
There might be some people driving around with true rear coilovers, but how many miles did they do? What does it take to regard something as 'properly tested'? 5 cars having done 10k miles or 50 cars having done 100k miles? Im sure the last one doesnt fit the true coilover community.
It's very hard to predict if using true coilovers at the rear will damage the chassis or not.
But if you look at for example the e46 m3 subframe cracks what can happen if forces are not properly dealt with, thats not something you want to experience (and who's to say that things wont get even worse)
With normal coilover sets (kw/h&r/etc) with the conventional rear setup there are so many users that have done so many miles with it, that its pretty safe to say that that doesnt give any problems (although I have seen pictures of even front chassis perches/towers cracking due to stiffer springs)

Yes I agree with your points, it's an unknown to some extent. Intrax engineers suggest that on a street set-up (which mine will be) there is no need to reinforce as the spring rate will be soft. On a race spring set-up then they say reinforcement will be necessary. There are a number (how many I don't know!) of Z4Ms running around europe in this configuration with no issues that they have yet heard of.
Simpsons who install a lot of intrax stuff into e46m3s have done many without cage/reinforcement and have yet had a rear turret failure. But as you say, who knows how many miles and how long these cars are run, will the metal fatigue badly over time, not to mention that's a different chassis?
I think the front towers cracking come from yes stiffer springs but also the adjustable solid mount camber plates often used. As beedub suggests you should probably run the bmw reinforcement plates if you're running those.
Guido, do you think the rear strut brace or similar I linked at the beginning of this thread would do anything positive in this regard? I.e. not welded solution

Beedub wrote: ↑Fri Nov 10, 2017 6:06 pm good input their from above.

yes i once saw a pic of the z4 with a ballooned Front turret using the kw club sport since having mine on I've made sure to run the underside reinforcement plates and the SB , between these two i feel pretty confident in the additional strenthening.

Do you have any more info on the reinforcement plates? SB.. Strut Brace?

bradz wrote: ↑Fri Nov 10, 2017 6:18 pm

Beedub wrote: ↑Fri Nov 10, 2017 6:06 pm good input their from above.

yes i once saw a pic of the z4 with a ballooned Front turret using the kw club sport since having mine on I've made sure to run the underside reinforcement plates and the SB , between these two i feel pretty confident in the additional strenthening.

Do you have any more info on the reinforcement plates? SB.. Strut Brace?

It was these that I ran with my intrax on the e46m3
https://www.turnermotorsport.com/p-323- ... iced-each/
not sure if they fit our cars but I think so, beedub can confirm

Personally for me...

It has not been tested enough, at least the stock config is tried and tested.

My biggest worry was popping the top mount or snapping/bending the lower arm, if that happens... you ain't getting home... and its not an easy fix that the average garage can fix... whereas you can drive with a failed shock/spring with the OE config.

TomK wrote: ↑Fri Nov 10, 2017 6:16 pm Intrax engineers suggest that on a street set-up (which mine will be) there is no need to reinforce as the spring rate will be soft.

Easy to say....but are they willing to give a 2 year unlimited warranty on the chassis? I think not.
And in case of the e46 m3 subframe problems even that (2 year bmw warranty) wasnt enough, as problems started only after 5 years or so..
TBH most cars that are heavily modified and run on track do very limited miles (maybe 1k/year max) and are often not that long in posession (3 years or so and then they move on). If you're planning to keep and enjoy the car for years, I'd only go with tried/proven solutions, especially where it concerns the chassis/body. I mean a subframe or control arm is easily replaced, it may cost you 1-2k, but extensive repairs on a chassis....not so much (and will the chassis ever be the same again....)

Guido, do you think the rear strut brace or similar I linked at the beginning of this thread would do anything positive in this regard? I.e. not welded solution

Personally I dont think it will be effective agains the problems I can imagine. It only transferes some lateral movement to the other tower. It doesnt strenghten the lower welds etc.

bradz wrote: ↑Fri Nov 10, 2017 6:23 pm My biggest worry was popping the top mount or snapping/bending the lower arm, if that happens... you ain't getting home... and its not an easy fix that the average garage can fix... whereas you can drive with a failed shock/spring with the OE config.

I dont think that's the biggest worry that can happen.
I'm thinking more like spotwelds slowly seperating/tearing apart (for instance in the wheel wells and under the boot), tears in bodypanels etc.
And the problem is, lots of panes and constructions there in the chassis are double panels etc, so even getting to a spotweld to drill out and reweld is a huge problem and can mean cutting out other panels, then do the repair and then weld in a new panel etc etc.
Take a look at the youtube vids from redish motorsport and what they do. And that is on a known problem for which tried and tested solutions have been developed over the years. Can you think of doing that on a car that has new problems no one has ever seen before?
And what those problems could be is very difficult to predict. Its not that you're gonna increase load on certain parts, you're gonna change from parts that now and then get a load on it (only when the shock compresses/decompresses) to something that is continously loaded up (not only the increased load of the springs, but it will be loaded up all the time as long as the car sits on its wheels)

And why should you do it? The rear suspension only travels about 20cm max in extreme conditions (not on a track...). Sure a longer spring can be made so that it can control every step of that motion to the outer extends of that motion a little bit more carefully in terms of consistency in spring rate etc, but its not like the z4 is a baja buggy where long springs are required. A corvette still has a leaf spring and will still kick the z4's ass on a track....
I'd only go that route if I was an experienced body repair tech that would be able to repair the potential damages myself. (or could afford one obviously)

TomK wrote: ↑Fri Nov 10, 2017 6:22 pm

bradz wrote: ↑Fri Nov 10, 2017 6:18 pm

Beedub wrote: ↑Fri Nov 10, 2017 6:06 pm good input their from above.

yes i once saw a pic of the z4 with a ballooned Front turret using the kw club sport since having mine on I've made sure to run the underside reinforcement plates and the SB , between these two i feel pretty confident in the additional strenthening.

Do you have any more info on the reinforcement plates? SB.. Strut Brace?

It was these that I ran with my intrax on the e46m3
https://www.turnermotorsport.com/p-323- ... iced-each/
not sure if they fit our cars but I think so, beedub can confirm

thats them, they fit perfectly and spread the load As per the stock top mount, I've had them in since day one with non stock suspension. The KW CS setup is solid mounted with no rubber, and smaller mount plates which places more load in the middle of the tower, anyone running such setup really should do this for cheap insurance,

not sure its needed on those V3s, they running a progressive spring and appear to reuse the stock top mount.


Tom the car performs so well with the stock config and top end items i really wouldn't go down this route. But if you do cant wait to see how you get on!!

GuidoK wrote: ↑Fri Nov 10, 2017 7:10 pm

Thanks, appreciate your thoughts, you make a good case for the sensible option I guess. What still sways me the other way is that above and beyond the extra control in the spring is the ability to have access to a far wider range of spring rates than is available with a barrel style.
I thought the same about the rear brace and I'm seeking an opinion from a race shop, I suspect I'll hear the same thing.
I'm not sure though that the e46 subframe issue is such a great analogy for the forces involved here? I do though agree that getting access to fix any spot welds etc issues around that area is going to be an issue. Is it also really a potential issue that a load is subjected constantly as you suggest? I would have thought that would not be a problem as long as it is within tolerance?
It's frustrating as I'm sure there are owners out there with this set up that could maybe feed back to me, but not in the uk it seems.

TomK wrote: ↑Fri Nov 10, 2017 7:35 pm

GuidoK wrote: ↑Fri Nov 10, 2017 7:10 pm

Thanks, appreciate your thoughts, you make a good case for the sensible option I guess. What still sways me the other way is that above and beyond the extra control in the spring is the ability to have access to a far wider range of spring rates than is available with a barrel style.
I thought the same about the rear brace and I'm seeking an opinion from a race shop, I suspect I'll hear the same thing.
I'm not sure though that the e46 subframe issue is such a great analogy for the forces involved here? I do though agree that getting access to fix any spot welds etc issues around that area is going to be an issue. Is it also really a potential issue that a load is subjected constantly as you suggest? I would have thought that would not be a problem as long as it is within tolerance?
It's frustrating as I'm sure there are owners out there with this set up that could maybe feed back to me, but not in the uk it seems.

FWIW their are actually lots you can do with the rear spring on this car, as long as you willing to switch out to a linear and have a good enough damper with adequate valving to suit....

Beedub wrote: ↑Fri Nov 10, 2017 7:31 pm Tom the car performs so well with the stock config and top end items i really wouldn't go down this route. But if you do cant wait to see how you get on!!

Thanks, you're probably right. I've got a few months before I'm going to do anything about it. Lot's of time to think about new shiny bits

Beedub wrote: ↑Fri Nov 10, 2017 7:37 pm FWIW their are actually lots you can do with the rear spring on this car, as long as you willing to switch out to a linear and have a good enough damper with adequate valving to suit....

My understanding was that most spring manufacturers like KW, Intrax for the barrel spring will do way way less spring options than they offer for the coil over.

yeah your right so , however you can pair up a swift spring in correct diameter and length and the options are endless really.... as long as you have a damper that can support the spring rate... your not limited at all, its just abit of a wait to get the springs, they aren't even expensive!

Beedub wrote: ↑Fri Nov 10, 2017 8:12 pm yeah your right so , however you can pair up a swift spring in correct diameter and length and the options are endless really.... as long as you have a damper that can support the spring rate... your not limited at all, its just abit of a wait to get the springs, they aren't even expensive!

Ok thanks, I hadn't heard of this, will look into it.
As you say springs are generally pretty cheap, at least relatively

TomK wrote: ↑Fri Nov 10, 2017 8:22 pm

Beedub wrote: ↑Fri Nov 10, 2017 8:12 pm yeah your right so , however you can pair up a swift spring in correct diameter and length and the options are endless really.... as long as you have a damper that can support the spring rate... your not limited at all, its just abit of a wait to get the springs, they aren't even expensive!

Ok thanks, I hadn't heard of this, will look into it.
As you say springs are generally pretty cheap, at least relatively

another one for springs are HYPERCO....

if you go with a a control control or the likes of TCK you can actually specify what spring rate you want at the back, and then they valve the damper around your choice nitron were also willing to do this for me when i was talking to them while deciding which company to use.

Beedub wrote: ↑Fri Nov 10, 2017 8:35 pm

TomK wrote: ↑Fri Nov 10, 2017 8:22 pm

Beedub wrote: ↑Fri Nov 10, 2017 8:12 pm yeah your right so , however you can pair up a swift spring in correct diameter and length and the options are endless really.... as long as you have a damper that can support the spring rate... your not limited at all, its just abit of a wait to get the springs, they aren't even expensive!

Ok thanks, I hadn't heard of this, will look into it.
As you say springs are generally pretty cheap, at least relatively

another one for springs are HYPERCO....

if you go with a a control control or the likes of TCK you can actually specify what spring rate you want at the back, and then they valve the damper around your choice nitron were also willing to do this for me when i was talking to them while deciding which company to use.

For sure I'm going to go with Intrax again, the dampers will be custom valved accordingly to include both increase the increase in power and reduction in weight particularly the unsprung part(AP, APEX) over a regular M. I had their 1k2 setup before and I've been missing it ever since, this time I will add their ARC which allows even softer spring rates. Just need to save a few pennies now, it's £4k's worth around

wow big money..... !!