Suspension Upgrade

Hello,

Need advice on what to do in regards to suspension upgrade/refresh. I've been tracking my car for 5 years now with stock ZCP suspension till this year. I do about 5 to 6 track days a year, so nothing serious, but could be doing more in the future. Beginning of this year I've installed a set of Nitron R1 and all other components remains stock with 95,000km on the car.

At my last 2 track days I've noticed the front end would get a little unstable under heavy braking. The front thrust arm bushings looks okay from visual inspection but it is something that I want to change out at some point.

I've also been planning to do a full suspension refresh at some point and have been slowly acquiring parts over last couple years. Last year I picked up the followings from a local member. All below parts are brand new. Have all the parts listed in this thread. https://www.m3post.com/forums/showthread.php?t=1781245

- AKG aluminum subframe bushings
- AKG poly 95A diff bushings
- Rear spherical bearing conversion.
- Meyle 3147100005 bearings
- Custom tapered washers

My question is, should I just install all the above and add solid thrust arm bushings and call it a day? Or should invest in SPL parts? My car is not a daily, strictly weekend cruises and track days.

Also anyone know why AKG has a warning on their site about their aluminum subframe bushings may crack the subframe and needs to be monitor, while others don't?

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I think the rear arms are a good investment, as they accomplish two things. Give you much easier and more adjustability than stock, and replace the bushing on one side of 4 of the arms. For money you'd spend you buying the bearings and spherical washers, and assuming you'll be paying someone to press them all in, I think you're better off buying the arm set. I strongly recommend the GC set as they come with dust covers, so for a car that sees street use, they are much better.

I had the GC rear arms + full SPL up front on my M3 track build. If I were to do it again (which I will be soon), I'll do the GC rear arms and do just the monoball front bushing, use both stock arms and just do a bump steer tie rod end.

Not sure about the AKG SF bushings. Maybe due to improper installation?

For reference, these are the arms: https://groundcontrolstore.com/collections/e9x/products/bmw-e8x-e9x-adjustable-arm-set

MaximusB wrote

Also anyone know why AKG has a warning on their site about their aluminum subframe bushings may crack the subframe and needs to be monitor, while others don't?

I don't know – but, for what speculation is worth....

AKG seems to have a lot of generic warnings about bushing materials. Like, they tend to say all bushings of a given material have the same NVH increase (low/medium/high), regardless of location or application. Consensus here seems to be that, in our cars, there's a big difference in the NVH added by aluminum powertrain mounts (a ton) and aluminum subframe mounts (little to none perceptible) – yet AKG lists them all as having "high" NVH increase. It's like they're pasting standard pros/cons and warnings across applications rather than offering tailored advice about each individual bushing option in each application.

To be fair, they're probably right more often than they're wrong, and there are so many possible material/application/chassis combos that trying to offer tailored advice on everything could get out of hand real quick.

In this case, I feel like the complete lack of conversation in our community about subframe cracking with solid mounts is evidence that that's not really a problem worth worrying about.

tsk94 wrote

I think the rear arms are a good investment, as they accomplish two things. Give you much easier and more adjustability than stock, and replace the bushing on one side of 4 of the arms. For money you'd spend you buying the bearings and spherical washers, and assuming you'll be paying someone to press them all in, I think you're better off buying the arm set. I strongly recommend the GC set as they come with dust covers, so for a car that sees street use, they are much better.

I had the GC rear arms + full SPL up front on my M3 track build. If I were to do it again (which I will be soon), I'll do the GC rear arms and do just the monoball front bushing, use both stock arms and just do a bump steer tie rod end.

Not sure about the AKG SF bushings. Maybe due to improper installation?

Thanks for the recommendation.

Just so I'm clear, what you're saying is replace the rear arms with GC that you suggested. Then just do monoball up front and use stock arms?

Other than the GC arm having dust covers, what else made you pick those over SPL?

MaximusB wrote

Thanks for the recommendation.

Just so I'm clear, what you're saying is replace the rear arms with GC that you suggested. Then just do monoball up front and use stock arms?

Other than the GC arm having dust covers, what else made you pick those over SPL?

Yes, exactly.

The dust boots are big reason. They go a long way to help increase longevity of the ball joints by keeping dust, debris, etc. out of them. I used the full SPL front arms on my car, so I'm familiar with the SPL parts and their quality - which is good. So are the GC arms, and they offer much better value imo at $850/set vs. $1350/set from SPL.
I had used the GC arms on a 1 series build prior, so I was familiar with the product and very happy with the quality of the pieces so I bought them again for the M3 I built, and will go with them again on the new M3

+1 on the GC value!

I bought the rubber boots and the installer and added them to the SPL parts for the same protection. Was a hassle and I’d have just gone GC if doing it again.

This is exactly why I instantly crossed off any SPL/exposed spherical stuff in my approach and build embarking on this ~5 years ago. If the car is street driven or even track. You really should add a checklist to inspect and replace the joints. And expect to replace them sooner if driven on the street. Ie. not a racecar or trailered everywhere, forget about it. Have a damp/wet track day? Think about that too along with going off into grass, wet grass or kitty litter/debris etc.

tsk94 wrote

I'll do the GC rear arms and do just the monoball front bushing, use both stock arms and just do a bump steer tie rod end.

Is there a bump steer tie rod end with dust boots like the GC rear arms?

Not a fan on SPL stuff on a street car, i've seen several street cars with tie rod play less than 1 yr of use.

This thread is giving me the willies. I just put SPL end links on my street car. FML

IamFODI wrote

This thread is giving me the willies. I just put SPL end links on my street car. FML

They’re on tens of thousands of cars and the end links are the least worrisome.

It’s a little bit tedious but I think a worthwhile investment if installing heim joint suspension arms. I think this is the only option for the front.

https://www.race-parts.com/raceparts-heim-joint-protective-rubber-boots

Any issue with the GC seizing? Been reading a few other threads about SPL arms and that they tend to seize making it hard for future adjustments.

MaximusB wrote

Any issue with the GC seizing? Been reading a few other threads about SPL arms and that they tend to seize making it hard for future adjustments.

You def want to protect the threads on any of the adjustable arms with copper grease.

DRLane wrote

You def want to protect the threads on any of the adjustable arms with copper grease.

This. Had no issues myself.

This post about SPL arms is a bit concerning. But note I was found it last night and didn't have time to read up on the full story/background around it.

https://www.m3post.com/forums/showpost.php?p=27502383&postcount=17127

MaximusB wrote

This post about SPL arms is a bit concerning. But note I was found it last night and didn't have time to read up on the full story/background around it.

What post?

DRLane wrote

What post?

Oops.. forgot to include link.

https://www.m3post.com/forums/showpost.php?p=27502383&postcount=17127

MaximusB wrote

https://www.m3post.com/forums/showpost.php?p=27502383&postcount=17127

Wow. Scary.

MaximusB wrote

Oops.. forgot to include link.

https://www.m3post.com/forums/showpost.php?p=27502383&postcount=17127

I mean, if that’s keeping you up at night I wouldn’t drive. Every part is subject to failure. I don’t believe the final report was ever shared on the impact that sheered the bolt.

I’ll gladly put 100% faith behind SPL, but I also love owning the full mechanical experience of my car. Requisite bolts are torque painted, I replace torque to yield BMW bolts every time they’re removed, take suspension parts off to clean and lubricate at least annually, and doing a look over often. Gives me an excuse to be in the garage and enjoy this part of the experience.

What do you guys do with the headlight leveler on aftermarket arms?

Based on online photos, it doesn't look like any of the rear aftermarket arms (SPL or Ground Control) have a place to bolt the headlight leveler on to.