E36 Roll Center Correction Experience(s)

**jakermac** · 10-01-2020, 01:02 PM

Originally Posted by aeronaut

I need to remove about 0.3mm.

But jesus....why do I need to make custom spacers.

Agreed. But you don't need more than about .010" precision and that should be easy enough to hit with a bench grinder, angle grinder or even a good sharp hand file.

**aeronaut** · 10-01-2020, 01:55 PM

Good point, some combination of your list and/or some sand paper on my flat plate could fix it.
Detailed measurements show 0.18 to 0.36mm needs removed (depending on pairing of spacers).
SLR is sending me new spacers for a different reason, and I'm hoping this gets fixed too.

**aeronaut** · 10-05-2020, 11:03 AM

Summary of where I'm at:
- MRT kit: Would not recommend.
- TMS kit: Asked what their RC correction is (via chat and email). They responded via email with the Ackerman adj range. They don't seem to know the RC correction.
- SLR kit: Fitment problem. They've sent replacement spacers and replacement outer pins, and it's still not 100% right. I can make it work with some precision shims from McMaster (and some custom fit of those shims.)

I'd think that maybe my kingpins are out of spec, but OEM ball joints fit perfectly, and the MRT outer pins fit perfectly.

Putting it all together today, and I'll document on my build thread.

**fbirch** · 10-05-2020, 10:04 PM

We're waiting for you to purchase, install and test every available RC kit on the market and tell us which one is least bad once you've exhausted all possibilities ;-)

**aeronaut** · 10-05-2020, 10:18 PM

LOL! Yea, it shouldn't be this difficult.

**fbirch** · 10-06-2020, 02:04 PM

Way back in early July, I communicated with a fellow named Ian Shea at Turner, with my questions and his answers shown below:

Q: How thick is the aluminum block that lowers the control arm end?
A: The bracket is 1.25" (31.75mm) thick where it meets the control arm, the rest of the bracket is .75" (19mm) thick.

Q: Also, does this kit result in the LCA end getting any closer to the backside of the brake disc? I run StopTech BBK and the front rotors are bigger than stock.
A: No, this kit shouldn't cause the LCA end to shift any closer to the rotors or cause any interference with any BBKs. These are currently in production and due into stock in October

**aeronaut** · 10-22-2020, 08:23 AM

Well, while I'd recommend the SLR kit over the MRT kit, the SLR kit still causes rubbing between my rotors and LCA. Maybe it's some combination of 95M3 kingpin geometry, 325mm rotors, and a few washers for extra camber. Other than grinding the LCA ends, there are a few 'fixes' for this, but they all cost a chunk of money. Something I'll think about over winter. I'm pretty confused how folks put a BBK (usually thicker rotors) AND a roll center correction kit, without issues.

IMG_20201019_152320.jpg

**FredK** · 10-22-2020, 10:38 AM

Originally Posted by jakermac

I would kill for something like this. CAD designed, CNC'd Aluminum spindle with a bolt on hub/bearing assy from an E90 with a raised mounting point (about 1.5 to 2" would do), relocated (for faster steering) and bumpsteer corrected tie rod attachment, roll center correction (maybe a modular setup to allow adjustment) and some sort of modular setup for brake caliper attachment for a variety of brake configurations. Oh, and they come in at about 1.5-2lbs lighter than OEM!

SLR has something like this that they have developed, but I don't think it's on their website, you have to get in touch with them. It looks really sweet.

According to SLR, it "Mounts E90/F30/F82 hubs, radial mount brakes, tons of strut options, adjustable track, trail, Ackerman & KPI. Knuckle is reversible so you don't need L & R spares."

The following pic was from a Facebook post.

SLR.jpg

**aeronaut** · 10-22-2020, 10:59 AM

Wow. That looks like it's on an E46, or at least for an E46 damper. But wow.

**ScotcH** · 10-22-2020, 04:03 PM

Oh shit ... they actually made a billet kingpin! Damn (definitely not an e46 though)

- - - Updated - - -

Originally Posted by aeronaut

I'm pretty confused how folks put a BBK (usually thicker rotors) AND a roll center correction kit, without issues.

Well, the GC stuff works great ... we run it with wilwood 330x30 rotors, no issues.

**MPWRCPE** · 10-22-2020, 04:25 PM

Originally Posted by ScotcH

Oh shit ... they actually made a billet kingpin! Damn (definitely not an e46 though)

- - - Updated - - -

Well, the GC stuff works great ... we run it with wilwood 330x30 rotors, no issues.

What is bearing life like with the rod ends on the GC stuff? I think they recommend inspection after every session which seems a bit extreme?

**jonb94118** · 10-22-2020, 05:20 PM

Originally Posted by MPWRCPE

What is bearing life like with the rod ends on the GC stuff? I think they recommend inspection after every session which seems a bit extreme?

I run the GC Kit - using a 5/8" thru bolt and custom spacer between the spindle and GC Control arm bearing. I actually remember asking Scotch about it years ago who helped me. In any case, as for the rod ends, with any rod end/spherical you are going to have wear and I replace my rod ends maybe once per season when they develop play. The ends themselves are cheap and can be sourced anywhere. I think Ground Control puts statements like that in their product information to deter people from thinking that this type of kit/solution is a set and forget type of thing. For the average track day type person, I wouldn't even bother with roll center correction to be honest. Just keep your control arms/ride height at a decent level, maybe do bump steer correction - if after measuring toe change throughout travel you find that it's needed. As for clearance to the rotor - I also run a thick Wilwood rotor up front and don't have a problem. I might have clearanced my control arms at some point, but the other difference might be that I am using an offset control arm bearing that will create more space between it and the rotor/spindle. A centered outer control arm bearing will bring the spindle/rotor closer to the control arm.

**ScotcH** · 10-22-2020, 08:33 PM

Yeah, inspect all the time ... replace ... never, lol. I think we have 3 or 4 years on ours, never had an issue. We have replaced the rod ends on our rear arms, but the tierods have been ok.

**aeronaut** · 10-23-2020, 09:48 AM

Originally Posted by jonb94118

I run the GC Kit - using a 5/8" thru bolt and custom spacer between the spindle and GC Control arm bearing. I actually remember asking Scotch about it years ago who helped me. In any case, as for the rod ends, with any rod end/spherical you are going to have wear and I replace my rod ends maybe once per season when they develop play. The ends themselves are cheap and can be sourced anywhere. I think Ground Control puts statements like that in their product information to deter people from thinking that this type of kit/solution is a set and forget type of thing. For the average track day type person, I wouldn't even bother with roll center correction to be honest. Just keep your control arms/ride height at a decent level, maybe do bump steer correction - if after measuring toe change throughout travel you find that it's needed. As for clearance to the rotor - I also run a thick Wilwood rotor up front and don't have a problem. I might have clearanced my control arms at some point, but the other difference might be that I am using an offset control arm bearing that will create more space between it and the rotor/spindle. A centered outer control arm bearing will bring the spindle/rotor closer to the control arm.

Where are you sourcing your offset outer control arm bearings?

I LOVE the quicker steering ratio of the RC correction kits. The GC correction method doesn't provide increased steering ratio, or I would have gone that way.

**jonb94118** · 10-23-2020, 11:33 AM

https://groundcontrolstore.com/colle...correction-kit

If you look at the bearings, you'll see that they are offset.

**aeronaut** · 10-23-2020, 01:10 PM

Originally Posted by jonb94118

https://groundcontrolstore.com/colle...correction-kit

If you look at the bearings, you'll see that they are offset.

Yep, that's exactly why the LCA won't rub the rotor when using GC's.
The ID of the bearing sleeve is 5/8" ?

Although, for $400....that's almost the cost of the SLR tubular LCA's, which provide the needed clearance (I think).

**jonb94118** · 10-23-2020, 06:14 PM

Originally Posted by aeronaut

Yep, that's exactly why the LCA won't rub the rotor when using GC's.
The ID of the bearing sleeve is 5/8" ?

Although, for $400....that's almost the cost of the SLR tubular LCA's, which provide the needed clearance (I think).

Not saying it's the solution for you, but the actual cost of the bearings is $200 including the hardware for the spindle. I don't use that hardware myself, but the bearings and housings are great. As for the tubular control arms, I would consider a wear item if you go down that path.

https://groundcontrolstore.com/colle...nt=35605196675

**aeronaut** · 10-23-2020, 06:30 PM

The challenge is I want to keep the steering ratio change. So I'd want to adapt the GC offset sphericals to the SLR kit, which at first glance, doesn't look possible.
What I could do is machine my own offset spherical carriers. Well, if I had a lathe, a mill, and talent.

Not sure why tubular LCA's are considered a wear item?

**MPWRCPE** · 11-12-2021, 11:32 AM

Well, to bump this into 2021 I just picked up the full E36 race kit with tubular arms & RC correction from Sean @ SLR. Quality looks to be fantastic.

My factory arm ball joints gave up last weekend after the Q-race and put me out for the weekend.

I'll be doing the install this weekend with setup/alignment to follow, then testing them out Thanksgiving weekend for the championship race lol.

Will report back!

Originally Posted by aeronaut

The challenge is I want to keep the steering ratio change. So I'd want to adapt the GC offset sphericals to the SLR kit, which at first glance, doesn't look possible.
What I could do is machine my own offset spherical carriers. Well, if I had a lathe, a mill, and talent.

Not sure why tubular LCA's are considered a wear item?

Did you get the SLR mini-kit straightened out? I don't remember reading if you had or not.

**golgo13** · 11-12-2021, 02:29 PM

I've seen a few failures with the SLR stuff, so I don't think it's a silver bullet.

Dave, how often were you changing the factory ball joints?

**MPWRCPE** · 11-12-2021, 03:25 PM

Originally Posted by golgo13

I've seen a few failures with the SLR stuff, so I don't think it's a silver bullet.

Dave, how often were you changing the factory ball joints?

Not often enough Noah. A few years of track use and a full season of race use, with a few decent curb impacts thrown in for good measure. Luckily I found it while mounting sticker R7's for the main race so I did not drive on it. Front end felt off all morning and I couldn't pin it down until we checked for play. I did a wheel bearing check before loading up but did not do a tie rod/ball joint check, my mistake.

I agree there's no silver bullet, but maintenance/replacement should be easier with SLR considering bearings vs ball joints. Guess we'll see!

**aeronaut** · 11-13-2021, 04:04 PM

Originally Posted by MPWRCPE

Well, to bump this into 2021 I just picked up the full E36 race kit with tubular arms & RC correction from Sean @ SLR. Quality looks to be fantastic.

My factory arm ball joints gave up last weekend after the Q-race and put me out for the weekend.

I'll be doing the install this weekend with setup/alignment to follow, then testing them out Thanksgiving weekend for the championship race lol.

Will report back!

Did you get the SLR mini-kit straightened out? I don't remember reading if you had or not.

I'm still running the SLR mini-kit. Mostly figured out in that there's only 2 threads or so past the lower control arm attach stud. Also agree with the other statements that the SLR kit not a panacea. I check torques after every weekend and every once in a while one nut will be an 1/8 turn loose. Otherwise, I'm happy with the kit.

**jordaneast** · 11-15-2021, 09:42 AM

I occasionally auto-x my ZHP and have done 1 track day so far. I am finally finishing up an e30 project. I hope I can get a lot more track time next year when it is finished.

**MPWRCPE** · 11-15-2021, 10:10 AM

Originally Posted by aeronaut

I'm still running the SLR mini-kit. Mostly figured out in that there's only 2 threads or so past the lower control arm attach stud. Also agree with the other statements that the SLR kit not a panacea. I check torques after every weekend and every once in a while one nut will be an 1/8 turn loose. Otherwise, I'm happy with the kit.

Good to know. Got the kit installed with no issues, really nice stuff!

Off for an alignment this week then we'll see how she does.

What difference were you able to make in the front bar? I run the large GC and will back it off to full soft, but I also have the medium bar to test with.

**aeronaut** · 11-15-2021, 12:42 PM

Originally Posted by MPWRCPE

Good to know. Got the kit installed with no issues, really nice stuff!

Off for an alignment this week then we'll see how she does.

What difference were you able to make in the front bar? I run the large GC and will back it off to full soft, but I also have the medium bar to test with.

If you're asking me, I only have a UUC bar. I should probably go up in size with my spring rates, but that's pretty far down on the list right now.