E46 M3 roll center correction?

[klodkrawler05]

I did some searching on the forum as well as google, short of the bimmerworld arms or the SLR race kit it seems nobody offers roll center correction for the M3 chassis. Ideally I'd like to keep my stock control arms and add roll center correction.

It seems e30/36/90 all have kits for adjusting roll center without replacing arms, what am I missing here with the e46 m3 that makes that impossible to offer?

I did find this picture in a build thread using what seems to be the ground control tie rods but I can't find any info/mention of the balljoint which is holding the knuckle up off the control arm:


http://www.bimmerworld.com/Suspensio...DmMaAozc8P8HAQ

[Novablue454]

The SLR "mini" kit utilizes the stock arms

http://slrspeed.myshopify.com/produc...race-and-drift

[klodkrawler05]

Ah thank you! I missed that when checking their website for an m3 kit, I'll shoot them an email and see what they have to say!
Thanks,
Brad

[bostonaudi]

Personally don't like those extender kits at all, and have seen them break. Note how they always say these kits aren't for street use - it's not because a better roll center is dangerous on public roads, it's because if you hit a bump hard or often enough these damn things might just break. The right way to do it is to manufacture a new steering knuckle with the ball joint and tie rod geometry lowered from the get go. I've seen few companies commit the engineering to do that, and many race classes forbid modified geometry, so it becomes an expensive toy for DE or autocrossing.

I did score a pair of modified knuckles for a previous track car and the effect of modified roll center is for real, makes massive improvements in grip, bump steer gone and the additional benefit of the car needing less static camber to get that grip.


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[klodkrawler05]

I did score a pair of modified knuckles for a previous track car and the effect of modified roll center is for real, makes massive improvements in grip, bump steer gone and the additional benefit of the car needing less static camber to get that grip.


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Thank you for the words of warning! do you have any pictures or additional info on your modified knuckles?

I compete in Gridlife Time Trials and Optima Ultimate street car events so to say the rule books are open is an understatement!

I had considered custom knuckles. That was the solution I used on my c5 although there were off the shelf options for them.

[ScotcH]

Been running that extender on our e46 race car for years without issues. We did have one break, but it was in a major impact with another car that also destroyed the wheel. Otherwise, we've not seen any issues.

FYI, the Ground Control roll correction ball joint replacement for e36 also work in the e46 control arms. I can't confirm if it's the same for M3, but I suspect so. Just measure the balljoint press in diameter to confirm. Them just weld on an extension (NOTE: You must do this right ... it's a cast piece, needs to be pre-heated and tig. Get a pro to go it), then just run a 1/2" bolt through it.

[bostonaudi]

Been running that extender on our e46 race car for years without issues. We did have one break, but it was in a major impact with another car that also destroyed the wheel. Otherwise, we've not seen any issues.

FYI, the Ground Control roll correction ball joint replacement for e36 also work in the e46 control arms. I can't confirm if it's the same for M3, but I suspect so. Just measure the balljoint press in diameter to confirm. Them just weld on an extension (NOTE: You must do this right ... it's a cast piece, needs to be pre-heated and tig. Get a pro to go it), then just run a 1/2" bolt through it.

I saw one break on a Porsche 944 just doing laps at a DE a while ago, same idea and construction. If this does break, you can imagine what happens to car control.

GC isn't in the business of selling junk, if you do use these would just watch them carefully and don't use them for street duty at all.

I have pics of mine somewhere on my PC, will post up when I find it.

Note that the knuckles I bought weren't modified, they were completely new cast units from scratch. Essentially the ball joint and tie rod points were extended down almost 2 inches, which gave a ton of room for *proper* lowering.

Edit to note that sometimes you can find factory units that have better geometry. When I was tracking a highly modified Mark 5 GTI, the trick was to grab the spindles from an Audi TT (and more or less the entire front end!). The Audi came with all aluminum parts, lower unsprung weight and had better roll geometry. H2Sport was the company that was casting new knuckles for these cars, turned my Mk5 into a bona fide FWD track weapon.

[klodkrawler05]

Yup that's the sort of thing I'd like to find for the m3 as wel, if your able to post pictures that would be fantastic!

Getting some great feedback in this thread thanks to everyone whose posted so far!

My e30 with m3 suspension is incredibly easy to adjust roll center. I wish the e36/46 had utilized a similar system.

[Novablue454]

I highly doubt anyone has broke one of the SLR mini kits. I piled my car in to a wall and bent/broke almost every suspension component EXCEPT for the SLR bits. Those things can take a major hit.

[jonb94118]

Been running that extender on our e46 race car for years without issues. We did have one break, but it was in a major impact with another car that also destroyed the wheel. Otherwise, we've not seen any issues.

FYI, the Ground Control roll correction ball joint replacement for e36 also work in the e46 control arms. I can't confirm if it's the same for M3, but I suspect so. Just measure the balljoint press in diameter to confirm. Them just weld on an extension (NOTE: You must do this right ... it's a cast piece, needs to be pre-heated and tig. Get a pro to go it), then just run a 1/2" bolt through it.

Scotch-are you using the SLR kit or the GC kit out of curiousity?

When you measure your bumpsteer through compression and droop, are you removing your springs and raising and lowering the front from your static rideheight and measuring total toe with toe plates? Or, are you using a bump steer guage?

[bostonaudi]

This is the H2Sport spindle for the Golf Mk5 platform. As you can see, the left unit has the ball joint and tie rod geometry significantly lowered. The effect of these spindles was simply unreal. My car could corner so hard it would consistently flip out the cars traction control and probably though I was about to have an accident. This part allowed about 2" of lowering without compromising anything.


h2sportspindles.jpg

[klodkrawler05]

In the corvette world that's a "common" way to lower the car while maintaining performance. I haven't been able to find anything similar for the e46m3 yet.

[bostonaudi]

In the corvette world that's a "common" way to lower the car while maintaining performance. I haven't been able to find anything similar for the e46m3 yet.

The challenge with this part is machining it. H2Sport had challenges finding a place that could machine it consistently and never could turn these out in numbers. They only shipped around 10 sets for the Mk5 and through constant calling I managed to get a pair.

[klodkrawler05]

Yea, the Corvette ones are a solid machined billet, easier to produce but certainly not cheaper. I know Wisefab makes quite a few knuckles for cars but hasn't jumped on the bmw train yet.

drop-spindles-w-watermark-and-text-web-view.jpg

it seems for whatever reason correcting roll center isn't a big priority for BMW folks, I'm not sure why as the Mac-strut setup could certainly benefit from it.

[ScotcH]

Scotch-are you using the SLR kit or the GC kit out of curiousity?

When you measure your bumpsteer through compression and droop, are you removing your springs and raising and lowering the front from your static rideheight and measuring total toe with toe plates? Or, are you using a bump steer guage?

I have the GC ball joint replacement kit on ours, with the weld on spacer. it came like that from BimmerWorld (it's an ex-WC car). The last time I actually measured the bumpsteer was on my e36, about 8 years ago, using a laser and home built gauge. Never done it on the e46, but I can tell you that the car with the bumpsteer kit handles better than the car without

[bostonaudi]

Yea, the Corvette ones are a solid machined billet, easier to produce but certainly not cheaper. I know Wisefab makes quite a few knuckles for cars but hasn't jumped on the bmw train yet.

drop-spindles-w-watermark-and-text-web-view.jpg

it seems for whatever reason correcting roll center isn't a big priority for BMW folks, I'm not sure why as the Mac-strut setup could certainly benefit from it.

As long as you don't completely dump the car, likely because the E36 already has reasonably good roll center. I run my E36 as high as I can set the PSS9's and it's still pretty low and handles well.

The VW's factory roll leaves no room for lowering before the roll center drops below the ground, its horrible stock. The front control arms are almost level at stock height then start losing camber curve as soon as you lower it. Then people scratch their heads when an expensive set of new coilovers is no faster than stock.

- - - Updated - - -

Yea, the Corvette ones are a solid machined billet, easier to produce but certainly not cheaper. I know Wisefab makes quite a few knuckles for cars but hasn't jumped on the bmw train yet.

drop-spindles-w-watermark-and-text-web-view.jpg

it seems for whatever reason correcting roll center isn't a big priority for BMW folks, I'm not sure why as the Mac-strut setup could certainly benefit from it.

These are $2900/pair. That's a pretty sizeable commitment. H2Sport was cast iron and $900/pair. Also heavy.

[klodkrawler05]

Yep,

they weren't an option for the faint of wallet that's for sure. Generally speaking though neither is paying $900 for a pair of Cast knuckles.

I'm going to explore the SLR option further as well as the GC balljoint, those seem to be the closest "plug and play" options currently.

[bostonaudi]

Yep,

they weren't an option for the faint of wallet that's for sure. Generally speaking though neither is paying $900 for a pair of Cast knuckles.

I'm going to explore the SLR option further as well as the GC balljoint, those seem to be the closest "plug and play" options currently.

What exactly are you building, HPDE car, or club racer? Have you checked rules on these? Altered geometry is typically pretty well controlled by class.

Other option is to not lower it so much, but that really depends on the car's requirements. A little more static camber can compensate lowering, course that starts to compensate braking etc.

I don't think the roll corrected BW race arms are too badly priced at $1200 for the pair. Personally I'd feel a lot more sure of the car with those than somewhat iffy extenders taking on stress in a position where if they fail or get loose the car will go where it wants.

http://www.bimmerworld.com/Suspensio...trol-Arms.html

[klodkrawler05]

It's a dual purpose car for Optima Ultimate Street Car events (read big money, unlimited ruleset) and Gridlife Time Attack which is our local midwest series time attack (less money, equally unlimited ruleset)

I have seen those arms and relative to the C5 knuckles they're cheap, I'm curious to hear more about your reasons for being comfortable with those arms but not the extended balljoints? both methods of roll center correction use an Aurora bearing with a through bolt and a machined tapered spacer to go into the OEM spindle/knuckle. Doesn't seem that the custom arm would be any stronger as it relates to sheering at the joint/knuckle than just the extended balljoint by itself.

[bostonaudi]

It's a dual purpose car for Optima Ultimate Street Car events (read big money, unlimited ruleset) and Gridlife Time Attack which is our local midwest series time attack (less money, equally unlimited ruleset)

I have seen those arms and relative to the C5 knuckles they're cheap, I'm curious to hear more about your reasons for being comfortable with those arms but not the extended balljoints? both methods of roll center correction use an Aurora bearing with a through bolt and a machined tapered spacer to go into the OEM spindle/knuckle. Doesn't seem that the custom arm would be any stronger as it relates to sheering at the joint/knuckle than just the extended balljoint by itself.

After looking at their parts closer, you're right, now I don't like the arms either! That's an area that takes a lot of stress, if you go this route and tend to hit rumble strips a lot I'd make sure to inspect them often and carefully.

[ScotcH]

After looking at their parts closer, you're right, now I don't like the arms either! That's an area that takes a lot of stress, if you go this route and tend to hit rumble strips a lot I'd make sure to inspect them often and carefully.

Agreed ... check the welds often! We've had exactly 1 fail in 6 years, and it was because of a major wheel to wheel hit. Otherwise, no issues. I think as long as the bolts are tight and the welding is done right, it's a good solution.

[ScotcH]

Here is how I have it on our other car, without weld on extension. I drilled out the hole to 5/8", then used a stainless 5/8" collar, plus the hardened bearing spacers for clearance. Instead of the GC supplied stud, I used a grade 8 5/8" bolt. The stud is too short for our use.

IMG_20170110_220909.jpg

IMG_20170110_220841.jpg

[klodkrawler05]

That sure looks pretty beefy!

No issues with failure of that setup to date for you guys?