lowered ride height geometry

[YAOGinanM3]

Does anybody know what happens to the front and rear suspension geometry when you lower the ride height of an E36 M3? Are there parts available to correct the roll center height after lowering? What about bumpsteer and akerman changes?

Cheers!

[turbosporttsi]

RRT, Ground Control, BimmerWorld, etc all have bumpsteer and roll center correction, though you might have to call to get pricing/info. I don't think they have anything for the rear. I also don't think they make anything to change ackerman.

[Eddie916]

What's roll center? Is that the same as camber?

[YAOGinanM3]

Originally Posted by Eddie916

What's roll center? Is that the same as camber?

Eddie916,

Roll center is an imaginary geometric point about which the chassis is trying to roll around on the long axis of the chassis. Camber is not the same thing as roll center. Camber angle is the vertical angle of the wheels and tires viewed from the front or rear along the path of the car.

You have a roll center in front and a roll center at the rear of the chassis and if you draw a line between the two you can see the relationship change as you alter the roll center height. These points move around all of the time (except when the car is stationary) depending on what the suspension is doing at the time you are looking at it. A lot of the way a car handles or behaves can be seen by this imaginary line between these two imaginary points in space.

Depending on the suspension design type, when you lower the chassis ride height the roll center height is also normally lowered, usually even faster then the ride height (depending on geometry of course) and this allows more body roll. More body roll on a strut suspension chassis is bad because the more roll you allow the less grip you have due to reduced camber which reduces the tire contact patch. So normally unless you correct the roll center height you will be losing grip on the end of the car you lowered unless of course you add more static camber or relocate the pivot points of the suspension to restore/correct roll center height.

So if you lower the front of your car significantly more than the rear you may have been the cause for that new found increased push in the corners.

HTH!

[bmwpowere36m3]

^ Well it seems like you have you answer, yes there are kits available but they are expensive, extensive, and difficult to properly adjust (RRT and BW come to mind). The short of it is on M3's the front end geometry is compromised because the roll center falls much faster than the center of gravity.

So, that means the front end can only be lowered mildly (some club racer's ride on 4x4's ) and needs to be STIFF (compared to general: stiffer = understeer). M3's benefit from stiff front spring rates (spring and sway bar), obviously to a point.

[GotBHP?]

Originally Posted by YAOGinanM3

Eddie916,

Roll center is an imaginary geometric point about which the chassis is trying to roll around on the long axis of the chassis. Camber is not the same thing as roll center. Camber angle is the vertical angle of the wheels and tires viewed from the front or rear along the path of the car.

You have a roll center in front and a roll center at the rear of the chassis and if you draw a line between the two you can see the relationship change as you alter the roll center height. These points move around all of the time (except when the car is stationary) depending on what the suspension is doing at the time you are looking at it. A lot of the way a car handles or behaves can be seen by this imaginary line between these two imaginary points in space.

Depending on the suspension design type, when you lower the chassis ride height the roll center height is also normally lowered, usually even faster then the ride height (depending on geometry of course) and this allows more body roll. More body roll on a strut suspension chassis is bad because the more roll you allow the less grip you have due to reduced camber which reduces the tire contact patch. So normally unless you correct the roll center height you will be losing grip on the end of the car you lowered unless of course you add more static camber or relocate the pivot points of the suspension to restore/correct roll center height.

So if you lower the front of your car significantly more than the rear you may have been the cause for that new found increased push in the corners.

HTH!

Don't forget to mention the reason that lowering the roll center too 'quickly' causes the roll angle of the car to increase: Lateral forces act upon the vehicle's CG, and it is the distance between the CG and the instantaneous roll center that creates the roll moment. Increasing this distance between the CG and roll center increases the roll moment for a given lateral acceleration, and thus you get increased body roll.

I have heard of train suspension designers putting the roll center *above* the CG of the train, which causes it to actually lean into turns

In addition to roll center spacers, or whatever you want to call them, I have seen bump steer correction spacers on E36's as well. I don't know if any of the companies out there offer these, but they should...

[284Shooter]

Holy crap,,, just put the car back to stock ride hight and forget about it......

[bennyfizzle]

Yeah quick everybody back to stock suspension QUICK.

We're all going to lose literally tenths of seconds around a race track because our cars are too low and look too good

gogogogogogogo

[TheM3nsah]

Originally Posted by bennyfizzle

Yeah quick everybody back to stock suspension QUICK.

We're all going to lose literally tenths of seconds around a race track because our cars are too low and look too good

gogogogogogogo

ill beat you to it!!!
hurryyyyyyyyyyy we alll gotta get back stock!

[Rennmeister M3]

There's too many big terms for the BF.c kiddies. You just need to slam yo ride and talk about stretch and poke and a bunch of other faggoty horsechit.

How dare you want to actually consider dynamics.

Also, Ackermann is pointless to adjust in a street car.

[Tommay85]

I don't know how big of a deal this roll center thing is with our cars. But with VWs and mustangs it's a HUGE deal. Serious handling issues when you lower those cars more than an inch.

A spindle drop is and always will be the best way to lower a car. For some reason though, these kind of kits are not available to most modern cars. Old muscle cars and any truck are the only vehicles I've seen with this kit available.

Seems the 60s muscle car guys actually know a thing or two with their "poor handling" lead sleds....

Yes I'm ranting because lowering with springs and then having to deal with adjusting the suspension is just more cost and seems completely idiotic when a simple spindle drop kit would be so much easier and cheaper. Well cheaper with my cougar at least.

Food for thought, I'm running el cheapo falken azensies(however you spell it) and haven't had a single lowered E36 come close to my times auto-crossing and I suck in all reality. So yes, stock ride height handles better.

[RRSperry]

Live axles and "A" arms... We ain't got those. (although nothing wrong with A arms..)

Bumpsteer? You run out of suspension travel b4 you have any issue with bumpsteer.

[284Shooter]

My point was this is a street car, in the E36M3 forum NOT the track forum. If you are pushing your car THAT hard on the street, very soon you'll have a thread parting your car out.

The Subie and Honda aftermarket has kits with extended balljoints and rod ends to correct for big drops. How much does it help the street driver,,, probably not a whole hell of a lot. Would I like to have the proper geometery with my drop, sure. Is it worth the thousands it would take to do it for a street car,, again,, probably not.

[YAOGinanM3]

Originally Posted by 284Shooter

My point was this is a street car, in the E36M3 forum NOT the track forum. If you are pushing your car THAT hard on the street, very soon you'll have a thread parting your car out.

The Subie and Honda aftermarket has kits with extended balljoints and rod ends to correct for big drops. How much does it help the street driver,,, probably not a whole hell of a lot. Would I like to have the proper geometery with my drop, sure. Is it worth the thousands it would take to do it for a street car,, again,, probably not.

Hi Shooter,

So are you telling me that the people in this E36M3 group is a bunch of posers? I didn't realize this when I saw the title of the forum. I was under the impression that any group of M3 owners would have an interest in making educated decisions and sharing product experiences about buying modifications that work and can actually improve what it is they are trying to improve about the car's handling grip and performance.

How do you know the improved geometry is not worth the cost which you also don't seem to know? You must be guessing because so far nobody has posted anything solid except to call and ask some of the popular parts houses what they offer to correct these issues. By the way none of the posted vendor website have anything on their websites to resolve the specific geometry issues I was asking about.

It used to be that BMW people used to be serious about their car's performance and looks just came with the territory, how things have changed since the days of the 2002.

Cheers/Chip

[RRSperry]

since 99.1% of people here drive street cars, on the street, there is no perceived benifit to trying to correct a problem that doesn't effect on street performance.

For a dedicated track car it might be meaningful.

[284Shooter]

Chip,

Originally Posted by YAOGinanM3

Hi Shooter,

So are you telling me that the people in this E36M3 group is a bunch of posers? I didn't realize this when I saw the title of the forum. I was under the impression that any group of M3 owners would have an interest in making educated decisions and sharing product experiences about buying modifications that work and can actually improve what it is they are trying to improve about the car's handling grip and performance.

Not that people aren't interested in it, but that most don't have the knowledge to do it correctly, including myself. It can take race teams years to develop a car. For street duty, even a dropped car with horrible set-up should corner at speeds that will land you in jail or the morgue.

How do you know the improved geometry is not worth the cost which you also don't seem to know? You must be guessing because so far nobody has posted anything solid except to call and ask some of the popular parts houses what they offer to correct these issues. By the way none of the posted vendor website have anything on their websites to resolve the specific geometry issues I was asking about.

You're 100% correct, I have no idea how much it would help. There is a thread in the track forum now that is dealing with this. You would likely get better answers from threads in the track forum like this one: http://forums.bimmerforums.com/forum...ght=bump+steer Just the parts for the test arms and rod ends are running over $800, and they are spherical bearing parts. Not something I would daily drive. Here is another thread with a kit for sale: http://forums.bimmerforums.com/forum...ght=bump+steer If this was a big problem on street driven cars, there would be a sh!t pile of aftermarket parts for it already. Would I like to have an option to buy a set-up made for dual duty? You bet. Could I take advantage of it? Probably not, but that doesn't mean I wouldn't buy it

It used to be that BMW people used to be serious about their car's performance and looks just came with the territory, how things have changed since the days of the 2002.

Cheers/Chip

Old cars are fun because there have been so many improvements since they were made that you can see huge gains with little investment. Newer cars, not so much.

I wasn't trying to crap on your thread. Sorry that you took it that way. Good luck with finding this information. I will be the first one to congradulate you when/if you get this figured out.

Regards,

Chris

[YAOGinanM3]

Originally Posted by RRSperry

Live axles and "A" arms... We ain't got those. (although nothing wrong with A arms..)

Bumpsteer? You run out of suspension travel b4 you have any issue with bumpsteer.

Hi RRSperry,

If Koni Challenge GS and GT results are any indication there is nothing wrong with live axles either, at least on the race track.

I have not had a chance carefully consider the suspension design and geometry on my recently acquired E36 M3 yet. I've been too busy for the last several years trying to coax my S197GT Mustang's suspension to work better in the canyons along Mulholland in the S.F. valley and Malibu.

But it's amazing what you can do with some measurement, thought and a lot of carefully selected off the shelf parts to what is basically a hacked up Lincoln LS and Jaguar S Type DEW98 sedan chassis with the SLA front and rear suspesnion bits stripped out of it.

Cheers!

Originally Posted by RRSperry

since 99.1% of people here drive street cars, on the street, there is no perceived benifit to trying to correct a problem that doesn't effect on street performance.

For a dedicated track car it might be meaningful.

Hi RRSperry,

Everything you do to your car affects performance. Where you happen to drive it makes no difference.

HTH!

Originally Posted by 284Shooter

Chip,

Not that people aren't interested in it, but that most don't have the knowledge to do it correctly, including myself. It can take race teams years to develop a car. For street duty, even a dropped car with horrible set-up should corner at speeds that will land you in jail or the morgue.

You're 100% correct, I have no idea how much it would help. There is a thread in the track forum now that is dealing with this. You would likely get better answers from threads in the track forum like this one: http://forums.bimmerforums.com/forum...ght=bump+steer Just the parts for the test arms and rod ends are running over $800, and they are spherical bearing parts. Not something I would daily drive. Here is another thread with a kit for sale: http://forums.bimmerforums.com/forum...ght=bump+steer If this was a big problem on street driven cars, there would be a sh!t pile of aftermarket parts for it already. Would I like to have an option to buy a set-up made for dual duty? You bet. Could I take advantage of it? Probably not, but that doesn't mean I wouldn't buy it

Old cars are fun because there have been so many improvements since they were made that you can see huge gains with little investment. Newer cars, not so much.

I wasn't trying to crap on your thread. Sorry that you took it that way. Good luck with finding this information. I will be the first one to congradulate you when/if you get this figured out.

Regards,

Chris

Hi Chris,

Hey I didn't take it that way. I just was surprised at the lack of interest in how things like springs that folks are changing on their cars changes other stuff like suspension geometry and steering geometry.

I've been a suspension freak for 40 years and have for the most part only driven German made cars (various German Fords, VW's BMW's Porsche 911 and 914/6) until I bought one of the new S197 Mustangs in '05. I've sort of been away from the Germans since then having just a bunch of fun tweaking and testing, tweaking and testing the less refined but very entertaining S197 Mustang GT. I've been trying to keep it more street car than race car because it's a DD but the dark side has been calling out to me.

The E36 M3 is for my 15 and 17 year old sons to drive. It's our project this winter to completely rip out and rebuild the suspension from the subframe bushings up and the same for the brake system. So I'm looking around gathering up information and getting a feel about the BMW folks here and for out little project. What I keep finding is that BMW folks are still rabid about BMW's but not for the same reasons they used to be back in the day.

Our local BMW club used to meet twice a month and attend a lot of parking lot autoX events. They seem to have disappeared completely and in its place is an L.A. area club website with no club events posted on it. It makes me sad. There are plenty of Porsche folks and even more Corvette people out there who still have the same sporting heart that was once lead by the ranks of BMW owners.

Cheers/Chip

[284Shooter]

Chip,

I hear you on the wrenching. There are still plenty of drivers who do their own work and tweek the cars themsleves.

Ahh Mustangs. You can buy a set of high performance heads and cams for the price of a set of E36M3 aftermarket cams. The '94 to '03 Mustangs are probably the cheapest way to get into a HPDE/Track car for the least outlay of cash. You can basiclly build one from the tires up out of parts catalogs. I would love to own a Saleen.....

I think the more you explore the E36's, the more you'll see that there is a split between the folks that drop for looks, the folks that leave it stock~ish for good performace and road manners, and most of us that fall in between. I think most of us trust that a modest drop and a few tweeks of camber, offset, shock damping and tires will get the car "good enough" to be dangerous. The vast majority of us will drop between .75" to 1.5" and then play with shocks and camber to get the car to handle the way we like it. It seems to work, though I think most would admit that they never really stop tinkering to get it 1/10th better.

If you want to check out a very good dual use set-up, loos at the Dinan stage3. You'll see the front end basiclly sits at stock height, but the spring rate, dampers and camber are all spec'd. (of course that's a secret) The cars drive under braking, lift under throttle and don't have much of the "modified" look but they handle extremely well.

I was looking at products from white line, etc. to see if they made any replaceable ball joints (we can use E30 aluminum control arms to utilize these) and rod ends with different length shafts dependant upon drop, etc. I couldn't find any that I find acceptable for street and occasional track duty. Hopefully, you find that I was slacking and missed some good stuff. If so, let us know. The next time I need tie rod ends or control arms I'll upgrade!

A 15 and 17 year old with an M3. You must really trust your kids!

Chris

[YAOGinanM3]

Originally Posted by 284Shooter

Chip,

I hear you on the wrenching. There are still plenty of drivers who do their own work and tweek the cars themsleves.

Ahh Mustangs. You can buy a set of high performance heads and cams for the price of a set of E36M3 aftermarket cams. The '94 to '03 Mustangs are probably the cheapest way to get into a HPDE/Track car for the least outlay of cash. You can basiclly build one from the tires up out of parts catalogs. I would love to own a Saleen.....

I think the more you explore the E36's, the more you'll see that there is a split between the folks that drop for looks, the folks that leave it stock~ish for good performace and road manners, and most of us that fall in between. I think most of us trust that a modest drop and a few tweeks of camber, offset, shock damping and tires will get the car "good enough" to be dangerous. The vast majority of us will drop between .75" to 1.5" and then play with shocks and camber to get the car to handle the way we like it. It seems to work, though I think most would admit that they never really stop tinkering to get it 1/10th better.

If you want to check out a very good dual use set-up, loos at the Dinan stage3. You'll see the front end basiclly sits at stock height, but the spring rate, dampers and camber are all spec'd. (of course that's a secret) The cars drive under braking, lift under throttle and don't have much of the "modified" look but they handle extremely well.

I was looking at products from white line, etc. to see if they made any replaceable ball joints (we can use E30 aluminum control arms to utilize these) and rod ends with different length shafts dependant upon drop, etc. I couldn't find any that I find acceptable for street and occasional track duty. Hopefully, you find that I was slacking and missed some good stuff. If so, let us know. The next time I need tie rod ends or control arms I'll upgrade!

A 15 and 17 year old with an M3. You must really trust your kids!

Chris

Chris,

Hey I forgot to say thanks for the links. I love working on cars, I even install suspension and bolt-on engine stuff for some of the local S197 people for free. Literally tons of suspension stuff has passed through my garage and installed on S197 cars so I've seen a lot of bad and some good stuff for these cars. My wife thinks I'm nuts but I like playing with cars whenever I can and these guys have managed to keep my garage Freezerator FULL of my favorite beer for the last 4 years or so.

As far as the E36 M3 suspension goes I'm going to pretty much set it up as stock as I can with some specific changes for durability like the RMS. I'm probably just going to stick Ground Control/Koni SA dampers in the car and keep the stock springs or possibly install H&R O.E. Sport springs. I really do not want to mess up the basic suspension and steering geometry if I don't have to. Stock E36 M3's are pretty sweet driving just as they come when the bushings and dampers are fresh but they seem to go away pretty quickly in terms of mileage. There are plenty of other things that this series/generation BMW is notorious that I also need to budget for like the cooling system.

This car is supposed to be my kid's car and as such I don't really want to spend more time and money correcting suspension geometry that got changed if it could have been avoided by simply leaving well enough alone. I've been playing exclusively with German cars (O.K. there was that '69 Boss 302 I restored and my new S197GT in 2005) for nearly 40 years and I have learned a thing or two in that time.

My '05 Mustang is not a refined a street car any more (not that it was ever that refined) it suffers from racecar-itis lately. I still use it as a DD but it is a bit stiff legged and likes being driven more than cruised. I need to avoid this with the little E36 M3, I need it to remain a "nice" car. My sons think the Mustang is too much work to drive and has way too much power and hard riding and noisy. But I wanted to get them a car with very good dynamics and decent safety equipment on the cheap. IMO the E36 M3's are really a bargain if you get one with reasonable mileage and no rust.

Thanks again for all your help!

Cheers!

[284Shooter]

Sounds like you have a game plan.

If you want to do some basic "go-fast" stuff that will allow you to tinker with the set-up, looks at camber plates (Vorschlag and Ground Control seem to be most used, but TC Klein makes a nice set too), Adjustable rear control arms (SPC makes an inexpensive steel set, Turner, etc. sell nice aluminum units), HR Sports are decent spings, and Koni's are how I'd go if I was doing mine over and not going to adjustable coil-overs. I wouldn't expect as many miles out of the Koni adjustables,, but I think they're a more comfortable ride. If Koni would make a full strut instead of inserts, I'd like them that much more!

Used coil over kits come up all the time. This may be the way to go, as you can inexpensively change the spring rates as well as set your ride height, then corner balance.

I currently run Bilstein Sports with HR Sports. I find the Bilsteins too be to harsh for daily driving. They do very good with slower type response, but quick damping is too rough in my opinion. In fairness, I run Treehouse eyeball front control arm bushings, and Powerflex rear training arm bushings, but I had the Billy/H&R combo before these and the ride and NVH didn't change any noticeable amount after the LCAB/RTAB's were changed.

[CMG]

I vote for this being the best thread this week. I only had the brainpower tonight to read like two posts but I'll be back tomorrow to read more. I adjust coilovers, swaybars, ball joints, etc. and I realize I don't have the slightest idea what I'm doing. Pretty soon my 240 will be 100% pillow ball so I think I should do some learning quick.

[dRock13]

Originally Posted by bmwpowere36m3

^ Well it seems like you have you answer, yes there are kits available but they are expensive, extensive, and difficult to properly adjust (RRT and BW come to mind). The short of it is on M3's the front end geometry is compromised because the roll center falls much faster than the center of gravity.

So, that means the front end can only be lowered mildly (some club racer's ride on 4x4's ) and needs to be STIFF (compared to general: stiffer = understeer). M3's benefit from stiff front spring rates (spring and sway bar), obviously to a point.

why my front is high....

[GotBHP?]

Originally Posted by CMG

I vote for this being the best thread this week. I only had the brainpower tonight to read like two posts but I'll be back tomorrow to read more. I adjust coilovers, swaybars, ball joints, etc. and I realize I don't have the slightest idea what I'm doing. Pretty soon my 240 will be 100% pillow ball so I think I should do some learning quick.

There are some excellent books that go over all of these items. I suggest some of Carrol Smith's books if you are a beginner or not an engineer, and Milliken/Milliken if you are.

[RRSperry]

My 2 cents...

If you are going to let your sons drive the M3, I suggest you modify them first.

Even in broke dick, worn out, used up condition, the M3 is still way better than they are. It will write checks their skills can't cash. Any suspension changes you make reduces the recovery margin of error. In stock form, the M3 is really predictable, gives lots of warnings, and pretty easy to catch and correct if you overcook it. The more poly, spring rate, shock damping, sway bar diameter, sticky tires you put on, reduces the gap and all of a sudden, you're into OH CRAP territory.

I know our local BMW chapter has teen aged driver safety track days, you should check to see if yours does too. It might be the best $ you spend.

I'd sure hate to be the parent that unleashed an untrained 16yo with a M3 on the outside world, when the 2am knock on the door, or phone call comes...

Ok, rant off.

Ever wonder why Steve Dinan cars aren't very low? (E36 M3 is .5 inch lower than stock) Answer, because that's what works in the real world...

My world contains speedbumps, driveways, potholes, rough roads, and debris that falls off other peoples POS cars...lol

I have H&R OE Sport springs, Koni's, UUC swaybarrians, and rubber bushings. (I do have the Ground Control derlin RTAB limiters) I think it's perfect for the street. Nobody with a more "sporty" suspension has ever driven away from me on the club tours. Usually it's the other way round. Their cars are so stiff and usually skittish on real roads that they are very uncomfortable and dial it back... And I'm talking 7-8/10's. That said, those cars would walk away on a race track...(maybe not a really bumpy one like Nelson Ledges)

[ScotcH]

The bumpsteer is nearly perfect when the control arms are parallel to the ground. In the M3, this happens with a mild drop. When we measured our race cars, the heights were 5.5" and 6.25" at the front and rear jack points. This ride height gave the best handling, and the measured bumpsteer and camber gain in bump was perfect.

The bumpsteer and roll center kits are only needed if you go very low. Since our rules have a min ride height of 3", we didn't need them.