Whats your approach to chassis tuning for your car?

[8600RPM]

My goal is to ultimately turn my e92 into the ultimate track car while still keeping it comfortable inside with stock seats (for now. Rears removed), booming sound system which I enjoy and basically a nice interior so I can continue to cruise the west coast with my gf to hit about 40 track days a year. I started tracking my e92 m3 15 months ago and within a year I did about 45 track days and got hooked. Car was basically stock aside from the PFC BBK I added 6 months into the year. A couple months ago I started getting suspension going, further engine tuning and heading toward meeting my goal stated above.

I think it is tempting to start adding every single monoball and removing every last piece of rubber or moveable bushing, Its tempting to stiffen everything up. I know that was the direction I was going but over the past couple months I have read, researched and tried a variety of different things and decided on my chassis strategy that worked best to meet my goals.

First thing I began to understand is unless you are relying on pretty heavy aero which would be a much lighter car than mine is, overall chassis stiffness is not nearly as crucial. Body movement and weight transfer is needed to reach desired grip and that movement and chassis movement must be balanced and kept in check to meet your desired handling desires in terms of faster speeds, body movement, maneuverability, confidence, turn-in, speed of body roll vs your personal preference and skillset etc

I had 2 tires in mind that I liked which were RE-71r which I used most of last year and the hard side-wall, grippy and heavy nature worked really wel lwith my zcp suspension. I really liked the PSC2's but ultimately for the stock car I had, I found the sidewalls were too soft and I could not get enough heat into them quickly enough with my stock suspension.

Now however I had the opportunity to ensure full utilization of my desired tire so chose the PSC2 for many reasons such as desired feel, grip, side-wall, lightness was key. I also could drive on it daily if needed although I have a complete second spare set of wheels/tires.

Ultimately I paired them with 20 pound per wheel SIgnature monobloc forged and chose 275/35/19 rear and 255/35/19 front as that is the size I grew confident with over last year after trying several setups. So my core was a very light weight tire/wheel with a relatively soft sidewall and pretty high grip with moderate camber needs.

Next was working with my dampers of choice which were the PSI racline Ohilns ttx46 front and ttx36 rear. This came with eibach ers springs 570 front and 450 rear (true coilover which I waned as well). I wanted a true coilover for multiple reasons but largely to maximize the chassis control, minimize chassis stress and maximize the overall balance front to rear with the ability to use a much more balanced (equalized) front-rear spring rate. Performance shock designed this system for someone who waned a track car but still drove the car to the track and around town if desired. So I went with their recommendations.

I subsequently researched and calculated to the best of my abilities and their recommendations were as spot on as Ive learned any settings really can be "spot on"

This setup basically gave me wheel rate spring rates of 500 front and 330 rear spring rates. This was just about right as my third goal, which is consistent with most of you, is to minimize the body roll and camber change at the front of the car by keeping things as stiff as can be while keeping the rear loose enough and more loose than the front in order to put down power and allow rear grip to put down power through slow-medium cornering

Next in general came damper settings. After much research and trial and error (still a work in progress) I have found more luck with higher compression to rebound damping, especially in front. This is secondary to the same reason for wanting relatively higher front spring rates to rear which is to keep the front roll down and thus camber change down which ultimately leads to the highest grip through corners in a macpherson strut based car. This is of course only if thins are not too stiff where you end up sliding off of the track which I did many times when trying the RE71r with too much compression and a jacked overly stiff chassis brace I forgot I had under my car!.

Overall damper settings used more compression than rebound front and rear as well as more damping overall in front than rear for the same reasoning as stated. Stiff front and softer rear for grip.

Now next was stability in fast sweepers, switchbacks and overall control with change of directions around a track. In short I ultimately found the best feeling in terms of body control and confidence as well as overall grip in low-medium corners with an approach I consider a pretty "balanced approach"

Spring rates that were not crazy high, damping rates that were relatively aggressive but again not crazy (with a focus on more compression than rebound) and stock m3 sway bars which are kind of middle of the road impact on roll.

So the combo of "middle" spring rates, damping, and sway bar with the focus on limit front roll and max rear grip again had to be balanced with the rest of the chassis and suspension components. I had a few things on each end of the car to consider besides those 3.

Front, I eliminated the big rubber strut bushing and put the dinan monoball and I chose the TTX46 front damper because from all of my research it was the most effect at creating rigidity at the strut location and thus ultimately inherently limiting roll and thus minimizing camber change and therefore maximizing grip. I am sure every damper maker makes this claim so I wont go into it but the fact it is a through rod, thick damper, rigid forged aluminium, TTX uses almost no gas pressure and thus has no additional strut movement, no cavitation and essentially eliminates as much as possible of the reasons that a strut can contribute to more front roll.

In the rear I knew I wanted subframe solid bushings for overall suspension function and chassis stiffening. I had also had dinan toe arms already installed. I also found I had the brace under the xpipe which ties our rear shock towers together left and right way over tight and replaced with a huge steel ultra racing brace.

With the car in this state I initially had too little body movement both front and rear and using my old alignment settings of -2.8 camber front with slight toe out and -1.8 rear with slight toe in was not nearly enough body movement in the slow-medium corners as the inside of my tires were the only part getting used despite hard cornering.

So front and rear needed a bit more roll and movement believe it or not so got rid of the oversized chassis brace under the car and put small black one on which made a nice difference. I removed the dinan toe arm as the oem arm is already monoball on each end and the nice curved shape actually provides about the nicest and smoothest suspension movement you can ask for if you need a bit more movement to create grip. The rear was not just body roll but grip in general due to not ideal camber setting as well as in my view the dinan arm was too stiff for my setup.

I already had softer sidewall tires so wasn't going to change that.

In the front I simply dialed out some static negative camber and was able to set it at -1.5 front. Paired this with -1.2 rear and saw tire temperatures become even across the tread again and the grip started to come back nicely both front and rear.

Last I guess was figuring out ride height. I know I didn't want to rely on ride height to eliminate roll and camber change since too low screws geometry. I lowered my car evenly front and rear at almost GTS specs and left it there. Nothing crazy Again another "middle" type approach which goes along with everything else in my plan.

What was nice as well is I did not have to rely on static negative camber as much as I used to so at -1.5 front and -1.2ish rear, I had a lot more grip on the straights in terms of braking hard and putting down power when rear end straiaghened out coming out of a corner. I got a lot of roll elimination from my strut itself, spring rate and compression heavy damping.

The areas I deviated from some is I am not going with bigger sway bar in the front approach to limit roll. I frankly don't need any less roll at this point with my goal and my car at higher weight (not caged or stripped) and not running aero)

I also didn't have to lower my car as much to meet my goals which kept geometry in check.

Other thoughts are in my view you need to allow movement in the chassis unless you are a full out race car as otherwise you will put stress on parts of the car that the car was not designed for. My goal was to let the front and rear suspension geometry move in the way bmw intended as I feel they did a pretty great job and the subtle movement is very progressive with the way they use curved arms as a type of spring and a mix of bushings which allow full range of movement with no binding but also still leaves some deflection which means some room to let things "wiggle" and meld into the pavement for grip because at my skill level, I am not precise enough or skilled enough to manage a car with no room for error or no suspension movement at al. Plus in my view its not good for the car from a structural standpoint and for me, very importantly a comfort standpoint.

With all of this, my car is still perfectly comfortable without changing any damper settings to cruise around all day or do a 10 hour road trip to a track event which was a key goal.

Last, plan is to leave the differential bushings stock, tranny mounts stock and engine mounts stock. I will just replace them relatively frequently.

I did replace the rear strut upper mount with a monoball which I wanted for the most precise damper/suspension utilization as I could get but otherwise not going to replace any other stock bushings with monoballs or solid etc unless they were already on the car. Going to replace stock M bushings ofen enough to keep everything fresh and consistent as possible.

In the end, I realized there are so many factors that influence second by second change in suspension kinematics that a lot of it at the end is simply by going out to the track with a timer and playing with settings and seeing what feels best and is fastest. I calculated motion ratios for the dampers and re-calculated relative front to rear damping utilizing provided shock dynos and in the end our macpherson strut car also adds an element of suspension design approach that simply does not follow classic non-macpherson strut chassis design approach.

To me this is all fun and I love it but its also frustrating as hell. In the end the fun the love for this sport prevails and I am sure Ill be back telling you all how every single thought I just wrote ended up ultimately failing me!!

Just posted this for discussion-interested in hearing others approaches and variations from the norm.

[M3 Number 86]

Just need great suspension and sticky tires.

[admranger]

Originally Posted by M3 Number 86

Just need great suspension and sticky tires.

and talent.:thumbs:

Dual purpose cars are always a compromise. You just have to decide what level of compromise you're willing to live with. For me it was Eibach pro kit springs (actually, a better street ride) and a big front bar.. That's it. Well, I also didn't want to pony up $5k for JRZ or MCS remote doubles since I have no room for any more HPDE World Championship trophies. Adjustability is the key to making the compromises less, umm, compromising.

[M3 Number 86]

Originally Posted by admranger

and talent.:thumbs:

Dual purpose cars are always a compromise. You just have to decide what level of compromise you're willing to live with. For me it was Eibach pro kit springs (actually, a better street ride) and a big front bar.. That's it. Well, I also didn't want to pony up $5k for JRZ or MCS remote doubles since I have no room for any more HPDE World Championship trophies. Adjustability is the key to making the compromises less, umm, compromising.

Maybe not hpde but have you though about hpdcr? High performance driving canyon racer. Lol

[bigjae1976]

You need to be aware of variables that may make you chase the tuning...like driving skills.

Any suspension worth a damn has been tested by the manufacturer. They should be able to get you really close with some fine tuning. That's what you're paying thousands of $$$'s for. The dampers are dampers.

If you get the best shocks ever...you might spend hours at the track tuning it...which would cost a lot of money. Track time, tires, fuel, frustration, etc.

[admranger]

Originally Posted by M3 Number 86

Maybe not hpde but have you though about hpdcr? High performance driving canyon racer. Lol

High performance driving commute racer is what I do now.

[PrimeBMW]

What is my approach? I ask those that know much more than I. Fortunately I have teamed up with a great performance shop (AR Auto Service). Plus I selected a shock that has second to none customer service. MCS will get you or your shop a baseline setting. I have MCS singles on my e92 m3 and have not had to move away from their recommendations. (I did move away which ended up being slower). Now I also have MCS triples on my e46 m3 race car. In the past tuning this suspension was beyond my scope......as it is re-tuned (given spring, sway bar, weight changes, wide body/wider track) I will attempt to grasp all the little details.
Do you have anyone in your area that can provide tuning help? Performance shop or Pro driver?

[M3 Number 86]

Originally Posted by admranger

High performance driving commute racer is what I do now.

nice one

[M43S7RO]

8600RPM, you mentioned a chassis brace a few times. Was this just the Ultra center support brace at the xpipe? I've taken a look at that in the past and thought it couldn't do anything additional but it sounds like from your experience it did tighten up the rear, correct?

[Richbot]

I like your approach. You have to make the car do what you like or you're just a lemming.

I think the diff is a not-insignificant part of chassis tuning that most people who track these cars ignore for whatever reason. We do a lot of tuning to make concessions for power-down performance, tuning around a factory diff that kindof sucks for performance driving, with an engine that should not be able to give the big rear tires these cars can fit any real trouble if not for the abrupt, late lockup.

It's not near as easy to screw up a car with dampers as people make it out to be. If the car is less comfortable on the street than it was when you started, you've probably screwed up, good dampers are good if you us a reputable damper supplier, start from the middle of the adjustment range, adjust from there (agree MCS has a good baseline in the can for these cars, at least for street rates I have no idea how they do with higher rates). Don't try to fix a roll stiffness/compliance or alignment issue with a damper (this is where people really lose the plot, throwing damping changes at a problem they should be looking elsewhere to fix).

Pretty simple.

Lowering a car only messes up the geometry if it messes up the geometry, I feel like this "dropping a car wrecks the handling" thing is internet lore from the days of cut springs and Fox body Mustangs. Yeah you can't just slam a car and use the bumpstops for your whole suspension all the time (though our cars do corner on the bumpstops from the factorry), but that doesn't mean lowering the car makes it worse around a racetrack with good dampers and appropriate bump travel choices. I have seen no data to support that lowering these cars screws up the geometry significantly (so long as you have enough alignment adjustment afterwards especially in back that's an issue with stock parts), and there's a great deal of time to be had in dropping the CG height. For a dual-purpose car, I get that you don't want to set the car up low (I feel the same), but lowering in general makes cars faster around racetracks, it's physics, almost all racing series spec a minimum ride height of some sort for this reason, and racers shoot for the lower the better, so long as the car will turn and is compliant over bumps. The Grand Am series cars all converged on a relatively low ride height especially in the rear, almost tucking a 275/35-18

[crzydave17]

Originally Posted by bigjae1976

You need to be aware of variables that may make you chase the tuning...like driving skills.

Any suspension worth a damn has been tested by the manufacturer. They should be able to get you really close with some fine tuning. That's what you're paying thousands of $$$'s for. The dampers are dampers.

If you get the best shocks ever...you might spend hours at the track tuning it...which would cost a lot of money. Track time, tires, fuel, frustration, etc.

You could very easily go backwards after throwing on some coilovers while you try to tune them to your liking. And at that point, you had better be a very consistent driver to be able to tell the difference between better driving or better damping.

Hi Jae! haha

[bigjae1976]

Originally Posted by crzydave17

You could very easily go backwards after throwing on some coilovers while you try to tune them to your liking. And at that point, you had better be a very consistent driver to be able to tell the difference between better driving or better damping.

Hi Jae! haha

Is this the phallic trailer hitch ex 370z driver Dave?

[crzydave17]

Originally Posted by bigjae1976

Is this the phallic trailer hitch ex 370z driver Dave?

It is! although I removed the chubby when I got a real trailer. and it is a 350Z, but close enough.

Picked up an E90 M3 6-ish weeks ago. Now I completely understand all your hooning. (not like I didn't before, but now I really do.)

[bigjae1976]

Originally Posted by crzydave17

It is! although I removed the chubby when I got a real trailer. and it is a 350Z, but close enough.

Picked up an E90 M3 6-ish weeks ago. Now I completely understand all your hooning. (not like I didn't before, but now I really do.)

Finally you saw the light! Congrats! E90's are so fun!

[Redd]

Good read! That's for taking the time to experiment and share your findings. It helps me with a few decisions on what to do next to my own daily driven occasionally tracked car.

[Estoril Blue]

Originally Posted by PrimeBMW

Now I also have MCS triples on my e46 m3 race car. In the past tuning this suspension was beyond my scope......as it is re-tuned (given spring, sway bar, weight changes, wide body/wider track) I will attempt to grasp all the little details.
Do you have anyone in your area that can provide tuning help? Performance shop or Pro driver?

I'm doing this from memory - but I thought that the stated MCS position on their 3-ways was that they are complex to set-up and adjust properly - and that they should be used in race applications where a qualified suspension engineer was available.

I read that when I was choosing my doubles.

[PrimeBMW]

Originally Posted by Estoril Blue

I'm doing this from memory - but I thought that the stated MCS position on their 3-ways was that they are complex to set-up and adjust properly - and that they should be used in race applications where a qualified suspension engineer was available.

I read that when I was choosing my doubles.

Honestly properly set up singles will be faster than slightly off doubles or triples. The performance gain if all are set up ideally is fairly small. Certainly small enough that singles are perfectly fine for HPDE folks.