Z4MC: reducing understeer: increase or reduce front pressures?

[Screamer]

Hi all,

Going on a trackday at Oulton Park (UK) tomorrow and am interested in people's advice on how to give myself more front-end grip via tyre pressures. Last time I was there, I was fighting front slip from my 19" CSL's through some of the more sweeping, larger-radius corners, so would like to make the car a little less prone to do that as much.

The problem i've got is knowing whether I should reduce the front pressures compared with the rears (tyre is less rigid, larger contact patch on circuit by my reasoning), or increase them (increases the front tyre's load capabilities, means it's less likely to collapse and roll over under hard cornering from what I've read). In various places, i've heard both being suggested, so was hoping for some more Z4-specific info.

Thanks!

[Randy Forbes]

Increase front tire pressure over the rears is the general rule, but how much is dependent on multiple factors.

On a Z3M Rdstr (totally different car, but my most recent experience to offer as an example) I would run 3-1/2 to 4-1/2 higher PSI in the front than the rear.

[Screamer]

Thanks Randy - much appreciated. Will give that a go.
I'm guessing that uping them is particularly effective on our (Z3's and 4's) cars because there's also the weight of fairly large engines up front that lean on the tyres while cornering, perhaps more than some other cars..?

[dwm]

Tire pyrometer can help tremendously in making tire pressure decisions. You're sort of flying blind without one. I'd pick one up.

[Palantirion@BMS]

The general rule is to increase pressure on the end you want to slip more. I don't think that a tire pyrometer is as useful a tool as you eyes. Look at the tread, is it grained? lightly? heavily? This indicates how hard you are using that tire, and you can usually tell how the tread width is being used by the way the graining changes across the face. How far down the sidewall is the rubber being scrubbed? You should see some degree of scrub maybe 1/4 inch "around the corner" from the tread. If you see more, that tire is probably under inflated for those conditions. If you don't see wear except on the tread surface, drop 2psi and you will probably increase your grip.

First seek to maximize the grip of each tire, as well as you can for the circuit and temperature. Then take away grip (IE: add 2psi) from the rear if you want to reduce understeer.

Also make sure you honestly appraise your driving style. Most understeer is driver-induced. Don't drive hard into a turn, drive hard out!

[Screamer]

Thanks for the reply Palantirion, but hang on: you're saying that taking away pressure is the way to add grip?! Isn't that exactly the opposite of what everyone else has been saying? Your reasoning makes sense though, and is what I originally thought (lowered pressures - within reason - means more tyre in contact with the circuit). Like you say, I guess it's a case of first getting the settings so that you're using 1/4 inch of the sidewalls, and then tweaking around there to get things how you want them. Just that everyone else seems to be saying that if you want a bit more front-end grip, you actually increase front pressures, rather than reduce them...

[Vodka G]

Thanks for the reply Palantirion, but hang on: you're saying that taking away pressure is the way to add grip?! Isn't that exactly the opposite of what everyone else has been saying? Your reasoning makes sense though, and is what I originally thought (lowered pressures - within reason - means more tyre in contact with the circuit). Like you say, I guess it's a case of first getting the settings so that you're using 1/4 inch of the sidewalls, and then tweaking around there to get things how you want them. Just that everyone else seems to be saying that if you want a bit more front-end grip, you actually increase front pressures, rather than reduce them...

nope is true, when you have understeer you want to INCREASE your psi on the rear.

we know that the front is not getting enuff grip (hence is understeering) so if you take away increasing the psi in the rear help balance out this deficient of grip up front and makes the car more netural

i had to do the same thing on my TT (a diff car) to combat the heavy understeering

[The HACK]

Thanks for the reply Palantirion, but hang on: you're saying that taking away pressure is the way to add grip?! Isn't that exactly the opposite of what everyone else has been saying? Your reasoning makes sense though, and is what I originally thought (lowered pressures - within reason - means more tyre in contact with the circuit). Like you say, I guess it's a case of first getting the settings so that you're using 1/4 inch of the sidewalls, and then tweaking around there to get things how you want them. Just that everyone else seems to be saying that if you want a bit more front-end grip, you actually increase front pressures, rather than reduce them...

There's a certain PSI where the grip of the tire is maximized. Depending on the brand and make of the tire it can vary from 38-44psi HOT.

So to figure out what to do when you're understeering/oversteering, you need to figure out how close you are to the ideal hot pressure and add air/remove air to increase grip to the end that is slipping. So if you're coming into the pits with 45psi front and 38 psi rear, and your tire's ideal grip level happens around 38 psi hot, taking air out of the front may actually DECREASE understeer by increasing the amount of grip up front. However, if your hot pressure is 36 psi front and 38 psi rear, adding air to the front may also DECREASE understeer because you're adding grip up front.

So you see, there's no simple formula in "adding air up front = less understeer" or however you think you understand understeer or oversteer. The situation is compounded by the fact that while driving on the street you will never reach the hot pressure you're likely to see on the track, nor in autocross environment. So you'll see autocrossers bump their pressure way up to close to the ideal tire pressure while hot when they do their timed runs. What BMW puts as a recommendation, for example, 30 psi front and 32 psi rear (I'm putting numbers out of my @ss here), may initially result in an understeer state, but as the tires heat up the pressure may equalize (understeering, or the front tires slipping, causes the front to heat up faster) and ultimately you may end up with a neutral stance once both tires heated up to temp. So in this situation, inflating the front up by a couple of PSI may solve understeer on the street but ultimately introduce understeer again when tires are up to temp.

If you're not confused enough to continue reading, you also need to figure out which "understeer" you have. Steady state, corner entry understeer or corner exit understeer. How you cure each may differ.

[Palantirion@BMS]

There's a certain PSI where the grip of the tire is maximized. Depending on the brand and make of the tire it can vary from 38-44psi HOT.

So to figure out what to do when you're understeering/oversteering, you need to figure out how close you are to the ideal hot pressure and add air/remove air to increase grip to the end that is slipping. So if you're coming into the pits with 45psi front and 38 psi rear, and your tire's ideal grip level happens around 38 psi hot, taking air out of the front may actually DECREASE understeer by increasing the amount of grip up front. However, if your hot pressure is 36 psi front and 38 psi rear, adding air to the front may also DECREASE understeer because you're adding grip up front.

So you see, there's no simple formula in "adding air up front = less understeer" or however you think you understand understeer or oversteer. The situation is compounded by the fact that while driving on the street you will never reach the hot pressure you're likely to see on the track, nor in autocross environment. So you'll see autocrossers bump their pressure way up to close to the ideal tire pressure while hot when they do their timed runs. What BMW puts as a recommendation, for example, 30 psi front and 32 psi rear (I'm putting numbers out of my @ss here), may initially result in an understeer state, but as the tires heat up the pressure may equalize (understeering, or the front tires slipping, causes the front to heat up faster) and ultimately you may end up with a neutral stance once both tires heated up to temp. So in this situation, inflating the front up by a couple of PSI may solve understeer on the street but ultimately introduce understeer again when tires are up to temp.

If you're not confused enough to continue reading, you also need to figure out which "understeer" you have. Steady state, corner entry understeer or corner exit understeer. How you cure each may differ.
-What he said.

If you want some very good reading on the subject I recommend Drive to Win by Carroll Smith.

[Screamer]

Thanks both! To be honest, your descriptions of it not being so clear-cut make much more sense to me (even if it means having to be much more clever with pressures). Almost bought Drive to Win ages ago as it happens, but settled on Going Faster (Skip Barber) instead. Great book, but haven't finished it yet, so don't know if it covers the same subject.

[pal]

Palantirion's and the THE HACK's analysis is spot on. One thing to note is that the decision is dynamic depending upon the track, the weather conditions and more importantly how you, the driver, feels that day. Be very aware of your driving style, esp through corners, and the behavior of the car. Everytime you come into the pits, look at the the tread and sidewalls carefully- are you rolling too much? Is the front rolling more than the rear? How is the feathering on the tread- front vs rear, side to side? And then play with tire pressures ...

First time out, I noticed that my front left (driver side) tire was rolling onto its sidewall and it was more than the front right (track had more challenging right turns) so I bumped up the tire pressure 2 psi on the passenger side and 3 psi on the driver side. Next session was a hundred times better.

Also, I have noticed over the past few track events that 36 psi front and 34 psi rear (on stock tires, stock suspension, stock wheels) seems like a good starting point on every track and then I adjust from there between sessions.

One more thing to note is that don't focus too much on the car and nitty gritty details but rather on technique and driving style- much more fun and a quicker way to improve.

[Palantirion@BMS]

Thanks both! To be honest, your descriptions of it not being so clear-cut make much more sense to me (even if it means having to be much more clever with pressures). Almost bought Drive to Win ages ago as it happens, but settled on Going Faster (Skip Barber) instead. Great book, but haven't finished it yet, so don't know if it covers the same subject.
-Going Faster is really good book. It's language is basic but it covers everything you need to know as a beginning driver. I ended up giving mine to a friend after I read it. as it better suited where he was with his driving. The reason I like Drive to Win so much (and Smith's other books) is that it is very technically detailed, going into the physics behind traction and the inner workings of shock absorbers, and then linking that knowledge to the driving experience. It's perhaps overkill for a casual driver, but if you start tuning your car or just have a highly inquisitive mind then it could be useful.

[70RTY]

I have heard that the installation of the strut brace can help reduce understeer. Is this correct?

[Palantirion@BMS]

I have heard that the installation of the strut brace can help reduce understeer. Is this correct?
-Stiffening a car's chassis (as opposed to the suspension) increases the tire's contact patch efficiency. The chassis/frame/unibody/etc. is essentially a giant, inefficient torsion spring. This spring has no damper (shock absorber) to quell oscillations. Flexing and oscillation change the positions of the suspension arm pivots relative to the tires. This reduces the suspension's ability to properly position each tire and therefore effects the contact patches.

Adding a strut bar is like adding a beam to an unsupported section of a bridge. Tie two end points together and the structure becomes significantly stiffer/stronger. This added stiffness helps to more accurately locate the tires and increases traction.

[The HACK]

I have heard that the installation of the strut brace can help reduce understeer. Is this correct?

No.

If you look in the engine bay you'll notice the strut is already triangulated with a set of two braces to the chassis bulkhead. Anyone telling you that adding a set of strut brace on the E85/E86 chassis reduces understeer is just trying to justifying their $300 purchase.

Having the struts braced to the chassis bulkhead is 1,000X more effective than having the two struts braced to each other.

But it sure looks cool.

[Caddyshk]

No.

If you look in the engine bay you'll notice the strut is already triangulated with a set of two braces to the chassis bulkhead. Anyone telling you that adding a set of strut brace on the E85/E86 chassis reduces understeer is just trying to justifying their $300 purchase.

Having the struts braced to the chassis bulkhead is 1,000X more effective than having the two struts braced to each other.

But it sure looks cool.I seem to recall a number of issues with broken or loose strut braces in the factory setup?

[pal]

Having the struts braced to the chassis bulkhead is 1,000X more effective than having the two struts braced to each other.

But it sure looks cool.

That is correct.

But dismissing the strut tower brace as a pure cosmetic add-on is something I dont agree with. Coming from an Audi TT which has a super stiff structure (short wheelbase, short hood, underbody bracing, strut tower tied to the firewall/bulkhead and the strut tops, tube frame reinforcements etc), I felt the M Coupe lacking in the stiffness department mostly on the front ... this has gone with the OEM strut brace and the car feels a lot more sure footed.

As far as banishing understeer, I dont think it does that but it does improve the feel and confidence on a road course. Incremental improvement and some may not find it worth the $$ while others do ...

[Palantirion@BMS]

No.

If you look in the engine bay you'll notice the strut is already triangulated with a set of two braces to the chassis bulkhead. Anyone telling you that adding a set of strut brace on the E85/E86 chassis reduces understeer is just trying to justifying their $300 purchase.

Having the struts braced to the chassis bulkhead is 1,000X more effective than having the two struts braced to each other.

But it sure looks cool.
-From a strength standpoint I agree with you. But there is no way that the two supplemental strut braces tied to the bulkhead will keep the shock towers aligned from lateral stress. The geometry doesn't work. The BMW strut brace stiffens the strut towers laterally, the supplemental braces stiffen the towers longitudenally (relevant to braking forces).

[The HACK]

I think at this point we'll have to agree to disagree...

But my parting rationale: If a supplemental strut brace really would make that much of a difference in structural rigidity or prevent the front suspension from flexing, wouldn't BMW include it in the chassis in the first place? They've shown in past chassi (is that how you spell multiple of chassis?) that when adding additional support would improve handling, they wouldn't hesitate in adding it to a running production. Case in point, the front cross brace on the E36 M3 was a late addition...It didn't come on earlier production M3s. Or the strut brace on the E46 M3s (although I still think that was more marketing than anything else, I put the same brace on my E46 323Ci and felt absolutely no difference in handling. But it look really good).

I think this is certainly one of those parts where everyone has bought into the "marketing" magic, like cross drilled rotors and cold air intakes.

[pal]

I think this is certainly one of those parts where everyone has bought into the "marketing" magic, like cross drilled rotors and cold air intakes.

We must agree to disagree on the strut brace issue and front end stiffening :thumbup:

[RobMCoupe]

Nice discussion here. Always learn something here.

I'm not as technical as other folks here. I was a bit doubtful about the strut brace like Hack. Then I said what the heck and get it because it sure looks cool. There is a difference how the car behaves with one. It's more apparent on long sweepers with uneven pavement. W/O strut brace, I need to constantly adjusting my angle slightly. With strut brace, I can hold the angle much better.

It's just the way I feel.

[MGRMLN]

Increase front tire pressure over the rears is the general rule, but how much is dependent on multiple factors.

On a Z3M Rdstr (totally different car, but my most recent experience to offer as an example) I would run 3-1/2 to 4-1/2 higher PSI in the front than the rear.

Absolutely.
I generally run +3 in the front vs the rear to help neutralize understeer.

[MGRMLN]

I think at this point we'll have to agree to disagree...

But my parting rationale: If a supplemental strut brace really would make that much of a difference in structural rigidity or prevent the front suspension from flexing, wouldn't BMW include it in the chassis in the first place? They've shown in past chassi (is that how you spell multiple of chassis?) that when adding additional support would improve handling, they wouldn't hesitate in adding it to a running production. Case in point, the front cross brace on the E36 M3 was a late addition...It didn't come on earlier production M3s. Or the strut brace on the E46 M3s (although I still think that was more marketing than anything else, I put the same brace on my E46 323Ci and felt absolutely no difference in handling. But it look really good).

I think this is certainly one of those parts where everyone has bought into the "marketing" magic, like cross drilled rotors and cold air intakes.

You give car manufacturers too much credit. They are not in the business of optimizing cars. That is the domain of the aftermarket.
BMW creates cars that are a part of a Product "ladder". For example, a higher priced M3 must be made to be faster than the lower priced M Coupe. So they hobble the M Coupe.

[stephenti]

Increase front tire pressure over the rears is the general rule, but how much is dependent on multiple factors.

On a Z3M Rdstr (totally different car, but my most recent experience to offer as an example) I would run 3-1/2 to 4-1/2 higher PSI in the front than the rear.

I've generally run more pressure in front vs. rear in prev cars... but w/ the M Coupe, a shop that does a lot of BMW's recommended approx 4psi higher at the rear... any validity to this?

[Screamer]

Hi guys - just stumbled back across this thread. Thanks for all the replies/discussion - hopefully this is one of those threads that'll be of good use to others for quite some time.

Will look into Drive to Win, especially as it deals with the technical specifics - just the sorta stuff I like to fill my head with, even if it takes me a while to make good use of it (that said, I tend to find that anything explaining car workings/physics always has some use from the day you learn it, although it can become more or less important later on e.g. when you come to look at suspension upgrades etc).

I can confirm that the brace DOES make a difference, even in the Coupe. Frankly, talk of it being less effective in the coupe because of the stiffer bodyshell is nonsense. It's installed between the front struts because that's where it's 'needed' - an area in which both the roadster and coupe are identical. Having said that, it is a pretty subtle modification for normal road driving - to me, it only makes itself known when you're attacking corners, as you'd expect I guess. It just makes the car that little bit more neutral and seems to help make the car a little more eager to dive at the apex on turn-in. As we've established in this thread, the idea with tyre pressures is to alter them to maximise grip, and then to deliberately reduce grip at one end to adjust the car's behaviour to suit the driver. Making the car's default setup more neutral with things like the brace makes it more likely that you're not going to have to take away as much grip from one end of the car to get it to feel good. As Palantirion says, it also (and more importantly) makes the car more consistent, so it's behaviour is less likely to change in different situations simply because the car's struts aren't moving around as much, especially when that movement can be different on the left strut compared to the right strut. When you've got an adjustable suspension setup, having the car's chassis be more consistent (i.e. the car will do the same thing, understeer or oversteer, in almost all types of corner) makes it much easier to get your settings right.

Here's a plan i've got for my next trackday: on all 4 tyres, draw a line in chalk up the side of the sidewall and across the tread. That way, I should be able to do a lap, come back in, and see where the chalk has worn away. Depending on how much chalk is left on the sidewall, I can then adjust pressures to get the whole tread, but nothing more, being used. Once i've done that on all 4, it's just a case of making adjustments to suit my driving.

As for why the Z4M doesn't have a brace: well it clearly should have. Many cars have the firewall braces, even when their struts are right next to the firewall (they tend to be really short and often twisted versions of the firewall braces in the Z4). On top of that, loads of cars that have struts further from the firewall also have the strutbrace (e.g. my old RX-8). The Z4 has it's struts further from the firewall than just about any other car i've seen. Clearly, the futher the struts go from the firewall, the weaker they become - they're further from something soild to which they can anchor themselves. I believe the lack of a factory-fitted brace is down to many things: BMW don't fit it to all models because certain engines are 'incompatible' with it (is it just the oil filler cap location, or does the brace phyically not fit over the top of some of the engines?). Given that the incompatible engines aren't the smallest ones (bigger engine = more likely brace won't clear it), it'd be a bit of a marketing nightmare for BMW if some of the lower-end models came with a brace fitted (thus highlighting BMW's thoughts that the Z4 does need it) but some of the higher-end models didn't given that the chassis is the same. On top of that, officially, BMW say that the brace isn't compatible with the M models (my local dealers won't fit it for that reason). Now, that could only be because it, and the rest of the Z4 range, existed before the M models, but it could also be because of the usual technical silliness e.g. the clearance over the engine and/or bonnet doesn't meet official BMW minimums, etc. Also, I wonder if a car supplied with a strutbrace fitted would effectively class as a different chassis and would therefore need crash testing again, or even just verifying for sale again in all its markets..?

[silversprint]

Don't wast your money on strut braces. It won't make any noticeable difference changing handling characteristic or making lap times faster. The car is just fine. If you do buy one take it of for a track session and see if there is a difference. I bet it won't be noticeable. The Z4M is the stiffest BMW made. It doesn't benefit much from chassis stiffing.

If you want to get rid of your understeer put skinner tires on the the rear. You simply have too much tire rear and not enough on the front. Lessen the stagger. It would be better to go larger on the front but its very difficult to put tires larger than 45s on the front, specially in 19s. Sure 19s look great but they are definitely slower than 18s or 17s both in gearing and weight.

With the tires you have you can't really lower tire pressure too much on the front because the F1s have soft sidewalls. So pick a moderate pressure for the front and increase rear tires pressure. If you crank up rear tire pressure you may find that the understeer is still there to some degree. The effects of tire pressure on understeer/oversteer has a limit. It's better to have some understeer than to have the rear end sliding coming out of every corner with too much tire pressure. You have to find a balance.

Something else to try is adding more negative camber on the front, at least -2.5 degress, to get more front end grip under load.

Have fun. Post some pics. We need more Z4M track picks.

[Pinecone]

WRT strut braces, easy answer. Look are the Z4 race cars. Do they run them? If so, they WORK. Otherwise the would not run them, because they add weight to the front end. And realise, the forces on the strut brace under cornering loads is TENSION. The towers are trying to pull away from each other. The stock braces to the firewall are too angled to help in that regard.

WRT tire pressures, for street tires, the optimum pressure may be up more in the 50 psi range. You have to experiment. And there is more than just the max grip pressure. Higher tire pressures stiffen the tire sidewall, so the tread stays more in contact with the surface. You have to experiment. Add front tire pressure and see what happens. Reduce it and see what happens. Make 2 psi changes, and do go up and down a good bit to see what happens.

One thing to realize in tuning a BMW suspension versus the books is, to reduce understeer in a BMW you INCREASE front roll stiffness. Which is opposite most cars. This is due to the lousy camber curve that has the tire roll over as the body rolls. You will see that racing or serious autocross setups for BMW run very stiff front roll bars, lots of static negative camber, and little to no rear roll bar.

[silversprint]

This should help. M-coupe specific. It was posted on TrackHQ.com.



http://www.trackhq.com/forums/attachment.php?attachmentid=1327&d=1175772451

http://www.trackhq.com/forums/attachment.php?attachmentid=1328&d=1175772451

[Palantirion@BMS]

This should help. M-coupe specific. It was posted on TrackHQ.com.



http://www.trackhq.com/forums/attachment.php?attachmentid=1327&d=1175772451

http://www.trackhq.com/forums/attachment.php?attachmentid=1328&d=1175772451
-VERY cool flow chart :thumbup:

[Pinecone]

Sway bar info is wrong. On BMW you stiffen front bar to reduce understeer.

We run Full stiff on front bars on all our cars. The E46 M3 and Roadster run full soft rear bar, the LTW runs full stiff front and rear for autocross (smooth pavement).

[silversprint]

Not if the front no longer rolls excessively. Once you add enough bar or spring it acts like any other Mac strut suspension. From that point on you get more understeer.

The graph does say that the front Swaybar should be stiffened if the front still rolls excessively.

[thekurgan]

So, on this graph, it mentions tire pressure being assumed optimized, is that with the chalk method or a pyrometer of some sort, or would you examine tread patterns after tire break-in or soon thereafter?

[The HACK]

WRT strut braces, easy answer. Look are the Z4 race cars. Do they run them? If so, they WORK. Otherwise the would not run them, because they add weight to the front end.

Damn I can't believe I actually agree with you. :D

http://i284.photobucket.com/albums/ll30/onebluemcm/Lime%20Rock/DSC00047_edited-1.jpg

[335audioman]

For all of you who are trying to find the best way to get rid of the orange reflectors on our cars....just copy the car above! Those reflectors blend right in with those dog paws and bones. :)

As for the tire pressure discussion, I have 19x8.5 and 19x10's with 245/275 PS2's and I run 36 up front and 34 in the rear. Car handles wonderfully.

[Palantirion@BMS]

Damn I can't believe I actually agree with you. :D

http://i284.photobucket.com/albums/ll30/onebluemcm/Lime%20Rock/DSC00047_edited-1.jpg
-Interesting that almost everything under the hood looks stock. I wonder if there are rules limitations might explain the lack of a brace. I can't tell if they are running camber plates, but it doesn't look like they are running D/A shocks - let alone real racing shocks. I assume the heat shielding = headers :dunno:

[The HACK]

-Interesting that almost everything under the hood looks stock. I wonder if there are rules limitations might explain the lack of a brace. I can't tell if they are running camber plates, but it doesn't look like they are running D/A shocks - let alone real racing shocks. I assume the heat shielding = headers :dunno:

Koni Challenge Rule Book:

http://www.google.com/url?sa=t&source=web&ct=res&cd=1&url=http%3A%2F%2Fwww.grand-am.com%2Fassets%2FKONIRules.pdf&ei=IUq3SN3REILwsAOYiNWEAw&usg=AFQjCNGlQLjfTYZeKXe3bmA82UZlrGG0eA&sig2=A0pKph0pwkauzd4PnlK63Q

7-3.1 No modifications to suspension components are allowed unless otherwise approved per
vehicle make and model.
7-3.2 Shocks and springs may be replaced with commercially available aftermarket or OEM units
provided they are used without modification to any other components. Coil-over shocks
may be used provided OEM pick up points are utilized. KONI shocks are mandatory on all
KONI Challenge Series cars beginning 01/01/09
7-3.3 Caster and camber adjustments may be made with approved fitting of camber plates to an
allowable limit of negative 3 degrees or as specified by Grand-Am.
7-3.4 Front and rear sway bars may be added or replaced with aftermarket bolt on sway bars
affixed to the OEM sway bar mounting points.
Welded in sway bars are not permitted unless OEM in which case no modification is allowed.
Cockpit/driver adjustable sway bars are not permitted.
7-3.5 Any suspension bushing, sub-frame bushing, engine mount, transmission mount or
differential mount may be replaced with non metallic substitutes of the same dimensions
that do not require modification to any other component. The replacement bushing cannot
change / offset the location of any component
7-3.6 No spherical rod ends or similar applications are permitted with the exception of shock and
sway bar ends.
7-3.7 Offset ball joints may be used for camber adjustment.

If the rules allow it I can almost guarantee there's a camber plate underneath those strut towers. Also the rules permits strut and shock braces:

7-10.7 It is permitted to install a removable strut between the opposite strut tower points, front or
rear, (all classes) and permissible to run two symmetrical rearward running struts from the
shock towers to the center of the front firewall.

If you follow this thread, there *might* be an explanation as to why everything under the hood appears so stock:

http://forums.bimmerforums.com/forum/showthread.php?t=1011233

It appears they haven't figured out a way to make the new OE ECU do what they want it to do. I have to assume they probably would want to alter the air box and do some engine magicalry to it, but to get positive result from say, intake and exhaust work, they MUST be able to get some flexible ECU and to run the Bosch ECU it appears they're penalized by 250 lbs.

[deknight]

This should help. M-coupe specific. It was posted on TrackHQ.com.



http://www.trackhq.com/forums/attachment.php?attachmentid=1327&d=1175772451

http://www.trackhq.com/forums/attachment.php?attachmentid=1328&d=1175772451

This great info. Bro. Thanks for sharing. I like that you specified the point in the turn where oversteer or understeer happens since that makes a big differance. For me it is more mid turn and corner exit. I am going to remove my front sway bar. Or I may remove my rear wing.

I have a front splitter and diffuser on the way so I can use my rear wing, but that will not happend until November.:bawling:

[silversprint]

the Z4M has great Aero. The front bumper is very low and the bottom of the car is flat. When you go to the ROVAL the car should be stable all the way to over 150 mph in stock trim.

If you are going to run a wing on the back it may be a good idea to run bigger front tires or lower the front of the car slightly.