A street car is a car that is designed to tackle with SAFETY,ALL sorts of surfaces, including mild gravel, and bumpy roads, and all this with some kind of comfort.

Maybe where you live my friend, all roads are flat, with good maintained tarmac, with proper angles in the turns, etc...

Where i live, this is not the case... pot holes, saddle bumps, eroded tarmac... etc...

In your arguments you are using the term "lowering" without taking into consideration that in order to do so the absorbers AND coils have to be matched to maintain drive-ability (and safety)... but the lower you go the smoother the road should be in order for the suspension to work, and vice versa... rally cars have tall suspensions...yet their ability to corner (in the roads they are driven) is far superior than an equivalent "lowered" versions.

Yes Porsche Boxster does have a lowered version but this is with different shock/coil combination for one, and i seriously doubt it can will corner better in the roads i drive in, than lets say a Mitsubishi EVO X (which is a superb driving machine)... in a track though (smooth surfaces) the Boxster will be quicker.

When i use the term geometry it is conjunction with the real world, and this is why it was designed, to be safe and effective in various conditions...that is why the height is important to be maintained...

So all things should be in perspective, to the road surface the vehicle is going to be driven on, they cannot be viewed as separate values.

It is not rocket science to lower a car a agree with you... but in my opinion all these thing we are discussing should be taken into consideration.

For BMW... cheap solution Eibach/Bilstein, better solution Bilstein PSS9, or KW Variant3... check these out before looking into any "M" solutions

LOL!  You have never driven on the 5 freeway in southern California apparently.  The US has the worst roads in the world apart from a third world banana republic, maybe a 500 mile stretch of road through the plains of Kansas would be smooth, not California.  I've removed chunks of asphalt from the road under hard braking the asphalt is so cheap and crap here.

You are really confusing a lot of issues here and unnecessarily.  Again, you are oversimplifying and simply not accounting for real world examples.

1-No I'm not discounting anything, neither are the spring makers.  Aftermarket springs are generally equal to or higher rate than stock.  OE dampers tend to be softer, you are not going to get into trouble because of stock damper rates buying a proper Eibach, TRD, Swift or HR lowering spring kit and, this is simply not true and doesn't make any sense.  Not to mention they have already calculated the acceptable range of spring rates for the dampers in question, it's not some backyard hick w/ a Still throwing darts at a bunch of numbers and using a blow torch to cut down some springs.  Stock valving in the dampers can accomodate a wider range that you think and most are dual tube, not monotube.  Look at the FRZ/BRZ.  Dramatically different rates but same damper rates from the factory.  Ideally you would change spring rates for each track.

2-No, just no....a lowered rally car on a track would be faster than a tall rally car.  They are only taller because they need clearance driving over dirt roads in Cyprus.  That ride height also changes based on the circuits conditions, it is not static.  They use coilovers, not factory settings.  They also use skinny tires in bad weather.  Are you going to suggest we all put 150 section width on our wheels w/ metal studs to go faster around a track?  Come on.

3-You keep assuming a lowered car can not retain or improve on suspension travel or ride comfort.  While generally true based on half assed planning and hacks, this is not absolutely true, not at all.  Pretty much every stock suspension can be improved if done right.  They pretty much come flawed from the factory simply because they picking the cheapest compromise the bean counters/accountants will allow.  There are so many compromises they have to make in selecting damper and spring rates like allowing for various tire compounds across the country and various wheel/tire size packages as options.  Factory settings have a huge envelope to play around with.  This is far from ideal in either speed or comfort.

4-I find it ironic that we recommended various coilovers and kits to begin with and you were against the idea.  But not you recommend going w/ those same aftermarket solutions over solutions provided by 'M' the same people that actually make the car and designed it to be used in what you call 'real world' conditions.  I'm not sure I follow your logic.  By your train of thinking I'd think M offered the best solution because BMW actually built the car, considered all the variables, offer the suspension on their factory cars (M3/5. etc) and support it w/ a warranty and liability falls on them if they install it. 

I think I'll just leave it here as comparing a Boxster and Evo is hinting at going down a road not worth traveling.  I appreciate that you track your car, so do I and many others that use coilovers on the street.  Including manufacturers.  Tracking your car is helpful but not a validation to be a the last authority on anything.  Whether you think my degree in automotive technology, ASE certification and specialization in engine and chassis management mean anything is up to you.  It shouldn't need an appeal to authority because everything I said is mathematically and physically sound and has been repeatedly proven.  You made a decent point in relative terms to ride height under certain 'typical' conditions but have really taken what should have been a clear simple post and gone way too far w/ it IMO trying to mak it into some absolute rule, "Never lower a street car at all."

I am really taken back by your reply... i find it a little too aggressive...

I didn't mean to sound like an authority, and i am sorry if it sounded to you like that... i have had many fast cars with many many different suspension combinations... and have had done a few track schools... that's all... i don't design cars like you (i am a specialist dentist... nothing to do with cars i am afraid)... 

I spoke in general fashion, from my not so small experience... and not trying to be a know it all...

I am sorry if i offended you or the forum...

Opinions?

I want to get some Eibach springs but my friends (who also happen to get air bags in their cars and drop them to an inch off the ground) keep telling me to get coils since I'd want to lower it more than what springs can do for me...

Getting back to your question (and away from the physics/law of inertia/etc), I'd suggest the Bilsteins PSS10 coilovers... if you're the kind that switches wheels every so often to achieve a different look, keep your ride "hellaflush", you'd want some adjustability in both height and comfort. The PSS10s can take a beating and built a lot better than cheaper suspension brands. And when you dial in the height just right, it really looks nice, especially on an E46 M3 (had a friend with this setup and he went up and down the state getting Eurotuner coverage). You owe it to your Bimmer than just Eibachs! 

Wow, just remembered this thread, came into it and was kind of shocked. So much information to absorb...

Thanks you guys, I'll be looking into it more and if I need help, I'll be back.