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Discussion Starter #1
Setup
GC coilovers, Koni single adjustable, 440F/400R #/in (this is about 45% stiffer than stock and 20% than my old Dinan III)
Dinan rear bar in middle position
Dinan front strut brace
TC Designs sway bar brackets
SSRs with 275 RA1s (track) - Dinan 275 PS1F/2R (street)
aligned at 1 degree negative in front at about 1/8 inch higher than Dinan III (adjusting front camber to 2 1/2 for track results in just enough toe-out for nice turn-in without being "twitchy")

Track
Pretty much everything i had hoped for and maybe more
More forgiving - able to make fine adjustments to line and drive different lines passing or being passed - better response and control approaching limit (exceeded expectations)
Very well balanced
Better behaved under braking
Quicker -- i'd only been to Buttonwillow once, a year ago, on street tires -- my best laps were 7-8 sec quicker. allowing 3 sec for tires and 2 sec for experience, leaves 2-3 sec for suspension. However, i was still overbraking at least half the turns and believe that i can more safely work on further improvements. Will have a better idea of speed when i get to Thunderhill where i've got some history. Hopefully will see KJK at the track this summer and he can drove it for an informed 2nd opinion.

Anecdotes
had the pleasure of gradually closing on an (old) viper (compently but not expertly driven) under braking and cornering with enough extra speed through the corners that he couldn't pull me on the straights, then passing and going away
driver of stock Boxster S (experienced, but not expert) came over after session to find out why he couldn't close on me in corners

Street
Not bad but not great - at low speeds ride is FIRM but not harsh, "busy". Drove about 500 mi on varied freeways and good secondaries to track - high speed ride is quite acceptable.
The front suspension travel is reduced from about 4 1/2 inches to 3 1/2 inches (depending on how the bump-stops are factored in) and that at the slightly lowered but not extreme ride height there is only and inch of travel to the stop. This make speed bumps and potholes a problem -- fortunately i don't have too many of either. i may try raising the car a bit more, but don't want to reduce the rear camber too much.
The track handling improvements carry over to the street.

Conclusion
if you really want to track an M5 and you don't have a serious pothole problem, this is the way to go (double adjustable Konis would be better, but who knows when they'll deliver them)
if you're never going to the track, buy a Dinan stage III (with JRZ shocks if you can afford it)
if you're thinking about tracking the M5 or track a couple times a year i'm really not sure if the Dinan III with adjustable camber plates (as reputably available from GC) or the GC coilovers with "street" springs (and Dinan rear bar) is better. The GC linear springs are going to be more predictable on track, but i'm concerned about the front spring travel for street use (i'm assuming spring travel is the same 3 1/2 inches and with less stiff springs there it will be even easier to bottom out)
 

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stever,

Good write up. I am having the "issues" with the "street" springs as you have described. I believe that the street springs are 350F/315R.

My set up:

275s on all four corners, on stock rims, with PS1s. Dinan rear bar set on the outside hole. The front Konis are set to full firm and the rears are set one turn from full soft. I have the GC camber plates set to about 1.25 degrees more negative camber than stock (-1.75 total negative camber). Ride height is about 13.75 (front) inches center of hub to fender...

The suspension absolutely rocks on smooth surfaces...however, throw in an unexpected square edge bump, and the front supension bottoms harshly. A sharp G-out with a bump will bottom the front end. Speeding (faster than necessary)ouich over a railroad crossing will bottom out the front end.

One thing nice about where I live is that I am about 80 miles from Discovery Automotive and about 90 miles from Ground Control:cheers:

On Monday, I drove by GC (after my dyno run) and told the owner my situation. He then went back inside and did some calculations. He then brought out a new set of front springs for me that had a very,very slight progressive wind that would offer me a slightly higher ride height and with about a 15% increase in stiffness...I have the springs sitting in my garage and I hope to install them this week. He also said that I should not have an issue with the rear suspension if I have not been bottoming it...

So far I have been happy...With this suspension set up, it almost makes you fearless to take corners at speeds faster than you really need to go...but is that not the reason that we are all here?:M5launch: :M5launch: :hihi:

Mark
 

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Thanks for the reports! The issue of front bottoming seems to be in every thread of people who have GC's setup.

stever,

When you mentioned potholes and such being a problem, does this mean you have experienced some bottoming out with the 440lb/in front springs also?

Chuck
 

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stever said:
The GC linear springs are going to be more predictable on track, but i'm concerned about the front spring travel for street use (i'm assuming spring travel is the same 3 1/2 inches and with less stiff springs there it will be even easier to bottom out)
dumb question maybe, but wouldn't this also be a concern on the track as well?

your Dinan Stage III had the Konis or JRZs?

just curious, thanks :M5thumbs:
 

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Discussion Starter #5
the only bottoming i've experienced was on very sharp speed bump in a parking lot, but i've yet to drive the car full of people

i suspect the best that can be done is raise the ride height a bit

i had the original Dinan 3 since the car was new 40 k mi ago

if you run front shocks near full hard you may find the center position on the Dinan bar works better
 

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stever said:
the only bottoming i've experienced was on very sharp speed bump in a parking lot, but i've yet to drive the car full of people

i suspect the best that can be done is raise the ride height a bit

i had the original Dinan 3 since the car was new 40 k mi ago

if you run front shocks near full hard you may find the center position on the Dinan bar works better
Stever,

Sounds like a good setup! The estimated gains you see on-track are impressive.

Any major squeaks or noises?

Could you please tell me the approximate max ride height front and rear? This would need to be a fender lip to center of roundel measure to factor out tires and wheels. What are your ride heights now? Do you have a feel for whether you could crank the front perches up too far and experience spring bind? We need to figure out the max perch height, so we don't get coil bind. It sounds like you're not getting spring bind with your current perch setting. Coil bind is a loud slam, not a bumping sensation. A speed bump in a parking lot can easily be 3" tall. I doubt if you have that much jounce travel if you're under 13.5". Under this scenerio, a 1000lb spring could produce bottoming! The ride heights must be 13.5" or so in front to maintain adequate suspension travel.

I have noticed that GC is offering quite a few different spring setups these days with their new Eibach barrel springs. These are good springs as they minimize twist, noise and rubbing with lower streetable rates.

Is this setup giving you kidney problems on the street? This is their more aggressive spring rates.

Sounds like the car is neutral. I would expect that with the f/r spring rate bias you have. The rear control arm has some leverage that reduces wheel rate, but the rear "is" lighter with about 53/47 ratio. This spring combo seems to make bigger bars unnecessary and the Eibach monster bar kit may be a good match.

I might just buy this kit....it sounds optimal!
 

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EdP,

I think you misunderstood. Stever is expressing some concern for lower spring rates combined with low ride heights, on the street. The 400+ spring rates Stever has are apparently causing ZERO bottoming on-track & no bottoming on the street, except for a big speedbump.

Speedbumps are a special situation. Speed bumps require adequate jounce (compression) travel & the spring rate has little influence if you're moving fast. If you slam the car, jounce travel drops to substandard values, & under this scenerio, speed bumps wil be a problem with any spring rate or design. A 3" speed bump will generally produce bottoming, if you have only 2" of compression travel. The only exception is if you crawl over the bump and the suspension does not compress. Keep in mind that the M5's 520i underpinnings were designed for a particular static ride height. BMW and the aftermarket tuners are progressively chipping away at the limited 520i jounce travel. The GC front mounts add a bit of precious jounce travel compared to the stock turntable and mount. They offer another 3/8" of jounce over the silly Dinan plate that sandwiches between the mount and tower.
 

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Lscman said:
Stever,

Sounds like a good setup! The estimated gains you see on-track are impressive.

Any major squeaks or noises?

Could you please tell me the approximate max ride height front and rear? This would need to be a fender lip to center of roundel measure to factor out tires and wheels. What are your ride heights now? Do you have a feel for whether you could crank the front perches up too far and experience spring bind? We need to figure out the max perch height, so we don't get coil bind. It sounds like you're not getting spring bind with your current perch setting. Coil bind is a loud slam, not a bumping sensation. A speed bump in a parking lot can easily be 3" tall. I doubt if you have that much jounce travel if you're under 13.5". Under this scenerio, a 1000lb spring could produce bottoming! The ride heights must be 13.5" or so in front to maintain adequate suspension travel.

I have noticed that GC is offering quite a few different spring setups these days with their new Eibach barrel springs. These are good springs as they minimize twist, noise and rubbing with lower streetable rates.

Is this setup giving you kidney problems on the street? This is their more aggressive spring rates.

Sounds like the car is neutral. I would expect that with the f/r spring rate bias you have. The rear control arm has some leverage that reduces wheel rate, but the rear "is" lighter with about 53/47 ratio. This spring combo seems to make bigger bars unnecessary and the Eibach monster bar kit may be a good match.

I might just buy this kit....it sounds optimal!

It is funny, the firmer spring that GC gave me for the front end does look like a barrel...

What will happen to my handling of my car if I install the heavier front spring and not replace the rear spring with a heavier spring to maintain the correct "bias"?

What should I expect in the terms of handling if I move to the middle hole of my rear bar?

Thanks,

Mark
 

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i think the stiffer fronts would tend to increase understeer, while moving the rear bar to the middle hole will stiffen the rears and increase oversteer. The combination might work out well.
Mike

drallen said:
It is funny, the firmer spring that GC gave me for the front end does look like a barrel...

What will happen to my handling of my car if I install the heavier front spring and not replace the rear spring with a heavier spring to maintain the correct "bias"?

What should I expect in the terms of handling if I move to the middle hole of my rear bar?

Thanks,

Mark
 

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mottati said:
i think the stiffer fronts would tend to increase understeer, while moving the rear bar to the middle hole will stiffen the rears and increase oversteer. The combination might work out well.
Mike
Thanks Mike...

This is starting to get fun....and informative

Your explainations are helping me stay off the guard rails...

Mark
 

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Discussion Starter #13
No noises or squeaks

The ride is about 13 5/8 - 13 3/4 in front (i'll make a more accurate measurement tomorrow when i get the car on a level surface and hopefully double-check the Dinan ride height on another car) and the strut is nearly touching the bump-stop

coil binding cannot possibly be a problem with the amount of travel permitted before hitting the bump-stop

It looks to me like the GC assembly does NOT add jounce by the design of the strut which is an inch or so too long to permit lowering car below stock height

as delivered, the perches were down about 1/2 inch from the top which put the car at least an inch over stock height -- to acheive the above ride height, perches are now .425 and .500 above the low position

as i said, the ride is busy at low speeds but not harsh and not a kidney banger -- Tony has installed coilovers and driven lots of M3s but has only driven one other M5 which had KWs set at a lower ride height -- he was pleasantly surprised by the lack of harshness in my car

i really have no problem bringing the car up to stock ride height except that i don't really want less negative camber in the rear
 

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Stever, the information you provide is invalueable & appreciated.

I hear the bumpstops are quite soft & a good bit of deflection occurs before it limits compression. The OEM-spec strut housing height (Koni) is definitely a major barrier with respect to jounce, but I believe the upper perch was raised compared to stock. If the Koni housing was shortened, it would preclude the use of big wheels in front. The upper mount was not raised much, since the nut is positioned similar to stock and does not protrude from the shock tower hole.

Sounds like the nose of the car can be raised a bit more?. I would prefer close to 14" if it was achieveable without causing bind or something.

Is the rear suspension raised near max? Can you achieve anything near 14" back there? The softer 315 rear barrel springs do not allow a ride height much above 13".

edit: I re-read your post. Sounds like you had to lower the setup from as-shipped settings to achieve your ride height. It appears your car ride height is adjustable between about 13-1/4" and 14-1/2" with these particular springs and threaded sleeves....nice range!

Can you please share your front and rear Eibach Part numbers with us?

This is what I've been wanting to hear!!!

------------------------------------------

I have heard of 540i cars running the 400+ front barrel spring in combination with the softer rear 315 barrel spring. This combo works OK, but creates some inherent understeer with stockish car setup.

An oversize rear swaybar with a stock front swaybar would help compensate for the bias change...as would more neg camber in front and non-stagger wheels. That setup might be workable & perhaps more streetable.

Some folks may not be aware that GC's kits now allow the rear spring and shock to be removed from the exterior, without gutting the interior. This is a seriously desireable feature for spring swaps & I think it was a running change in production...not sure.
 

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Lscman said:
Stever, the information you provide is invalueable & appreciated.

I hear the bumpstops are quite soft & a good bit of deflection occurs before it limits compression. The OEM-spec strut housing height (Koni) is definitely a major barrier with respect to jounce, but I believe the upper perch was raised compared to stock. If the Koni housing was shortened, it would preclude the use of big wheels in front. The upper mount was not raised much, since the nut is positioned similar to stock and does not protrude from the shock tower hole.

Sounds like the nose of the car can be raised a bit more?. I would prefer close to 14" if it was achieveable without causing bind or something.

Is the rear suspension raised near max? Can you achieve anything near 14" back there? The softer 315 rear barrel springs do not allow a ride height much above 13".

------------------------------------------

I have heard of 540i cars running the 400+ front barrel spring in combination with the softer rear 315 barrel spring. This combo works OK, but creates some inherent understeer with stockish car setup.

An oversize rear swaybar with a stock front swaybar would help compensate for the bias change...as would more neg camber in front and non-stagger wheels. That setup might be workable & perhaps more streetable.

Some folks may not be aware that GC's kits now allow the rear spring and shock to be removed from the exterior, without gutting the interior. This is a seriously desireable feature for spring swaps & I think it was a running change in production...not sure.
Rick,

Thanks again for all your help with the unknown on the E39 suspension...

Any idea on what type/weight of springs that GC gave me for the front?

The Eibach # is 144179

The GC # is 180.64.75

Thanks,

Mark
 

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Discussion Starter #16
i'd say front and rear are adjustable between 13 1/8 and at least 15 inches -- nothing binds at the lower end of the range and i'd say ride height over 14 inches (pretty close to stock) is academic anyhow

rear Eibach number is 1000.250.0425
swear i recorded front number, but can't find it now and it doesn't show up on my photos, will get it next time i pull a wheel off

the bump stop is about 2 1/2 inches and i wouldn't expect it to compress much more than an 1 1/4 -- including the bump stop compression i don't jounce is less than 2 inches at present ride height
 

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stever said:
i'd say front and rear are adjustable between 13 1/8 and at least 15 inches -- nothing binds at the lower end of the range and i'd say ride height over 14 inches (pretty close to stock) is academic anyhow

rear Eibach number is 1000.250.0425
swear i recorded front number, but can't find it now and it doesn't show up on my photos, will get it next time i pull a wheel off

the bump stop is about 2 1/2 inches and i wouldn't expect it to compress much more than an 1 1/4 -- including the bump stop compression i don't jounce is less than 2 inches at present ride height
Can I send you a check to have your tire removed to read the spring? I am considering this kit. Seriously, I think jacking the car up will allow you to rotate and read the spring, since it's above the tire. Hurry up before the paint washes off! Thanks buddy, pal, friend.
 

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drallen said:
Rick,

Thanks again for all your help with the unknown on the E39 suspension...

Any idea on what type/weight of springs that GC gave me for the front?

The Eibach # is 144179

The GC # is 180.64.75

Thanks,

Mark
No ideas. GC or Eibach will need to be contacted with Eibach spring part#'s to get your specs. I imagine you have the street springs. The Eibach site does have their spring catalog on-line, so you can probably figure it out without speaking to a Tech.
 

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stever said:
the front springs are Eibach 165.64.96, 6.5-550
That was interesting...

I just called up GC and my new front springs are 7" 430# springs and stevers are 6.5" 550# springs...

Mark
 
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