so has anyone ever figured out the stock spring rates for the m coupe?

I can't believe no one has measured in all this time...

Originally Posted by AC

I can't believe no one has measured in all this time...

not sure about the front, but the rears are variable so the answer is not straightforward

AAAAAAAARGH!

I need to determine new spring rates and I have zero basis other than heresay (most seem to like 400 to 450 front and 500 to 600 rear). With all the forums and all the great info that one can find dig up on just about every part of our cars, it's curious that no one ever put those spring on a dyno!

That's going to be very stiff, 450F and 600R. I'm running Eibach 300F and 450R. I don't know the stock rates but because the stock springs are longer, they can be much softer, maybe 250F and350R.

Originally Posted by AC

AAAAAAAARGH!

I need to determine new spring rates and I have zero basis other than heresay (most seem to like 400 to 450 front and 500 to 600 rear).

Well, a bit more hearsay here for ya... I have 450 front and 525 rear, and recently co-drove a coupe with 450 front and 575 rear. I *strongly* recommend you go no higher than 525 in the rear... and then only if you absolutely positively want to emphasize autox handling over street use.

A good friend of mine has much softer springs - I know I can't recall the exact numbers but I believe the rears were ~400 pounds/in - and he's absolutely loving them on the track. This is on his '00 M coupe with Koni DA coilovers and front camber plates.

TC Kline apparently has a custom 500 pound barrel spring that is supposed to be excellent. I'm going to order a set tomorrow and see if they're any improvement over the 525s I have right now.

Mike

Originally Posted by Mike S

TC Kline apparently has a custom 500 pound barrel spring that is supposed to be excellent. I'm going to order a set tomorrow and see if they're any improvement over the 525s I have right now.

Mike

The rear barrel spring is a must-have item!

oh...great

A well known club racer who campaigned a MCoupe for 2 years recommended spring rates in the range of 650/700lb rear and anywhere between 600 and 750 front! He found that even 575 rear would coil bind in hard turns resulting in nasty moments..... Anyone know if GC offers barrel type spring or if they work with their rear height adjusters?

AC -

I have Ground Control co's with 6" springs at each corner: 375 lb front, 525 barrel type at rear. Very happy with set-up, but recently detected very slight coil binding at rear. May simply increase rear ride height (to gain a bit more suspension travel), but am considering changing springs.

Since I like my ride height (and car is corner balanced), am not considering switching to a 7" spring.

Ground Control, I believe, does have a 575 lb spring with more pronounced "barreling" (ie, greater difference between OD of top/bottomost coils and middle coil), but have heard that it may not sit properly on the spring perch.

I may give Jay at GC a call to discuss. If I go to a stiffer spring in back, I'm likely to also go a bit stiffer in front.

Interested in your research as well as recommendations of others.

Neil

Karl A from the Roadfly board recommended min of 650 in the rear to prevent coil bind. He ran less than 600 in the front tho..like 450ish i believe. I have 600"s and do get some coil bind on the street, havent experienced any on the track yet.


T

Originally Posted by AC

oh...great

A well known club racer who campaigned a MCoupe for 2 years recommended spring rates in the range of 650/700lb rear and anywhere between 600 and 750 front! He found that even 575 rear would coil bind in hard turns resulting in nasty moments..... Anyone know if GC offers barrel type spring or if they work with their rear height adjusters?

Originally Posted by Neil

AC -

I have Ground Control co's with 6" springs at each corner: 375 lb front, 525 barrel type at rear. Very happy with set-up, but recently detected very slight coil binding at rear. May simply increase rear ride height (to gain a bit more suspension travel), but am considering changing springs.

Neil

I also have this setup but haven't noticed any binding problems yet. I have the rear adjustors set at their lowest position. I also have a spare set of the upper nylon perches which CG told me could replace the lower rear adjustors if further lowering is desired (1/2" - yikes!). I haven't tried putting them in yet though, not sure I will or should for the street.

I am very interested in hearing more about rear spring options and benefits though.

Originally Posted by Tommy V

Karl A from the Roadfly board recommended min of 650 in the rear to prevent coil bind. He ran less than 600 in the front tho..like 450ish i believe. I have 600"s and do get some coil bind on the street, havent experienced any on the track yet.


T

Karl has been co-driving my coupe since early this year and agrees the suspension is very well set up with the current rates. He and I both examined the 500 pound barrel springs and are excited about their prospects.

The suspension is completely different from his previous setup so he doesn't comment on any particular component, but he's open for any questions you may have.

The car is set up for SCCA autox in the ASP class. I recently drove a coupe with the same Koni DA coilovers I use, but it had 575 rear springs. They were too stiff for an effective autox setup in my opinion.

Mike

Mike -

What is the length of TC Kline's 500# spring?

How does the shape compare to Eibach's 525# barrel spring?

What is the OD of the bottom coil that sits on the perch?

Neil

Originally Posted by Neil

Mike -

What is the length of TC Kline's 500# spring?

How does the shape compare to Eibach's 525# barrel spring?

What is the OD of the bottom coil that sits on the perch?

Neil

I believe it is 7" long. I'll confirm that when my call is returned by Pete at TC Kline. If I recall correctly, it looks similar to the 525# barrel spring: it's a full barrel, with what appears to be either a 2.5" or 60mm i.d. at each end flaring to ~5" in the middle.

The part that interests me is that it doesn't use any seats at the top of the spring - at least the one I viewed wasn't configured with one. I've broken two of the GC plastic upper rear mounts in the last six months and I'd like to eliminate that particular failure point if it's at all possible. My friend, Patrick Avakian, who has these springs tells me they are completely quiet, which surprises me considering the lack of an upper "bushing."

They do require a different bottom perch than Patrick already had on his car, but the new perch appears virtually identical to the GC adjustable rear perch so I'm going to try that combination unless Pete advises against it.

I'll post back with any updates.

Mike

Mike -

Curious as to how you broke the nylon upper spring mount.

Was the suspension bottoming out such that the threaded sleeve was slamming into the mount?

Also, even deleting that peice, I fear that TCK's 7" spring would increase my ride height more than I'd prefer.

Neil

Originally Posted by Neil

Mike -

Curious as to how you broke the nylon upper spring mount.

Was the suspension bottoming out such that the threaded sleeve was slamming into the mount?

Also, even deleting that peice, I fear that TCK's 7" spring would increase my ride height more than I'd prefer.

Neil

I'm not sure what caused the nylon mount failures. They occurred about two months apart, so there wasn't a single event at the root of it. So far the new parts - redesigned according to GC - haven't failed, but I'm still wary. I don't recall the suspension bottoming out and I only see the slightest hint of coil bind on the rear springs, and only near the ends of the spring. It could have happened going over a speed bump, but not anywhere else. I think the damage probably occurred when lowering the car off the jack stands. A misaligned spring can easily cause the problem and my car has been up and down literally dozens, if not hundreds, of times in the last six months.

I ordered the new springs today. They're not sourced with a specific length, unweighted. They're designed for the entire family of springs to achieve a consistent ride height on the car, no matter the spring rate. In other words, they don't know. If you'd like I can take some ride-height comparison photos of the Eibach 525 non-barrel vs TC Kline's 500 barrel springs.

The springs are 60mm i.d. They'll work with the GC rear perches, but TC Kline's perches are designed a bit different to cause less spring / perch interference. I'm trying them with the GC perches first to see if there are any significant problems.

Mike

I've got the 525 'barrels' on the back of my GC setup (Z3 Coupe). Differences in driving behavior, environments, and rear-suspension geometry (Z3 vs M) may account for this. These 525's are 2.5" diameter at the ends, and the barrel shape is very hard to observe without a straight-edge.

I recentry got a set of 475 barrels (also 2.5" diam.) from GC to try; these are fairly extremely barrel-shaped. I only got so far as fitting them on the car and running the trailing arm up and down. Because the first winding departs from the base circumference so fast, there isn't a full ring to seat on the perch. As they compress, I noticed they would tend to slide off the perch slightly. I tried the coil in various orientations and exercised the travel, but I didn't find any position that I was comfortable with. I put the 525's back on the car... still need to return the 475's to Jay.

I originally had 450 (or 470) straight coil, 2.25" diameter from my Roadster setup, but besides the fact that it would bind in extreme situations, the front/rear setup didn't feel balanced. Under hard cornering, it would feel as though the car were rocking diagonally onto the outside rear corner. After swapping upto the 525's, the handling felt much nicer.

BTW, the fronts are 250's and they don't feel too soft at all. I thought I'd read that the M engine (S52) was heavier than the M5x engine used in the Z cars... perhaps that's a factor?