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Discussion Starter #1
So I want to refresh my 130k mile suspension this summer and want to start gauging options. I'm not sure the what the list of consumables I must replace when I do a refresh, though.


Option 1

  • Bilstein Sports/Koni Sports
  • KMAC camber plates
  • Upper Front Strut Mount
  • Rear Shock mount
  • What else?

Option 2

  • BC Coilovers w/ camber plates
  • What else?

At this point, I'm a little confused with the additional hardware needed when doing a suspension refresh. Do coilovers include the strut mounts in the package? Do I need front strut mounts when I'm also getting camber plates?

I'll basically make my purchase based on the best value since both options seem like they will end up around the same price.
 

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Budget?

I currently have Ground Control coilovers with Matt's thrust arm monoballs and love them.
 

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Discussion Starter #3
Budgeting around $1000 + $100 for misc. hardware. BC's cost $1000 but I'm not exactly sure what other consumables I should replace with them
 

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What organization are you looking to autox with? BMW CCA or SCCA or ?

Kmac plates (at least in the past) have a poor record on the E39 M5 -- search the board. I believe Lscman covered the issue in depth many years ago. Note also, that if you are staying with stock springs, camber plates whether they are Kmac or GC, etc, will add to the stack height and increase ride height (personal experience speaking here).

I would point you toward GC latest coilover design - red tubes up front with extra clearance for rear wheels up front with no 3mm spacer needed and top adjust rear shocks. Their camber plate design is high quality and comes with the kit already installed, so no need to buy any other strut parts. Same in the rear -- upper GC mounts included.
 

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Discussion Starter #5
I'll be running with SCCA; the NJBMWCCA chapter isn't very strong with autox.

I did some searching and it does seem that KMAC are not the ones to go with. If I could find some cheap used Dinan plates, I would consider them as an alternative. Otherwise, I would have to go with GC plates with replacement struts. I don't mind the ride height increase as I sometimes scrape on my driveway with the stock suspension.

I do think GC coilovers are out of my budget, even though they are extremely nice.

Now the question is that do BC's come with all the strut mounts?

What would be good spring rates for the M5 too? I want to get the rear to rotate easily. Would 8k/8k (447 lb/in) be fine or should I go stiffer with 10k/10k (559 lb/in)? I have a stock rear swaybar but would consider getting the 18mm Eibach bar for $125 at Autozone.
 

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M5 is out of its element on an Auto-x course, you need to stiffen up the rear suspension (more so springs than shocks) and a thicker rear roll bar. Another suggestion is wider tires up front + GC camber plates b/c the Beast will tend to push due to its enormous weight (angular momentum in abrupt turns?? - somebody please check my physics). PCA NNJR has a good Auto-x program, I might give it a try this summer if timing allows.
 

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Discussion Starter #7
I know that the M5 isn't the greatest autocrosser. My goal isn't to be competitive but to have fun while dialing out the original understeer. If I wanted to get competitive, I would sell the M5 and get an E36 M3 sedan.

If I need stiff suspension, I'm guessing 10k/10k would be the best for me. If I need more, I would then get the Eibach rear sway. Does that sound like a good plan for autox?

PCA does have a nice program and they run on the same huge lot as SCCA does. I do want to get out on the track once with an organization, but $50 per autox is much cheaper than the $500 it costs for a weekend track day.
 

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I think a Dinan rear sway bar will be useful in that you can dial in the stiffness as needed depending on your other suspension/tire setup. Auto-x is a good place to start, but purely bang for buck, $50 for 10 x 1 min of parking lot fun is a lot more expensive than $300 for 4 x 30 min of track time! Just my 0.02c.
 

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You'll be in ESP with the SCCA, but you mentioned you're not really interested in being competitive (which the M5 is not in ESP without serious to the rule prep and even then would be hundreds of pounds heavier than the competitive ESP cars), so that isn't a concern.

I know nothing about the cheap coilover alternatives, so I would search the board for those threads and take the advice of those who went too weak on the spring rates -- make sure you don't. You want something in the range of 550 lbs/in up front which is 9.8kg/mm (i.e. 9800kg/m or right at "10k" you refer to). Typical "track" Ground Control setups then use a 350 to 380 lbs/in spring in the rear (you probably do not want to go much stiffer than 380lbs/in in the rear). A 380 lbs/in spring is about 6.8kg/m, so it would appear that something in the range of 10k/7k spring rates would match up with the typical range of GC setups. Note, and this is a *big* note, this assumes that we are talking about linear springs here (I have no idea what the coilovers you are asking about are comprised of).
 

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Keep an eye on the rule changes

A couple of scenarios:

SCCA is switching from Stock to Street (eliminating R compound DOT "slicks") and requiring street tires of 140 tread wear or better next year, then 200 tread wear in 2015. This appears to be fact. What is not known is whether they will allow Camber Plates in street. The latest Fastrack had it removed, but I am hoping they add it back in, in the final revision. If they do allow plates, F Street offers the best place to run an M5, and it should be somewhat competitive. The M3 and the Mustang Shelby GT will probably spank it but, otherwise it should place well, regionally.

If this occurs (they allow camber plates), the likely setup is a rear bar (eibach), with steel mounting straps, stock wheels all around, 275/245 or 275/265 (if changing the fronts at the event). Koni Yellows, stock springs, and camber plates that do not add height (Ground Control). That's what I am planning for.

If camber plates are not allowed in street, and you want to run them (I will be running them next year), the best move is to STX where you can add Camber, but are limited to 9" wide wheels, and 265mm all around. You won't be competitive here, but, it looks like it will be a blast.

Otherwise it's ESP. I haven't considered that class (in the BMW, but I considered purchasing a Mustang) as I wouldn't have a chance regionally, but I am sure others can chime in.
 

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Discussion Starter #11
Good tips!

I haven't made any steps forward yet as I'm contemplating selling my M5 for something else, to be more competitive. I figure I could get a decent STX (or is it STU?) running E36 M3 for the price of my M5.

Eitherway, I may want to wait for the new rules to come out before I make any choices.

Sent from a plane on a treadmill
 

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Ground Control camber plates do add to ride height, between 1/4" and 3/8", been there, done that many years ago with stock springs. Switched to Dinan springs after that issue. They assured me that the plates did not add any stack height, but that was incorrect. This was back in 2005 when I bought them, but I'm pretty sure that the plates they sell today are the same.

M5 is not allowed in STX or STU, not that it would matter since it would have no chance at being competitive in those classes.

Even with lots of negative camber, the M5 suffers from too soft spring rates and sway bar rates imo. It would really need a huge front bar to get the transient response needed. The rear bar is mildly helpful for sure, but it really needs front and rear rate increases (speaking from the better part of a decade autocrossing the M5). BTW, with the stock spring ride height, the maximum negative camber you can get up front with the Ground Control plates max'd out is about -1.8° which is not even close to enough. With the Dinan spring ride height, I can get -2.3°, which with the soft Dinan springs and stock front sway bar still isn't enough.

It has no chance against the E9x M3 in F-stock. The M3 is a hidden jewel as far as stock class BMW autox competitiveness (just look at what Rich in the St Louis region did with it last year in A-stock, and now it's in F-stock). I'm running the E90 M3 this season in F-stock street tire class on BFG Rivals, and so far have PAX'd 1st and 4th overall out of 100+ drivers locally. It's a vastly better platform than the E39 M5 on course in every aspect of performance. The one spot the M5 owns is low-mid range torque, but the problem there is putting it to the ground in the M5 as it just wants to bust the rears loose whenever it can (and just going with a stiffer rear bar makes this issue worse). The M3 just *hooks* like crazy coming off elements and really puts the power down. I'm still amazed when I drive it on course. :)
 
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M5 is not allowed in STX or STU, not that it would matter since it would have no chance at being competitive in those classes.
Doesn't this specifically allow it (Appendix A)? Or is it excluded, elsewhere?

Sedans & Coupes NOC (non-
sports-car-based; 4-seat
minimum; 3.1L to 5.1L normally
aspirated or up to 2.0L forced
induction)

It won't be competitive here, I get that.

Thank you for sharing your experience. I am playing the rest of this year with the M5 in F stock-eating tires. I am also considering selling it for something more competitive, but I love it, which is what makes this such a tough decision. My goal is to learn to drive again! Then assess what I am doing.

 

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Interesting. It used to be specifically called out as an exception along with a few other cars from ST* classes, but I don't see that in the 2013 rules unless I'm missing it.
 
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