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Suspension Upgrade ? for KarlS (and others)


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Karl, you seem to have a pretty good handle on this topic from the posts I’ve seen so I’d welcome your thoughts, and of course, input from anyone else as well. I’m running an ROW M030 setup with a dedicated set of 225-285 Michelin Sport cups on 18” Carrera wheels for autocrossing. My alignment specs are factory stock with the exception of 1 degree negative camber in front. The suspension and tire upgrades moved me out of Stock into Improved class. My GT3 seats, by themselves however, put me up another notch into Production class where further suspension mods are allowed.

So, I’m trying to decide if there is any point in changing to a more elaborate coil-over setup with adjustable shocks, bars etc. The advantage gained by lowering the car with one of these setups is going to be limited by the fact that I don’t want to give up normal use on the street. I figure I can go another ½” to ¾” lower without too much risk but probably not much more than that. Would a PSS9 set-up with GT3 adjustable bars be a meaningful step up from what I have currently? Should I be looking at one of the more expensive proprietary suspensions like the JRZ, or would that be a waste of money for what is basically a street car? What other options should I be considering? (Yeah, another driving school is planned, but we’re talking about the car here. :rolleyes: )

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Mike,

As with most things concerning a dual street/track car, you'll be dealing with trade-offs here. The basic problem is that the better you get the suspension for the track/auto-x, the less comfortable and practical it will be for the street. You are the only one who can make the decision of how far down that continuum you are willing to go. Of course, the other variable is cost. That being said, here's what I think.

The first improvement you can make is roll bars. The 996 likes a lot of front roll stiffness, so upgrading to a thicker, adjustable bar should help no matter what else you do. The GT2/GT3 bars are a good and they are adjustable, although there are some aftermarket bars out there that are similar and may cost less. Having adjustable bars also allows you to do some tuning at the track without an alignment system.

Next you can work on the shock/spring combination. Any replacement/upgrades need to be done in matched sets. By matched, I mean where someone has done some testing to ensure a particular shock works well with a particular spring rate. This is a complicated area with lots of variables, so this is one place where working with an accomplished suspension tuner can pay big dividends.

In this area there are three strata above where you are with the M030:

Adjustable street systems like the PSS-9 or H&R (approx. $2500 installed)

Double adjustable, remote reservoir systems from ProTrac, JRZ, Moton, and others (approx. $5000 installed and up)

Triple adjustable, remote reservoir systems from the same vendors (approx. $7000 installed and up)

The street systems are obviously the cheapest and may be the most compliant for street use. They do offer some adjustability for rebound/compression but generally not to as fine a degree as the next two levels. I don't auto-x but some of the people I know who track their cars in DE are not completely happy with the PSS-9 set-up for the track, feeling it is too soft.

The double adjustable set-up may be the ultimate street-track set-up but it is significantly more expensive. You also have to find some place to mount the remote reservoirs, which may mean some cutting or drilling, although nothing major. They are harder to install and maintain, requiring a nitrogen canister to recharge them and a special tool to check them. Not a big deal but some extra expense involved. For street comfort, you can probably go as stiff as 400# front and 650# 7" rear springs, which is still very soft for the track but will feel very stiff on the street. I ran 650# front and 800# springs rear and most people (including my wife) considered the car to be too uncomfortable to ride in. Of course, it didn't bother me at all :lol: Just as a comparison, a Cup car runs 1200# front and 1300+# in the rear and a GT# RS runs several hundred pounds more than that.

The one nice thing about this set-up is that you can go full soft on the struts for street duty and with a couple minor adjustment procedures and a shot of nitrogen, stiffen them up for the track. I know someone with an 03 996 that is running the JRZs and he swears his car rides better now than it did with the stock suspension. I haven't ridden in the car so I don't know if I believe him, but the point is you don't necessarily have to sacrifice ride all of the ride quality to get good handling.

The triple adjustables are for pro racers who know what they are doing when it comes to fine suspension tuning and I think the price performance just isn't there for an amatuer-driven street/track car.

BTW, don't get sucked into strut braces, they are a waste of money IMHO. However, a bolt-in cage that uses the strut tower mounts will offer a significant increase in stiffness and a welded cage will provide substantially more. There are also some things you can do to eliminate rubber from your suspension that will help with turn-in and set, but that's a topic for another post.

My final piece of advise is not to try to do this as a DIY. Find a good shop that has experience with suspension tuning for the track on 996s and work with them. You want to get educated and know what you are asking for but a competent shop can save you a lot of expensive mistakes.

Karl

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Good info Carl. I have been researching the same stuff for my car.

What is your opinion on single springs verses shorter springs with helpers?

You mentioned getting rid of the rubber bushings. Where can I get poly or metal bushings? I guess the cup car is a logical option. Any part numbers? I need to get that **** parts book for the cup car! Hopefully motorsports will call me back one of thes days.

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Karl,

Great post and advice. I think I may try the incremental approach and start with the swaybars. Going from street tires to the Sport Cups made me very competitive at our local PCA autocross events, so for now at least a major upgrade isn't essential, but then everyone is always looking for an edge. :rolleyes: From there I can decide whether to take the next step. Thanks!

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What is your opinion on single springs verses shorter springs with helpers?

You mentioned getting rid of the rubber bushings.  Where can I get poly or metal bushings?  I guess the cup car is a logical option.  Any part numbers?  I need to get that **** parts book for the cup car!  Hopefully motorsports will call me back one of thes days.

Here's the deal with springs. For the track you want as stiff as possible to minimize dipping under hard throttle or braking. Unfortunately, not all tracks are billboard smooth and if you go too stiff, you'll end up with the car bouncing all around over bumps. The solution to this is a progressive spring rate - one that starts out fairly soft but then stiffens under heavier loading. This allows the spring to absorb the small bumps but still be stiff under load. Progressive springs are made made varying the spring coil stiffness by placing the coils either closer together or farther apart. The downside to progressive springs for racing is that you'd need a zillion combinations of spring rates for various tracks.

The dual springs you see on Cup cars emulate a progressive spring and make it much easier to tune the springs for specific tracks. The main spring is the one you are using most of the time under load, so you select this one for ideal stiffness. The helper spring is just there to absord initial bumps, so you choose it based on how bumpy the track is. By keeping a few different mains and a few different helpers, you can put them together to form a lot of different combinations.

The GT3 street car uses a progressive spring in the rear. The Cup car uses dual springs all around.

As for the Cup car parts, you've got mail.

Karl

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For street comfort, you can probably go as stiff as 400# front and 650# 7" rear springs, which is still very soft for the track but will feel very stiff on the street. I ran 650# front and 800# springs rear and most people (including my wife) considered the car to be too uncomfortable to ride in.

Karl (or Loren), for the sake of comparison, what is the rating on the standard and M030 996 springs?

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