Suspension Upgrade questions for a Gen 2 ACR with Koni s

[GTS Dean]

Dean, recognizing that the way to adjust for bump steer is by shimming the steering rack or moving the inboard toe links at the rear, how do you go about measuring it? I don't see any mention of it in the FSM. Just trying to wrap my head around a feasible way to ensure that it's set properly.

BUMP STEER ADJUSTMENT PROCESS

First - it helps a bunch if you have adjustable spring perches. Assuming you have the ride height you like and can live with, measure and record your frame clearance front and rear for your preferred "Curb" height, along with your toe reading. Get a stack of blocks of consistent height - (I used extra pieces of 3/4" oak flooring) and start with a stack that fits closely under both sides of the frame at "Curb." Loosen your spring perches a bunch to remove preload and count turns from where you started. Pull 2-3 blocks from each side, (puts the suspension in "bump, or jounce") record both the height and toe-in or -out. install one block and record height/toe. Install successive blocks and record readings until you have covered at least 3-4 inches of travel (into "rebound or droop"). Move to the rear and repeat the process.

Now, you need to graph the toe-in (+) or toe-out (-) at each height at each end. If you used a string or laser on each side to measure, you can determine if both sides are in time with each other. If they're not, you may have wishbone alignment cam imbalance from side-side, (I've seen some horrendous examples of this in photos over the years!) or tie rod length imbalance. If you use the 2-plate/2-tape method, you may be chasing your tail a little bit. Now, compare your curve plots with the graphs in the Service Manual and see if you're in the shaded area and roughly parallel to the recommended curves. If your initial plots are close to the service manual, you're lucky! If not, you have some real work to do.

Next, you have to visualize the arc of the spindle vs the arc of the outer toe link. You want the arc centers of the spindle and the inner toe link to be very close to the same height at Curb. You also want the tie rod lengths to be close to equal right-left. Plotting the curves after you've made adjustments will illustrate the contribution of shim & tie rod length changes. I did this on my car something like 20 years ago and found my graphs to freshen up my recollections. I also found all my track setups, tire pressure, alignment and temperature data from track days way back to 1998! If you look at the graphs, pay attention to the yellow and cyan lines - which represent the left and right front toe curves. You will note that they change a lot, with the last graph indicating practically zero toe on the right, and about 1mm change on the left through the normal range of travel. I figured that was good enough. You will also note the diagram on page 2 which shows the rack geometry and inner toe link offset from the rack mounts. And, the basic truth that raising the rack causes more toe-in (rebound) and toe-out (bump).

It is a time-consuming, iterative exercise. But, it is OH SO REWARDING when you've done the work and gotten it right!!!

Most serious racers - road, drag, or oval - have probably done this enough that they could give you immediate recommendations on adjustments after looking at your curves. A competent race shop can probably do a full-on bump steer/alignment/corner weight setup in half a day. Doing this on your own after work or on weekends could take as much as 3 days.
Suspension Curves 1.JPGSuspension Curves 2.JPG

[71firebird400]

Dean, thank you so much! I am fascinated by your knowledge of dialing in the Gen 2 suspension. I have found no better source of information than your posts over the years and really appreciate the time you invested in writing that all up. You are doing the community a favor by documenting your experience.

[SilverACR]

I have had really good luck with the MCS system. They work great on the track and the street. I found they are a excellent ACR replacement shock.

I have found other systems like BC and Aldan not suitable for street and track. KW is a good product, but developed in Europe where tracks are smoother, spring rates are a bit harsh. Product support can be time consuming.

MCS dampers do a great job of masking heavier springs, making them feel quite a bit softer than they actually are. This is a direct result of having a proper force curve and forces to effectively control the spring. The benefit is that you can spring the car quite a bit heavier to reduce pitch and roll movements while still retaining the pliability one would seek for road use.

Standard valving for these damper's accommodates a wide range of spring control, so a wide range of spring rates can be used without re-valving. Remote systems
Nitrogen can be adjusted as well, with a 8lb increase in spring force per 10psi change.

Contrary to what many think, these shocks are made and assembled in the USA, with select parts made in Europe. The product support is really great also, a shock repair or setup problem can be resolved right away.

This has been my experience, yours may differ.

Just one comment on KW customer service. I had them rebuild my rears this spring and all in I had them rebuilt in 10 days. That

- - - Updated - - -

Well they haven

[SilverACR]

This post cut off issue sucks... KW customer service is good... I tried to detail why based on my experience and what cost I saw, but I am not retyping it...

[Gavm360]

Some Aldan Eagle Feedback, adjusted spring preload (found my passenger rear far off from others) and the ride is much improved, this is only a baseline starting point but it's in the right direction.

Got advice to bring the car to ROANOKE in Illinois (I'm in Chicago) to get corner balanced and aligned. Does that sound reasonable?

[SilverACR]

Some Aldan Eagle Feedback, adjusted spring preload (found my passenger rear far off from others) and the ride is much improved, this is only a baseline starting point but it's in the right direction.

Got advice to bring the car to ROANOKE in Illinois (I'm in Chicago) to get corner balanced and aligned. Does that sound reasonable?

Dave at Roanoke is one of the best out there and it was good advice to take the car to them.

[Hssssss]

Thought I would update this older post with the final result of my outcome. I went the route of Aldan American from JonB for upgrading my koni coilovers and the difference was night and day. I see a signifiant improvement I am slowly dialing in the settings on the Aldan's. I'm happy with my decision and time will tell how they perform in the long run.

[sparkrn]

I have had a great outcome with the Aldan American shocks also. Put about 3000 miles on them this summer and can’t be happier. Good looking made product with a lifetime warranty. My Gen 2 never has rode this good since forever. These shocks were a vast improvement over the original coil overs. I highly recommend this product.