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Don't adjust ride height without corner balancing


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Although embarrassing to air my mistake, I thought I would post this in hopes I might save someone else from the same problem: If you have adjustable coilover shocks, do not attempt to change your car's ride height unless you are doing it while corner balancing with scales.

I rationalized that if I set the ride height using the factory measuring method (documented in multiple places on this site) I would get "close enough" to a balanced car for a 996 that isn't tracked. Wrong. I worked on a level floor, with a full tank of gas (per spec), new tires with factory-recommended tire pressures, using the factory-recommended ride height measurement points, drove the car a few yards after each change to settle the suspension, and after a lot of hard work I was dead on with each of the four measurements. A local indie shop, not really performance oriented, vetted my approach and said it should be fine, it's what they would do.

Even after a perfect-to-the-spec alignment this morning the car pulls to the right, enough at 40 mph with hands off the wheel to change lanes in less than 50 yards. My effort was wasted and I'm out the cost of that alignment. The car goes in for a pro corner balance to correct the issue and I'll end up paying for another alignment. Lesson learned.

In truth, the effort wasn't entirely wasted because I learned about the stiffness of the chassis, how even a minute change of 1mm in shock adjustment can affect all four wheels, and how each of the wheels is affected. Dialing in the ride height was a PITA but a learning experience that I believe transfers to doing a corner balance.

If you install height-adjustable shocks, you must corner balance for optimal handling even if your car is a daily driver and not tracked. Bless you suspension techs who do corner balancing for a living!

Edited by Coaster
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Also the height and compression of the springs cannot be independently adjusted for PSS9 and I'm sure that doesn't help.

Ahsai, had I been faced with any more adjustments to make I might have twisted the car into a German pretzel.

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Also the height and compression of the springs cannot be independently adjusted for PSS9 and I'm sure that doesn't help.

Ahsai, had I been faced with any more adjustments to make I might have twisted the car into a German pretzel.

Lol I would have warned you if you had told us you were gonna DIY on height adjustment on PSS9. It's a job best left for the pros...even if you had all the equipment and tools you need, lots of experience and black magic involved I heard :)

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Of course one of the problems is that people try to use PSS9/10' to adjust the height of their car and they are not really height adjustable. If you look carefully at the installation instructions they are only supposed be be set with a 5mm range, which is really more for balancing and not for height adjustment. But people see how much thread are on the collars and try to lower the cars beyond the proper range ignoring the instructions.

Edited by Dharn55
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That's an easy misinterpretation to make. In my copy of the instructions, it's half German and half English with translations interwoven in the text. The excerpt in the 6speedonline post was taken from the German Technical Inspection Association (TÜV) approval letter included in the installation instructions. Heading up the section where that excerpt was taken is this verbiage:

The following instructions refer to the German regulations. In other countries different regulations may apply.

It seems to be more of a "department of transportation" issue than a technical issue with the shock. Maybe all-English instructions have US DOT verbiage, which of course would prevent lowering the car much at all.

Edited by Coaster
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  • 2 weeks later...

Thought I would circle back with information from the corner balancing.

The car went in with the ride height set exactly to Porsche spec for an x74 suspension but without the use of scales. The alignment was also set dead-on to x74 specs. Everything looked as correct as it could be but the car had a tendency to pull to the right. Once on the scales the reason became apparent:

FL: 752 FR: 544

RL: 1066 RR: 1147

So, once again, you can do everything to set the ride height according to spec but still be WAY off on the balance and the handling of the car will suffer. Lesson learned. :rolleyes:

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I only have about 30 miles on it so far but it feels like a much improved car. Since I was in for the corner balance and alignment I went ahead and installed adjustable sway bars front and rear - something I've been thinking about doing for years. With the PSS9's, new sway bars, and new ride height, it's kind of like having an adjustable x74 suspension. The sway bars probably had the most impact on feel and handling but the ride height and alignment made the whole package.

The shop I trust far more than any other I've used so I went with their setup recommendations for how I drive. They lowered the car another 5mm then dropped the front another 5mm for a 20mm rake, bringing it to 108 front and 128 rear. The front camber is at -0.8 with some "extreme" toe at +1.0, and the rear is at -1.7 with +2.0 toe. Not at all factory settings but a rake and alignment they say will reduce the 996 tendency to push through corners. They do lots of race cars as well as street drivers like me and they think I will be pleased. On the drive home it did feel like the bump steer problem I had is almost gone.

Heading out in a few minutes to drive the local twisties (Ortega Canyon) then loop around to the local Autobahn (I-5 through Camp Pendleton). That should give me a good feel for the changes and put a grin on my face.

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I'm running 18" wheels. The distance from the ground to the top of the front wheel arch is about 25 1/8". Visually, the stance doesn't look different than the x74 height I set. No problems at all with driveway transitions or speed bumps.

Handling wise? I'm a very happy boy! Pushing it in the twisties, the car has a beautifully linear feeling turn-in and is flat and sure-footed in the corners even with bumps. No bobbling when switching directions. At high speeds it has straight-line stability that is so effortless and confident you might be tempted to engage cruise control and take a nap.

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  • 1 month later...

Coaster:

It would be interesting to see your After numbers on the corner balance.  And, what your new ride height numbers are at all four corners.  Which corner was adjusted? Also curious of the number of turns required at each adjuster to accomplish the balancing.  Are we talking only one or two turns to produce a big change in loadings?  I, too, set up my PSS9's to X74 specs (and stayed within the Bilstein TUV limits) for ride height at all four corners.  I need to find a shop with scales.

Did you set corner balance with or without driver weight in the seat?  The shop manual says No.  Your before numbers showed 127# bias on the left side.

THANKS

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My final corner weights, showing a 50.4% RL+FR cross weight:

 

FL:  674    FR:  630

RL: 1149    RR: 1077

 

My final ride height, as measured from the factory reference points on the chassis:

 

FL: 105.5    FR: 107.5 

RL: 127.0    RR: 129.0

 

I'm assuming the shop adjusted all four corners in order to set a 20mm rake and achieve a cross weight close to 50%.  My work gave them a reasonable starting point only.

 

AFA number of turns, when I did the adjustment I found it more manageable to use a reference point.  In my case I used a caliper and kept track of distance from the bottom of the locking nut to the start of the adjusting threads on the damper barrel.  I would use the same approach if I had scales.  It's so easy to lose track of "number of turns" and have a big unaccounted error after a lot of adjustments (and boy, did I make a lot of adjustments!).  Toward the end I was moving height in 1mm increments to produce a change in height.

 

When I did the ride height adjustment I used factory recommendations: a full tank of gas, tire pressures set to 36psi front and 44psi rear, top up, nothing in the trunk except the spare tire and stock tools, and nothing else in the car.  When the shop did the corner balancing they used 1/2 tank of gas, my weight in the driver's seat, and the rest the same as my work.

 

Sometimes it takes doing something myself and doing it wrong in order to learn.  Notice how the final ride height numbers aren't by-the-book exact matches?  In the end, height had only a close relationship to balance.  I also neglected to disconnect the drop links from the sway bars before measuring.  The drop link / sway bar connection results in preload on the springs and has an effect on height and balance.

 

No two ways about it, find a shop that does corner balancing. When you have adjustable height dampers, corner balancing is not just for racing, it's about setting up your car for proper handling and tire wear.  My car felt so good after this recent work that I just took it on a 6,000 mile cross country road trip.  It handles better and is more enjoyable to drive than it has been since installing the PSS9's 10 years ago.

 

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Very cool.  Data is always good.  And, doing it yourself, doing it wrong, ... is a great way to learn.

I wonder how much the drop links contributed?  I have Tarrett adjustable links, but have not tried disconnecting to see if they are preloading or not.

 

Now I am really anxious to find a shop with scales.

 

 

Edited by DWS964
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I have Tarrett adjustable links as well.  With the car up on jacks (i.e. no load on springs) the links are adjusted to connect to the sways on each side easily, without force.  As soon as the car is on the ground any difference in weight side-to-side exerts pressure through the sways that results in preload on one side or the other.  At least that's how the shop tech explained it to me.

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