Fun With Air Ride – Part 3

Traction, grip, roll center, instant center, compression and rebound, and damping versus spring rates.  Scrub radius, camber, UTQG?  As one might imagine, this is going to be a little technical.  Please hang in there – I’ll make it as easy to understand as possible.  And, if there are any questions, it’s easy to get in touch with me for clarification.

As I mentioned in Part 1, our goals for our suspension are as follows:

  1. A more comfortable ride
  2. Reduced understeer, to the point of neutral handling
  3. Improved lateral acceleration
  4. Less body pitch and roll in braking and cornering
  5. No sacrifices in acceleration or braking performance
  6. No excessive maintenance demands or tire wear

With our goals, a tight budget and an overwhelming notion that air ride was our suspension medium of choice, our project began.  We developed a thorough knowledge of the inner workings of our stock suspension, and learned that we had a modified McPherson Strut setup in the front, and a more traditional coil spring/tube shock setup in the rear.  Both ends featured the obligatory upper and lower control arms with assorted ball joints and bushings.  Luckily, the factory suspension setup and its associated geometry would lend themselves nicely to a proper handling and comfortable riding car, and it would not be necessary to reconfigure the suspension in either the front or rear of the car in order to meet our goals.  Of course, there was the temptation to create something more exotic, but this would not be possible within our budget.  Needless to say, this “more exotic” setup is still in my mind, and I will find a way to put it into play some day.  It’s kind of what we do…

  • AIR RIDE –
    • PRO’S: Adjustable Spring Rates give us the ability to fine-tune the suspension for handling and/or comfort.  A progressive spring rate offers improvements in comfort.  Changes in the steering characteristics are also possible by adjusting the spring rates, as well and providing a platform for managing body pitch and roll.  Air springs are much lighter than either the factory or aftermarket coil springs, reducing both the total vehicle weight and unsprung weight, both of which benefit the drivability of the vehicle stability, comfort, acceleration, braking and fuel economy.
    • CON’S: Potential for reduced reliability and increased maintenance requirements.

Because changes to the suspension type and basic geometry would not be made, selecting the best shock absorbers and struts for this project was the next step.  It is no exaggeration to say that the choices are veritably endless.  Monotube, twin tube, long travel, short travel, lowered, single-, double-, triple- and quadruple-adjustable aftermarket versions from dozens of manufacturers and Countries of Origin.  Racing suspensions, street suspensions, entire kits or individual components…even bespoke systems with every possible variable made to the user’s desires and specifications – the possibilities are staggering.  If you are the type to “overthink” the details, the topic of shock absorbers can be a dream or a nightmare.  As many of you know, I am the Heir to the Throne of the Kingdom of Overthinkers (although I would contend that inferior minds “underthink” the details – and I’ve seen countless custom suspension systems that could have benefited from more thought).  The choice of a shock absorber for my application would effect both the comfort and handling of my car.

The first-generation Cadillac CTS carries GM’s “Sigma” chassis designation – designed in Europe by Opel, which was owned by GM at the time.  So when I say that Opel spent a lot of money engineering the chassis, one understands the connection.  The point is, the chassis was painstakingly designed specifically for the suspension to attach to the chassis in a specific manner, in specific locations.  I could see no practical way, short of building a whole new chassis, to improve on this.  So, I decided to work with the existing chassis

Front Struts
Photo courtesy of Raymond Barrios

mounting points.  Therefore, direct-fit shocks and struts would be required.  This narrowed the search a lot.  However, the number of choices available was still enormous, and I needed to narrow it down further.  Knowing that air ride would provide me with infinitely adjustable spring rates told me that I wanted as much adjustability as possible. My budget told me that I wanted to go to Walmart and pick up their least expensive set of factory-replacement Monroe shocks.  I eventually settled on 2-way adjustable coilovers, which allow for the compression damping and rebound damping to be adjusted independently of one another – an elegant solution for those looking to improve both comfort and handling.  Furthermore, the threaded bodies would provide the ability to adjust the ride height independently of the spring rate, so I could have the spring rate that I desired at any ride height.  The diameter of the shock body would perfectly allow for me to use airbags that would slip over the body of the shock, easily replacing the coil spring that came with the coilover kit, whereas the diameters of the factory shock bodies were too large to allow the ‘bags to fit in that location. In the end, I chose a set of KW Coilovers, made in Germany and approved under Germany’s strict TUV standards.  The rebound is adjustable in 18 steps, and the compression is infinitely adjustable.  (There were complications that would effect the air bag mounting locations in the rear…more on this later).

  • KW Coilovers, Version 3
    • PRO’S: Major improvements in both handling and comfort. Decreased body pitch and roll.  Adjustable damping, well matched to the nominal spring rates of the air bags.  Extremely light weight, reducing unspring weight and total vehicle weight, for better ride, comfort and handling, acceleration, braking performance and fuel economy.  TUV Certification means that these shocks should last a lot longer than the factory units, while performing at a superior level, excellent for long-term reliability.
    • CON’S: Require extensive adjustment and a break-in period to optimize.

At this point, the air ride system and coilovers set were installed, with the stock wheels and tires retained for the time being.  This is when the suspension system falls into place, and its character begins to emerge.  After an extended period of brainstorming and a great deal of very stimulating technical conversation, I chose a company to provide the parts and install the air ride, complete with coilovers.  We decided on 1/4 inch DOT approved airline and specified some baseline settings for the system.  An aluminum air storage tank would be installed, preventing the danger of scaling inherent in steel tanks, since compressed air collects water and steel is prone to rust.  Water traps are present, of course.  As a further safety measure, a Schroeder valve was installed, allowing the tank to be filled in case the on-board compressors should fail.  The air ride control system can be configured to offer 3, 4, or 5 preset air pressure levels, and there are a host of other features as well.

At this point, since I personally know many people and companies capable of providing the parts and installing air ride in my vehicle, I would like to say a few words about why I chose the air ride installer that I did.  To begin, it was not a personal decision.  I did not choose a “friend” to do the job. I have many installers who are much closer friends than Ray at Air Ride Equipment, who I chose to do the job. In the opinions of some of my closest friends and members of my immediate family, it turns out that there are people who believe that I may be a challenging customer. Whether this is true or not, the fact is that I do have certain expectations of my service providers.  This IS business.  Because of these expectations, I prefer not to do business with friends.  If there is any dispute, it can be hard on a friendship.  I don’t have a lot of friends, and would hate for business to get in the way of an otherwise thriving friendship. Furthermore, Ray has a great deal of well-documented experience, he is well known to many people that I know, frequently works air ride into the factory suspensions of high-end cars (while retaining the factory suspension’s functionality, including stability control, ride control, and in the case of the Cadillac CTS-V, the ultra-high-tech magnetic dampers.)  He offers a lifetime warranty on parts and labor, makes adjustments for free, and stands behind every install in a way that makes me feel as if I might not have to fight for adjustments if something is simply not right.  In technical conversations, Ray and I clicked, our suspension philosophies are very similar, and he has a lot of knowledge based on a lot of experience, which he is not hesitant to share.  Is he the most technically knowledgeable air ride installer that I know? No. I have one acquaintance that is literally writing a book on the subject.  Is his technical knowledge sufficient? It’s much more than sufficient.  And each second spent under a car, obsessing over every detail, making sure everything was done just right, on 260 vehicles and counting, has earned him this knowledge.  If I intended to build a complete custom chassis, would I have chosen Ray?  I might not have…I have never seen a chassis he has built.  But that was far beyond the scope of work on this project. And Ray has the attitude about customer service that dovetails very well with my OCD.  Was Ray the only choice for this? No. Was he the best? A month after the installation was done, and a couple of weeks after the 500-mile retorque and inspection, I still think so.

As you can see, with the air ride and the coilovers, we have addressed most of the shortcomings with the factory suspension already.  So, what is left? Suspension system adjustments, and the vitally important wheels and tires.  These will be covered in future installments.

But I am in a position to share my first impressions.  When I rolled up to the shop, my car was sitting outside, in front of the service bay.  Ray was taking some photos with his

Untitled
Photo courtesy of Raymond Barrios.

phone for posterity.  It sat low, much lower than I would dare drive it.  I later found out that this wasn’t possible anyway, since at its minimum height, the inner fender liners sat on the tires.  Ray informed me that the bump stops had not been installed, but that they would be during the 500 mile-retorque and inspection.  No problem.  After a cursory instruction period, Ray hopped into the passenger’s seat and we were off for a test drive.  Even at the preset ride height, the ride was low but comfortable.  After a slight drag over a steep driveway, we were off.  Alabama Street in Redlands suffers from a high degree of neglect and disrepair, and as a result, it is very rough.  The car rode stiffer than I was used to, but it was compliant and pretty comfortable.  As we moved away from Alabama Street,  the roads smoothed out considerably.  The ride smoothed correspondingly, with just a hint of “bounciness” in the rougher portions of the road.  The damping, which was adjusted to its softest setting, was not sufficient for the spring rates.  But it was close.  Very close.  And the ride was pretty good. But how would it handle?  Well, that would have to wait.  The drive from Redlands to my home in Chino was unusually smooth considering that this part of Interstate 10 was not well maintained.  I found myself looking for bumps to roll over at freeway speeds, and saw plenty, but felt few.   I believed it was going to work exactly as I had hoped.  There would be further developments, but we’ll cover them in our upcoming Part 4…

 

 

 

 

 

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