November 9, 2016Suspension Truth by Fat Cat Motorsports

‘Dancing with the road’ – sharing ideas about our success with creating street-friendly yet responsive FCM Elite suspensions

 

 

I’m motivated to write this blog post as I’m composing an email to a new Elite customer in Australia. My comments to him reminded of me a few builds we did that gave better results than the factory dampers or even a respected aftermarket replacement (always pleasant to hear!). But I wanted to describe WHY I could get these results, what principles i was applying that made a difference compared to companies with much larger R&D budgets and many more ‘official’ engineers than we have at Fat Cat Motorsports (just me, an undercover physicist!).

 

Rewind the clock to early 2014: I had been sick for a while in early spring with time to do nothing and it got me thinking about ideas behind what a suspension really needed to do, vs. what people thought it ‘should’ do. When I was recovered sufficiently, I made this video I called ‘How to Handle a Raw Egg, Isolate and Control.’

 

Then, a couple months later in summer, I had been working with customers for some time integrating the idea of high-performance driving with street-compatibility. I’d been contemplating the situation that many people are dealing with: how to make a fun-to-drive suspension that is still soft-enough but not TOO soft? This is the age-old question with tuning performance cars that see significant street driving.

Especially because the vast majority of our Bilstein monotube-based FCM Elite suspensions are not adjustable for damping, it’s very important for me to understand what our customers need their vehicles to do and how to implement it. I sometimes think of myself as the ‘Suspension Whisperer’ because I need to ferret out the subtle behaviors without relying on simply ‘turning a knob.’ With nearly 1,000 unique FCM Elite suspension created since 2004, I have been able to continually refine my understanding and implementation of suspension tuning to get smoother ride, faster lap times, and more grip. So much of this success almost paradoxically comes from having the suspension do less, and treating the entire vehicle is moving as one unified whole instead of separating the ‘front’ and the ‘rear’ which creates a disjointed, harsh, unsettled behavior.

This unified behavior is why ‘Flat Ride’ is such a crucial design choice and fortunately, many factory suspensions these days come with Flat Ride tuning. For those who haven’t seen the video where I discuss the experience with my Audi S4 Avant customer who played with Flat Ride using his airbag suspension(!) even before I began working with him, you can hear me share that story in this video:

Once you have Flat Ride created by the proper choice of front and rear frequencies, you have a vehicle that naturally wants to ‘settle down’ after a bump or dip, because the rear suspension is able to oscillate a little faster to ‘catch up’ with the front. This is a natural phenomenon, like going for a walk with a friend, needing to stop and tie your shoe while your friend keeps going. You need to speed up for a second to catch up to them and your vehicle suspension has to operate in the same way.

 

Now, all that prefaced, let’s return to the present day, November 2016: This is an email I’m sending to Simon, a new FCM Elite customer in Australia who has a very long commute (40,000 km, or about 24,000 a year!). He’s also a former road-racer who would like to maintain good control but also need more ride comfort than the current suspension allows. Through engaging with him and answering his questions, I realized much of the recent success my Elite customers and I have enjoyed is from actualizing the philosophy of ‘Aggressive Comfort’ and ‘How to Handle a Raw Egg: Isolate and Control.’

As an example, we had a really excellent development project with EricSMG, who drives a BMW E46 M3 couple. The thread where Eric shares his feedback is here and while it’s long, you can search for his username (okay and mine as well!) to jump to the most crucial posts though many other comments are interesting as well:

http://www.m3forum.net/m3forum/showthread.php?t=534318

A summary of Eric’s feedback is here:

Revision 1:

http://www.m3forum.net/m3forum/showpost.php?p=1067334751&postcount=111

Revision 2:

http://www.m3forum.net/m3forum/showpost.php?p=1067466122&postcount=174

and Eric’s introductory post:

http://www.m3forum.net/m3forum/showpost.php?p=1067219409&postcount=1

Below is my email to Simon:

Hi Simon,

I’ll address a few point in your consult form that would help optimize your road comfort and also point toward the feel and control you’re looking for:

Simon:”Rear Whiteline adj sway bar set on middle setting. Chassis bracing (front strut bar, rear body brace, + tow bar (best 3 point rear chassis brace you can buy, but heavy!)”

“What is your main ride or handling complaint about your vehicle? If you know what the current suspension brand is, enter here or leave blank.: Car crashes through bumps (jacking down). Nice ride on the freeway until road gets uneven/cracks/joins in concrete freeways are sharp/jarring. Bilstein 3000gT front damper, P11 JDM Bilstein Rear damper.”

SJA: The chassis bracing is definitely an asset to improve ride quality / decouple road impacts from being conducted through the suspension into the passenger compartment. While the dampers are almost certain jacking down, part of the problem with jarring impacts on uneven roads is from sway bar stiffness and the side-to-side coupling behavior intrinsic to their action.

You may want to experiment with softening the Whiteline rear bar another notch and see how the ride quality changes. You can also use a slightly longer / firmer rear bump stop that would provide independent wheel control without coupling the wheels together as the sway bar does. The difference one or two packers make when you’re at the point of a little bump stop contact is quite eye-opening! I used this to good effect on my BMW sedan at Thunderhill raceway, adding a single packer to the right rear suspension to add a little more entry oversteer / slip angle going into Turn 1 (about 90mph entry if you’ve brave enough!). You can also take the packers out if you want to keep ride soft on more broken roads. The idea also of using spring rubbers is worth exploring (just an older reference webpage):

http://fatcatmotorsports.com/FCM_products_spring_rubbers.htm

 

I can obtain them from my bump stop vendor.

Simon: “My only concerns are while i want comfort, i don’t want the car to feel soft/boaty and feel that softening the dampers to create comfort (especially up front where they are fairly stiff now), while maintaining a match to the spring rate might make that the case given that i am only using factory spring rates.”

SJA: Very reasonable concern. What I’ll share from my experience (with various vehicles and most recently our BMW sedan that I kept OE springs on for nearly a year, playing with various recipes and also tracking the car very hard) is that using firmer low speed compression damping and softer low speed rebound is a key to providing good comfort and also control. You can check out a few posts in this thread about an E46 M3 we tuned Bilstein HDs for where he kept the fairly-soft OE springs for better ride quality:

If you just look for posts by our customer EricSMG that’ll help you see what’s going on. I also posted a compression curve and made a video detailed improvements I found comparing our dampers vs. Bilstein vs. Koni, and even how we can get firmer lower speed compression but also softer high speed compression force vs. Ohlins:

There is a local Ford Fiesta ST we just finished working on and he’s using the Bilstein B14 (PSS) original spring rates which fortunately DO provide Flat Ride (that’s another thing to check on your car – you may want / need to increase the rear spring rate simply to make sure you get Flat Ride plus to help account for the added load you’re handling for work).

“Suspension is installed! Took me a few hours but everything went easily. Much more compliant / less harsh, and still feels like it’s on rails. I need to set the ride heights and corner balance it next. I’ll pop over to the shop once (I) get it squared away – so you can check it out.”

fcm_review_max_fiesta_st_elite_kbo_rr_1

(from our 2015 Fiesta ST FCM Elite customer Max, who is using the standard Bilstein B14 (PSS) spring rates which fortunately provide Flat Ride! Max’s setup has KBO v1.9, Ripple Reducer, and our latest FCM Elite valving methods to ensure no ‘jacking down’ is occurring.)
In short, I don’t need to go crazy with designing our FCM Elite suspension to have too low speed compression because that can also add harshness, but when you have softer springs some added LS bump damping is really your friend. This design choice is totally in keeping with the ‘rally’ philosophy of allowing the tire to stay in contact with the ground vs. artificially jacking the suspension down and keeping the tire dug up in the wheel well as your current suspension does. It’s quite interesting to note that Volkswagon is one of few manufacturers I’ve found that actively uses more low speed compression in their more ‘exclusively’ models. I’ll blog about this at some point too. Given they have goofed with the whole diesel emissions scandal, I felt some positive news was worth sharing!
Once there’s enough LS bump damping in play, the chassis really responds to an initial steering / braking maneuver very well and you almost feel like you have more spring! You do, in a way – but it’s a DYNAMIC spring from the damper’s behavior vs. a static spring that would drive up the ride frequency and cause stiffness across the shock velocity’s range. You only want / need a stiffer initial transient response from more LS compression and then to have the damper soften up beyond that while providing enough resistance to help control big bump that would tend to bottom the suspension.
You can see what I’m getting at in the E46M3 video and also the rally tuning video which you’ve already seen no doubt.  I made that video a long while ago and really have a much stronger understanding and experience with how far we need to watch the relationship between compression and rebound damping – I now test dampers to at least 15 in/sec and sometimes up to 22 in/sec (which is the range of our current Roehrig 2VS dyno’s capability). I can also feel from my ‘butt dyno’ that our own BMW’s current Revision 7 tuning has too much high speed rebound or not enough high speed compression (we’re talking beyond 15 in/sec) and will be correcting that in the next revision. “
Indeed, I’ve found it very important to minimize jerk in the suspension’s behavior. I wrote about that a bit in this article I published on The Truth About Cars:
I’ll draw an analogy to any type of rapid movement is required to move in any given direction smoothly and without injury. Consider one’s stance when running, dancing, playing tennis, martial arts, sprinting, watching a cheetah chasing a gazelle, or even simply walking.  In the related realm of vehicle suspensions, having a slight bias toward more low speed compression damping than low speed rebound, the suspension is naturally picked up, to rest ‘on the balls of its feet.’ If you need a primer about these two, visit my ‘How Shocks Work’ video series linked here:
If you’re sitting and can stand up, or just visualize this exercise, picture balancing on the balls of your feet. I remember from both dance and tennis lessons that you can feel a little ‘spring’ in your step, that supple light bounce-bounce-bounce sensation where your lower body is connected but fluid. Watch any video of Bruce Lee and how quickly he can move, how prepared he is for any approach. This same sense of relaxed control, puts the entire vehicle in a state of being poised, ready to ‘dance’ with the road. Whether it’s one bump or many, you’re saying ‘okay, bring it! I’m ready!’ That’s what a suspension with the slight compression bias is communicating in engineering terms. This is what a REAL WORLD suspension needs to function! Giving examples of NASCAR, Formula 1 are totally irrelevant but many aftermarket builders will emphasize REBOUND damping because it’s easier and cheaper to make a twin-tube damper that creates lots of downward-pulling, flat-footed rebound force instead of to generate the necessary low and mid-speed compression that provide a smoother, suppler, more controlled and firmly-responsive ride / handling dynamic.
As a commenter in the Truth about Cars site mentioned, the dynamic set point is moving downward, which is bad for maintaining good ride quality.
So by imagining that every vehicle on the road, in the real-world we all inhabit, needs to ‘dance’ with the road, I am seeing and feeling the interaction between driver, vehicle, and ground as a three-way dance, a kind of folk dance where the driver is in control of most large amplitude movements (via steering wheel, brake, and gas) but the ground will surprise the other two by tossing in bumps and dips of all sizes and speeds, so the driver / vehicle interaction has to deal with that. Ultimately, the ground doesn’t care so much about how the driver and vehicle feel about it. The ground – Mother Earth – does what she does. Humans carve roads in some cases, but erosion happens and we can’t guarantee those roads will stay in good shape. In many places ‘road’ is a laughable term and it’s in THOSE situations that I particularly see the idea of ‘Aggressive Comfort’ (or even just ‘Comfort’) and the principles of ‘Isolate and Control’ being so important.
You need feedback from your driving inputs, which the added low speed compression helps provide by promoting rapid weight transfer during turn-in; even more rapid than using rebound which work the opposite corner to the one you’re loading. You also need a different type of isolation and control when dealing with from sudden or high-frequency road features that are not important to follow but more to manage (or filter out).
I have a video or two I’ll be creating on this subject related to some new discoveries I’ve made in the realm of tuning for street, backroad, and rally driving. I’ve got a new piston design for the Bilstein monotube I’ll be creating / testing and patenting. The previous meeting I had with an examiner for a patent company said yes, indeed, the technology I showed him meets the criteria for patent-ability. I’m very excited to see so many pieces of understanding coming together and further emphasizing the sense that my quest for Ride Harmony is the most noble cause I can pursue. It follows the principles of Nature, both respecting Her laws and pushing Her to see what secrets she might reveal!

One comment

  1. Great post! It’s great to see fellow hatch backers going with FCM tuning and I’m starting to see my words of wisdom from TTAC + FNW sites being repeated by other FIAT Abarthers on FB groups!

    I’m excited to learn about your new piston design especially since I’m starting to save for a KBO build for the front dampers on my Abarth ;).

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