Everything about Fat Cat Motorsport Suspension

[EthanolTurbo]

bigjae46 Another comment on your ride frequencies, based on the corner weights and spring rates you provided. You have some mismatch in the side-to-side ride frequencies, looks like around 2.49 / 2.67 Hz front and 2.29 / 2.46 Hz rear. The LF and LR springs should be IMO 50 lb/in and 100 lb/in higher than the corresponding right. Also, I'm not sure if you're on stock sways due to NASA point limitations, but your setup does appear to be pitching right now but perhaps less than before? The damper behavior is likely affecting the overall real-world ride frequency compared to the undamped frequency, and there may be some bump stop contact happening as well. In fact, given the rebound-biased nature of the dampers I'm certain that's another factor to consider as a non-linear behavior you're fighting. I'm guessing that your current damper settings even with D/A are likely still giving a rebound bias though admittedly that's an informed ASSumption on my part.

My suggestion would be to separate the front and rear more, something like 425 / 375 front and 800 / 700 rear to get ~2.30 / 2.31 Hz front and 2.45 / 2.46 Hz rear. That'd be about 6% Flat Ride. To keep a similar FRC / handling balance you'd want a slightly bigger front bar, like an Eibach 27mm or just deal with the slightly looser handling with alignment / pressure / other adjustments.

If we were going to work together, I'd really want you to get a Ground Control front tubular Race and start with it on a softer setting. It's such a great piece with a HUGE adjustment range and you ought to get some weight off the nose of the car as well.

Then, as another change to address the low speed understeer, you'd likely want to reinstall the factory rear bar (or any small bar that fits). Without a rear bar, any car will experience terminal understeer in high steering angle (large weight jacking) maneuvers. This is due to an asymmetry in the roll center migration front vs. rear. The front bar being present limits the dynamic roll center change while on the rear with no bar, the droop is higher and the rear roll center changes more. This acts like a dynamic understeer effect which is what we experience particularly in slower turns with higher steering input / weight jacking. Kudos to Emilio at 949Racing who pointed this out. If you look for some posts by him or anyone else who understand the phenomenon, it makes sense and echoes my prior experience when I used to run Miatas with no rear bar and got terminal low speed understeer. I always recommend any racer run a rear bar - and a good quality adjustable end link to prevent bind & preload.

I think the current pitching behavior, the lack of rear bar, rebound bias in the TC Kline, and near-certainty of bump stop interaction and dynamic spring rate changes due to jacking down are all points to address to get further optimization from your tire contact patch. You can make a few changes even with your current TC Kline (and maybe run them even softer than you have them, I don't know what settings they're at currently) and likely get further improvements. But unless the TC Kline design allows you to bias the damper more toward 'rally-style' tuning, especially at high damper velocities, you WILL need a superior damper to get to the next level.

I really do think a good front tubular bar will be part of that package. There is something to be said for running as little overall bar as possible, but not when you're dealing with pitch and probably can't get on the power aggressively enough or if the car is still pitching / oscillating back-and-forth, your results are limited. I didn't ask about your LSD type and behavior which also plays a role.

It sounds like you've done great to this point - I'd like to see you get even faster. The FCM Elite Stage 2 will be a good choice and also show others on this forum that you don't have to sell a kidney to get an awesome Fat Cat setup.

Question: do you only spec dampers remotely via data input or can someone ship you their car, send you the mod list and have you spec everything out based on seeing/driving the car in person?

[Suspension Decoder]

Question: do you only spec dampers remotely via data input or can someone ship you their car, send you the mod list and have you spec everything out based on seeing/driving the car in person?

Short answer: if I've done a build for that vehicle or already gathered all parameters I consider essential, then the process is very straight-forward. If I've never gathered the data or there isn't a known database of the values I need then I ask the customer to get those data or pay me to do it. I have flown or driven out to a customer site to analyze a vehicle per my methods, never had a car shipped out to me. Frankly, I'd rather take a road trip or flight (especially if to San Diego) than clean out my garage to fit a car here! Interacting with an owner is important to me and doing that in-person, when possible, is best.

Medium-long answer: there are some key variables I need to account for in order to be comfortable re-engineering a factory suspension AND making changes to yield the maximum safe suspension travel and maximum usable grip via minimizing contact patch load variation. I have enough respect for factory Mech Engr's that I'd want to understand how the factory suspension was designed, what the current suspension has done differently than factory, and then what I need to change to get improvements inline with the owner's goals. So it's more than spec'ing dampers; if the goal is fastest lap times or maximum comfort then I have to be free to recommend new components if the current ones aren't up to muster.

FYI, I use this procedure I developed years ago as the starting point on gathering vital parameters. Then I usually ask for a stock front and rear damper assembly so I can measure the spring rate on y Longacre tester, the dampers on my Roehrig 2VS, and the bump stop on the latter as well. I also correlate the expected static load to the spring compressed height so I can estimate how much suspension travel is available before the factory bump stops engage. Every single OE suspension I've looked at engages the front bump stops almost immediately, usually combined with soft overall front compression damping and firm rebound. All of these parameters are quantitative ways to verify a driver's qualitative experience of things such as limit understeer, harsh ride, wallowing, etc. Often by someone's description of their cars behavior, I can guess pretty closely what their dampers will look like on the dyno.

https://fatcatmotorsports.com/PROC_FCM_SUSP_CHAR_2015.pdf

also this playlist shows various steps in the procedure:

https://www.youtube.com/watch?v=yHr3yKcuESk&list=PLaHHNmjjz4mB9CpQ7aiks1U7 pUJWn0ham
===

For a vehicle I've already done these measurements on, a client only needs to fill out my FCM Elite consultation form and then engage with me for the consult call. I strongly recommend all new FCM customers get corner weights - even pure comfort customers.

If it's the first time and I don't have enough data or can't trust the data that's out there (e.g. a motion ratio without the supporting raw data to justify it), then someone has to gather those data. If my client is willing and able, they can do the characterization procedure on their own. I'm usually available in case there are questions during the process. Also, most competent (race-oriented?) shops can do the measurements if you show them what they need to do. A lift can be helpful but you'll need a transmission jack as well. Most of the time when I've done it, I've put the car on jack stands and used the floor jack to raise / lower the wheel to get suspension travel data.

The key sections are 2, 3, and 4. for suspension travel measurements then damper / spring motion ratio, and sway bar dimensions / motion ratio. I like to do bounce testing (section 1) when possible although some suspensions are so stiff (spring, damper, or both) you're just flexing body work or bouncing off the sidewalls. A big reason I like to do section 2 is to check the specific wheel & tire package at full compression and full steering lock to see where the points of potential interference are and also how much bump travel we might be able to safely free up via shorter bump stops, shorter damper bodies, or both.

[Suspension Decoder]

bigjae46 Back in 2017, I worked with a NASA ST4 E36 M3 racer, Percy. He got an FCM Elite Stage 3 setup for his car and was impressed at all the improvements over the TCK. While his may not necessarily be the same as your E46 TCK, they are likely very similar in design approach. The amount of NOISE his dampers produced, and the hysteresis, was about the worst I've ever seen / heard!

Note that his was an FCM Elite Stage 3 NOT the FCM Elite Stage 3 Ultimate which supercedes the Stage 3 and I developed in the 2020-2021 time frame. I'd say his results then are comparable to what my Stage 2 gives today as I began to focus even more on that 'tarmac rally' style approach. More bells and whistles on the Stage 3 Ultimate for a full damper velocity range tune (very low to very high), but any Stage gives you the necessary ingredients for a nicely-optimized suspension.


"So I had more mid-corner grip with your setup than I did with the TC Klines and that was very noticeable." - Percy

[bigjae46]

At this point it practically IS a guarantee to go faster when switching to FCM. People show up with TCK, Ohlins, MCS, JRZ, Moton, whatever and always go faster with an FCM Elite Bilstein-based setup.


The TC Kline front and rear have a fair amount of low speed jerk in bump which isn't good for tire grip or lap times (or comfort - amazing how those three are connected...!).

The TC Kline front rebound is less aggressive than OE which is better for overall grip and compliance but it still has a linear-esque curve and IMO too much HS rebound. Also too little HS compression.

The TC Kline rear bump is VERY soft while the rebound builds fairly linear it seems (up to 10 ips at least). You get into jacking down by 3 in/sec and the rear is constantly going to be pulling you into the bump stops. Not good.

The twin-tube design shows a decent amount of hysteresis - it simply can't be as consistent as a well-tuned monotube, esp. in hotter driving conditions.

Most people don't know what to ask a vendor to change - I sure didn't at the beginning of my suspension adventures. There are certain behaviors a damper can produce which - no matter the setting - will result in worse lap times and/or comfort (again, they're more connected than you may realize).

Think 'tarmac rally style' suspension tuning more than 'NASCAR style' (rebound-biased). Almost everything out there is the latter, while the superior and provably faster approach is the former (which is how I tune).

That's so much to digest...give me some time and I'll provide a detailed response. I very much appreciate the offer for the consult! I want to make sure I have my stuff straight beforehand.

One quick question. Let's say I do get my car from 2590 lbs to 2475lbs and I can get the corner weights back to 50/50. Would I need to re-optimize the dampers? Springs? Or both? The pitch setup I had didn't seem terrible until I pulled a bunch of weight off the car.

I'm going back to 450lb front springs. Man, it was so good! I like being different. I love it when I tell people I have a gutted caged car with 450lb front springs. They tell me that it's too soft. Then I tell them the lap times I'm running...watch the jaw drop!

[bigjae46]

Suspension Decoder read last few pages.

Thanks man!

[Suspension Decoder]

That's so much to digest...give me some time and I'll provide a detailed response. I very much appreciate the offer for the consult! I want to make sure I have my stuff straight beforehand.

One quick question. Let's say I do get my car from 2590 lbs to 2475lbs and I can get the corner weights back to 50/50. Would I need to re-optimize the dampers? Springs? Or both? The pitch setup I had didn't seem terrible until I pulled a bunch of weight off the car.

I'm going back to 450lb front springs. Man, it was so good! I like being different. I love it when I tell people I have a gutted caged car with 450lb front springs. They tell me that it's too soft. Then I tell them the lap times I'm running...watch the jaw drop!

I appreciate a bit of prep though honestly just pick up the phone and call when you have some free time!

First, +/- 10-15% weight or spring rate changes will not make a dramatic affect on the car's optimization, especially if you're reducing weight. Added lightness is always the preferred direction to go because the dampers become more effective and if anything you can just soften the springs if needed. For ~115 lb of weight loss, you *might* want to recheck where the weight falls (use the Racer's Edge section to calculate new ride frequencies per corner). If you're more than 0.1 Hz off side to side, you might notice that.

If you have a current weight and a target weight, I can tune the dampers to be well-optimized in for that lower weight: I've done this in the past. Though as I said, making it lighter is better than adding subwoofers, a minibar, etc.

Yeah, the BMW E46 seems to have pretty good anti-dive so a ton of front spring is NOT needed nor is is beneficial. Plus, when you're pitching, all that front spring just makes the weight transfer off and bounce back to the rear, over and over and over and over again... like a seesaw going down the road. It's 'sporty' and stupid - and slower.

Blowing a skeptic's mind with how well Flat Ride works is the best part next to actually going faster with less work to stay at the limit.

[maupineda]

I have a set of nearly new HR rear shocks for anyone going this route. I have a for sale post on them.

[bigjae46]

bigjae46 Another comment on your ride frequencies, based on the corner weights and spring rates you provided. You have some mismatch in the side-to-side ride frequencies, looks like around 2.49 / 2.67 Hz front and 2.29 / 2.46 Hz rear. The LF and LR springs should be IMO 50 lb/in and 100 lb/in higher than the corresponding right. Also, I'm not sure if you're on stock sways due to NASA point limitations, but your setup does appear to be pitching right now but perhaps less than before? The damper behavior is likely affecting the overall real-world ride frequency compared to the undamped frequency, and there may be some bump stop contact happening as well. In fact, given the rebound-biased nature of the dampers I'm certain that's another factor to consider as a non-linear behavior you're fighting. I'm guessing that your current damper settings even with D/A are likely still giving a rebound bias though admittedly that's an informed ASSumption on my part.

My suggestion would be to separate the front and rear more, something like 425 / 375 front and 800 / 700 rear to get ~2.30 / 2.31 Hz front and 2.45 / 2.46 Hz rear. That'd be about 6% Flat Ride. To keep a similar FRC / handling balance you'd want a slightly bigger front bar, like an Eibach 27mm or just deal with the slightly looser handling with alignment / pressure / other adjustments.

If we were going to work together, I'd really want you to get a Ground Control front tubular Race and start with it on a softer setting. It's such a great piece with a HUGE adjustment range and you ought to get some weight off the nose of the car as well.

Then, as another change to address the low speed understeer, you'd likely want to reinstall the factory rear bar (or any small bar that fits). Without a rear bar, any car will experience terminal understeer in high steering angle (large weight jacking) maneuvers. This is due to an asymmetry in the roll center migration front vs. rear. The front bar being present limits the dynamic roll center change while on the rear with no bar, the droop is higher and the rear roll center changes more. This acts like a dynamic understeer effect which is what we experience particularly in slower turns with higher steering input / weight jacking. Kudos to Emilio at 949Racing who pointed this out. If you look for some posts by him or anyone else who understand the phenomenon, it makes sense and echoes my prior experience when I used to run Miatas with no rear bar and got terminal low speed understeer. I always recommend any racer run a rear bar - and a good quality adjustable end link to prevent bind & preload.

I think the current pitching behavior, the lack of rear bar, rebound bias in the TC Kline, and near-certainty of bump stop interaction and dynamic spring rate changes due to jacking down are all points to address to get further optimization from your tire contact patch. You can make a few changes even with your current TC Kline (and maybe run them even softer than you have them, I don't know what settings they're at currently) and likely get further improvements. But unless the TC Kline design allows you to bias the damper more toward 'rally-style' tuning, especially at high damper velocities, you WILL need a superior damper to get to the next level.

I really do think a good front tubular bar will be part of that package. There is something to be said for running as little overall bar as possible, but not when you're dealing with pitch and probably can't get on the power aggressively enough or if the car is still pitching / oscillating back-and-forth, your results are limited. I didn't ask about your LSD type and behavior which also plays a role.

It sounds like you've done great to this point - I'd like to see you get even faster. The FCM Elite Stage 2 will be a good choice and also show others on this forum that you don't have to sell a kidney to get an awesome Fat Cat setup.

Ok, took awhile reading and re-reading. I'll send a PM in a few moments.

I was planning on installed a Hotchkis bar, mostly to reduce weight, but it seems the GC bar will do about the same thing with more adjustability. I cut the rear sway bar brackets from the rear subrame - weight. There was a point where the car did turn really well at low speeds. Even with this setup, I'm at 41-44mph at COTA T11 which is comparable to anything I've seen (in person and video) on Hoosiers and race slicks.

My corner weights are LF 791, RF 691, LR 728, RR 655. I have duals and IIRC the rebound and compression are in the middle or close to it. I was running a LF 450 and RF 400 spring, I liked it. The flat ride calculator shows 2.42hz/2.40hz front and 2.61hz/2.62hz rear with LF 475, RF 400, LR 900, RR 800. Bounce freq ratio is L 1.08 and R 1.09.

For the group, what is the difference between stage 2 and 3?

And thank you!

[bigjae46]

The twin-tube design shows a decent amount of hysteresis - it simply can't be as consistent as a well-tuned monotube, esp. in hotter driving conditions.

Interesting statement. The one thing that has been consistent is my car is not nearly as fast in hotter conditions in comparison to other cars. I drive in an instructor group so it's mostly the same drivers/cars every time at the track. When its cooler out, I can catch 4-5 cars on the first green lap and pull away quickly through the turns. When its hotter, its 2-3 and I don't pull away in the turns. It changes, I pull on the straights. Just this past weekend, it was 95 degrees and I had two cars kinda glued to my rear bumper through the twistier section...the same section where I can pull car lengths on them when its cooler.

This past weekend the car also got much worse lap after lap. I drove 3 laps and came in. This has been consistent through the years. I just blamed the tires but was never convinced that was the issue. I'm on almost dead NT01s but the car should not have been as far off as it was.

[Suspension Decoder]

Each FCM Elite Stage is tuned to minimize rod force and provide as close to neutral jacking as possible, meaning 'rally-style' tuning.

The difference between each stage is how much technology I introduce to achieve more optimization over a wider range of damper velocities, damper displacements, and damper frequencies. Or you can say, how much noise / vibration / harshness filtering I can integrate to maximize tire contact patch. You pay more, you get more tech and refinement.

FCM Elite Stage 1 is along the lines of what most would call a basic revalve, except I focus on preventing either jacking down or launching up. Plus, I ensure the fill pressure is reasonable.

FCM Elite Stage 2 adds the Ripple Reducer, which reduces high frequency noise and jitter. It's noticeable over small amplitude / high frequency features like cracked / broken roads without major holes. I have also noticed that using Ripple Reducer has allowed me to reduce the nitrogen fill pressure further.

FCM Elite Stage 3 Ultimate builds on top of Stage 2 by using additional technology and methods to create a multi-stage damping profile on both compression and rebound. features blow-off capabilities and other behaviors depending on the vehicle's needs. The earlier Stage 3 had a blow-off valve integrated on the compression side which provided a nice 'chop the top off bumps' feature. However, I found that the rebound forces still were building and could result in high-speed jacking down. It was subtle, but present to a sensitive driver. So I was motivated to keep enhancing my design which in 2020 resulted in the Stage 3 Ultimate.

I have been semi-casually studying Reiger Suspension and have in mind to build my own rally dampers at some point. I've been able to do a few SCCA rally builds for customers who have had some success (one championship, lots of positive feedback from top drivers on their setups). I love pounding backroads, driving through potholes without excessively worrying about breaking something (within reason of course), and hitting rumble strips on the track without the car getting upset. Each Stage does a good job with that kind of compliance, although Stage 3 Ultimate is my current 'ultimate tarmac rally' build with 'hydraulic bump stop' integration. I can maintain minimal jacking down or launching across the entire damper profile.

A track driver would definitely appreciate the refinement of my top-end service. Anthony Zwain at Edge Motorsports helped inspire me to refine the Stage 3 into the Stage 3 Ultimate based on his comments of racing at Buttonwillow and having some issues with compliance through the Bus Stop (if memory serves). His critiques seemed cured now Most tracks are smoother than the average bad city road so you may notice the differences more in the real-world vs. at the track, depending upon how much of the track surface you're using. Again, spend as much as you can afford. I stand by the statement I've made many times that the FCM Elite Stage 2 will kick the butt of just about anything I've seen. It's more about the philosophy (starting with Flat Ride) than having to buy the most expensive dampers available. I really wish there was a way to have more enthusiasts / racers understand that knobs are not buying you results but more likely just extra headaches. Sigh.

In terms of how I test the dampers: my Roehrig 2VS can cycle a damper up to about 22 in/sec. I run Stage 1 and Stage 2 dampers to 15 in/sec because once I get past the digressive knee at 5-7 in/sec the slope is fairly constant (typical digressive damping behavior). On a Stage 3 Ultimate build, I test to the 22 in/sec limit of my dyno because we're not in Kansas anymore...

Two builds at the same stage may look and feel different because the implementation is UNIQUE to the vehicle and application. But everything gets a 'tarmac rally' style tune using the tech I've allocated to that Stage. This is why I need corner weights and other information instead of having something off-the-shelf ready to ship. So my FCM Elite approach is more about learning what you want to get from your car then I apply as much technology as you can afford to maximize grip by applying my understanding of minimizing contact patch load variation (as Milliken and Milliken define as 'maximizing grip').

In general, for the future to anyone reading, please do not PM me. I do not get notifications and prefer contact via the FatCatMotorsports.com website, or mail or phone (shop # to start and then cell # if I like you). I responded to bigjae's PM because he posted here and I'm actively checking this thread at the moment!

[Suspension Decoder]

Interesting statement. The one thing that has been consistent is my car is not nearly as fast in hotter conditions in comparison to other cars. I drive in an instructor group so it's mostly the same drivers/cars every time at the track. When its cooler out, I can catch 4-5 cars on the first green lap and pull away quickly through the turns. When its hotter, its 2-3 and I don't pull away in the turns. It changes, I pull on the straights. Just this past weekend, it was 95 degrees and I had two cars kinda glued to my rear bumper through the twistier section...the same section where I can pull car lengths on them when its cooler.

This past weekend the car also got much worse lap after lap. I drove 3 laps and came in. This has been consistent through the years. I just blamed the tires but was never convinced that was the issue. I'm on almost dead NT01s but the car should not have been as far off as it was.

Ah so you are describing what many would call damper fade, a flaw twin tubes are notorious for. Even on lighter cars like Miatas, the typical 'degassed Koni doubles' many autocrossers used to run (still do?!) were tough to predict. The more I drove and learned about the Konis (stiffer springs, more damping about to send them in for a 'revalve' for stiffer springs), I more I ended up hating the Konis on my Miata.

It's been Bilstein monotubes only since 2003. A perfect canvas to craft a Harmonized Ride.

P.S. I will say that KW - which seems based on Konis - does a better job on their KW Variant 2 and 3 than say TC Kline or Koni SA / DA. It's the least-bad twin tube I've found. Not necessarily competition-worthy (again, fade, lack of compression damping, etc.) but it won't break your back. The KW Competition / monotubes though I've found very rough and badly-tuned. I don't get why but I think they expect most people to want 'sporty feel' and run pitch setups, etc. so they overdamp the rebound.

[cobra]

Just throwing it out there since you're actively posting - I measured motion ratios on my M3 using potentiometers and they were 0.94 in front, and 1.14 (shock) / 0.63 (spring) in rear. This can have a noticeable effect when doing frequency/damping calcs. After updating, the numbers seemed to correlate better to what I was feeling in the car as well. Namely, with the understeer/oversteer characteristics and jacking down.

I am curious about your selection of bilstein monotubes if you are also concerned about lowering gas pressures from a ride comfort point of view. I guess with your compression blow-off you don't need much gas pressure?

[Bry5on]

Just throwing it out there since you're actively posting - I measured motion ratios on my M3 using potentiometers and they were 0.94 in front, and 1.14 (shock) / 0.63 (spring) in rear. This can have a noticeable effect when doing frequency/damping calcs. After updating, the numbers seemed to correlate better to what I was feeling in the car as well. Namely, with the understeer/oversteer characteristics and jacking down.

I am curious about your selection of bilstein monotubes if you are also concerned about lowering gas pressures from a ride comfort point of view. I guess with your compression blow-off you don't need much gas pressure?

Was the relationship pretty linear for the motion ratios? Care to share the plots? Curious as the e46 has an instant center basically at the diff which makes for lots of lateral displacement throughout the travel. No real migration of the rear roll center but a whole lot of jacking sadly.

[Suspension Decoder]

Just throwing it out there since you're actively posting - I measured motion ratios on my M3 using potentiometers and they were 0.94 in front, and 1.14 (shock) / 0.63 (spring) in rear. This can have a noticeable effect when doing frequency/damping calcs. After updating, the numbers seemed to correlate better to what I was feeling in the car as well. Namely, with the understeer/oversteer characteristics and jacking down.

I am curious about your selection of bilstein monotubes if you are also concerned about lowering gas pressures from a ride comfort point of view. I guess with your compression blow-off you don't need much gas pressure?

cobra, thanks for your interesting post. I always trust direct measurements on the exact platform for maximum accuracy. The M3's front MR appeared very slightly higher than my non-M ( Obioban asked me to verify the front before doing his setup!). If the rear spring MR is closer to 0.63 than 0.7 then the rear spring rate needs to be even higher to achieve Flat Ride. It's quite disjointed to have a very low rear spring MR and a VERY high damper MR. Too easy to screw up the damper and have that behavior override the spring, changing the car's characteristics. I think a lot of M3s (and E46/E36 in general) suffer from poorly-optimized damping. The newer platforms with lower rear damper MRs don't suffer as much.

I also find it useful to physically bounce the car to get a sense of how much friction / stiction is present. To illustrate this, just a couple weeks ago I met up with Andrew ("Farkle") to get started on an FCM Elite build for his M2C track toy. He's currently testing Ohlins DFV that came with pitch and was hating the ride frequencies. Did some calcs (we measured motion ratios on his car together a few years ago) and swapped in softer rear springs. He was expecting the front to go from ~2.3 Hz to about 1.8 Hz front. The rear would stay at around 2.3 Hz. I suggested we do a physical bounce test in his garage and at least with the displacement we could induce into the suspension, we obtained about 2.1 Hz front and 2.2 Hz rear.

Before the test I bet him $100 that the front would be higher than he had calc - turns out I was right! The front was nearly 20% higher than calc'd and the rear was about 5% lower. He still had Flat Ride though at a much lower ratio than he was expecting. Also, IIRC he has monoballs on most of his suspension arms and his sway bars are articulating smoothly per his comments. But, there's still some unexpected friction in the system increasing the effective front ride frequency. I think it was eye-opening to him. I was reminded how important friction is when setting up a VW Touareg a couple years ago. The calculated OE frequencies SHOULD have given a marsh mellow ride (~1.0 - 1.1 Hz!) but the real-world results were in the 1.5 - 1.7 Hz range. That car on OE bushings had a TON of stiction! The calculated MRs were really just a rough starting point in that extreme case.

Did you do physical bounce tests as well to verify what your calculations suggested? Can you use your data acq setup on various road surfaces to see how the damped ride frequencies compared to ideal / calculated over small / medium / larger bumps? Your raw data would be most interesting to see if you're willing to share it.

Bry5on cool note on the rear IC and jacking. This may be why using Flat Ride is particularly helpful to keep the jacking under control, provided the dampers / bump stops aren't inducing more vertical motion than needed via the rear suspension bottoming out then popping up. Do you know if other earlier platforms that rear axle behavior? The E36 I imagine would be very similar.

[ethan]

Was the relationship pretty linear for the motion ratios? Care to share the plots? Curious as the e46 has an instant center basically at the diff which makes for lots of lateral displacement throughout the travel. No real migration of the rear roll center but a whole lot of jacking sadly.

Bry5on cool note on the rear IC and jacking. This may be why using Flat Ride is particularly helpful to keep the jacking under control, provided the dampers / bump stops aren't inducing more vertical motion than needed via the rear suspension bottoming out then popping up. Do you know if other earlier platforms that rear axle behavior? The E36 I imagine would be very similar.

Would you guys comment on the impact of that rear roll center and motion ratio for divorced spring vs rear coilover setups?

Does applying the motion ratio to your spring calculation really account for all of the differences in suspension performance between these two rear setups?