Everything about Fat Cat Motorsport Suspension

[duracellttu]

It’s killing me. I have the shocks on my bench waiting— I just don’t like to do projects to my car in spring/summer/fall, so I don’t miss out on driving time.

Soon 🙄

Trust me, I can totally relate. My car is in the garage on quick jacks with half the suspension torn out. I’m dying to get this installed.

** Added a few notes to the first post about spring length, ride heights, damper warranty, rebuilds, and KBO. **

[Obioban]

It’s killing me. I have the shocks on my bench waiting— I just don’t like to do projects to my car in spring/summer/fall, so I don’t miss out on driving time.

Soon 🙄

[duracellttu]

Excellent summary! I’ll be sending FCM a set of dampers for rework this winter. Pretty excited to experience them for myself!

I ended up going with the Stage 3 Elite kits and hoping to get them in mid-late October. Can’t wait to get them installed. I’ll be reporting back with a review for sure!

[Obioban]

Excellent summary! I’ll be sending FCM a set of dampers for rework this winter. Pretty excited to experience them for myself!

[duracellttu]

There has been a lot of recent discussion and interest about Fat Cat Motorsports (FCM) suspension. Let's use this thread as a consolidated source of information.

I will start off by breaking down the discussion into a few different topics:

1. Background on FCM
2. Flat Ride
3. FCM Dampers
4. Spring Options

Background on FCM

Here is the company's website: http://www.fatcatmotorsports.com/

YouTube Channel: https://www.youtube.com/channel/UCKa...DXcdeRtq4Fbukw

In short, FCM is located in Redwood City, CA (outside of San Francisco). The owner of FCM was a member on the m3f and is a member on the nam3fourum here as well. Not only that, but he owns an e46 330i converted race car that he calls "Christina". He posts here on occasion and has a ton of great content on his YouTube channel (link above).

FCM also offers consulting, reach out to them for pricing.

Flat Ride

Flat Ride Thread: https://nam3forum.com/forums/forum/m...

Flat Ride Calculator Spreadsheet: http://www.fatcatmotorsports.com/FCM..._M3_Online.htm

The YouTube channel has several videos on how FCM defines "Flat Ride" and "Ride Harmony". He also has a video on some basics about how to use the flat ride spread sheet calculator Check that out HERE.

There is already another thread on this topic, so I wont recreate the discussion, but here is the Cliff's Notes version. The approach to achieving Flat Ride and ride harmony is defined by understanding the relationship between the front and rear bounce frequencies in your suspension. You can calculating the bounce frequencies by using front and rear spring rates and plugging them into the spreadsheet calculator. The ratio of these bounce frequencies (R/F) should be >1.0 to achieve flat ride. That means your rear bounce frequency needs to be greater than the front. For a more comfort focused setup, target ~15% Flat Ride and for more of a GT setup ~7%. You can also calculate the front roll couple (FRC) by entering in your sway bar dimensions. Don't worry, the spreadsheet has dimensions for several of the most common sway bar options on the e46 already listed in a table. Understanding the total stiffness (front and rear) will allow to calculate the FRC. The FRC is a metric used to determine to understeer and oversteer. For the e46 M3 a range of low to upper 70% FRC are typically what owners run.

NOTE: Everybody's personal preferences differ. The above target my suggestions based on the research and learning I've done. Use these is information as a guide, but ultimately you need to decide what suites your needs and desires. Use at your own risk. Better yet, get some consulting time with FCM and have them advise you.

As a reference, here are the suspension calculations on a stock e46 M3. These details are listed in the spreadsheet calculator by default.



FCM Dampers

If you want to learn more about suspension fundamentals, check out his YouTube playlist HERE. There are some good videos to learn the basics.

Let's talk about the dampers before springs, because if you choose to go with the FCM dampers you will need to know the correct spring ID and lengths to be compatible.

At this time FCM only offers two different kits, Stage 2 and Stage 3 Elite. He no longer offers a Stage 1 and I'm not even sure what the original Stage 1 specs were. Both Stage 2 and Stage 3 kits are optimized dampers using custom internals that FCM has designed and refine over the several years he has been in business. He uses an off-the-shelf H&R Street Performance coilover kit (P/N 50415), which at basically rebrand Bilstein monotube damper. These dampers are NOT adjustable, but are tuned to the spring rates your choose when calculating the specific Flat Ride you want. Neither Stage 2 nor Stage 3 come with any warranty. FMC will rebuild dampers and charge by the hour for that labor.

EliteStage 2 Details - Custom build dampers (as described above) with "Ripple Reducer". Watch the video HERE on details for what Ripple Reducer does.

Elite Stage 3 Ultimate Details- Custom build dampers (as described above) with "Ripple Reducer" and "Kerb Blow Off" (KBO). What the video HERE on details for what KBO does.

NOTE: When discussing pricing, it important to know that you are responsible for purchasing the H&R kit on top of what FCM charges for rebuilding for either Stage 2 or Stage 3. I know that they are in the process of updating their pricing structure, so reach out to FCM for the latest. That being said, this is a custom kit, and priced accordingly. It is more expensive than most off-the-shelf kits.

Here are some additional details for the H&R front and rear damper damper shafts. You will need to know this info for making sure your camber plates and rear shock mounts fit correctly. I am using Vorshlag camber plates and rear shock mounts. They have all the dimension info already, just let them know you are using the H&R dampers.




Spring Options

I wont go into a lot of details here, but lets first talk about the springs that come with the H&R Street performance kit. FCM has measured the springs in the H&R Street Performance kit (see the data below). They are 323 lbs/in (front) and 445 lbs/in (rear) linear springs. Be aware that the spring rates that come with this kit do no give you Flat Ride. These spring rates result in 1.8 Hz front and 1.6 Hz rear bounce frequencies. Consider getting new springs.



For those going with aftermarket springs, Swift, Eibach, and Hyperco are all good options.

FRONT - The H&R front dampers use a 60mm ID lower spring perch. If you go with a linear spring, then your camber plate will obviously need a 60mm ID upper spring perch. A 7 inch spring length will work well for giving you a 13.5" front ride height (measured from the middle of the wheel to the fender arch).

REAR - The H&R kit comes with adjustable rear spring perches with I believe accommodate a 60mm (or 2.25 inch) ID spring. I don't have them yet, so I can confirm (I'll be sure to follow up and updates this section accordingly). The spring perch you use for the rear spring will dictate what spring length you should use. If you use the H&R perch from the kit, then a 6 inch will work. If you use a Ground Control or Rogue Engineering articulating spring perch, then use a 5 inch spring. That should get you a 13.0" rear ride height (measured from the middle of the wheel to the fender arch).


Final Thoughts

If you found this useful and end up reaching out to FCM for a kit or consultation, please mention this thread. I'm happy to add more information as I learn more. Let me know if you want me to add anything else specifically to the sections above.