Everything about Fat Cat Motorsport Suspension

[bigjae46]

Uhhh... aren't the non-M missing the mounting tab for sway link?

No. The TC Klines on the car now were on my 330Ci. I pulled the entire assembly out of the 330Ci and put it in the M3.

[jvit27]

Pulling the trigger, finally. Can't believe I'm a year behind!

Got some Bilstein PSS - yes non-M but they are non-adjustable monotubes. They physically fit although I am sure the springs and actual valving is a bit different. Jalad said I may need some different rods - $100? This set of coilovers is $1239, H&R are $1400. Now I need to get my lazy ass to the track, ballast the car up to 3000lbs, corner balance, and then send the results to Jalad.

Uhhh... aren't the non-M missing the mounting tab for sway link?

[BlueBimmers]

Small world, a respected local shop owner was just telling me about Fat Cat. I've lots to learn from this thread.

[nervous24]

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.

Since you know the instant center location, do you have the suspension hardpoint location coordinates? A friend is wanting to dive deeper into the kinematics and dynamics of my setup.

[bigjae46]

Pulling the trigger, finally. Can't believe I'm a year behind!

Got some Bilstein PSS - yes non-M but they are non-adjustable monotubes. They physically fit although I am sure the springs and actual valving is a bit different. Jalad said I may need some different rods - $100? This set of coilovers is $1239, H&R are $1400. Now I need to get my lazy ass to the track, ballast the car up to 3000lbs, corner balance, and then send the results to Jalad.

[Suspension Decoder]

I believe the street performance is, that's the one FCM modifies because the internals are similar to Bilsteins. Suspension Decoder correct me if I'm wrong.

Yes, H&R is essentially white-labeling the Bilstein. The internals are exactly Bilstein. H&R likely makes their own strut housing or has Bilstein make one to their specs (not sure which one). H&R seems to specialize in making custom springs. The ones that come with their coil-over kits I only sometimes find useful / usable for my customers. The front is typically too short in length and too stiff in rate, having you live in the front bump stops (which are usually 200 lb/in and fairly long). Sometimes the rear spring is reusable, depending on your application, but typically you'll want to change both. And, if your corner weights are different enough left vs. right, you might want to use different rates as well!

As a side note, I'm the process of updating the spreadsheet as I do another iteration to Christina's suspension (mostly focusing on the front end). I may soften springs all around or just up front to increase the Flat Ride relationship (there's very little right now). Based on real-world bounce results, I think using a rear spring MR of 0.63 (as came from the direct measurements by cobra) would under-estimate the bounce frequency. I do believe the rear damper motion ratio need to be increased for better accuracy. I find (and OEMs have known this for a while) that while geometric measurements get you in the ballpark, especially when it comes to system friction, the real-world constants often differ from theory. What the tires actually experience is what matters most, in my mind and experience.

EDIT: I would be very interested in some feedback from drivers who use the spreadsheet, know corner weights, and can perform bounce frequency tests with dampers at soft (if adjusters are available).

[Suspension Decoder]

Do all the H&R coil over kits for BMW models use a Bilstein mono shock branded H&R?

From what I've seen, any H&R Street Performance coil-over (or RSS) will be a Bilstein-based monotube that is rebuildable. The H&R strut tube (with the 40mm polished chrome surface) has 'Bilstein' clearly stamped near the top of the tube, just below the chamfer where the threaded shaft begins.

[Cronenberged]

Do all the H&R coil over kits for BMW models use a Bilstein mono shock branded H&R?

I believe the street performance is, that's the one FCM modifies because the internals are similar to Bilsteins. Suspension Decoder correct me if I'm wrong.

[maupineda]

Not sure if all. But z4m kit is.

[digger]

Do all the H&R coil over kits for BMW models use a Bilstein mono shock branded H&R?

[bigjae46]

I called Suspension Decoder a couple of days ago. The one thing that you'll immediately notice is that he loves talking suspensions! Really had a great back and forth and answered all of my questions. Even when I asked about some terms like jacking down he explained them in a manner I could understand. I liked how he brought up relatable real-world examples which allowed me to connect them to my own experiences. Now this thread makes a lot more sense to me. I think the consult fee is absolutely worth it just to talk to Shaikh. I walked away with a clear picture of how I can improve the car, the why behind those steps, and an expectation.

I liked how he brought up his experience from making really stiff setups then moving to the rally tuning. Then I thought about how every student I instruct in a modern M car, I always have the conversation of driving in M mode vs comfort. Every time, the driver is far better in comfort. I observed one beat his previous PR by 3 seconds. I knew about flat ride which is mostly springs but Shaikh helped make all of the other stuff fall into place like gas force, jacking down and up, etc.

So the plan is a Stage 2, GC front bar and then test it. The only unknown is the rear bar. I really liked the difference it made. If I'm still getting a lot of understeer, I will need to replace the rear subframe to install the rear bar. I cut the brackets off to save a 1/2 lb lol

[cobra]

Over what range did you measure the motion ratios? I generally exclude wheel vs. damper travel data below static height and focus on static height to full bump. Any non-linearity going into droop would skew the calculated MR.

This was pretty much the full range of shock travel. My shocks are a little shorter than stock hence only 120mm and not 140-150. Either way, it looks pretty linear so I didn't bother clipping the ends.
You asked earlier what shocks - I am running a custom monotube setup with piggyback reservoirs and base valves, 22mm front and 16mm rear shaft diameters, at about 75psi.

[Suspension Decoder]

My car is stock other than the shocks/springs. I removed the spring and disconnected swaybar for these measurements.
Towards full droop, the lower control arm touches the spring at quite an angle. I was measuring at the center of the spring mount

Over what range did you measure the motion ratios? I generally exclude wheel vs. damper travel data below static height and focus on static height to full bump. Any non-linearity going into droop would skew the calculated MR.

[cobra]

cobra do you have solid subframe bushings, stock, other? There’s some vertical displacement in the bushings that will technically effect MR too. Not much but good to have in the thread record. Thanks for the data! Subframe and other bushings will also change your ride frequency as they are springs too of course

Everything is a spring if you push hard enough!

edit: it just occurred to me that you probably measured without the spring in place, in which case the bushing question is irrelevant.

My car is stock other than the shocks/springs. I removed the spring and disconnected swaybar for these measurements.
Towards full droop, the lower control arm touches the spring at quite an angle. I was measuring at the center of the spring mount

[Bry5on]

cobra do you have solid subframe bushings, stock, other? There’s some vertical displacement in the bushings that will technically effect MR too. Not much but good to have in the thread record. Thanks for the data! Subframe and other bushings will also change your ride frequency as they are springs too of course

Everything is a spring if you push hard enough!

edit: it just occurred to me that you probably measured without the spring in place, in which case the bushing question is irrelevant.