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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Wed, Sep-19-2018, 04:58:26 PM   #21
ethan
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Quote:
Originally Posted by TheM View Post
In my experience when I went with flat ride values, the pitching on the street was a bit more comfortable but on the track the car had so much oversteer that each corner was a severe challenge and I could not trail brake AT ALL without spinning. So that's why you see race guys with softer rear springs than flat ride. Softer rears regain that important rear traction. If you want the best of both worlds then you could try a stiffer front antiroll bar and soft or removed rear bar. Only one way to find out!
I don't think Shaikh is suggesting that you need to go stiffer in the rear than is usually recommended to achieve Flat Ride(TM). Instead he's saying we're generally oversprung in the front, since most of the roll couple on that axle comes from the bar anyway. Presumably then you'd adjust your handling using bars in the way you suggest and accept slightly more dive/squat in order to gain some ultimate grip. I think that's the theory anyway.
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Old Wed, Sep-19-2018, 05:30:41 PM   #22
mcfreid
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

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Originally Posted by ethan View Post
I don't think Shaikh is suggesting that you need to go stiffer in the rear than is usually recommended to achieve Flat Ride(TM). Instead he's saying we're generally oversprung in the front, since most of the roll couple on that axle comes from the bar anyway. Presumably then you'd adjust your handling using bars in the way you suggest and accept slightly more dive/squat in order to gain some ultimate grip. I think that's the theory anyway.
Eh, it seems to be that that is exactly what Shaikh's math is showing. Assuming you're going stiffer sprints in the front, then you need to proportionally increase the stiffness in the rear (at about 2x the stiffness in the front). The conclusion I see from this is: instead of getting stiffer springs in the front, get a stiffer front roll bar - or softer rear roll bar (up until those solutions are not sufficient to achieve what you're after with a stiffer suspension).
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Old Wed, Sep-19-2018, 05:41:39 PM   #23
ethan
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

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Originally Posted by mcfreid View Post
Eh, it seems to be that that is exactly what Shaikh's math is showing. Assuming you're going stiffer sprints in the front, then you need to proportionally increase the stiffness in the rear (at about 2x the stiffness in the front). The conclusion I see from this is: instead of getting stiffer springs in the front, get a stiffer front roll bar - or softer rear roll bar (up until those solutions are not sufficient to achieve what you're after with a stiffer suspension).
Right, I think we're in agreement. I typically see numbers like 600F/700R and higher on the good coils (MCS, JRZ, etc) even on cars with a fair bit of weight reduction. By Shaikh's math, you wouldn't need more rear spring than that, but you'd drop a couple hundred up front.

Obviously YMMV - use the spreadsheet.
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Old Wed, Sep-19-2018, 06:13:50 PM   #24
ShaikhA
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Quote:
Originally Posted by TheM View Post
In my experience when I went with flat ride values, the pitching on the street was a bit more comfortable but on the track the car had so much oversteer that each corner was a severe challenge and I could not trail brake AT ALL without spinning. So that's why you see race guys with softer rear springs than flat ride. Softer rears regain that important rear traction. If you want the best of both worlds then you could try a stiffer front antiroll bar and soft or removed rear bar. Only one way to find out!
I can understand and relate to your experience. That's a big reason why I wanted to quantify the handling balance of the car when considering springs, sways, and bump stops. Few people have an idea of how the bump stops are working on their car and those often have a big impact on handling. Excessive rebound damping + rear bump stop engagement is a MAJOR cause of oversteer. Also, as I've mentioned, 'matched' sway bar sets with a larger rear bar will induce more oversteer and make the suspension less forgiving at the limit.

The FRC (front roll couple) is a key to the handling balance. If you look at whatever setup you're running and aim for an FRC of about 73-76%, you'd have a pretty neutral setup. Alignment settings also matter (like how much rear toe-in you're using) but at a baseline level, FRC is key.

Do you want give some general examples of a setup of 'popular' setups? I'm not sure what everyone is running and a public discussion of specific numbers would help everyone out. I can point out how to take a setup that has pitch and turn it into one with Flat Ride while still having a neutral balance on the track.
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Old Wed, Sep-19-2018, 06:25:39 PM   #25
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Hey Shaikh - for those looking for DD/canyon/occasional-track day suspension setups, one of the common recommendations is to TC Kline SAs. With their spring choices, the softest front spring you can go is 300 or 350 (almost twice as stiff as OEM in the front). In order to maintain a flat ride, you'd need then a 600 or 700 spring in the rear. For a DD that seems like too much rear spring for comfort (though I haven't felt it myself). What alternatives would you suggest for those looking for daily drivable, but better handling, aftermarket suspension setups?
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Old Wed, Sep-19-2018, 06:40:07 PM   #26
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Shaikh,

Any thoughts on how to get useful data on the stiffness of the inconsistent OD (possibly also ID) CSL front sway?



Known:
-CSL sway weight (4.12 kg)
-M3 sway weight (6.26 kg)
-CSL OD at the thick and thin points (30.8mm at the thick points, will measure the thin)
-M3 sway OD (it's a solid bar) (26mm)
-M3 and CSL sways are the same length/dimensions/angles other than OD
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Old Wed, Sep-19-2018, 06:59:20 PM   #27
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Hey mcfreid, before offering spring rate choices for DD/dual-purpose use, I'm going to put this vid out there as a caveat to how well-tuned the TC Kline may or may not be. At least from my testing of the E36 M3 TC Kline DAs, they had far too much compression (I never thought I'd say that, but the Porsche Cayman rear dampers had a similar issue!) and the adjust simply wouldn't let you make them soft enough to not having 'launching' issues. By 'launching,' I mean when the struts / shocks generate enough force at a sufficient compression velocity to make the car JUMP up in the air.


That said, let's look at two examples based on your question:

Example 1

Taking the factory FRC of 75% (+/- 2%) as a good baseline for aftermarket setups, I go 300 / 550 on springs. Bounce freqs of 1.77/1.84 Hz front/rear (4% Flat Ride). These springs would reduce the FRC to ~73% so slightly more oversteer-oriented but still driveable I'd say. You might want to run a bit more rear negative camber or more rear toe-in. Also, if you wanted more capability to get on the throttle early, install a 28mm front bar (factory is 26mm). Would the E46 non-M bars fit the M3? The 30mm front bar is a bit too big for this applications, IMO, so the 28mm would be a better choice.

As a related example, I installed those 300/550 rates for my second track day on my E46 330i, along with an Eibach 28mm front and kept the OE 18mm rear. It was neutral enough with the 3.46 rear + WaveTrac diff, ~77% FRC, and with Flat Ride. I need a higher-quality diff to put power down more aggressively in very tight turns, but >40mph, the car was just fine and very driveable. With a higher-HP M3 and more effective clutch-type diff (OE or especially aftermarket) this FRC range would be very driveable. You can definitely go higher in FRC (upper 70%, to lower 80%) and have more capability to get on the throttle earlier.

===

Example 2

For a 350 lb/in front, you'd want a 650 lb/in rear. Freqs of 1.91 / 2.00 Hz (5% Flat Ride). With 28mm front / 18mm rear bar you'd have 75.6% FRC, so neutral/stock-like balance.
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Take our short Ride Harmony survey and earn a credit on FCM Elite Bilstein damper services
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Old Wed, Sep-19-2018, 07:09:09 PM   #28
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Shaikh, could you confirm the rear spring motion ratio for rear coilover setups? I've seen a variety of numbers thrown around, so it'd be nice to have an authoritative value for use with your spreadsheet.
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Old Wed, Sep-19-2018, 07:13:15 PM   #29
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Quote:
Originally Posted by mcfreid View Post
Eh, it seems to be that that is exactly what Shaikh's math is showing. Assuming you're going stiffer sprints in the front, then you need to proportionally increase the stiffness in the rear (at about 2x the stiffness in the front). The conclusion I see from this is: instead of getting stiffer springs in the front, get a stiffer front roll bar - or softer rear roll bar (up until those solutions are not sufficient to achieve what you're after with a stiffer suspension).
I would be cautious relating to simple spring rate ratios since those don't consider the wheel rate and corner weights, but I know it's convenient to do that and I see it everywhere. It's certainly better to aim for rear 1.5X the front instead of 1.1X, say! This is why I like using the spreadsheet so we can speak in terms of frequencies. The difference between 5% pitch and 5% Flat Ride in handling response, smoothness, and overall composure is pretty amazing...!

You still need a stiff-enough front spring for your intended ride height, but I would do my best to keep front ride frequency no higher than 2.3 Hz and make rear 2.4 Hz. Moderately soft low speed rear damping helps promote throttle-friendliness, where I see some setups tend to have higher gas pressure and higher low-speed bump which can make the car skittery/twitchy on hard throttle.

If a 500 hp Corvette and 450 hp Porsche can be designed with Flat Ride, I think it's worth considering for a dual-purpose street/track BMW. I've proven it works. My goals for this winter and into next year are to buy and have Edge install an S54 motor/drivetrain / tuned diff for my E46 330i sedan and continue fine-tuning the suspension setup for that situation. It'll be a bit of a Holy Grail for me as I love the engine sound and response of the S54 so damn much! Ever since riding in my brother's Laguna Blue...
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FCM Elite Ride Harmony suspension spreadsheet for: E46 M3, Shock dyno testing / driving feedback: E46 M3 (with Eric_SMG)

Take our short Ride Harmony survey and earn a credit on FCM Elite Bilstein damper services
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Old Wed, Sep-19-2018, 07:24:43 PM   #30
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Default Re: FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffn

Quote:
Originally Posted by ethan View Post
Shaikh, could you confirm the rear spring motion ratio for rear coilover setups? I've seen a variety of numbers thrown around, so it'd be nice to have an authoritative value for use with your spreadsheet.
Hey ethan, from what I measured some years ago, the rear damper motion ratio was 1.05:1. I believe that's been quoted before I got on the scene as well. I find the motion ratio to be curious - there's a directly-measurable mechanical motion ratio and also an 'effective, bounce frequency' motion ratio that incorporate the real-world behavior of the friction / stiffness of suspension linkages and bushings. I'm not sure is anyone has determined how much the spring might bind in the higher-travel, spring-over-damper rear setup vs. the factory location. As spring length increases, spring bind / warp under load increases.

Getting real-world bounce frequencies really requires 'dead dampers' and I've only done that experiment fully once (an Audi S4 using air springs and totally drained Bilstein, as I discussed in my 'Why Flat Ride Matters' video), and partially on the rear of a Miata when I drilled and drained the nitrogen / oil out of the factory shocks then bounced the rear (obviously not as accurate with un-drained fronts present!).


So the 'effective' motion ratio of your particular BMW for ride frequency and damping calculations could be different based on changes you've made to the suspension, or bushing wear / binding / etc.

I think it's important to keep friction in mind (and I have to remind myself of this) as it's easy to assume every vehicle has the same effective 'bounce' motion ratio.

For simplicity sake, I would use 1.05 for a rear coilover setup and, if possible, bounce the car with as soft a damper setting as possible to see how the real-world frequencies work out. Would be interesting to see your feedback from those tests added here! For reference, a video on doing bounce frequency testing:


EDIT: continuing the theme of 'everything affects everything else', a highly-pressurized damper will make the bounce frequency appear much higher since it'll be harder to initially compress the suspension, even if the damper's low speed forces are quite soft! From info I've received and tests I've personally done, MCS, JRZ, and many other monotube are typically providing >40 lb of gas pressure which will definitely make getting accurate bounce frequencies harder with a functioning damper. In another video I point out that part of the problem with high gas-pressure is the induced frequencies the damper gas force creates, which over-excites the tires.
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FCM Elite Ride Harmony suspension spreadsheet for: E46 M3, Shock dyno testing / driving feedback: E46 M3 (with Eric_SMG)

Take our short Ride Harmony survey and earn a credit on FCM Elite Bilstein damper services

Last edited by ShaikhA; Wed, Sep-19-2018 at 07:30:09 PM.
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Discussing FCM E46 M3 Ride Harmonizer suspension spreadsheet (bounce freqs, FRC, roll stiffness) in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)