e46 M3 suspension setup, or how to not downgrade your car with suspension mods

[mrgizmo04]

it was my direct response, without clarifying, to his videos on YouTube...just not my style, but I get how and why some might click with his style.

Not my objection to his points, I realize that wasn't clear, at all.

Have you driven the setup for an extended period of time to experience the difference, or just philosophically not your style?

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[mrgizmo04]

I disagree with the statements made about gas force in that video and his other one about the same topic.

Ohlins r&t require gas pressure to make compression force.

What do you disagree with?

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[bigjae46]

Why? They do every tedious thing everyone is talking about.

Following his spreadsheet has resulted in nothing but transformative results.

My home track is shit and all of the braking zones are super bumpy while the rest of the track is just bumpy. It casually runs within 2-3 seconds of the NASA TT3 record despite bad driving and meh Toyo RRs. Flat ride found me over 4 seconds from a low 1:50 lap to high 1:45s.

At the smoother tracks, I’m pretty sure I could use more spring rate in the front. The one place where my car isn’t as good is on tracks with a lot of late apexes. There you really need that extra weight transfer to the rear tires to drive the car out.

[fattycharged]

Why? They do every tedious thing everyone is talking about.

it was my direct response, without clarifying, to his videos on YouTube...just not my style, but I get how and why some might click with his style.

Not my objection to his points, I realize that wasn't clear, at all.

[Cronenberged]

It's shit like this that would keep me away from FCM 😂


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Why? They do every tedious thing everyone is talking about.

[fattycharged]

It's shit like this that would keep me away from FCM 😂


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[cobra]

Make sure to watch a lot of Shailh's videos on his channel, there is a lot to learn.

Here is a demo of gas shock pressure effect https://youtu.be/DOK-BvIORVQ

I will repeat what I have said before. When I did my dyno session with him on Ohlins strut/shock at his shop in Redwood City, we discovered that there is way too much pressure in them and the valving was way tight. Force vs velocity curves (he printed me a copy but I misplaced it somewhere) were close to straight lines, so he recommended to run both fronts and rears at full soft irrespective of spring rates. Not ideal but it would help counteract the initial pressure and smooth out curves. I run them at soft street/autox/track without any adjustments.

Flat ride is a simple concept, where hang time needs to be introduced in the front via lower frequency/softer spring (to react slower) so that once the front rolls over that bump it gives enough time for the wheelbase to travel over it and allow the rear to hit the same bump so that both front and rear settle back down "together". Depends on the wheelbase, weight distribution, etc. Running high frequency/stiff fronts makes the car pitchy, where the front is disconnected from the rear. So when you run over thebump, the front reacts and settles quickly, then the rear runs over the bump and settles independently. That is a much less comfortable/bouncy ride. Vs having front and rear settle at the same time.

If you don't need the car to transition fast like on an autox course, you can go much softer all the way around as long as you don't bottom out.

Just remember that springs impact front to rear comfort (flat ride vs pitch) while also the roll side to side. Swaybars only impact roll. You need all components to work together to get proper balance.

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I disagree with the statements made about gas force in that video and his other one about the same topic.

Ohlins r&t require gas pressure to make compression force.

[mrgizmo04]

For the R&T kit, it seems that Ohlins chose the high front spring rate to control body roll and have it work with the stock front sway bar. With a stiffer aftermarket front sway bar, the front springs don't have to control as much roll; therefore, a softer spring rate can be used.

Correct, most people don't understand that, and their r&t kit literally swaps out only the struts/shocks and springs. It assumes you change absolutely nothing else - top mounts, rsm, swaybars, etc. But noone selling coilover kits cares to incorporate your other setup and goals unless you call around. Like what swaybars you will run and how the car will be used.

Now Barry at 3dm and team are figuring out the next phase of their support for enthusiasts who have different camber plates (that somewhat started with the strut/knuckle spacer), how to offer different spring rates, what lengths, how that impacts droop/bump, how to make it work for various ride heights people want to run, what shims/spacers to include, etc.

Fun stuff.

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[Slideways]

Make sure to watch a lot of Shailh's videos on his channel, there is a lot to learn.

Here is a demo of gas shock pressure effect https://youtu.be/DOK-BvIORVQ

I will repeat what I have said before. When I did my dyno session with him on Ohlins strut/shock at his shop in Redwood City, we discovered that there is way too much pressure in them and the valving was way tight. Force vs velocity curves (he printed me a copy but I misplaced it somewhere) were close to straight lines, so he recommended to run both fronts and rears at full soft irrespective of spring rates. Not ideal but it would help counteract the initial pressure and smooth out curves. I run them at soft street/autox/track without any adjustments.

Flat ride is a simple concept, where hang time needs to be introduced in the front via lower frequency/softer spring (to react slower) so that once the front rolls over that bump it gives enough time for the wheelbase to travel over it and allow the rear to hit the same bump so that both front and rear settle back down "together". Depends on the wheelbase, weight distribution, etc. Running high frequency/stiff fronts makes the car pitchy, where the front is disconnected from the rear. So when you run over thebump, the front reacts and settles quickly, then the rear runs over the bump and settles independently. That is a much less comfortable/bouncy ride. Vs having front and rear settle at the same time.

If you don't need the car to transition fast like on an autox course, you can go much softer all the way around as long as you don't bottom out.

Just remember that springs impact front to rear comfort (flat ride vs pitch) while also the roll side to side. Swaybars only impact roll. You need all components to work together to get proper balance.

Sent from my SM-G950U using Tapatalk

For the R&T kit, it seems that Ohlins chose the high front spring rate to control body roll and have it work with the stock front sway bar. With a stiffer aftermarket front sway bar, the front springs don't have to control as much roll; therefore, a softer spring rate can be used.

[mrgizmo04]

Make sure to watch a lot of Shailh's videos on his channel, there is a lot to learn.

Here is a demo of gas shock pressure effect https://youtu.be/DOK-BvIORVQ

I will repeat what I have said before. When I did my dyno session with him on Ohlins strut/shock at his shop in Redwood City, we discovered that there is way too much pressure in them and the valving was way tight. Force vs velocity curves (he printed me a copy but I misplaced it somewhere) were close to straight lines, so he recommended to run both fronts and rears at full soft irrespective of spring rates. Not ideal but it would help counteract the initial pressure and smooth out curves. I run them at soft street/autox/track without any adjustments.

Flat ride is a simple concept, where hang time needs to be introduced in the front via lower frequency/softer spring (to react slower) so that once the front rolls over that bump it gives enough time for the wheelbase to travel over it and allow the rear to hit the same bump so that both front and rear settle back down "together". Depends on the wheelbase, weight distribution, etc. Running high frequency/stiff fronts makes the car pitchy, where the front is disconnected from the rear. So when you run over thebump, the front reacts and settles quickly, then the rear runs over the bump and settles independently. That is a much less comfortable/bouncy ride. Vs having front and rear settle at the same time.

If you don't need the car to transition fast like on an autox course, you can go much softer all the way around as long as you don't bottom out.

Just remember that springs impact front to rear comfort (flat ride vs pitch) while also the roll side to side. Swaybars only impact roll. You need all components to work together to get proper balance.

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[Slideways]

Comparing the stock spring rates to some of the considerably higher ones mentioned in this thread made me think of this video. A. Biermann, BMW's VP of engineering, said that the E46 was setup pretty stiff from factory and some people complained on the test rides lol. Starts at 3:58

[cobra]

Edit: I redid my measurements tonight more carefully. I did them multiple times to account for measuring errors - that's what Rear 1, 2, 3, etc means. The results were pretty dang consistent, and most importantly the rear is different than the values I was referencing which were 0.70 and 1.05.

Front = 0.94
Rear spring = 0.63
Rear shock = 1.14

Based on this...

-Ohlins 400/630 spring rates yield 2.1Hz and 1.82Hz, or 86% R/F ratio.
-With a 630lb rear spring and 300lb front spring, both will be at 1.82Hz.

I would really love for someone else to do these measurements and make sure we're all using the right numbers. Small differences in spring ratio has a big effect on frequency...

[DJAM3]

That was also my thought regarding the "oscillating rear". Sounds like it was underdamped.

[Tbonem3]

Regarding Duracell's experience, my immediate thought was that the damper is not controlling (rebound) the stiff 700lb spring well enough, which makes it feel bouncy.

Try a stout damper like MCS! My 628lbs feel so perfect. No bounciness, just firm. I only needed to slow the rebound by a few clicks on the mcs. Even on full soft it had almost slow enough rebound. Dampers make a huge difference! Feels better than my B6s with 550lb springs.

[K-Dawg]

My journey for a OEM+ comfortable street setup continues. As you mentioned my attempt at using 350/700 on the TCK SA didn't work out. After reaching out to TC he told me that the SA damper limit was a 700# spring, but didn't have enough compression to be good and recommended a DA. I didn't want to go that route so I opted for a FCM custom setup. Even with those dampers I wasn't getting a comfortable ride with a 700#. I've attempted to get flat ride to work on my street car with little success. Maybe it's the bad LA roads, not sure. Moving back to a 350/500 setup completely eliminated the oscillating rear, but I felt the front end needed to be stiffer.

That being said, my current setup is 400/600 but I don't have much seat time since I'm doing some new engine and tune upgrades. TC's recommendation for “great balance” is 400/500 on a street car. After all the experimenting, I agree that most would be happy with that setup. If you want stiffer, TC recommended 400/700. TBoneM3 has a lot of good suspension info on his journal page, which I've been following. He has gone down this same path we are discussing.

IMO flat ride should only be considered for track cars. It has proven results and many members really like it. Some might argue otherwise, but for me it wasn't providing the street solution I was looking for. Hope this helps.

Flat ride only for track cars? Why have many (most?) suspension designers historically used it on street cars? The E46 M3 is intended to be driven on the street, and has flat ride from the factory. Although, it seems manufacturers have gone to a more pitchy, overdamped setup for some reason. More "sporty" feel, don't care, don't know any better, some actual reason?

What do you mean by "oscillating rear"? It doesn't make sense that you would have more movement with stiffer springs.

Flat ride theory makes sense to me. While a suspension designer may be able to use brute force damping to mask a naturally unsettled car, it seems more efficient for the car to be naturally settled without added damping, then apply a small amount of damping to fine tune things as necessary. The inertia of a car bouncing around back and forth is not conducive to grip or comfort, and using damping to cover this seems like a band-aid.

I can say this... In the ownership of my M3, as I've gone from 550/600 lb/in F/R spring rates, to 300/600 and now 155/375-750 (Eibach), the car has become far more pleasant to drive.

I'm intrigued by the quest for desirable handling characteristics while still maintaining comfort. In my mind, a "perfect" suspension would allow the car body to "float" (have essentially no vertical movement) as it goes down the road, and at the same time the tires are maintaining a steady or constant force on the pavement as they roll down the road. I suppose this would be a numb driving experience, so it would also have to have perfect road feel.

Like lots of other things in life, the more I've learned about suspension design and theory, the more I realize I don't know (I don't know much). I've also come to realize that most people have absolutely no clue what they are talking about when it comes to suspension systems. Automobile suspensions are far more complex than they appear on the surface. Most of us don't have the opportunity to try a significant number of different spring/damper setups over the ownership of our car, let alone test multiple setups back to back in a somewhat controlled environment. And even if we did have that kind of opportunity, most of us would not be able to tell what is actually going on with the suspension from the driver's seat, or accurately determine what was changed in a blind test.

Good discussion!