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      09-10-2021, 06:25 PM   #1
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Suspension enlightenment and engineering - philosophical post

Had some thoughts as I've grown on my car modding journey and thought I'd share.

I started out, as most do, reading stories of people modding their suspensions and getting many perceived benefits: i.e. upgrading to coilovers improving the ride quality and performance, RTABs, alignment settings, etc etc. I installed coilovers, changed my alignment, and I loved the responsiveness, the reduced body roll, the perceived performance improvements. But as I got a lot of experience both street driving, track driving, and autocrossing with this setup, I wanted more. I read and researched more about suspension from many sources (youtube videos, fatcat motorsports content, technical articles on alignment, scrub radius, steering axis, dynamic alignment changes like camber gain, weight transfer, roll center, damping), and as a result, my view on car modding has evolved a lot.

I used to think, given all the experience and stories on this forum, I'll mod my car and it'll become better. Now, I'm realizing, there's a ton of nuance when it comes to tuning a car's suspension, and it's all designed holistically. BMW engineers specify all the components to get certain suspension parameters close to targets in order to get desired, safety, grip, understeer/oversteer, characteristics. Everything is engineered with everything else in mind. The springs and sway bars determine roll stiffness, the front/rear roll stiffness have a target ratio, amount of roll and dynamic camber curve is designed together, the wheels are chosen for fitment as well as scrub radius with the whole setup.

Additionally engineers have a ton of institutional knowledge from years of releasing many models, and they have specific philosophies of their own. I.e. BMW sports cars feel different to drive than do Porsches or Toyotas. This is a result of differences in philosophies of what makes a car good to drive.

When we mod our cars, we're creating our own driving characteristics in an unknown direction. Example: you add negative camber by moving your strut mounting position, it also alters the steering axis inclination and scrub radius. What's the overall effect going to be? We'll get more negative camber, but what do we give up?

I haven't even mentioned the added complexity of designing dampers. They have a huge impact on the dynamics, because they add (or reduce) the stiffness on the order of 100s of pounds, and they do so *dynamically* i.e. in proportion to shock travel speed. BMW designs their dampers to make a BMW feel like a BMW, whereas Toyota designs their dampers differently for a different feeling with different priorities in mind. When you change to an aftermarket damper, who knows how it'll feel and what priorities they optimized, and what they gave up. I.e. adjustable shock bodies give up suspension travel in order to get a wide range of ride height adjustability. Some coilovers have a huge amount of rebound damping to give you responsive turn-in and better road feel at the cost of grip on rough road surfaces. And finally how the alignment changes dynamically is changed as you change roll stiffness.

This post might seem anti-mod, but it's not. The purpose of this post is to balance out the glowing mod posts on this forum with more context. I'm actually pro-mod for the uninitiated because it puts you on a journey of learning more about cars, and you learn a lot more than you do by reading the forums. Also I don't want to discount the information on the forums - they are a huge trove of information, although imperfect, but still useful!

It's been a very insightful journey for me. But at the end of it, I'm leaning more towards leaving cars as stock as possible, and only making minor adjustments where I am confident they're needed. The right way to mod essentially requires you to become an automotive engineer and consider the whole system holistically. To test a hypothesis, capture data, and iterate. Which is totally possible and many race teams do it successfully, but it's not something that the every day forum member has the resources for.

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      09-11-2021, 11:29 PM   #2
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Said it many times before, everything is a compromise, everything, but you'll learn something along the way.
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      09-12-2021, 06:47 PM   #3
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BMW makes their M cars for a "sporty" feel, perhaps some models more than others. This is very different from a track set-up, which some folks are after (myself included).

I don't think you need to be an automotive engineer to change parts. For suspension mods, in particular, having lots of experience with the parts you are installing and how they should be set up is an excellent idea. This is likely a mechanic or a race prep shop.
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      09-12-2021, 08:06 PM   #4
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Also certain things to consider is in what the individual is wanting or modding, trims down the line are different and can't really be clumped to generalization no matter the make.
Non M Z4 vs M, when you look at shared components on Non M used in an E46 that is catered to the mass, not one individuals needs. Engineers designing components for a Non M E46 they think of the family car toting the kids around to soccer practice then going for a grocery run aren't thinking of potentially driving their car as spirited as someone wanting more thrills in a z4 for example, also thinking of tire consumption and so forth with the tune.
There's a fine line in R&D when it comes to the outcome of having to reengineer suspension of one car vs sharing those parts from across the entire product line to make it work. Manufactures make for the masses, not for the individual driving style, hence more safe understeer tune rather than oversteer. Never thought I'd see so many bitch that a Supra is tail happy, but there's tons of complaints of too much oversteer on the first 2020 tune.

I think this is a big reason now you see "track pack" trims coming out in a lot of new production cars these days. Track edition RCF, how many track packs dodge has going now I can't even keep them straight anymore. AND that's why they cost so much more than base models as well as get limited production run numbers. It costs a lot more and time to reengineer suspension for one set of wants/needs.

I agree with some of what's talked about with forum bias when it comes to mods when you start reading on someone's personal experience with X mod done. It's also a thin line of some times fan boy excitement. But also when it comes down to R&D reputable aftermarket companies tend to do a lot. I had a very informative conversation the first time I rang into Apex for example.

Anyone doing any mod should always first ask what they want to get out of it to themselves. Another example is the give/take when changing your final drive gear ratio. I can't remember what I had been watching but was so true when they said it takes a very special and bold person to indulge a track set up suspension on their daily, and coming from piss pore Michigan roads an extra seat padding if you have a fixed back seat wouldn't be a bad idea . So many say they want a sport or stiff suspension, until they actually have it and have a sore rear and noggin after.

Just take the due diligence to do as much research about what ever you want to do before making the plunge. There was a time, when I first got my Z4 that I said I'd never mod the car....that ship sailed a very long time ago
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      09-13-2021, 09:06 AM   #5
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I am an automotive engineer and can tell you that suspension and tire tuning is probably one of the most difficult parts of developing a car. Compromise is the key word here. Every change affects ride, noise, handling, cost and more. The best thing I can recommend is to first do driver mods. Any kind of driver training will do much more for you than mods on the car. The fastest driver will be the one who can use the full capability of their car, not the guy who has $10k in mods but can't push the car beyond 8/10.

If you do want to change up your car, first understand what you want the car to do, then do as much research as possible. If you want something track-focused, you're going to lose street comfort. If you want street comfort, your car won't be as good on the track. And when it comes to suspension and tires, you will absolutely get what you pay for. The reason Ohlins and high end Bilsteins are so expensive is because they do OEM level R&D and need to get returns on those costs.

If you want to move away from stock, start with the wheels and tires first. The spring/shock setup you need for a 200TW track focused tire will be completely different than the setup for a 300TW PS4S or an all-season tire. Slicks will be in a completely different world. When you're doing suspension, any old rubber bushings should be replaced as well. Worn out bushings can make the car crashy over bad pavement and can negate any benefits from new springs/shocks. Any car that sees street driving should have rubber bushings. I would only go poly or solid mounts if the car is dedicated for track use.

Then after suspension and a good alignment, you can use alignment settings or sway bars to fine tune your setup. The key is to only change one thing at a time so you can learn your car. Getting help from an expert really helps here too. I spent half a track day fighting terminal oversteer in my Miata. I was adjusting my shocks but could not get the rear to hook up in corners. A buddy of mine who is a test driver for Michelin took the car out and after two laps diagnosed the issue as not enough tire pressure in the rear. The sidewall was folding over on the tire. We added 2psi in the rears and the car would not let go.
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      09-13-2021, 11:37 AM   #6
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Lots of great comments.

Quote:
when it comes down to R&D reputable aftermarket companies tend to do a lot. I had a very informative conversation the first time I rang into Apex for example.
This is something I feel the companies could and should be doing a better job of. The problem is, when you look at the product pages for MSC, Bilstein, Ohlins, KW, pretty much any suspension company, they don't really tell you what their goals were, what they compromised on, and in what ways it will differ from stock. How will the NVH be changed? Ride comfort? Will the car be more composed? How much stiffer will it be? There's no data available around any of this, which is a shame.

I can understand some of the reasoning, proprietary/trade secret. But I'm at a loss without that information, and can't justify a purchasing decision without it.

As for race shops, I don't have much experience. Perhaps because I live in NY where these are few and far between. Perhaps because I'm afraid to spend a bunch of money and not get a good result, or I can't trust someone unless they have specific experience with the Z4 and can explain what they felt could be improved and why, for what goal.

PS The fat cat motorsports guy, Shaikh, has some videos expressing the dissatisfaction above.
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      09-13-2021, 06:21 PM   #7
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Quote:
Originally Posted by filtercoffee View Post
This is something I feel the companies could and should be doing a better job of. The problem is, when you look at the product pages for MSC, Bilstein, Ohlins, KW, pretty much any suspension company, they don't really tell you what their goals were, what they compromised on, and in what ways it will differ from stock. How will the NVH be changed? Ride comfort? Will the car be more composed? How much stiffer will it be? There's no data available around any of this, which is a shame.

I can understand some of the reasoning, proprietary/trade secret. But I'm at a loss without that information, and can't justify a purchasing decision without it.
.
A very philosophical approach.
It can be compared to both book smart vs street smart also glass half full or half empty. You can be given all the data in the world, but if you havenít experienced different grades of mod changes influencing nvh how will you know exactly how each mod affects your individual application or understand no, mild, and harsh without feeling it.

For goals on say adjustability on dampers for example, no harm to simply ask the company. What was the base start in constant of lightest and what for the heaviest setting in X damper coilover or what ever part of tuning. Worst question is the one not asked. If not thrilled with generic product descriptions then ask the manufacturer. Iíve talked to lots of reps and companies of different nature but never did I get a push off response. Itís true no matter what mod. ESS can give you all the data on the gains of each supercharger but until you feel it to compare what does 40% gains ďfeel likeĒ in your car. Mods are always when you ďwantĒ more than stock for what ever X result.

It will become trial and error and with all the amount of variables itís difficult for anyone to say yep 100% you fell this or get that. Similar to when I use to set up archery equipment, I could set a bow up for me to be a tack driver, but itís not going to work for the guy I hand it to the same way, the human factor. Itís a rabbit hole where yes, money is always sacrificed, not matter a positive or negative experience. It becomes a damned if you do damned if you donít.

I go back to previous life experiences growing up. Shoes are to people as tires are to cars. You donít wear hiking boots to run a marathon, sandals to hike Everest. Until you pursue a good set of hiking boots how do you know how long the break in time on a pair of boots. All trial and error and the more you do, the more you learn. First bad set of blisters and you start looking into polypropylene and wool blend sock combos for hiking. When I finally find a pair of boots I fall in love with I normally buy a few pair as always with my luck they stop making them when Iíve worn a set out.

Itís the rabbit whole to learn and grow and through the blood sweat and tears hopefully itís a gratifying experience. Every piping student Iíve ever had Iíve always said the moment playing pipes or music becomes no longer fun or enjoyable you move to something else that brings a new chapter in life. If modding a car no longer brings joy or gratifying experiences for you absolutely look for the best of a stock car in X trim to enjoy as it frees time and funds for the next chapter. Nothing wrong at all in enjoying a car stock.
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      09-16-2021, 03:34 PM   #8
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Trial and error is definitely required to dial it in, and to learn your own preference.

You will see my coilovers for sale and I've definitely learned a ton about suspension from the experience. and I could dial them in a bit better but... yeah not worth the BST in this case (blood sweat tears, and time/money).
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      10-13-2021, 06:25 PM   #9
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Quote:
Originally Posted by bwright657 View Post
I am an automotive engineer and can tell you that suspension and tire tuning is probably one of the most difficult parts of developing a car. Compromise is the key word here. Every change affects ride, noise, handling, cost and more. The best thing I can recommend is to first do driver mods. Any kind of driver training will do much more for you than mods on the car. The fastest driver will be the one who can use the full capability of their car, not the guy who has $10k in mods but can't push the car beyond 8/10.

If you do want to change up your car, first understand what you want the car to do, then do as much research as possible. If you want something track-focused, you're going to lose street comfort. If you want street comfort, your car won't be as good on the track. And when it comes to suspension and tires, you will absolutely get what you pay for. The reason Ohlins and high end Bilsteins are so expensive is because they do OEM level R&D and need to get returns on those costs.

If you want to move away from stock, start with the wheels and tires first. The spring/shock setup you need for a 200TW track focused tire will be completely different than the setup for a 300TW PS4S or an all-season tire. Slicks will be in a completely different world. When you're doing suspension, any old rubber bushings should be replaced as well. Worn out bushings can make the car crashy over bad pavement and can negate any benefits from new springs/shocks. Any car that sees street driving should have rubber bushings. I would only go poly or solid mounts if the car is dedicated for track use.

Then after suspension and a good alignment, you can use alignment settings or sway bars to fine tune your setup. The key is to only change one thing at a time so you can learn your car. Getting help from an expert really helps here too. I spent half a track day fighting terminal oversteer in my Miata. I was adjusting my shocks but could not get the rear to hook up in corners. A buddy of mine who is a test driver for Michelin took the car out and after two laps diagnosed the issue as not enough tire pressure in the rear. The sidewall was folding over on the tire. We added 2psi in the rears and the car would not let go.
Dude, for someone who has spent a lot of time with test drivers developing the suspension design for the Alfa Romeo Giulia QV, it never occurred to me to bring my Miata to them to fix the happy rear: I had to dial the front back to balance things!!
Will try playing with pressure!
Got a 2.5L MK3 with 235s on TE37s and Ohlins which feels more competent than my stock Z4M but is unbearable to drive in town.

Thanks!!!
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      10-14-2021, 11:42 PM   #10
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Quote:
Originally Posted by filtercoffee View Post
It's been a very insightful journey for me. But at the end of it, I'm leaning more towards leaving cars as stock as possible, and only making minor adjustments where I am confident they're needed. The right way to mod essentially requires you to become an automotive engineer and consider the whole system holistically. To test a hypothesis, capture data, and iterate. Which is totally possible and many race teams do it successfully, but it's not something that the every day forum member has the resources for.
I didn't make this journey with the Z but did it with my 4Runner modding it for off-roading / overlanding. And while I really like the end result I came to the same realization that I don't want to modify my Z any more and really prefer to keep it as close to stock as possible. Always wanted to get coilovers but more and more inclining to throw OEM in there

PS: but maybe I'm just getting old and lazy

Last edited by vt100; 10-14-2021 at 11:49 PM..
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      10-22-2021, 01:16 PM   #11
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never mention the ..old... word.... ever!!!!

oh and we dont talk about fight club either...
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      10-22-2021, 09:14 PM   #12
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Originally Posted by Vanne View Post
never mention the ... word.... ever!!!!
Fair enough, lazy and stupid then
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      10-22-2021, 11:38 PM   #13
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Lololol.
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