PSA: Think twice before lowering your car

[Obioban]

when I bought my chassis, My brief after refreshing the suspension was merely to improve the body control and increase the agility.
It was conservative like yours.
No track activity for this vehicle.
My ideal was my E36 M3 with stock springs and Bilstein sports (B8).
Despite the similarity in suspension layout to the E36, it did not respond the same way to a damper change to Bilstein B6.
Hard to believe +250 pounds makes that much difference, but there is more inertia in the chassis.
I think my ideal would be stock springs and an aggressively valved damper.
I had to go up in spring rate to more closely approach my ideal.

+165 lbs 😜
(manual vs manual)

[T.J.]

Cobra, your points on travel, comfort, and practically are all valid but may not apply to vehicles used primary on good tarmac. BMW has to design the stock car to be acceptable for pretty terrible roads and clearances. We can look around and see more purpose built sports cars are designed with less travel per their expected use.

Handling- I’ll give you that the roll couples are worse but what about COG and weight transfer? Steering response? How does the stock suspension maintain geometry with the grip possible in todays tires? Would you argue that a stock suspension would be faster around a track?

[Obioban]

Cobra, your points on travel, comfort, and practically are all valid but may not apply to vehicles used primary on good tarmac. BMW has to design the stock car to be acceptable for pretty terrible roads and clearances. We can look around and see more purpose built sports cars are designed with less travel per their expected use.

Handling- I’ll give you that the roll couples are worse but what about COG and weight transfer? Steering response? How does the stock suspension maintain geometry with the grip possible in todays tires? Would you argue that a stock suspension would be faster around a track?

Weight transfer is better at stock ride height than lowered-- the CoG change is less impactful to that than the roll centers.

Stock ride height (which I believe is what he's making the case for) does not mean stock suspension. Stock ride height does better with the grip of todays tires, because (among other reasons) you get an actually useful camber curve. This also translates to faster around a track-- better camber curve = less static camber required = shorter stopping distances (and better tire wear/even heat distribution). Plus, reduction of bump steer makes it much easier/possible to be faster through corners.

[Casa de Mesa]

Stock ride height (which I believe is what he's making the case for) does not mean stock suspension. Stock ride height does better with the grip of todays tires, because (among other reasons) you get an actually useful camber curve. This also translates to faster around a track-- better camber curve = less static camber required = shorter stopping distances (and better tire wear/even heat distribution). Plus, reduction of bump steer makes it much easier/possible to be faster through corners.

This is why my car isn't as low as typical and the camber I'm running as a result isn't all that aggressive either. I don't track my car, but don't take it easy on it on back roads. I don't need super aggressive camber on the street and have wheels and tires that fit within the confines of the factory opening so I don't have to run excessive camber. I dislike the compromises of too much camber.

I can't disagree with the OP and also know the OP knows his stuff. The math is hard to get around, especially on the front end with McP. I have a dedicated racecar with McP front but has modified lower control arms (forward offset) and different chassis attachment points (raised) to offset the bad math that ensues with lowering the car. The steering rack is also raised. Even then, I've been poked at by people for "racing a 4x4" because the car isn't as low as others are. Ha!

All that to say, I'm still fine with getting rid of some wheel gap on the street

[oceansize]

Yeah Obi and others are track rats. Wanting to squeeze every last bit of performance which in the end trickles down to us in smaller ways. I'm grateful for their track experience because that enables us to reap the benefits of their dollars spent
We can learn and make some intelligent compromises. I just can't do factory ride height, just can't, looks too goofy. I also live in an area where the roads are for the most part phenomenal.

Edit: I also think most handling improvements are tire choice related (assuming you aren't setup horribly).

[T.J.]

Weight transfer is better at stock ride height than lowered-- the CoG change is less impactful to that than the roll centers.

Stock ride height (which I believe is what he's making the case for) does not mean stock suspension. Stock ride height does better with the grip of todays tires, because (among other reasons) you get an actually useful camber curve. This also translates to faster around a track-- better camber curve = less static camber required = shorter stopping distances (and better tire wear/even heat distribution). Plus, reduction of bump steer makes it much easier/possible to be faster through corners.

If you model the weight transfer across a single axle the roll center isn’t even part of the equation. Perhaps you are saying the distribution of front:rear lateral load transfer is better with stock height roll centers? Maybe, but that can be corrected for with spring rates and anti roll bars.

I assume the stock camber curve is better but I have not seen a data plot or computer model of the suspension geometry. As a MacPherson strut car, the curve isn’t going to be great, so that is an argument for stiffer suspension. Reduction of mechanical grip inherent to stiffer suspension depends on the smoothness of the driving surface. It’s incredibly complicated to analyze all these variables and say as a matter of fact that stock ride height is “better” than any other.

[cobra]

This is why my car isn't as low as typical and the camber I'm running as a result isn't all that aggressive either. I don't track my car, but don't take it easy on it on back roads. I don't need super aggressive camber on the street and have wheels and tires that fit within the confines of the factory opening so I don't have to run excessive camber. I dislike the compromises of too much camber.

I can't disagree with the OP and also know the OP knows his stuff. The math is hard to get around, especially on the front end with McP. I have a dedicated racecar with McP front but has modified lower control arms (forward offset) and different chassis attachment points (raised) to offset the bad math that ensues with lowering the car. The steering rack is also raised. Even then, I've been poked at by people for "racing a 4x4" because the car isn't as low as others are. Ha!

All that to say, I'm still fine with getting rid of some wheel gap on the street

I totally get it - like I said before everyone has their own priorities. My car isn't even truly stock height it's like 1/4" lower just so the wheel is more centered in the fenders. I guess my point is - people (including myself) have been convincing themselves that lowering = race car, without realizing the very real downsides.

I wish all the roads near me were smooth like oceansize, but sadly I have to drive over some pretty messed up roads on a daily basis. For him, the combination of moderate driving with smooth roads probably yields no noticeable downsides; and the awesome looks and feeling that brings outweighs all else. As the demands on the suspension increase then the downsides would start to rear their ugly head.

[cobra]

Weight transfer is better at stock ride height than lowered-- the CoG change is less impactful to that than the roll centers.

Stock ride height (which I believe is what he's making the case for) does not mean stock suspension. Stock ride height does better with the grip of todays tires, because (among other reasons) you get an actually useful camber curve. This also translates to faster around a track-- better camber curve = less static camber required = shorter stopping distances (and better tire wear/even heat distribution). Plus, reduction of bump steer makes it much easier/possible to be faster through corners.

Correct. A lot of times people compare stock suspension to lowered suspension ALSO with different springs, dampers, sways, etc. so it's not an apples-to-apples comparison.

If you maintain stock ride height and change the springs/dampers/etc you will realize a noticeable improvement over stock for sure.

[cobra]

Cobra, your points on travel, comfort, and practically are all valid but may not apply to vehicles used primary on good tarmac. BMW has to design the stock car to be acceptable for pretty terrible roads and clearances. We can look around and see more purpose built sports cars are designed with less travel per their expected use.

Handling- I’ll give you that the roll couples are worse but what about COG and weight transfer? Steering response? How does the stock suspension maintain geometry with the grip possible in todays tires? Would you argue that a stock suspension would be faster around a track?

That's a really interesting question and there are many variables. I am willing to bet a stock M3 is faster than many of the poorly set up "race car stiff" M3's out there, especially if the track is bumpy. I drove a stock low mileage M3 recently and was surprised just how good it is. A bit bouncy and harsh but traction, balance, and steering response was pretty good.

[maw1124]

Correct. A lot of times people compare stock suspension to lowered suspension ALSO with different springs, dampers, sways, etc. so it's not an apples-to-apples comparison.

If you maintain stock ride height and change the springs/dampers/etc you will realize a noticeable improvement over stock for sure.

I’ve been talking to Obi offline about this, and that’s exactly where I’m headed I think.

19” wheels give me the “look” I’m after, filling up the wheel wells. If I was on 18s, 100% I’d be trying to lower the car to close that gap. Some will see too much gap even on 19s at stock height. I get it; to each.

After aesthetics, you get to how you want the car to handle, and other “practicality” concerns — for me that’s simple, reversible, OEM quality, not a never ending science project and not tons of time or money. My practicality list is long, and while I can almost relate to throwing all of those aside, I just don’t have time in my life to do so (multiple cars, kids, homes and hobbies kinda thing). I need it done, done right, done quickly, and on to the next. So flatter, stiffer, better turn in, OEM enhanced and practical is a place I actually think you can get to with these (B6 up front, RTAB, sway bars, tire sizes and call it a day). Maybe I’m right, maybe I’m wrong, but that’s where I’m headed.

Weight is thankfully not my concern, though hollow sway bars might be lighter and stiffer, and who knows if B6 is lighter than stock.

The real question is when will I get around to it🤔

maw

[simonnim]

Stock suspension is created for balance of comfort and sportiness. The dampening, spring height, and ride height are what they were able to achieve with the budget given to the engineering team(which is created to achieve the most cost effective method...you know if you're an engineer) to create that balance. It means, there was a budget and it was met, and if they had no constraints, it would be represented by what is achieved in f1.

I think as long as aftermarket spends the time for research. Example, Bilstein literally sells OEM for BMW. Without constraint they can obviously take what they've learned to create coilovers to lower ride height thus lowering center of gravity and improving handling because of that alone.

As long as you're buying quality suspension, you'll improve handling. Period. Will you achieve balance without updating all of the suspension along with coilovers? Probably not because the balance was engineered alongside the suspension it was designed with.

[lemoose]

To me, much of the allure of M cars is their practicality- and their balanced ride height is part of that. One of the first things i did when i got my m5 was raise it back to a stockish ride height. The lowered stance you see below doesnt fit the character imo

[oceansize]

To me, much of the allure of M cars is their practicality- and their balanced ride height is part of that. One of the first things i did when i got my m5 was raise it back to a stockish ride height. The lowered stance you see below doesnt fit the character imo

I don't know about that, I think it depends on level of effort and a combination of several variables. The car at the link below looks fantastic lowered IMO.

https://bringatrailer.com/listing/2003-bmw-m5-61/

[Casa de Mesa]

I don't know about that, I think it depends on level of effort and a combination of several variables. The car at the link below looks fantastic lowered IMO.

https://bringatrailer.com/listing/2003-bmw-m5-61/

Yeah that thing is fantastic looking. Damn, I love the way 19" LMs look. Just an incredibly well executed design. I had LM reps on my car when I bought it and still think those are one of the best looking wheels on the E46 chassis.

And agree, that stance of that M5 is pretty mega

[cobra]

Stock suspension is created for balance of comfort and sportiness. The dampening, spring height, and ride height are what they were able to achieve with the budget given to the engineering team(which is created to achieve the most cost effective method...you know if you're an engineer) to create that balance. It means, there was a budget and it was met, and if they had no constraints, it would be represented by what is achieved in f1.

I think as long as aftermarket spends the time for research. Example, Bilstein literally sells OEM for BMW. Without constraint they can obviously take what they've learned to create coilovers to lower ride height thus lowering center of gravity and improving handling because of that alone.

As long as you're buying quality suspension, you'll improve handling. Period. Will you achieve balance without updating all of the suspension along with coilovers? Probably not because the balance was engineered alongside the suspension it was designed with.

We must also consider that a customer buying an aftermarket coilover kit is expecting it to feel and look a certain way. When you think about a "race car" suspension what do you think of? Stiff, direct, go-kart like handling? Completely compromised comfort in pursuit of performance? Low to the ground for the lowest center of gravity, since a race track is smooth you don't need much travel. But maybe that's not reality. What if someone spent $5,000 on a coilover kit that could achieve the best lap times possible, but felt plush and took an expert driver to extract its capability? Bilstein has to consider what the customer wants versus what might objectively be the "best". It also has to look badass, let's not forget. More compromises even in the aftermarket... especially with sports cars.