Saw real YMB M4 yesteray in Toronto

[redfox]

Originally Posted by catch

redfox my car comes in a few months. Want to see different options. Supersport springs almost look too low in pics, sports too high in the front... I'm debating KW HAS coils (i think thats what they're called)

Well, if you have active suspension, I would not recommend it. If you have passive, I still would not recommend it unless if it is a full coil over set. If you put on KW HAS on stock shocks, you are compromising millions of dollars of engineering for better stance. Just my 2c. Im not too concerned with stance.

[Merli]

Originally Posted by redfox

Well, if you have active suspension, I would not recommend it. If you have passive, I still would not recommend it unless if it is a full coil over set. If you put on KW HAS on stock shocks, you are compromising millions of dollars of engineering for better stance. Just my 2c. Im not too concerned with stance.

Disclaimer: This person above has not driven a car with KW HAS kit

How does adaptive suspension works? Well, the different settings (Comfort, Sport, Sport+) alters the ECU's tuning on how it ALTERS THE DAMPING RATE of the magnetic shock absorbers. That is, the ECU detects road conditions (small bumps, large bumps, potholes, etc) and quickly (hundreths of a second) sends electrical impulses to the magnetic dampers that alter their damping rate.

But.... but... but.... How is this possible, since the spring rates remain the same?

Going by your theory, by changing the damping rates and keeping the same spring rates, we have just completely bastardised our cars and eliminated "millions of dollars [worth] of engineering".

Well I'm no suspension engineer, but even I know that it's not quite that simple

There isn't a perfect match between dampers (rebound rates, internal valving design, piston sizes) and spring rates. Why? Because ROADS are variable. Even race tracks are variable. Some are smoother than others, some have higher G-force corners than othes. One car that's perfectly setup for one track and easily get upset by some mid-corner bumps at another racetrack.

That's why suspension systems operate in a RANGE of conditions.

Just by changing stock springs to BRAND X springs (whether they be H&R sport, H&R super sport, KW clubsports, KW HAS, whatever), doesn't mean that you've completely destroyed BMW's magical and perfect suspension system.

Do you know what the stock spring rates are? Nope, didn't think so. Then how can you say that going to KW HAS will upset the suspension?

....... You can't.

Even KW coilovers that you seem to hold in such high regard are extremely variable. You can get KW V3s with all sorts of different valving and spring rates depending on your application.

There is no perfect "one size fits all" suspension solution, and that's why changing BMW stock springs and replacing them with BRAND X doesn't necessarily "destroy" the suspension tuning.

It might, or it might not, depending on how that particular car is driven and on what surfaces.

[redfox]

Come on, was it necessary to discredit my opinion just because I do not have HAS on the car. Or to say things like even you can bla bla... Someone asked me a question. I answered and provided my opinion. LOL! And you took offence to that.

I have modified a few cars in my day, and have used springs with sleeves from various manufacturers, KW, Ground Control, etc.. Regardless of my experience with those products with other cars. Let us just focus on my logic that led to my view.

I base my hypothesis, and yes, it is just a hypothesis, hence my opinion, why I would not do it based on the following logic:

1) The system in the M4 adjusts the dampening rate based on known information, such as travel of the suspension, the spring rate, speed of car, steering angle, yawn, acceleration, etc..

2) KW HAS is changing at least one of the two variables, namely suspension travel and spring rate.

a) Assuming HAS have the same spring rate as the BMW stock springs (you are absolutely right, I do not know, hence had to arrive at my conclusion using a decision tree), a shorter spring (since sleeved) would lead to bottoming out on the stock dampers since travel is less, hence unlikely, but regardless one variable changed;

b) assuming KW HAS comes with springs that has increased spring rate to prevent bottoming out, how two variables have changed, which means KW had to do extensive testing to figure out what is the right spring rate. But hey, that spring rate needs to be able to handle multiple ride heights. Ah, so KW needs to use a spring rate that is suitable for the average ride height. If they stray from that, the the balance would be off. That is of course assuming they tested plenty to get to the average optimal. If you know they did, then great. I do not, hence leading us to point three.

3) These cares were tested over and over again on the green hell, and many other proven grounds around the world to arrive at the best compromise between comfort and performance based on the suspension program you are running. Without any knowledge of the programming of the adaptive suspension, am I supposed to think that the HAS lowers the car while increasing, or at least matching the balance of stock suspension. I am not sure, but just saying that my hypothesis is otherwise.

So that is my logic. Hence, I am unwilling to test with HAS. I also do not think that my driving skills can detect the differences all that well. Maybe I will, but who knows. Regardless, I want to retain the expensive suspension I purchased that is in perfect working order, not just for stance. Because that stance would cost me the programming (no longer accurate), damper life (constantly under more compression due to lowering ride height) and unknown geometric impacts.

A couple of more points...

BMW M Adaptive suspension dampers are not magnetic, that is GM technology I believe. The EDC adjust control valves which manages the flow of hydraulic fluid within the dampers

Do not think that I said we have completely bastardized our cars, just saying that you are throwing away countless hours of engineering for something that is not in the same league of engineering; could still be better if you know for a fact. I do not.

Note that I said the optimal balance between comfort and performance, achieved by the perfect match between dampening rate and spring rate, based on BMW engineers views, not mine

Finally, coilovers are superior to springs because you can match the right damper to the right spring, like you said, based on application. Not sure what do you mean by high regard. It is a more complete and highly adjustable solution, per your comment. HAS can only adjust height. If you are going to change a stock performance suspension, then you need to be able to dial it in or even better by changing variables. You can do that with coilovers, but not springs.

Originally Posted by Merli

Disclaimer: This person above has not driven a car with KW HAS kit

How does adaptive suspension works? Well, the different settings (Comfort, Sport, Sport+) alters the ECU's tuning on how it ALTERS THE DAMPING RATE of the magnetic shock absorbers. That is, the ECU detects road conditions (small bumps, large bumps, potholes, etc) and quickly (hundreths of a second) sends electrical impulses to the magnetic dampers that alter their damping rate.

But.... but... but.... How is this possible, since the spring rates remain the same?

Going by your theory, by changing the damping rates and keeping the same spring rates, we have just completely bastardised our cars and eliminated "millions of dollars [worth] of engineering".

Well I'm no suspension engineer, but even I know that it's not quite that simple

There isn't a perfect match between dampers (rebound rates, internal valving design, piston sizes) and spring rates. Why? Because ROADS are variable. Even race tracks are variable. Some are smoother than others, some have higher G-force corners than othes. One car that's perfectly setup for one track and easily get upset by some mid-corner bumps at another racetrack.

That's why suspension systems operate in a RANGE of conditions.

Just by changing stock springs to BRAND X springs (whether they be H&R sport, H&R super sport, KW clubsports, KW HAS, whatever), doesn't mean that you've completely destroyed BMW's magical and perfect suspension system.

Do you know what the stock spring rates are? Nope, didn't think so. Then how can you say that going to KW HAS will upset the suspension?

....... You can't.

Even KW coilovers that you seem to hold in such high regard are extremely variable. You can get KW V3s with all sorts of different valving and spring rates depending on your application.

There is no perfect "one size fits all" suspension solution, and that's why changing BMW stock springs and replacing them with BRAND X doesn't necessarily "destroy" the suspension tuning.

It might, or it might not, depending on how that particular car is driven and on what surfaces.