I have a 03 Z on a stock suspension it sits a little high in the back would the spring mount mod be an acceptable way to level out the car?? Or is this mod usually done by owners who already have lowering springs installed on their car. Would just like to drop my car a bit in the back not lower it all over..

THANX!!!!

 

It is an acceptable way of lowering your rear end, done by anyone who wants their rear end to sit lower.

I have only read one negative review, and think the reasoning behind it was shoddy at best (claimed that the rearward weight transfer had a detrimental effect on his steering feel - something about less weight on the front wheels). I am working on some calculations to debunk (or prove) this logic. Besides, I suppose all Zs with an even drop have this problem then

I didn't notice any ill effects when I cut mine, except for those usually associated with lower ground clearance.

 

That's just dumb. Lowering the rear by like .2 inches wouldn't change weight distribution. It's like saying people on coilovers who are flush in the front/rear suffer from this too.

 

Put a car on corner scales and see what happens. I'll bet your wrong. I'll also bet it changes you caster up from too, also changing the way your car handles.

Yes they do

 

Terrasmak

Thanks for defending me Bro......I have been swapping springs and shocks like a ****.....

I would also like to explain a little more to these guys just so that they can see where I am coming from.

OK here goes.

lets take a STOCK Z......and put some Hotchkis sways on it. (hang on I want you to understand HOW i discovered this)

we are going to go third hole up front and weakest hole in the rear....this puts both bars at 80% stiffer than stock...the car will handle exactly like stock except it will feel stiffer all the way around.

NOW....lets cut the recommended HALF an inch from the rear spring mount to even out the car.....WHOA! its not as stiff up front....lets fast farward through the hours of troubleshooting shall we.....in order to get the handling back we need to stiffen up the front swaybar, BUT they are already on the third hole (stiffest...4th hole is for the G35)

so in order to get the handling of the swaybars to be as they were BEFORE we cut the springmount we need to stagger the front swaybar...on one side we will leave it in the third hole and on the other side we will move it into the 4th (G35 hole) and go for a test drive....OK we got our handling back.....It fells a little weird because we lost some strut travel but it is doable.

Can you guys understand where I am coming from?

I did EXACTLY as described except that I had RS-R springs that have a .6inch drop all the way around (this keeps the car in balance same as stock except lower...

on a stock car...maybe a half an inch does not really seem like its all that bad....but when you are already lowered .6 inches all the way around.....and THEN do the spring mount mod.....WELL you are now .6 inches lower in the front and 1.1 inches in the rear.....


Hope this makes sense.

Try to get springs that drop exactly the same in the front as they do in the rear or REALLY close to it.

RSR- is even drop front and rear at .6 inches....If you really want to go lower i think the tanabe nf210 is 1.2 inches front and rear but that is a progressive spring...

you CAN eliminate wheel gap in the rear by choosing your spring carefully.

If you MUST try the springmount mod.....BUY an extra set so you can switch back if you dot like it.....in order to even out the STOCK Z you must cut half an inch off.....not the .2 that you guys were mentioning....

people who do the springmount mod do it for looks....if you look at the comments all you will see it "man that looks low" "looks good" "love it" "like it"
but wont see any comments about how it actually feels....I decided to do this cause i wanted to even out my drop....with no comments on anything bad happening i did it myself....immediately feeling sorry that i ever did it in the first place. the 4th hole on the front of the swaybar puts a TON of stress on the endlink and you can feel it binding....I actually tested this......

I am not telling anyone what to do with their car....only warning them what effects it will have in the end.....if you don't mind the negative effects....and want to go for it....do it....but i recommend you buy some extra upper springmounts in case you don't like it....I didn't and now they are on back order and i have been driving around like this for over a month hating it

hope this explains everything in detail.....

"calculations to debunk (or prove)" wont do anything....you MUST try it out yourself in order to understand whats going on.

People who say they didn't fell a difference....please POST your suspension setup.

Thanks!

 

Look, I had the same gut feel when I read it. But it is true. It is a fact that lowering the rear of a car, while keeping the front at the same height, transfers weight to the rear (and off the front wheels). This is a known and used principal in motorcycle tuning.

I am not advocating this point, and am in fact trying to prove that the weight transfer benefits outweighs the purported drawbacks in steering feel.

My hypothesis is that the weight transfer to the rear, and corresponding weight removed from the front tires, is negligible and acceptable compared to the benefits of lowered CG and improved weight distribution (aesthetic benefits non withstanding). Furthermore, once I get a ballpark figure on exactly how much weight is transferred to the rear (and off the front wheels/tires), I will be able to hypothesize whether this weight transfer can even have a noticeable effect on steering feel.

This can all be resolved with math, and given a certain set of assumptions (e.g. car weight distribution - f/r and left/right, ride height, etc), the exact weight transfer off of the front wheels can be calculated. As I said, I'm working on it.

 

To danimaldaisy-

Read my previous post. I disagree with you touting running an even ride height as being detrimental to steering feel. And even if it is, I posit that the benefits outweigh the drawbacks.

It is an interesting case, as I am running the same springs as you (RSR). I'm running Koni SAs. Hotckis sways front and rear (edit: these are 2nd gen sways, with 4 levels of adjustability up front).

As I stated, you are correct that the weight does transfer to the rear (and off the front wheels, to your point) when cutting the springmount. But until you come to me with some math, I will disagree with your assumptions (which is what they are, at best).

I cut my springmount 1/2" and didn't notice the same detrimental effects as you.

 

You forgot one big thing, when bike is lowered or lifted the rake changes, that is an important aspect of handling, also the angle fo the swingarm to the ground. When you raise or lower a car you also deal with these same aspects (caster )

Most people say it feels fine , but then again most people will also drive around for weeks with a tire 15 psi low. I don't believe most people.

Suspension tuning is not rocket science, but dam close.

 

I didn't forget it. That exactly what I'm trying to get at, as the rake - or height difference front to rear, is elemental to the calculations involving right height, weight distribution and center of gravity.

If we want to get real fancy, we can take acceleration into consideration given all the other variables (longitudinal acceleration pitch and weight transfer, etc). I am not doing this (yet), as the first step is to get the weight transfer figures given a ride height change in the rear.

Rocket science, exactly. Talk is cheap, but automotive engineering, well it's science.

 

I only described what happened to me on my car.......

if i wanted to reproduce the effects without doing the springmount mod....i could leave the front swaybar setting in the 3rd hole and stagger the rear....one side softest and the other side middle...or maybe even both middle.

I am glad we can agree on the weight transfer to the rear which was my point...

what part did you not agree on?

the differences on our cars is that you are running Koni's and i am running D-specs (not as good as the koni)

can you post your swaybar settings....and also front and rear strut settings?

you may have just tuned the suspension to work properly.....

remember

my post was speaking for the newb on a completely stock suspension with no way to tune struts or sways.....i had to throw the sways in there in order to better explain where i was coming from...fortunately everyone understood me.....I know what we agree on...just not sure what we don't agree on.


by the way...at least the OP now knows that he will have some weight transferred to the rear.

 

one last point....I may have a problem with the stock endlinks......reading on a thread about adjustable endlinks....it is possible that i am getting no preload on the rear endlinks making the car handle sloppy.......but I plan on looking into this....and quickly

 

Yes, we agree on the weight transfer.

I have a problem with you decrying this mod as being detrimental to steering feel and handling. You (in this thread and others) have commented on this mod as being a negative to steering feel and handling.

I didn't notice these same effects.

But, you obviously have a point in regards to the rearward weight transfer, so I am trying to get to the bottom of things.

I simply want to know how (using math, not just hearsay) weight distribution is altered given a 1/2" change in rear ride height, and discuss the direct and indirect effects of this change. That's all really.

 

rake on a bike is the angle of the head tube to the ground, the head tube is what your steering pivots on. Yes weight transfer is changed but the whole dynamics of the suspension are also changed do to the changing of the angles on the suspension components. These dynamics have a lot of effect, thats what i'm trying to get across, even in cars.

So basically for a few , forget the weight transfer stuff and think of what changing the angles on the steering components does.

 

Call a shop that does corner balancing, they may be able to give you a better idea of how muck movements like that effect balance and how much weight transfer actually happens.

 

I agree.

For the sake of this conversation, we first have to deal with the aforementioned effects on weight transfer off the front wheels from the 1/2" decrease in rear ride height.

After that, we can talk about the associated suspension geometry alterations and their effect on handling. For what we are trying to prove, suspension geometry changes are secondary to the effects of weight transfer and CG.

Besides, the point seems relatively moot since you can adjust the suspension geometry on the Z (caster, using aftermarket upper a-arms). Now, if you're telling me that the Z needs a rake to handle properly because of it's inherent suspension design, then we are opening a whole other can of worms, and I would obviously ask you to prove it to me.

I'll give you the mathematical proof to whatever I post. Then again, calling a shop would be a whole lot easier I suppose, but the geek in me won't let me off this easy.

 

wait a second, neither of you have called each other an idiot ricer yet.

I'm not used to all this rational discussion

 

well

Thats because I don't respond right away with insulting comments which lead to a flame fest.

You know....I can type something and 10 people will all read it differently...some will understand, others will not, and others will think you are insulting them.

I work at a school and deal with all kinds of people....maybe i have learned the art of "getting along".

We are all after answers here....but so far we at least agree on the weight transfer part.

Maybe if i was still in my 20's i would be an idiot, but it gets tiring after a while.

I joined this forum to get valuable info and contribute....

 

Did some research and came across these threads in some forums:

http://bimmer.roadfly.com/bmw/forums...8862391-1.html

http://forums.bimmerforums.com/forum...t-1209398.html


Cliffnotes from the above threads: Lowering the rear of the car or altering rake does not significantly affect static weight distribution.

I am still not happy though, and am working to prove it mathematically.


To terramask's earlier point, I think the next step after calculating the change in static weight distribution is to quantify the change in caster and it's effects.

 

I cut mines w/ stock suspension.. it brought the rears down 0.5" looks a lot better now..

 

Im not as learned on the engineering aspects of car suspension systems, nor do i even know the workings of each part, but one thing here does not make sense to me while i sit here thinking about what you both have said and am trying to grasp this concept:

Why in the hell would increasing or decreasing rake on a car even effect static weight distribution? If all weight on the car is fixed to begin with and not shifting according to an increase or decrease in rake (like raking a jar half full of water one way or the other and the more water shifting to one side therefore weight distribution), how could rake effect this? There must be some physics i am missing here?

Basically, despite how raked the car sits, the weight on both ends remains the same. I could see how changing rake could effect the involved suspension parts, as they are specifically engineered according to the cars initial ride height (ie raising the front could weaken handling due to the suspension components working below normal tolerances, but not a shift in weight having any effect, only angle of compenents like stated by terr.)

What am i missing?