Observation on sway bars

[GWL]

This weekend I took delivery on a set of M5 25MM & 18MM sway bars to replace the 22MM and 16MM bars on my 87 M6. Since I do not have a way to mount the M5 front bar yet, I decided to go ahead and install the rear 18MM bar. Just got back from a test drive on my favorite twisty piece of road and found that just the stiffer 18MM sway bar at the rear in combo with the stock 22MM at the front handles very well and is much improved. The car now turns in and holds a track much better than with the 16MM rear bar. As far as feel goes, it feels a lot like my 80 Euro with a full Alpina suspension. Alpina also uses a smaller front and stiffer rear in their sway bar set up for the E12 based E24s. It actually feels so good, that I am having some second thoughts on the 25MM front bar. I know a stiffer bar at the rear adds a bit of oversteer and stiffer fronts brings on more understeer, but I did not think that the increased bite at the front would feel so good with only half of the set on the car. 22MM front and 18MM at the rear just may be the right setup on my M6. Any thoughts? :? I need thoughts on this because once I weld the 25MM bar brackets on the car it will be very hard to go back to the 22MM bar.

[Brucey]

if you like it, it is good enough, some would say.

However, there are a couple of acid tests;

1. The race track. If you are quicker, that is the better set-up.

2. The 'adverse conditions' handling test. If it handles like a dream in the dry, but is an evil POS every time it rains, is it the best set-up? Too much rear sway bar can end up with lift-off oversteer and your car going through a hedge backwards... ask me how I know.....

BTW you can put some roll stiffness back in the front which only comes in on the limit by fooling with the bump stops. This way you might get the best of both worlds...

cheers

[GWL]

if you like it, it is good enough, some would say.

However, there are a couple of acid tests;

1. The race track. If you are quicker, that is the better set-up.

2. The 'adverse conditions' handling test. If it handles like a dream in the dry, but is an evil POS every time it rains, is it the best set-up? Too much rear sway bar can end up with lift-off oversteer and your car going through a hedge backwards... ask me how I know.....

BTW you can put some roll stiffness back in the front which only comes in on the limit by fooling with the bump stops. This way you might get the best of both worlds...

cheers

I think that stiffer bump stops is the way Alpina setup my Euro. I will run it this way for a while as I need to get the parts to mount the M5 front bar. I hope that by that time I will have a better idea of just how well it handles. As you said, it does behave just like my Euro with lift off oversteer and it drives hard through the corners on throttle. I may like it because after 27 years of driving the Euro, it just feels right. I do not race anymore, so I will probably never know for sure.

[ericono]

Bringing this one back from the dead.

BTW you can put some roll stiffness back in the front which only comes in on the limit by fooling with the bump stops. This way you might get the best of both worlds...

I think that stiffer bump stops is the way Alpina setup my Euro.

How would you recommend fooling with the bump stops to get the effects mentioned above?

Thank you,

Eric

[Da_Hose]

I can add that my experience is the same as GWL. I also installed just the 18mm on the rear and it really transformed the car, although I run a staggered setup.

I find that the understeer is neautralized and I have a much better feel of what the rear end is doing. When I pitch in, it feels way more balanced and throttle steer really is predictable. I put on some Pilot Sport 3's on the front which also helped a lot, but still have the Falken FK452's on the rear. We'll see what happens when I put the matching P3's on the rear this summer.

Jose

[GWL]

Bringing this one back from the dead.

BTW you can put some roll stiffness back in the front which only comes in on the limit by fooling with the bump stops. This way you might get the best of both worlds...

I think that stiffer bump stops is the way Alpina setup my Euro.

How would you recommend fooling with the bump stops to get the effects mentioned above?

Thank you,

Eric

Someone else will have to answer this as I am not versed in changing bump stops on Bilstein Shocks. The rears are easy, but many Bilstein fronts have internal bump stops

[GWL]

BTW, I did install the larger front sway bar. It soon became apparent that I needed to reinforce the sway bar mounting points on the upper mounting point on the suspension. I boxed in the mounts and have had no problems since.

[ericono]

GWL,

What about the feel of the car? How does the setup with the 25mm front bar compare to when you had the 22mm bar (either situation with the 18mm rear bar)?

Thanks,

Eric

[ericono]

Also, do you have any pictures of the modifications you made? And to clarify, you boxed in the mounts connected to the chassis or the mounts on the strut tubes?

Thanks again,

Eric

[Da_Hose]

You aren't running a staggered wheel set, correct George?

A stiffer front swaybar means more understeer, so I wonder if the 25mm might be too much with my staggered wheels?

Hmmmmmmm ......... Maybe the formula is as follows.

Use a 25mm front and 18mm rear with regular wheels.

Use a 22mm front and 18mm rear with staggered wheels.

Jose

[GazM3]

I use the thinner bar up front and it seems to be nicely balanced. I have front and rear strut tower braces and -2deg front camber which will effect the feel from the std setup

[GWL]

GWL,

What about the feel of the car? How does the setup with the 25mm front bar compare to when you had the 22mm bar (either situation with the 18mm rear bar)?

Thanks,

Eric

Since I do not race anymore it is difficult to evaluate just which set up is best for speed. However I liked the feel with the smaller front bar better. It may be because I was used to the Alpina setup. I have been running the thicker bar for several years now and it has become the norm. I would not reinstall the smaller bar now, but when first installed my impression was the thick rear & stock front with Sport Bilsteins was superior in feel.
The thicker front bar is definitely stiffer, thus the need to reinforce the upper mounting points.

[Brucey]

Bringing this one back from the dead.

BTW you can put some roll stiffness back in the front which only comes in on the limit by fooling with the bump stops. This way you might get the best of both worlds...

I think that stiffer bump stops is the way Alpina setup my Euro.

How would you recommend fooling with the bump stops to get the effects mentioned above?

Thank you,

Eric

BMW bumpstops act as supplementary springs and play a significant role in the suspension stiffness as soon as the suspension starts to compress.

If you are lowering the car all you need do is to use shorter bumpstops than stock at once end of the car and leave them long at the other end. Where the bumpstops are longer/stiffer than is correct for the suspension ride height, you will increase roll stiffness and thus reduce grip.

With Boge shocks all the bumpstops are external.

With Bilsteins the rears use external bumpstops (as per Boge) and the fronts use internal bumpstops hidden inside the insert.

The easiest rear bumpstops to use are 'M' ones or standard ones. M ones are shorter and a bit stiffer. Standard ones can be cut down a little but if you cut too much off the dust boot will fall off (it is normally located on the bumpstop) or the bumpstop will slide down the shock shaft.

The Bilstein front bumpstops available are shown here

viewtopic.php?t=3039&highlight=bilstein+bumpstops

And can be cut down very easily before fitting.

However a fellow bigcouper recently tried to order some from Bilstein UK and failed; they didn't recognise the part numbers or something. Whether he was speaking to the departmental idiot or they have changed the part numbers (and not bothered keeping a X-ref) I don't know...

cheers

[GWL]

Also, do you have any pictures of the modifications you made? And to clarify, you boxed in the mounts connected to the chassis or the mounts on the strut tubes?

Thanks again,

Eric

Strut tubes, Sorry this is the only picture I have. Not very clear

[ericono]

Brucey,

Thanks for the details on the bumpstops.

George,

Thanks for the feedback on the difference between sway bars and especially the image clarifying the reinforcement done. I am currently having some front struts built up for me and will ensure this reinforcement is done.

Thanks again,

Eric

[Noct]

Do Koni's use the external bumpstops up front like Boge? I heard somewhere it might be worthwile to pay whatever extra for Konis over the Boge shocks.

[dlvad]

if you like it, it is good enough, some would say.

However, there are a couple of acid tests;

1. The race track. If you are quicker, that is the better set-up.

2. The 'adverse conditions' handling test. If it handles like a dream in the dry, but is an evil POS every time it rains, is it the best set-up? Too much rear sway bar can end up with lift-off oversteer and your car going through a hedge backwards... ask me how I know.....

BTW you can put some roll stiffness back in the front which only comes in on the limit by fooling with the bump stops. This way you might get the best of both worlds...

cheers

Well said Brucey.