H&R Sway (Anti Roll) Bar

[PeterJ]

Hi all, Just recieved a set of Front & Rear H&R Sway Bars (including new bushes etc) for my 1998 2.8 Z3 which has Bilstein B4 (similar to stock) shocks & original springs and tyres Toyo Proxes C1S Front: 225x18 & Rear: 255x18. I do not want the car lowered coz so many speed bumps in cars parks etc here. I want to improve cornering stability especially reducing body roll (especially at the rear). I think the H&R Sway Bars are adjustable, but would welcome any suggestions of what settings to use given my set up?

Cheers!

 

[Aceman]

There are three settings on H&R arbs, you adjust them by means of bolting the drop links into one of three holes on the end of the arbs. The outer hole being the softest and the inner most holes the stiffest. I would suggest after reading many posts about the subject to either go for the softest outer setting which is still significantly stiffer thsn oem or the middle setting. Some people have found the stiffest setting too much and also puts a lot of strain on the the mounting points on the trailing arm and body which some have strengthened by welding extra plates on.

I would try the softest first and see what you think, they are easy enough to adjust later.

 

[PeterJ]

Thanks Aceman. What about the set up balance between front & back? ... I know it will be a case of 'try & see to what I want', but in general, I think a harder setting on the rear than front should tend towards oversteer, whereas harder setting on the front than rear will tend towards understeer, or do I have this the wrong way around?! It seems that the Z3 2.8 tend to slightly understeer & my experience is that this is true and with significant rear body roll...never had it 'jump out' yet as I stop pushing at that point...
Would you consider it best to have the same settings on both front and rear? especially given the extra engine weight of the 2.8 compared to the 1.9?
Perhaps try softest settings and the front and medium setting at the rear?...or the other way around? Just wondering what the general experience/view is?

Cheers!

 

[Aceman]

Well if it was me I would go for soft all round to start with and drive it for a couple of days then try going to medium on the rear as you say and see what the effect is. I dont have H&R arbs myself but have read plenty about them and from what you describe about your 2.8 being slightly understeery tallies with my experience from my 2.8 but the ///M is more of an oversteer setup as standard so a different experience to drive.

I think you are going to have to find your own preference with the setup as each person is different in how they drive coupled with what the roads are like out there you may settle on different settings to someone else. Trial and error is the phrase as suspension tweeking is very much a black art unless you are a professional at it.

Keep us all updated though of you experiences as it will be interesting to read and I am sure there are others out there that would appreciate the info.

 

[PeterJ]

Cheers Aceman!, will get my Z3 back in about three weeks time (more mods ) so will play with the ARB's then! will post my findings

 

[PeterJ]

Just took another look at my H&R Sway/AR Bars & there are only two settings on each side of the front & back...hope they are the right ones :O I will start off soft on both...

 

[Aceman]

I stand corrected looks like there are only 2 setting could of sworn I read there were 3 /

Here is a thread over on the coupe forum talking about the reinforced mounts;

http://www.z3mcoupe.com/forum/showthread.php?t=13335&highlight=H&R+roll+bars&page=3

If you scroll down there a few pictures.

Interesting equation for you to consider, quote from the coupe forum regarding the H&R arbs, dimensions are for the ///M arbs but principle still applies;

This stiffness of an ARB is proportional to the 4th power of its radius. The OEM front ARB is 23mm diameter (11.5 x 11.5 x 11.5 x 11.5 = 17490.0625) and the H&R ARB is 28mm diameter (14 x 14 x 14 x 14 = 38416) therefore the H&R front ARB is 2.19 times stiffer than OEM.

 

[zedonist]

I have them fitted, i have them on the softest setting all round so as per calculation twice the oem stiffness.

I think that a lot of problems can come from the adjustment, and people incorrectly think they should stiffen the rear. This is wrong for a rear wheel drive car as the aim is to keep both driven wheels on the ground, in this case it needs the front ARB to be the stiffest, hence why it is thicker than the rear. On a front drive car you have a stiffer rear ARB to the front for the opposite reason.

Just on the softest setting there is emense improvement in body roll and handling, I also have Bilstein B8 and Eibach springs fitted, sitting on 18inch rims, and I am very happy with the setup and ride.

 

[Gigsy]

I have them fitted, i have them on the softest setting all round so as per calculation twice the oem stiffness.

I think that a lot of problems can come from the adjustment, and people incorrectly think they should stiffen the rear. This is wrong for a rear wheel drive car as the aim is to keep both driven wheels on the ground, in this case it needs the front ARB to be the stiffest, hence why it is thicker than the rear. On a front drive car you have a stiffer rear ARB to the front for the opposite reason.

Just on the softest setting there is emense improvement in body roll and handling, I also have Bilstein B8 and Eibach springs fitted, sitting on 18inch rims, and I am very happy with the setup and ride.

That's not 100% correct - the aim is to adjust the front to rear roll stiffness balance and deciding what to do really depends what handling characteristic you're trying to dial in/out - it's not necessarily a RWD vs FWD thing.

As a generally rule though yes, a RWD car has a tendency to oversteer, so you would typically soften the rear compared to the front to counteract this and the reverse is true of FWD and most AWD/4WD cars.

However, most modern cars are set up to understeer a bit irrespective of whether they are RWD, FWD or 4WD since this is generally regarded as "safer" and the Z3 suffers a little from this trait too so a little extra rear stiffness (either by softening the front or stiffening the rear) wouldn't go amiss IMHO. However, I certainly wouldn't go too far with this as you don't want the rear to be too mobile on the road especially when you have the bonus of being able to power oversteer rather than relying on lift-over oversteer or some other such provokation.

To the OP, my advice would be as per the other advice above really. The new bars will increase roll stiffness front and rear so you won't really have much of a reference point to start with. Most manufacturers tend to balance the bars in their kits so matching the settings front and rear should give more or less neutral handling which you can then tailor to taste / driving style.

Personally, I'd set both to the softest setting and get used to that. Then start by adjusting the front ARB to see if that improves turn in / the early part of the corner. Once I was happy with the front, I'd then adjust the rear until I was happy with the overall balance of the car (this may mean going back and adjusting the front again at this point too).

The only one that can really says what's best for you and your driving style is you so don't be afraid to experiment. Also, playing with the tyre pressures can allow you to fine tune things between bar settings too (higher pressure to reduce grip, lower pressure to increase it).

 

[zedonist]

Yes Gigsy, you are correct you can play around to get under or over steer, but if you just want OEM designed neutral handling but to go around corners with less body roll then H&R ARB's on front and rear soft setting will give you that.

My point was the misconception people have that increasing the rear bar will make a Z better, i.e more grip on drive wheels, it won't, you need to increase the front. It is the dip at the front that causes the rear opposite wheel to lift.

But as you say this can also change under and over steer characteristics, so you can also tune for driving style / preference, and get a drifting stylee if required.