Geometry Settings Opinions

[Steve84N]

So I've played around a fair bit with my geometry settings but recently I put a B12 kit on and the alignment is now limited as a result of being lowered. I've got maximum camber up front and minimum camber on the rear but it still gives me more on the rear comparatively. I do also have H&R anti-roll bars set to the harder of the two settings on the front and the middle of three settings on the rear. Before the B12 this gave a good balance and I'm loath to soften the front as there's still a helpful amount of roll but it gives better turn in stiffer.

The problem I have is mainly mid corner when I'm getting back on the power, the rear will start to slide but then the front washes wide as the rear starts to rotate. This is not in a nice 4 wheel drift kind of way, more a fairly abrupt move sideways. In steady long radius corners it's the front that's pushing wide first. It's clear the balance isn't right but I'm torn as to whether I should increase the front camber to the same or slightly more than the rear or whether I should decrease the rear as I assume that it's the camber imbalance giving me this trait(?). It is a road car and I do close to 20kpa but I don't mind paying a bit more for tyres if they wear out a couple of thousand miles earlier.

Increasing the front camber means camber plates and these are £300-400 easily for a decent brand and I can't seem to find stack height information for the various options which is important as the B12 is a fixed height so ideally the plate would be very close to the thickness of the standard mounts which is 47mm. I like the look of the Eibach offering. I'm thinking that although this was my initial preference the expense is perhaps not justified as a lot of the time (like on motorways) I won't be getting best use out of the tyres.

Reducing the rear to more like 1 degree needs camber arms and most seem to also be £300-400 but the Powerflex version is much less at £144. Does anyone have any experience with them? From the picture do they look easily adjustable or is the inner nut going to be difficult to access?


Having read up a bit it seems like more castor would be a useful thing to have to increase dynamic front camber and steering weight/feel. Powerflex do an eccentric lollipop bush which adds around 0.5 degree of castor. Is this amount of increase going to be noticeable and worth £140? https://www.powerflex.co.uk/road-se...+Wishbone+Rear+Bush,+Caster+Offset/11515.html

Here is my current alignment settings (in degrees and minutes) so about 1.4 front camber and 1.9 rear giving a 0.5 degree rear bias:

Thoughts welcomed.

 

[Busterboo]

http://www.centregravity.co.uk/?

 

[Steve84N]

Thanks, although I've got a decent alignment guy much closer to me, was hopefully looking to hear from people with experience of running different geometries to help decide which way to correct.

 

[Ed Doe]

If you want less oversteer either soften the rear arb to give you more roll and therefore more grip, or start to increase the toe in angle at the rear. Under power the toe at the rear reduces and can end up toeing out depending on the RTAB bush flexility /age, which can result in more oversteer.

Personally though your issue sounds like an overly stiff rear arb though compared to the front, so that's where I'd start

 

[hopz121]

I can recommend Turner parts but they are not cheap.

I run Turner rear arms on my M3 they are a great bit of kit and mega easy to adjust too.

I plan on getting the front camber plates too eventually when upgrading to decent coilovers, the parts are not cheap but they work well and are made exceptionally well and lighter than OEM

 

[Steve84N]

My problem is too much understeer, not oversteer. I've already done RTABs with limiters so that's fine and before lowering I was about 1.3 front camber and 1.5 rear. The ARB balance felt about right but now the camber imbalance is greater and ideally would be slightly more on the front than the rear.

Part of me likes the thought that the front could grip as much as the rear does now if more front camber works but I'm concerned it may be too much camber for a road car and only really be of benefit when railing it round a corner which is limited as usually there's traffic. If I'd get more general grip from something like 1.3/1 degree normally then it makes sense to bring the rear down rather than the front up in terms of camber.

I've already got a Powerflex lollipop bush so only want to replace it with the offset version if it's going to make a noticeable difference.

 

[Ed Doe]

What tyres you running front and rear?

The comparatively small difference in camber front to rear will not result in understeer as you're describing it - that will be more a result of the arb settings in my opinion.

I'm running pretty much the same setup as you bar the arbs, but Im running m3 csl alignment and I've not had any issues with understeer, on the road or track... It's a far more neutral to oversteery setup, and feels perfectly balanced for my personal tastes...

I still reckon you'd benefit from softening the front arb, or if you really don't want to touch the front, then stiffening the rear before going down the route of buying expensive parts... A good setup is definitely possible with the kit you already have on the car...

 

[Steve84N]

F1 Asymmetric 3 225/40/18 and 245/40/18, probably switching to 235/40/18 front when they wear out.

I can soften the front bar easily but I feel like it's an artificial way to solve the problem. I've tried the rear on its stiffest setting and it goes too far, losing grip rather than benefitting from reduced roll.

If you have been able to achieve CSL settings then the camber difference is only about 0.1 degrees but mine is more like 0.5 degrees which is quite a lot.

Before I lowered the car I was running more like 1.2F and 1.5R which had much less of the issue I've got now. The bars are set the same.

 

[Ed Doe]

Why are you going to 235/40/18 on the rear? Surely that'll be detrimental to the handling?

It's up to you re the camber, have you had the camber pins knocked off your oe top mounts yet so you can get more adjustment? I'd recommend that first but yeah personally would use what you've got on the car to find the best setup prior to buying more parts. I've not found the car really needed any front/rear roll adjustment at all with the b12 kit - it feels communicative without losing the sharpness of the turn-in.

Whereabouts are you based and who is doing your alignments? If you're anywhere near TWG in Camberley I'd recommend them - Will the owner races himself and has an extremely good grasp of setting cars up properly - he would be able to sort out the alignment and give you something closer to what you're looking for without going the parts route just yet...

 

[Steve84N]

I'm already 245 rear and thinking of going 235 on the front to be almost square. 0.5" extra on the rims is closer to 10mm than 20mm anyway and a 30mm stagger is not needed on a car close to 50/50 weight distribution. Newer M cars are now specced with a 20mm stagger.

I have a decent alignment guy, all he does is alignments (Lee at FCM in Bristol). We've gone as far as we can on the standard adjustments including pulling the pins. I bought the bars before the B12 and to be honest they were too stiff for the shot standard suspension but now they compliment each other nicely.

I'm waiting for a reply about the stack height on Eibach plates. I guess the key thing I'd be interested to know is people's experience of running -2 degrees of camber on the front in terms of handling and tyre wear for a road car.

 

[Steve84N]

Stack height would add 6mm to the front ride height so I'm going to try rear camber arms having spoken to my alignment guy. He's concerned about being able to get a spanner on the inner nut when they are installed. Does anyone know if this is a problem on the Z4 and I need to get arms with the adjuster in the middle or are the Powerflex ones shown above fine?

 

[Steve84N]

Just to update this I've replaced the lower control arm outer bush with Powerflex and that alone allowed the alignment to lose about a third of a degree in negative camber. The car drives much better as a result with better turn in bite and it rotates mid corner nicely too. Still lacking a bit up front so I think I'll try the offset bushes for some extra castor. Will also switch to 235/40/18 up front and then if it's still not there it will have to be camber arms. There's not room to adjust the Powerflex ones though which is bad design, Eibach is the recommended option but it's over twice the price.

It's funny how car reviews never talk about geometry but moan about inert handling. I'm sure many cars would be transformed with a few tweaks as I've felt noticeable differences with small changes.

 

[GuidoK]

Usually from what I know extra caster gives more steering after the apex, so when on throttle. But it gives a less aggressive turn in. I think that has to do with the angle of the kingpin making that the actual steering angle (looked from above) becomes less. They dynamic camber only sets in once the suspension really loads up, so thats probably on the fastest part of the corner, when accelerating.

Caster gives more straight line stability (which seems logical as that is the opposite of a more 'nippy' (or twichy) car).
So that might suit your needs (you say you have good turn in but progressing through the corner understeer sets in).
But expect more outer tyre wear, and too much caster gives extra body roll, as the inner wheel comes up and the outer wheel goes down, creating more pressure on that wheel (at least intrax describes that effect on their site, its hard to visualize this geometrically)

From what I know about people in the US who do those time attack/autocross things on parking lots (1 car driving around a very small set out track) is that they use very wide front tyres (245 if it fits)

Have you tried setting the front arb a bit softer and the rear a bit harder (rear in the middle I guess)?
I always thought that the z4 mostly needed stiffening the rear arb (from a stock pov) and you even have less weight in the nose than I have.

That thing about the powerflex rear camber arms and the inner securing nut is a good one. I'm looking into those myself, but this is something I hadnt thought about. Do you already have the complete arms installed or just a bushing? (I dont fully understand what you said with "I've replaced the lower control arm outer bush with Powerflex")

 

[Steve84N]

Just replaced the bush where the standard adjustments are made and even though the old ones weren't visually bad there was clearly still some play in them.
http://www.powerflexsuspensionbushes.co.uk/powerflex-bmw-z4-e85--e86-rear-lower-arm-outer-bush-pfr5-4618-39943-p.asp

Thanks for your thoughts on castor. Powerflex used to sell an offset bush with a purple poly outer but now they only sell one which is twice the price with an aluminium outer, maybe they had problems. I've already got the standard Powerflex lollipop which is a purple outer.
https://www.powerflex.co.uk/road-series/product-details/Front+Wishbone+Rear+Bush,+Caster+Offset/11515.html

I will revisit the ARBs if the offset bushes don't work but I felt like I found a good balance before I lowered the car with the front on hard and the rear on middle. The rear doesn't like to be on hard with standard droplinks as they are at quite an angle, I couldn't even get them into the softest holes. I may be wrong about the balance as it was on original suspension but I'm loathe to reduce grip one end to get the balance I want if I can get it by increasing grip.

 

[GuidoK]

Thanks for your thoughts on castor. Powerflex used to sell an offset bush with a purple poly outer but now they only sell one which is twice the price with an aluminium outer, maybe they had problems. I've already got the standard Powerflex lollipop which is a purple outer.
https://www.powerflex.co.uk/road-series/product-details/Front+Wishbone+Rear+Bush,+Caster+Offset/11515.html

Are you sure about that poly outer offset bushing?
I havent seen that and I think its also impossible.
The offset bushing has to be pressed in because of the offset. You cant do that with a 100% poly bushing. All offset poly bushings for that spot have some sort of metal outer shell to facilitate press fit.

The stock powerflex lollipop has a purple inner (and black shore95a outer)

Here I have a spreadsheet with schematics for polybush options for the z4 chassis:

https://audio.home.xs4all.nl/zooi/z4/bussen/xls/
(but the latest powerflex rear camber arms and bushings arent put in there yet, have to make a new version.)

 

[Steve84N]

We're both wrong...

The bush I saw is for a Z3 but it most definitely is purple outer and aluminium inner. I had to press the non-offset version in and it worked just fine. It is indeed black outer, my mistake.

http://www.hackengineering.co.uk/product/powerflex-front-wishbone-rear-bushes-eccentric-e30e36-inc-m3/