I don't like electric assist stearing.

Correct me if I'm wrong, but I recall that Mercedes held out even longer.

Considering what he says: Yes, increasing the size of both the front and rear roll bars (aka stabilizer bars, sway bars, etc.) will reduce body lean. However it will not improve understeer unless the rear sway bar is increased more than the front.

No, I'm sorry you are just wrong. Regardless of how you "select" them, if you increase the stiffness of the front sway bar you will increase the amount of understeer. If you decrease the stiffness of the rear sway bar you will increase the understeer. If you do both you will

You have it exactly backwards to what you want to do. For what you want (decrease understeer or introduce oversteer) you need to stiffen the rear and/or soften the front.

You are comparing tangerines and kumquats. The mini is a super-light front wheel drive car. It is a veritable go-cart compared to the Z4. The Z4 will NEVER handle like a mini.

Um, yes, actually you do intend to use them incorrectly. Exactly incorrectly to be precise.

Exactly. So the premium option (after first ditching the bling-bling staggered tire setup) is to increase the rear stabilizer bar. That way you can dcrease understeer *and* reduce body roll at the same time!!

I do not think that last statement is correct. An adjustable bar allows you to tweak the tension from side to side on the same axle. It does not allow you to change the tension from front to rear because a) the bars are not tied together and b) nor are they fixed in position like a torsion bar (spring). The sway bar pivots in its bushings if the 2 wheels on that axle travel up and down together. It only applies cross force when one wheel moves up or down compared to the other wheel on that axle.

More like; They wanted to jam a big V8 lump in the engine compartment and couldn't manage to fit a steering rack in there too. A RB steering box is tiny by comparison and the tie rods, arms and links can be made to go all over the place to clear the engine.

An surprisingly, the RB in my 540 works quite well. Very crisp steering, handles like a dream. Not as crisp or nimble as my M3, but you wouldn't expect it to be.

All over the place describes the steering response, too.

Strangely I've got another make not dissimilar in size to a 5 Series which was also available with 4, 6 and eight cylinder engines. Diesel too. But with R&P steering and designed in the '70s. I'm not quite sure what there is about a small V-8 that would make fitting R&P steering any more difficult than with a six.

Albeit on a non-BMW, I added a larger front anti-roll bar and it reduced the understeer. The body roll had been causing the front end's geometry to become less than optimum and the new bar kept more tyre in contact with the road. Whether that would work with the Z4 I dunno but the "bigger fronts always cause more understeer" folk should probably add an "in general" in there somewhere.

If I were the OP I'd be putting on some Eibachs and new dampers. BMW suspension isn't always great from the factory for ride or handling. I did that on my E36 and coupled with decent tyres would out corner pretty much anything out there including my M3 and certainly any Mini.

Think about the end effect. If you reduce the roll stiffness at the front through either replacement or adjustment of the front bar, you will decrease understeer. If you increase the roll stiffness at the rear you will also decrease understeer. But if you increase or decrease them both in proportion it will not change the balance of the car. It's the proportioning between the front and rear roll stiffness you're trying to manage, right? So if one installs stiffer bars front and rear and wants to decrease understeer, one must stiffen the rear one more than the front one...in other words the front has to be relatively softer than the rear at the end of the change.

JRE

Whatever. I will turn it over to the engineers/technicians and tell them what I want to do.

Never said it would but I bet the suspension could be tuned to approach the handling of the stock Mini. I merely pointed out the Mini's suspension is more to the neutral side of balance than the Z4 and as a result will handle better than the Z.

Evidently I incorrectly assumed a larger roll bar would be stiffer than a smaller one.

When I still had the runflats on my Z4, I kept up with three well-driven Minis down the Tail of the Dragon (US 129 in western NC). While it gave me new respect for what can be done with FWD, I had no complaints about the Z4's steering, handling or the 050 tires. However, my wife requested that I do it solo the next time!

Tom K.

You'd be best to tell them what you *want* rather than what to do otherwise you'll end up with even more understeer and a ride like a truck.

Not to worry. I will tell them "I know Dave!!!!" and my problems will be solved (or they will be bored to death). ;>)

ADJUSTABLE antiroll bars. Not all bars *are* adjustable. In fact, most AREN'T. You simply stated that you were putting on a much larger one in front and a somewhat larger one in the rear. The net effect of doing this with NONADJUSTABLE bars is to enhance understeer. You MAY be able to adjust the relative balance of this with adjustable bars - and that's what Dinan is selling. Are you comfortable with crawling under your car to make those adjustments while testing or are you going to have to haul it back to a tech to do it every time?

You still haven't presented the engineers with that list, have you? Why not? Afraid to discover we aren't all idiots here?

In the right circumstances, the right bars can help. But simply slapping on a set without the slightest clue of how they work or what effect they will have is a foolish waste of money. You will ultimately end up with an ill-handling pig and a lot lighter wallet. If you're going to buy Dinan's stuff, you'd better plan on buying ALL OF IT. You aren't yet educated enough to get a satisfactory result doing it piecemeal. You would do well to avail yourself of your local BMW CCA chapter's experts to fill in your knowledge gaps.

-- C.R. Krieger