[Javi335]

Vendors will love this thread.

Watch and discuss. Better withouts sways bars?

[CJ421]

What he's saying may be true for Miatas but it's a different world for BMW. Stiffening the front suspension reduces the car's tendency to understeeer at the limit. There is zero benefit to having the front of our cars roll; roll cannot make the car turn faster. All the front needs to do is transfer weight.

The rear axle is different however; adding a sway bar back there generally reduces grip. I've observed a pencil thin rear sway bar on every BMW race car I've been under - pretty much insignificant in other words. The rear needs flex to allow the tires to maintain proper contact with the road e.g. be able to get power down. Rear flex is especially important for our non-M cars lacking a limited-slip differential.
Regardless whether you have an LSD or not, it makes little sense to stiffen the rear sway bar much if at all; if you want to rotate the rear with an RWD car, you don't need a stiff sway bar to do it - step on the gas. Front wheel drive cars can't do that, hence they add stiffer rear sways. Verdict: there should be a rear sway bar in our cars, just not an overly powerful one; the stock one or the M3 one at most.

My lack of an automotive engineering degree prevents me from being more technical. This is just how it is for our cars.

[ajsalida]

Well the key difference is Miatas have double wishbone front suspensions, BMW's have McPherson struts. Double wishbone is a superior design as far as keep tire vertical under large suspension movements. Mcp strut can't do that, only one hinge basically.

Other point is Miatas are super light cars (2200 lbs not unusual track prepped) and loading up a modern tire with weight helps up to a point. Consider also a 220 lb guy like me is 10% the weight of a Miata, to be that much of my 335xi I'd need to weigh like 375 lbs. Imagine trying to get outside right corner to hook up on a left turn like that, you'd want some roll.

Owned a Miata as a track car for many years, amazing handling set up correctly. Quite a lot of suspension tweaks on it would make no sense on a BMW. BMW front susp is, not as sophisticated, but that does not mean it is bad, BMW have got about as much as you can get out of McP struts. Rear is different, on modern BMW rear 5-link is state of the art, and can keep the tire aligned quite well under most of the suspension travel, so big bar not so much of a needed thing to keep tire hooked up.

Then you get into things like relative roll stiffness F/R, which is another story entirely.

Anyway, never completely trust a guy who names his cars after people and calls them he or she. Creepy. Esp the Senna one.

[Javi335]

Originally Posted by ajsalida

Anyway, never completely trust a guy who names his cars after people and calls them he or she. Creepy.

I always knew there's something fishy with Vettel ...

Great answers gentlemans thanks.

So, if i dont plan to get on a track with perfect surface, and its no in my plans get a LSD, in your opinion what size of sway bars do you think could be a good option for my 335i? should i keep stock ones? i asked this several times and no answer!

[ajsalida]

Matter of taste and what kind of shocks springs bushings tires etc. you're running presently and what you are trying to fix or achieve. So I would ask you what is it about your current susp that you don't like, and what do you imagine a upgraded version would do better?

FWIW I have wrecked the street handling of more cars than I care to count with big sway bars, frequently took them off after a bit. Really only for track use and maybe curing a factory tune towards too much understeer. Xi's understeer a lot and have other bad handling traits.

So for it a M3 bar (the thinner coupe bar, not conv) was a good choice to tighten up the rear and keep it from plowing like a tractor.

[e90pilot]

Some one explained it to me once and it made sense. It seems ass backwards to stiffen the front to have the car understeer less. However, in a non-M e90 there is so much deflection in the bushings and actual suspension flex that you actually loose camber while the car is cornering. Adding a stiffer front sway bar, m3 components, and a better chassis brace will prevent that form happening. Of course, adding a bar that's too stiff will cause the car to understeer for the reasons stated in the video. Also the heavier and more top heavy a car is, the larger the sway bar needs to be.

[CJ421]

Originally Posted by e90pilot

Some one explained it to me once and it made sense. It seems ass backwards to stiffen the front to have the car understeer less. However, in a non-M e90 there is so much deflection in the bushings and actual suspension flex that you actually loose camber while the car is cornering. Adding a stiffer front sway bar, m3 components, and a better chassis brace will prevent that form happening. Of course, adding a bar that's too stiff will cause the car to understeer for the reasons stated in the video. Also the heavier and more top heavy a car is, the larger the sway bar needs to be.

That's a characteristic of a MacPherson strut; the camber curve can go flat or even turn positive under compression. It's yet another reason to have a minimal amount of roll up front. That's why MacPherson strut cars run a lot of static camber - no real hope of gaining any when the suspension compresses.