Sway Bars for the E9x M3???

[JAJ]

Originally Posted by enigma

Very wrong. The cars CG determines the amout of weight transfer. All the bars and springs do is determine how much that makes the car lean. You can also use a sway bars to change the ratio of roll stiffness front to rear to induce or reduce understeer or oversteer.

Very right, actually.

The reason that putting a bigger bar at the front induces understeer is that it reduces front-end grip. A bigger bar at the rear induces oversteer because it reduces rear-end grip.

Despite the evidence, you want us to believe that bigger bars at both ends doesn't reduce overall grip?

What am I missing?

[enigma]

Originally Posted by JAJ

Very right, actually.

The reason that putting a bigger bar at the front induces understeer is that it reduces front-end grip. A bigger bar at the rear induces oversteer because it reduces rear-end grip.

Despite the evidence, you want us to believe that bigger bars at both ends doesn't reduce overall grip?

What am I missing?

Putting a bar on just one end of the car reduces grip at that end but increases grip at the other end. That of course ignores the effects on the cars camber curve which is usuallly favorible.

But if you put bars on both ends and just reduce the roll of the car and don't change the front/rear roll stiffness you don't change the ballance of the car at all, and you don't decrease the grip at either end.

If your theory was right, you could just take both sway bars off and have more grip, right?

[ace996]

Certain cars, especially those with MacStruts, benefit from stiffer sways in the front due to controlled camber-curves. I'm not so sure about the M, but my STI would keep more of it's negative camber by not leaning/compressing at turn-in and in-corner. The stiffer the bar...the more grip. Even if the ultimate grip is the same, the quicker transitional behavior and reaction of stiffer bars provide a better feel for performance driving.

Be good,
TomK

[JAJ]

Originally Posted by enigma

Putting a bar on just one end of the car reduces grip at that end but increases grip at the other end. That of course ignores the effects on the cars camber curve which is usuallly favorible.

But if you put bars on both ends and just reduce the roll of the car and don't change the front/rear roll stiffness you don't change the ballance of the car at all, and you don't decrease the grip at either end.

If your theory was right, you could just take both sway bars off and have more grip, right?

All of the effects, the movement of the CG off the centerline with roll and the camber curve of the suspension geometry, are second-order effects. As the car rolls, the CG moves away from the C/L. That transfers additional weight to the outside tire. Stiffer springs reduce roll and transfer less. Swaybars don't transfer less, they just roll less - a "stealth" reduction in performance.

The M3 suspension is all about travel and camber control - three track days and my tires are wearing evenly, even without any additional camber over stock. Very unusual.

The handling prescription, based on computer modeling for my E39 M5 was smaller bars and bigger springs to control weight transfer. I switched cars instead.

[enigma]

Originally Posted by JAJ

As the car rolls, the CG moves away from the C/L. That transfers additional weight to the outside tire. Stiffer springs reduce roll and transfer less. Swaybars don't transfer less, they just roll less - a "stealth" reduction in performance.

I think you would find both transfer exactly the same. For any given roll and CG position you know the weight transfer inside to outside. Asuming steady state.

Bottom line is the only way to keep a car from rolling is to transfer enough weight to offset the location of the CG. How you transfer it, springs, bars, magnets, air bags, ... doesn't really matter.