Stiff Front Sway Bar Thoughts

Hotrodz

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littlejuanito

Seems that the general consensus on running a stiffer front bar is that it will induce understeer but, why is the 370z the exception and more bar is preferred?

Can someone explain that to me. thanks.

Hotrodz

It not to complicated...most cars these day are setup to understeer because when the average Joe or Jane make a mistake and takes a turn to hot the correction to it is hit the brakes. The Z is no different and do to having a staggered tire and wheel setup it is more exaggerated. The increased rubber, traction and power of the rear wheel will overcome the grip of the front wheels and tires. Have more front bar helps combat that condition. This why many, me included run square at the track and still have the biggest bar available up front.

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littlejuanito

This is precisely where I'm confused

Wouldn't this situation cause understeer and having a stiffer bar induce even MORE understeer?

Not saying you guys are wrong, just wanna know why is this different in the Z?

Hotrodz

No...think NASCAR! The setup causes the car to push because there is not enough grip in the front to hold the car in place so even though the wheels are turned the car goes straight. Oversteer occurs when the front of the car turns (has more grip or resistance) and the rear rotates around do to the loss of traction in the rear.

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littlejuanito

Great. Thanks Hotrodz

MaysEffect

The Z is not the only exception. Almost every car with a greater front weight bias has a larger front bar. The wrong information has been spread over the past decade that the rear bar should be enlarged for a plethora of wrong reasons. In reality the only reason the bars should be increased is if you have a significant increase in torque or increase in weight and or spring rate.

Most cars understeer from either having too much weight on the nose, or not enough at speed, this is why a 50/50 weight balance is ideal or slightly rearward (48f/52r). Under braking and lateral forces, weight shifts forward and outward increasing load on the front tires. Too much load and you overload the tires and lose traction, too little and the tires won't grip. This balancing act is the most critical aspect of design.

The Z has more weight on the front axle, no where near the levels of a Subaru or VW. But combined with smaller tires, you get a loss of traction from tire overload. There isn't anything funky about the suspension design or alignment that would cause additional understeer.

Increasing sway bar size is rather compromising unless you're increasing the spring rate or the amount of lateral load (increased g forces from bigger, stickier tires). Adding a larger bar with the same factory tires will just increase the load on the outter tire and reduce the contact patch on the inner tire. This is no bueno, thus the plethora of complaints of understeer.

Adding a larger front bar will reduce roll as intended with increased lateral load or additional weight (downforce). Increasing the rear bar causes a cross weighting effect that will transfer additional load to the inner front wheel, sharpening steering response and tire grip. The downside being increased instability and increased load on the outter rear tire. The trade offs are vast if you aren't actually increasing tire grip and load capacity.

Hotrodz

Lol I was just trying to keep it simple. It is basic physics, weight, friction, force and power. Force=momentum and power=acceleration. I got a C in physics by the way so I'm no rocket scientist lol!

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cloudofevil

It also has to do with camber curve. If the camber curve can't keep up with the body roll then you need to reduce body roll. Plus excessive bodyroll is just harder to control.

MaysEffect

This is taken into consideration from factory. Thus the oem alignment specifications. Things start to change when you decrease or increase tire grip, IE larger tires, grippier' tires.

Reducing body roll in the form of a stiffer sway bar doesn't reduce camber curve however, in some cases of high load you may be increasing it. You will need to combine this with a higher spring rate to combat compression across the axle. Neither is a great option unless you increase tire traction and tire load.

and the melting pot of tuning begins

cloudofevil

Right, it reduces how far through the camber curve the suspension travels. Enough body roll and camber starts to increase.

MaysEffect

Agreed, but if you use a stiffer sway bar alone you are increasing the load on the outer tire. This is no better of a solution then allowing a higher level of camber gain, certainly if you already have a small amount of static camber (-1.5 degrees or less).

The tire sidewall is going to start to roll over more with the increased load and then you still end up sliding more. Most sway bars on the market increase the roll stiffness by over 20%, in some cases as much as 100%. This is most likely greater than going up a spring rate compared to the oem springs. At this point its really up to the driver how they manage tire heat. with increased roll stiffness you will be heating the outer tire significantly more.

cloudofevil

But not necessarily in proportion. Which is way adding a stiffer sway bar to the front of certain vehicles like the Z and M3 is a good solution to reduce understeer.

MaysEffect

Ok, but how much stiffer? 25% stiffer? 75%?

It's directly proportional to how stiff the bar is compared to the spring rate and corner weight. Its all guess work unless the manufacturer of the asb states exactly how much force it takes to bend the bar, which absolutely no one does. At max, some companies may give you a percentage compared to oem. If you get a bar that has a greater resistance to bending than the spring rate, you may end up exerting too much force on the tires. This again goes back to the level of grip the tires can make. You may reduce the sensation of roll, but this doesn't garranty more grip. Where it may give an increased level of force to overcome traction loss, you run the risk of overloading the tire at the limit and having a sudden loss of traction when the tire lets go, compared to a gradual loss of traction. I personally wouldn't do this change alone unless i have a tire that can support a higher load rating. Presumably double that of the corner weight.

But i think we all can agree, the first modification to ever be done is tires. Only then should you decide to change the ASB and/or spring rate.

cloudofevil

Sorry I meant the benefit of staying lower in the camber curve and the detriment of increasing the outside tire load are not necessarily in proportion. I think in the case of the Z it's better to increase the front roll rate even with the increase in lateral load transfer across the front axle. And yes, tires are the most important upgrade.