Sway Bars And Their Effect On Ride Comfort

[nuffsaid]

Hi all

What effect do larger diameter sway bars have on ride comfort?

Now I know that we are all told that they are not supposed to have any effect in the perfect road where it is flat and smooth, and where the bumps occur on each side at the same time, but as you may be aware, most city roads are quite honestly all over the place. You'll get huge bumps and dips that occur only on one side at any point in time.

A good quote "if the wheels try to move independently, as with a single-wheel bump, or in opposite directions when the car rolls then the anti-roll bar resists this tendency. Roll is reduced as intended but comfort suffers as the effective spring rate of each wheel is increased in the individual single-wheel bumps, although the combined spring rate of the two wheels is unchanged over joint disturbances"

I also feel that the harder poly links may stiffen up things.

I am currently using Whiteline 24mm front and 20mm rear sway bars + castor and camber bushes. Springs are reset factory ones, stock shocks. Compared to another R34 GTT with the same springs and shocks but without swaybars/castor/camber bushes, mine seems a little bumpier and uncontrolled. Of course the other car has slightly more roll, but it is much much more like factory plush. (i have gained the granny syndrome and want a nicer riding car now hahaha)

So with these sway bars, what is the effective spring rates?

Thanks

[nuffsaid]

PS: car is a pure daily that occasionally sees some spirited driving. it is a daily on some crap roads haha no track work planned for this vehicle

[salad]

It's very hard to calculate the rate of those swaybars because of all the bends and funny angles. Someone would probably have to work it out experimentally, and then measure the motion ratio to work out the effective wheel rate (spring rate at the wheel).

Anyway, swaybars do add to the wheel rate in single wheel bump (nothing in 2 wheel bump though), but because they work by pushing down on the outside wheel and lifting up on the inside wheel, they resist roll on both wheels. This means that a swaybar can provide the same roll stiffness as springs, but with a lower wheel rate, and hence you feel less discomfort. Although it's better than springs, it still does provide more discomfort than stock.

I would also be looking at your reset springs with stock shocks. You've lessened the travel of the shock, but the spring rate and shock valving is the same. This could mean you're riding the bumpstops causing the discomfort. Wrap a cable tie around your shock shaft and go for a drive, then you can see if you're using up all the travel and riding the bump stops.

[nuffsaid]

Cheers for that salad

Pretty certain it is not bottoming out as I have also trimmed quite a fair bit off the bump stops but will give that a shot.

It's not even really the big hits, but also the small undulations and so forth that feel uncontrolled. Maybe with the higher effective spring rates, the stock shocks just cant control and smooth the rapid movements.

[Sydneykid]

You can't directly compare spring rates and swaybar rates, the chassis dynamics are very different. Salad covered the 2 wheel versus 1 wheel scenario, but there are other considerations. The swaybar tries to duplicate what is happening to the wheel in recoil (from the bump) with the wheel that isn't. Plus the bar acts directly through the chassis mountings in the reverse direction. These actions and reactions cancel each other out to some extent. Compared to the single spring impact with has a simple pass on effect on that one wheel only.

The term "reset springs" always worries me, it's a complex process and very hit and miss regardless of the experience and quality of the resetter.

Polyurethane bushes add slightly to the "vibration" item in NVH, particularly link bushes. Since you have most likely only changed the D bushes, the effect is miniscule as the bar rotates freely, hence passing on very little of the impact directly to the chassis.

My guess would be that the standard shocks simply don't have the damping capacity to control the increased anti roll, let alone the reset springs. They didn't have it when they were new, so they sure as hell don't have it now.

A Skyline is a sports car, it suspensions system was designed with that in mind. They aren't a limosine and never will be, no matter what you do to their suspension the basic design criteria will always win out.

Cheers

Gary

[nuffsaid]

Thanks Gary

Ill switch out the sway bars and report back on the difference.

Anyone else have a similar experience before I attempt to put the stockers back on?

[Sydneykid]

Most people don't notice any difference in ride comfort with such small increases in swaybar sizes on a relatively heavy car. It's not until we start using 30 mm bars on light weight cars that come standard with 14 mm bars that we get any ride discussion.

I should mention tyres and to a lesser extent tyre pressure, their effect on ride comfort is often over looked. So it may pay to swap tyres with the car you are comparing.

Cheers

Gary

[Roy]

I am currently running around with std shocks and springs in my car with upgraded swaybars and the ride is pretty sporty. Its not harsh, but you wouldnt think the car has std shocks and springs.

Housemate drove the car and didnt realise i had removed the shocks as he thought it still rode firmly and handled well.

[nuffsaid]

I am currently running around with std shocks and springs in my car with upgraded swaybars and the ride is pretty sporty. Its not harsh, but you wouldnt think the car has std shocks and springs.

Housemate drove the car and didnt realise i had removed the shocks as he thought it still rode firmly and handled well.

Sounds good. care to elaborate Roy? how did is the car different on rough roads?

So there is a noticeable difference, still decent ride but not quite the "no effect" feeling that most people seem to reiterate

[Roy]

The suspension is firmer. It simply feels like there is more spring in the car. But not surprised considering the std stuff i have at the moment is out of a friends 210,000km car.

[nuffsaid]

Okay removed the Whiteline 24mm front and 20mm rear sway bar.

Obviously some more body roll, and less direct steering feedback.

However oddly, there is DRAMATICALLY much more comfort. So when someone says sway bars have next to no affect on comfort, I'd tend to disagree now. On rough roads, there is a significant improvement, and on the smoother ones, its better also.

Strangely even on speed humps when the 2 wheels land together, it seems to be a softer hit than with the bars on.

Learn something new everyday aye.

[Hargow]

Okay removed the Whiteline 24mm front and 20mm rear sway bar.

Obviously some more body roll, and less direct steering feedback.

However oddly, there is DRAMATICALLY much more comfort. So when someone says sway bars have next to no affect on comfort, I'd tend to disagree now. On rough roads, there is a significant improvement, and on the smoother ones, its better also.

Strangely even on speed humps when the 2 wheels land together, it seems to be a softer hit than with the bars on.

Learn something new everyday aye.

Hey Danny i'll take those sway bars off you if you don't want?? LOL

[nuffsaid]

Haha keeping them for now sorry, just in case the car becomes less of a daily and more of a dedicated weekend type car.

[MrStabby]

However oddly, there is DRAMATICALLY much more comfort. So when someone says sway bars have next to no affect on comfort, I'd tend to disagree now. On rough roads, there is a significant improvement, and on the smoother ones, its better also.

As SK stated, this might be evidence that your shocks are not up to the job, or more generally that the sway bars are intended for use with uprated suspension. I didnt notice any difference when i installed mine, but then again the Tein suspension i have is rock hard (spring rate and damping) already...

Strangely even on speed humps when the 2 wheels land together, it seems to be a softer hit than with the bars on.

That doesnt make much sense. Were the bushes properly greased? If the bar binds in the bushes it stops it working properly.

[nuffsaid]

Good point, on stock suspension maybe its more noticeable. As an overall package with some shocks+springs the effect may be less.

Bushes were fine, I wouldnt expect a lack of grease to cause resistance in the movement of the bar against the bush though, itll just be noisier.

PS: it is all by the 'seat of pants' feel which is quite different for everyone. Some people will think there is no difference