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Rear Sway Bar


Riceburner

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Wondering what people's thoughts are on this bar setup from T3. I'm trying to decide if I go for stiffer springs or I keep the current springs and go for a larger adjustable rear sway bar. Rear springs are in the 180-220lb region, rather than upgrade to 300lb springs will the the rear bar below give me a similar stiffness but with the added benefit of adjustability? Front end has 340lb springs and a 25mm sway bar.

 

Didn't the bob sharp and BRE cars run soft springs and huge sway bars?

 

https://technotoytuning.com/nissan/240z/techno-toy-tuning-rear-swaybar-z

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I'm a heavy springs, heavy front sway bar, no rear bar person for a powerful car with a Torsen type LSD. My reasoning is that the rear tyres have enough to do with putting down power without putting much extra load on them cornering while the front just has to steer. Works for me.

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Gareth. Here is a synopsis.

 

CARROLL SMITH’S CAUSE AND EFFECT GUIDE

RIDE AND ROLL RESISTANCE-SPRING

Too much spring: overall
• Harsh and choppy ride
• Much unprovoked sliding
• Car will not put power down on corner exit – excessive wheel-spin

Relatively too much spring: front
• Understeer – although the car may initially point in well
• Front breaks loose over bumps in corners
• Front tyres lock while braking over bumps

Relatively too much spring: rear
• Oversteer immediately on application of power
• Excessive wheel-spin

Too little spring: overall
• Car contacts the track a lot
• Floating ride with excess vertical chassis movement, pitch and roll
• Sloppy and inconsistent response
• Car slow to take a set – may take more than one

Relatively too little spring: rear
• Excessive squat on acceleration accompanied by excessive rear negative camber, leading to oversteer and poor power down characteristics
• Tendency to fall over on outside rear tyre and ‘flop’ into oversteer and wheel-spin

ANTI-ROLL BARS

Too much anti-roll bar: overall
• Car will be very sudden in response and will have little feel
• Car will tend to slide or skate rather than taking a set – especially in slow and medium speed corners
• Car may dart over one wheel or diagonal bumps

Relatively too much anti-roll bar: front
• Corner entry understeer which usually becomes progressively worse as the driver tries to tighten the corner radius.

Relatively too much anti-roll bar: rear
• If the imbalance is extreme can cause corner entry oversteer
• Corner exit oversteer. Car won’t put down power but goes directly to oversteer due to inside wheel-spin
• Excessive sliding on corner exit
• Car has a violent reaction to major bumps and may be upset by ‘FIA’ kerbs

Too little anti-roll bar: overall
• Car is lazy in response, generally sloppy
• Car is reluctant to change direction in chicane and esses

Relatively too little anti-roll bar: front
• Car ‘falls over’ onto outside tyre on corner entry and then washes out into understeer
• Car is lazy in direction changes

Relatively too little anti-roll: rear
• My own opinion is that on most road courses a rear anti-roll bar is a bad thing. Anti-roll bars transfer lateral load from the unladen tyre to the laden tyre – exactly what we don’t want at the rear. I would much rather use enough spring to support the rear of the car. The exception comes when there are ‘washboard ripples’ at corner exits, as on street circuits and poorly paved road circuits.

SHOCK ABSORBER FORCES

Too much shock: overall
• A very sudden car with harsh ride qualities, much sliding and wheel patter
• Car will not absorb road surface irregularities but crashes over them

Too much rebound force
• Wheels do not return quickly to road surface after displacement. Inside wheel in a corner may be pulled off the road by the damper while still loaded
• Car may ‘jack down’ over bumps or in long corners causing a loss of tyre compliance. Car does not power down well at exit of corners when road surface is not extremely smooth

Too much bump force: general
• Harsh reaction to road surface irregularities.
• Car slides rather than sticking
• Car doesn’t put power down well - driving wheels hop.

Too much low piston speed bump force
• Car’s reaction to steering input too sudden
• Car’s reaction to lateral and longitudinal load transfer too harsh

Too much high piston speed bump force
• Car’s reaction to minor road surface irregularities too harsh – tyres hop over ‘chatter bumps’ and ripples in braking areas and corner exits.

Too little shock: overall
• Car floats a lot (the Cadillac ride syndrome) and oscillates after bumps
• Car dives and squats a lot
• Car rolls quickly in response to lateral acceleration and may tend to ‘fall over’ onto the outside front tyre during corner entry and outside rear tyre on corner exit.
• Car is generally sloppy and unresponsive

Too little rebound force: overall
• Car floats – oscillates after bumps (the Cadillac ride syndrome)

Too little bump force: overall
• Initial turn in reaction soft and sloppy
• Excessive and quick roll, dive and squat

Too little low piston speed bump force
• Car is generally imprecise and sloppy in response to lateral (and, to a lesser extent longitudinal) accelerations and to driver steering inputs

Too little high piston speed bump force
• Suspension may bottom over the largest bumps on the track resulting in momentary loss of tyre contact and excessive instantaneous loads on suspension and chassis

Dead shock on one corner
• A dead shock is surprisingly difficult for a driver to identify and/or isolate
• At the rear, that car will ‘fall over’ onto the outside tyre and oversteer in one direction only
• At the front, the car will ‘fall over’ onto the outside tyre on corner entry and then understeer.

WHEEL ALIGNMENT

Front toe-in: too much
• Car darts over bumps, under heavy braking and during corner entry – is generally unstable
• Car won’t point into corners, or if extreme. May point in very quickly and then dart and wash out

Front toe-out: too much
• Car wanders under heavy braking and may be somewhat unstable in a straight line, especially in response to single wheel or diagonal bumps and/or wind gusts
• Car may point into corners and then refuse to take a set
• If extreme will cause understeer tyre drag in long corners

Rear toe-in: too little
• Power on oversteer during corner exit

Rear toe-in: too much
• Rear feels light and unstable during corner entry. Car slides through corners rather than rolling freely

Rear toe-our: any
• Power oversteer during corner exit and (maybe) in a straight line
• Straight line instability

Front wheel caster or trail: too little
• Car too sensitive (twitchy?)
• Too little steering feel and feedback

Front wheel caster or trail: too much
• Excessive physical steering effort accompanied by too much self return action and transmittal of road shocks to the drivers hands
• General lack of sensitivity to steering input due to excessive force required

Front wheel caster or trail: uneven
• Steering effort is harder in one direction than in the other
• Car will ‘pull’ towards the side with less caster – good on ovals, bad on road courses

Camber: too much negative
• Inside of tyre excessively hot and/or wearing too rapidly. At the front this will show up as reduced braking capability and at the rear as reduced acceleration capability. Depending on the racetrack and the characteristics of the individual tyre, inside temperature should be 10°-25° hotter than the outside. Use a real pyrometer with a needle rather than an infra red surface temperature device.

Camber: not enough negative
• Outside of tyre will be hot and wearing. This should never be and is almost always caused by running static positive camber at the rear in an effort to avoid the generation of excessive negative camber under the influence of aero download at high speed.
• A better solution is improved geometry and increased spring rate. Dynamic positive camber will always degrade rear tyre performance and if extreme, can cause braking instability and/or corner exit oversteer.

Bump steer, front: too much toe-in in bump
• Car darts over bumps and understeers on corner entry

Bump steer, front: too much toe-out in bump
• Car wanders under brakes and may dart over one wheel or diagonal bumps 
• Car may understeer after initial turn in

Bump steer, rear: too much toe-in in bump (same as solid axle steer on outside wheel)
• Roll understeer on corner entry
• Mid phase corner understeer
• ‘Tiptoe’ instability when trail braking
• Darting on power application on corner exit

Bump steer, rear: too much toe-out in bump (same as solid axle steer on outside wheel)
• Instability on acceleration
• Good turn in followed by a tendency to oversteer at mid-phase and exit

TYRES

Too much tyre pressure
• Harsh ride, excessive wheel patter, sliding and wheel-spin
• High temperature reading and wear at the centre of the tyre

Too little tyre pressure
• Soft and mushy response
• Reduced footprint area and reduced traction
• High temperatures with a dip in the centre of the tread

Front tyres ‘going off’
• Gradually increasing understeer – Enter corners slower, get on power earlier with less steering lock

Rear tyres ‘going off’
• Gradually increasing power on oversteer – Try to carry more speed through corner and be later and more gradual with power application

LIMITED SLIP MALADIES

Limited slip differential wearing out
• Initial symptoms are decreased power on understeer or increased power on oversteer and inside wheel spin. The car might be easier to drive, but it will be slow
• When wear becomes extreme, stability under hard acceleration from low speed will diminish and things will not be pleasant at all

Excessive cam or ramp angle on coast side plate (clutch pack) limited slip differential
• Corner entry, mid-phase and corner exit understeer. Incurable with geometry changes or rates – must change differential ramps. In 1998, virtually everyone is running 0/0 or 80/80 ramps.

SUSPENSION GEOMETRY

Excessive front scrub radius (steering offset)
• Excessive steering effort accompanied by imprecise and inconsistent ‘feel’ and feedback

Excessive roll centre lateral envelope: front or rear
• Non-linear response and feel to steering input and lateral ‘G’ (side force) generation

Rear roll centre too low (or front r/c relatively too high)
• Roll axis too far out of parallel with mass centroid axis, leading to non-linear generation of lateral load transfer and chassis roll as well as the generation of excessive front jacking force.
• Tendency will be towards understeer

Rear roll centre too high (or front r/c relatively too low)
• Opposite of above, tending towards excessive jacking at the rear and oversteer

Front track width too narrow relative to rear
• Car tends to ‘trip over its front feet’ during slow and medium speed corner entry, evidenced by lots of understeer (remember trying to turn your tricycle?)
• Crutch is to increase front ride rate and roll resistance and increase the camber curves in the direction of more negative camber in bump (usually by raising the front roll centre)

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All good info thanks chaps! I searched for Carroll Smith and came across that quote on performance forum.

 

The way I read through his definitions it sounds like I should be going for stiffer springs and leave sway bars out of it. I have mostly adjustable links on the suspension so camber, castor, toe front and rear is all manageable. The rear springs are just king spring lows, I thought they were 220lb but now I have read they are less. I guess the next step is to go for a custom rate.

 

What do you guys think of something in the 250/275lb range? I have bilstein shocks to go in the rear too.

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Gareth I had my front King lows KDFL08 springs measured at my suspension shop and they were actually 155 and 160 lb/in. From memory King advertise them as 200 lb/in.

I personally don't have much faith in their specs.

I am currently running the Kings with a 24mm sway bar up front and kings with no sway bar at the rear. It is great for the road but boat like on the track with a little understeer mid corner on the slow corners.

 

What spring rate are you running at the front? Are you thinking coil overs?

Don't want to go too stiff at the rear if the front is soft.

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Great topic guys. So much to say, but hey, you have to try it, test it and feel it. You can't manufacture a car set up on the forum. You can get ideas, but that's all they are. Guys will give you there set up, but don't drive on the tracks your going to drive on. Carrol Smith talks about bumps in corners, but has he driven a zed at PI lately . Theres way to many variables. Your driving style is different to others .you could be fast in and slow out. Or slow in and fast out. You might like a little over steer or perhaps under steer.

It's never ending . The pursuit of the fastest lap, and the best set up.

My advice is to get your ball park set up. Try it. And then change your set up one thing at a time and log book the changers. Some things make a big difference and some things don't do much at all.

Good luck Gareth. When you find the perfect setup let me know. Cheers.

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Gareth, why do you think you need a rear sway bar,and, a stiffer rear sway bar?

 

When racing, i ran a standard rear bar, and a thicker front bar, and would adjust the stiffness on front, by moving the drop links fore/aft,

The rear, by simply backing off the nylock nuts, it would reduce prpensity to oversteer, and also allow the car to "flop over" before bar started to work, ( good for wet tracks)

Spring were 250-275 front, 225-250 rear, a stiffer front, say 300-325 would have been preferable, as the front bars drop links could have been backed off a bit more if needed.

 

We cant easily fit blade adjusters to the bars in a Z, unless its custom fabricated, but unless you are after the nth degree, why would you need them?

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Gareth I had my front King lows KDFL08 springs measured at my suspension shop and they were actually 155 and 160 lb/in. From memory King advertise them as 200 lb/in.

I personally don't have much faith in their specs.

I am currently running the Kings with a 24mm sway bar up front and kings with no sway bar at the rear. It is great for the road but boat like on the track with a little understeer mid corner on the slow corners.

What spring rate are you running at the front? Are you thinking coil overs?

Don't want to go too stiff at the rear if the front is soft.

Interesting, I'd read they were around 180lbs. That's a massive front rear split for me 340lb front, 150/160 rear Mine seems ok on track, but looking at other in car vids I seem to have a fair bit push and from my steering inputs some understeer.

 

Great topic guys. So much to say, but hey, you have to try it, test it and feel it. You can't manufacture a car set up on the forum. You can get ideas, but that's all they are. Guys will give you there set up, but don't drive on the tracks your going to drive on. Carrol Smith talks about bumps in corners, but has he driven a zed at PI lately . Theres way to many variables. Your driving style is different to others .you could be fast in and slow out. Or slow in and fast out. You might like a little over steer or perhaps under steer.

It's never ending . The pursuit of the fastest lap, and the best set up.

My advice is to get your ball park set up. Try it. And then change your set up one thing at a time and log book the changers. Some things make a big difference and some things don't do much at all.

Good luck Gareth. When you find the perfect setup let me know. Cheers.

It's the tight arse coming out in me, I was hoping some keyboard racing might help get a better setup before I race again next decade. Lol! Time and budget mean racing could be a while off and I was thinking the adjustable sway bar might allow me to cheat a little and not have to buy/try several sets of springs before finding the right stiffness.

 

Gareth, why do you think you need a rear sway bar,and, a stiffer rear sway bar?

When racing, i ran a standard rear bar, and a thicker front bar, and would adjust the stiffness on front, by moving the drop links fore/aft,

The rear, by simply backing off the nylock nuts, it would reduce prpensity to oversteer, and also allow the car to "flop over" before bar started to work, ( good for wet tracks)

Spring were 250-275 front, 225-250 rear, a stiffer front, say 300-325 would have been preferable, as the front bars drop links could have been backed off a bit more if needed.

We cant easily fit blade adjusters to the bars in a Z, unless its custom fabricated, but unless you are after the nth degree, why would you need them?

Was your front bar the adjustable type? It seems I'm way too soft in the rear and the front rear split is too big. From most of the Australian Z track car videos I have seen everyone looks to have a lot less steering input through the corners and I have shortened steering arms. My initial turn in is fine, minimal and direct but as I progress through the corner it looks as though I increase steering all the way until the very exit. I guess as Gordo says that could just be my driving style and the Torsen diff might be causing the push.

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