BIGGER swaybars for a Q?

[elwesso]

This past week when I was at NOPI I was talking to the 240 guys about how they have bigger swaybars for their cars... They come with like a 28mm front and 20mm rear bar or something like that, similar to what the Q comes with...

As we know, the front bar is 1.4 times bigger than the rear bar (28mm/20mm=1.4)....

What would happen if we had a set of sway bars that were a little bigger.... Using the same proportion, we could run something like a 26mm rear bar and 36mm front bar.......

I remember tech saying that you dont want sway bar stiffness to exceed the spring stiffness..........

[ddrumman]

......As we know, the front bar is 1.4 times bigger than the rear bar (28mm/20mm=1.4)....

What would happen if we had a set of sway bars that were a little bigger.... Using the same proportion, we could run something like a 26mm rear bar and 36mm front bar.......

I remember tech saying that you dont want sway bar stiffness to exceed the spring stiffness..........

Maybe we can find the 24mm Stillens and just have the fronts that would be 33.6mm custom made.

Here's some older "tech" info on sway bars and body stiffness +.....

I got it from the archives. It was all crunched up and I tried to break it up a little so it's easier to read.

We have tried every combo on customer’s cars and my own.

You must visualize roll stiffness and get away from absolute values.

The Q is 55/45 weight distribution empty. This is far from ideal, the extra 200 lbs. means front springs must be a 5% stiffer and the rear 5% weaker for it to sit level. To avoid a pitching movement on the highway the rears are actually about 18% weaker so the rear bobs up and down at a very slow rate as this generates the lux ride most people are used to.

The 29mm [170 lb./in] front bar and 166 lb./in front springs vs. just 122 lb./in rear springs means that over 75% of the roll resistance is in the front so the rear rolls 3" for every 1" the front does. A 20 mm rear bar acts like a 50 lb. spring side to side...so the rear roll acts like 172 lb. springs side to side. The front is still very stiff but the rear redirects some of the roll to the front now but only 50 lbs. more worth which is miniscule to the 330 lb./in front stiffness. A 28 mm bar is 13% less stiff than a 29 mm bar. divide by 2 since the springs and bar were equal before so the front would be 6.5% less stiff and the rear would be 41% stiffer. But his still means rear roll just half as much. A race car might be almost perfectly balanced with 50/50 weight and 52/48 roll stiffness. A 29mm front and a 20 mm rear is close to 66%front vs. 75% with no rear bar. You almost split the difference between...75%factory.....65...... 55%professional racer This is a very safe ratio that won't get you into trouble in rain [with proper tires] because the Q has loads of rear traction except when you accelerate in rain....as you know from experience. Remember you have a viscous limited slip which if not worn out will also help out. 13931 When you add a rear bar you must take the car to a parking lot or track to safely understand what the change does especially in the rain as you are unconsciously aware of what to do with the stock car in an emergency . Up to a point the 20 mm bar will give you added confidence in normal emergency maneuvers but your stock shocks in rear will not be able to control the extra stiffness [they are set for 122lb/in springs not 172lb/in springs and bar in a turn with rapid back and forth movement. It is almost impossible to ride in a car which has the shocks stiff enough to fully control a super [above 22mm] rear bar as they won't move in straight ahead highway driving. The Tokico HP are only 15-20% stiffer than stock [or still 25% less than the 20mm bar needs] and these are noticeable on highway and about all most people will tolerate on a 8 hour trip. When you install the bar please upgrade your rear shocks or at the minimum install brand new factory rears! Remember the Q45A has this 20 mm bar but the shocks are set assuming the bar not so in standard or "t" cars where the 15.9 mm bar is only 20lb/in [barely know it's there so no stiffer shocks are required]. Note even the "t car" will wear rear stock shocks faster due to the bar...so they need replacing about every 50k vs. 60k on a standard Q.

All 90-96 Q have the mounting holes for rear sway bars --the available sizes are 15.9 mm from "t" and 20mm from "a". Whenever a rear bar is fitted the front bar is reduced from 29 to 28 mm. The Stillen solid rear bar is 24 mm and should be considered for racers only due to harsh impact and oversteer in rain!!!!!!

All years "a" have the 28/20mm bar. The 122 lb./in rear stock springs are soft for a lux ride ,the Eibachs are not that much stiffer [15%- 25% progressive] and the addition of the 50lbs resistance of the rear bar helps some but before the front springs consider the 24 mm Stillen bar [for expert drivers only-- much wet snap oversteer] as the extra 100 lbs. will further limit the rear roll. You can use some combination of rubber and the provided urethane to soften the first inch of impact harness but remember the wheel moves four inches for every 1" the bar moves [if rigidly mounted] more wheel movement if rubber is used. The factory supplied 20mm hardware does not allow the bushings to be compressed so there is little happening with the bar until the wheel moves about 2".....you must use metal washers between all the rubber bushing where they touch the bar on end links or replace with urethane/nylon bushings. To avoid deformation of bushing! Same as you did to front bar.

Enjoy!!

[Q45tech]

You cannot compare diameter to diameter [ratios] without noting that the front right angle arms are half [3"]as short as the rear right angle arms [6"]that makes the front twice as stiff as the rear if they were perfectly identical in shape and diameter.

Also the attack slope [the softness of the mounting and coupling system] is different in that the front has only 2 rubber bushing in the endlink plus a semi helm joint [right angle] and the rear has 4 rubber bushings.

The published spring stiffness [found in FSM] is for the springs alone not as mounted...........the actual as mounted springs with seats and offset mounting locations do not give this stiffness to the wheel.............subtract about 10% and correct for soft tire wall stiffness of a 65-60 series on 15" tire.

The real world rear body roll stiffness [without a rear sway bar] is ~~100 pounds per inch and with a 20mm rear bar is ~~ 130>140 pounds with the same tire and inflation [35 psi].

A rear 20mm [hollow] bar is about all the Tokico Blues can control with Eibach lower springs with decent shock life/replacement interval.

Don't be fooled by the Q41 rear sway bar's larger diameter the [longer] right angle arm length [track wisth narrower] and angles are different from the Q45 rear bar.

It does however approximate the 20mm rear [Q45] bar

[elwesso]

As I understand it based on your posts in the past, the shocks/springs are the limiting factor.... If you could somehow upgrade to stiffer springs and stiffer shocks, you could upgrade to a thicker bar in the front and rear...

If that was possible (springs/shocks), would getting a stiffer sway bar in the front and rear really help handling and still make the car somewhat streetable?? I assume if you had a 24-26-28mm rear bar and the appropriate front bar to make the car balanced, it wouldnt ride nearly as smooth as the installed 20mm bar.

[t3lh]

To add to the discussion.In general on a car with close to 50/50 weight dist; You tune a race car with springs and shocks primarily, then add bars.Street cars generally tune with bars first because bars dont add to the general straight line operation spring rate. There for you still get a comfy ride but better cornering.Now I say in general because as you move away from a 50/50 weight or are dealing with a solid rear axle the bars become much more important to the handeling characteristics of the car.

[BadQ45t]

My 84' 300ZX has upgraded bars, Eibach springs and KYB shocks too, but the bars made a huge difference. I think it is 28mm front and 26mm back if I remember, Addco bars, added the final touch to handling. The 84' was 50/50 on the dot for what it was worth.

I have added the Tein springs and KYB SR Specials to my touring Y33 and don't really feel the need for bigger bars.

[Q45tech]

Bars are springs that don't SPRING if going straight ahead, unfortunately the shocks are valved for oem spring stiffness and no consideration was reserved for bar springiness. Afterall the Q was not considered to be curvey pursuit vehicle except in a very rare emergency and then not for long [shock temperature control limits].

The Front effective 76-90 lbs [28mm vs 29mm] per inch [once the 2 bushings are compressed] is 35-40% of spring stiffness.

The problem is the LOSSES that occur while the bushings are compressed [up on one side down on the other]. If this is just 1/4" per side that's 1/2" that's 1/2" of arm motion or up to 2" of wheel motion before 100% of the bar stiffness is realized.

Just replacing [with solid or semisolid] the front rubber end link bushing can double the REAL stiffness of the front bar.

Just as adding washers to compress the oem rubber can significantly stiffen the front bar..................you can over do it making the Q front BONE AND TEETH JARRING with just the washers until the bushing splits open and fails. AGRRESSIVE Solids may bend or break the endlink assembly or the lower arm mounting hole.

I like the 16% less stiff [28mm] front bar stiffened with washers on the bushings..............seems easier to fine tune with the 20mm rear bar.

The raw 28 mm is 1.92 times [due to reduction by rt angle bar being twice as long a 6" rear] as stiff as the raw unmounted 20mm rear bar.

When thinking about tuning with washers/bushings just easier to visualize a 1.92 vs a 2.22 for me.

Hopefully you can see if springs are 55/45% the bars should be this plus extra for wet or acceleration conditions...............

If the bar doesn't engage until the bushings compress you can see that until the body rolls 1-2" the roll stiffness is a perfect 54/46% from the springs alone.

The safe understeer only starts at >1.5-2" of body roll depending upon bushing engagement slope. Tightening up the bushings will start the understeer earlier, so you must have a rear bar if you use washers to tighten the front bar................now 40-50 pounds in the rear cannot cope with 75-90 pounds of extra front stiffness comming in EARLIER in the roll process.............what you strive for is to extend the neutrality to say 2.5" of body roll [~~0.65 G].

Always REMEMBER the front tires are what limits the G load number because this is where the most weight is located............use the least amount of sway bar that will do the job!

[t3lh]

Always REMEMBER the front tires are what limits the G load number because this is where the most weight is located............use the least amount of sway bar that will do the job!

I under stand that your talking mostly stock situations here with an eye on safety.

But when you start using extreme suspension setups and higher HP out put you sometimes have to tune with a bigger front bar.

On a mostly stock car, I dont see anything wrong with going to larger bars front and rear, as long as you keep the ballance correct ( and are using a high perf tire!).

[maxnix]

I under stand that your talking mostly stock situations here with an eye on safety.

Actually, he is talking physics.

Your solution is standard easy fix for a poorly balanced suspension. Don't ignore where the most dynamic load is occuring, and your initial best guess settings should be more accurate.

[t3lh]

Actually, he is talking physics.

Your solution is standard easy fix for a poorly balanced suspension. Don't ignore where the most dynamic load is occuring, and your initial best guess settings should be more accurate.

Not sure what your saying?

I'm not disagreeing with him, my point was. Example:You have a fairly stock car that handles well. Now you add 100HP.You can throw the stock front sway bar in the trash because its not going to be able to ballance the added HP loosness ( in hard cornering).

Of corse a stiffer front bar is not the only sollution!

[FarFetched]

I might add something to this debate!Diameter of sway bar doesn't mean more torsion force. YoOu could have same diameter sway bar but made form different materail (alloy) and have superior road-control characteristics. I might draw a line between off-raod suspension and on-road one. I've seen and worked on set-ups for baja-type trucks. Sway bars used on those trucks are 5 piece unti, containitng center link (torsion bar) end-bars (adjustable setup) and links (also adjastable). They are superior on fire roads, also very well ballanced on road, allowing very conrolable cornering at any safe speed. I know, on-road cars are different, however, this type of set-up could be utilized for great comfort and more controlable ride (cornering) Something like that!

[Falkdesigns]

If you want custom bars made, Saner Performance Fabrications in Florida will make them for you, however you want 'em. sanerperffab.com

[Q45tech]

Notice that I use steady state calculations [power off] that way the coefficient of friction for the rear tires are not compromised and don't need correcting for in the equation.................obviously if you are accelerating the rear tires are slipping, if you are turning the rear tires are slipping.

The difference in static load on each rear tire is just < 200 lbs vs a front tire so that is roughly how much extra traction you have to play with .........calculating the rear vs front roll center of gravity is more difficult.

Anyway a 20mm rear bar creates 120-150 lbs of reverse weight transfer.

As far as I know the maximum torque increase on any Q we have seen here is ~~ 30 lb/ft above stock [without Nitrous].

Agreed if you have changed the springs to double oem stiffness you would need a bar that is double oem stiffness and the roll stiffness would double and the body roll would halve..............HOWEVER the weight transfer would be exactly the same if you didn't lower the body.

Body roll is often a good thing to let driver know what's happening, it is only bad if the suspension cannot gain enough to maintain the camber.

WHEREAS SWAY BARS ARE all about giving up traction at one end to better balance the steering wheel feel to the driver. If it feels more secure he/she may push a little higher speed into the turn.

It's very hard to persuade non racers to floor it in the middle of a curve and power your way out!

[t3lh]

It's very hard to persuade non racers to floor it in the middle of a curve and power your way out!

Also along those lines: Some people over brake or trail brake incorectly for circumstances and cause weight transfer related handeling problems.

I some times forget to bite my tounge and relise that I look at everything from a racers view. When probably most others dont.

[FarFetched]

Proper cornering techiques are critical even in every day driving.I wish those vehicle operators, not drivers, had gone to driving school, before passing DOT tests (barely), and listened what instructors told/showed them how to behave while operating motor vehicle!I've learned so much about cornering during my riding experiences. You don't make mistakes twice on a bike ! it hurts! Cheers!

[Q45tech]

Always remember that most of the 90-96 Q on US roads have NO rear SWAY BAR..............the 7% t cars and the 8% actives have sway bars whose bushings are trashed, so effectively the bar is not working.

So a new bushing 20 mm rear bar on a standard Q is a 33-40% stiiffer rear than 85-90% of the Q on the road plus the maybe 50-100 that have been modified with Springs etc.

[texasoil]

Of course, if you had and drove the ACTIVE suspension, the 'roll stiffness' question disappears since the system stiffens up the outside struts instantly without the straight ahead bone jaring of ultra stiff roll bars. Now if I could just tweak the active computer algorithms to keep if FLAT to say 0.8G instead of the present 0.5 G side load.

[t3lh]

Of course, if you had and drove the ACTIVE suspension, the 'roll stiffness' question disappears since the system stiffens up the outside struts instantly without the straight ahead bone jaring of ultra stiff roll bars. Now if I could just tweak the active computer algorithms to keep if FLAT to say 0.8G instead of the present 0.5 G side load.

In straight ahead operation the sways have little affect, most of the time.

[texasoil]

Not true--stiff roll bars transmit bumps from one wheel to the body MUCH more harshly than softer ones. Stiff roll bars effectively eleminate the ride comfort of independent wheel suspension.

Once watched a late 90's Thunderbird with 'racing' roll bars try to drive diagonally across a shallow 'swale' at the pavement curb. He had to get a running start because there was so little chasis compliance the rear wheel 'crossing' the swale would lift off the ground and spin helplessly (no limited slip diff.) (A 'Swale' is a shallow ditch with gently sloped sides BTW)

THis is why 'skid pad G force' is meaningless for a street/road/real world car. The roads are never perfect, and when they are most imperfect is when you most need a great chassis that allows the wheels to remain in firm road contact so you can make it around than tight undulating curve and not 'lose it' into the other lane or swap ends in a blink. Overly stiff shocks and roll bars will not allow maximum real world controlability.

[t3lh]

Not true--stiff roll bars transmit bumps from one wheel to the body MUCH more harshly than softer ones. Stiff roll bars effectively eleminate the ride comfort of independent wheel suspension.

Once watched a late 90's Thunderbird with 'racing' roll bars try to drive diagonally across a shallow 'swale' at the pavement curb. He had to get a running start because there was so little chasis compliance the rear wheel 'crossing' the swale would lift off the ground and spin helplessly (no limited slip diff.) (A 'Swale' is a shallow ditch with gently sloped sides BTW)

THis is why 'skid pad G force' is meaningless for a street/road/real world car. The roads are never perfect, and when they are most imperfect is when you most need a great chassis that allows the wheels to remain in firm road contact so you can make it around than tight undulating curve and not 'lose it' into the other lane or swap ends in a blink. Overly stiff shocks and roll bars will not allow maximum real world controlability.

I said most of the time, also most street people would never use bars as stiff as those in your example!

[maxnix]

I said most of the time, also most street people would never use bars as stiff as those in your example!

Oh, you'd be surprised! A lot of bigger is better type thinking out there.

Anyway, the point is it is a progressive phenomena. The larger the spring rate of the antisway bars, the more effect it will have on even staright ahead motoring.

[t3lh]

Oh, you'd be surprised! A lot of bigger is better type thinking out there.

Anyway, the point is it is a progressive phenomena. The larger the spring rate of the antisway bars, the more effect it will have on even staright ahead motoring.

HAHA, I guess I should have said most people with common sense....

Sure, on very uneven roads maybe.

[maxnix]

Sure, on very uneven roads maybe.

None of the ones I drive on are billiard tables.

Wouldn't need suspensions if they were.

[t3lh]

None of the ones I drive on are billiard tables..

What?? I thought TX was flat as a pancake!