EVOX_SPEED3
Member
Is this even an option for our cars. I would be happy with some lowering springs, and a front anti-sway bar. I know it's not as good as coilovers, but it would be much cheaper.
Anti-sway bars?
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SteveSonic
New member
It's important to always install a rear anti-sway bar when adding a front bar or else your FWD'r will understeer when pushed hard. However, the lack of a new rear bar can be compensated for somewhat by making sure that the new rear springs are variable rate springs and the spring rate really climbs high under high loads.
I've looked at the rear suspension a little bit and I'm sure a rear bar can be designed for it. Saab has been installing this type of rear suspension for the past few chassis so the engineering is known. GM probably "bought" the rear geometry directly from Saab when they owned the company.
Sonic Boomer
New member
I'd love to see anti-sway bars available for this car!
IMHO, it is impractical to lower the car any more than stock, but I'd love to tighten the body roll.
Maybe I'm full of crap, but it feels to me like the front isn't too bad, but the rear sucks big time. I'm kinda wondering if a rear sway bar would do the job by itself, but don't know if that would cause other problems similar to SteveSonic's post on under steer.
IMHO, it is impractical to lower the car any more than stock, but I'd love to tighten the body roll.
Maybe I'm full of crap, but it feels to me like the front isn't too bad, but the rear sucks big time. I'm kinda wondering if a rear sway bar would do the job by itself, but don't know if that would cause other problems similar to SteveSonic's post on under steer.
SteveSonic
New member
I remember how the early VW Rabbits would "lift a leg" (the inside rear wheel, parenthetically to piss on a hydrant) when pushed during autocross. It was perfectly normal for that chassis to do that and the Rabbits would often win their class. I'd guess today that the cars were set up with cut or otherwise high rate rear springs, and not rear anti-roll bars, as a fix for FWD understeer. An anti-roll bar will pull down the inside wheel of the loaded axle.
theenico
New member
As a previous owner of Rabbits and current owner of Sciroccos (same platform), I can say that they have bigger rear anti-sway bars than front anti-sway bars. That's not totally the reason they tend to hike the inside rear wheel though. They also have a torsion beam rear axle which is extremely similar to the Sonic's. That design is basically a sway bar itself. As the outside wheel/suspension is compressed the inside wheel is lifted. Since the car is also leaning, the inside wheel tends to come off the ground.
I will bet that, at an autocross, a Sonic will lift its inside wheel just like 90% of front wheel drive cars.
SteveSonic
New member
Thanks for clarifying. I've honestly (and obviously) never looked at or read about the Rabbit rear suspension. It was always a spectator sport to anticipate the inside wheel not rotating at all while the rest of the car sped through the cones.
We differ on our sway bar mechanics. My research and racing experience (autocross and open road track) have confirmed that the value of a sway (anti-roll) bar versus higher rate springs is how a sway bar effectively compresses the unloaded wheel up against it's spring when the loaded (outside) wheel is compressed. The end of the car with the bar is kept "flat" .. The "sway" is reduced.
The most important thing is to tune the chassis to have front/rear roll stiffness balance that generates a controllable, balanced (more or less) tire slippage.
theenico
New member
Our sway bar mechanics are the same. The bar holds up or "lifts" the unloaded tire when the opposite side is compressed. The reason the rear lifts is because the total front roll stiffness is generally sofeter than the rear on a front drive car. The opposite is true for rear engine cars such as the 911 that tends to lift the inside front wheel.
Take a sway bar at face value. It's a torsion bar with arms/levers. Now look at the Rabbit's or Sonic's rear axle. It's also a torsion bar with levers. Although a Sonic does not come equipped with a separate removabale rear sway bar, it could definitely benefit from one. As such, I plan on making one for my Sonic. Having a separate rear sway bar will allow for fine tuning the rear roll stiffness.
I'm not questioning your background. I'm actually agreeing with you. I too have an extensive background in road racing and autocross. I started my career as a fabricator at a shop that specialized in vintage Porsches geared toward the HSR group. We also built cars for PCA racing. I later moved to a shop that specialized in SCCA cars. There I built stuff for the Production, Improved Touring, A sedan, and GT classes for road racing and most of the autocross classes. My specialties were roll cages and suspension fabrication. I also campaigned an Improved Touring B Scirocco in club racing and competed in various customer cars at National level autocross.
Take a sway bar at face value. It's a torsion bar with arms/levers. Now look at the Rabbit's or Sonic's rear axle. It's also a torsion bar with levers. Although a Sonic does not come equipped with a separate removabale rear sway bar, it could definitely benefit from one. As such, I plan on making one for my Sonic. Having a separate rear sway bar will allow for fine tuning the rear roll stiffness.
I'm not questioning your background. I'm actually agreeing with you. I too have an extensive background in road racing and autocross. I started my career as a fabricator at a shop that specialized in vintage Porsches geared toward the HSR group. We also built cars for PCA racing. I later moved to a shop that specialized in SCCA cars. There I built stuff for the Production, Improved Touring, A sedan, and GT classes for road racing and most of the autocross classes. My specialties were roll cages and suspension fabrication. I also campaigned an Improved Touring B Scirocco in club racing and competed in various customer cars at National level autocross.
SteveSonic
New member
Theenico:
We're definitely on the same page about the suspensions. I think the high CG of the early Rabbit also contributed to its roll tendencies.
I've never seen how a add-on sway bar is mounted to a modern torsion rear axle. Will it be mounted to the chassis in blocks to control lateral movement, then with arms projecting forward of rearward into sliding blocks attached to the axle? Crude, but this is what I did on my historic racing Saab Sonett III and it works great. But on a road car are short arms with heim joints used to attach it to the axle?
We're definitely on the same page about the suspensions. I think the high CG of the early Rabbit also contributed to its roll tendencies.
I've never seen how a add-on sway bar is mounted to a modern torsion rear axle. Will it be mounted to the chassis in blocks to control lateral movement, then with arms projecting forward of rearward into sliding blocks attached to the axle? Crude, but this is what I did on my historic racing Saab Sonett III and it works great. But on a road car are short arms with heim joints used to attach it to the axle?
SteveSonic
New member
I've looked at a couple of Saab 9-3 sites for sway bar installs. The factory and the aftermarket bars are mounted under the torsion bar axle and bolted to the ends of the axle. I'd describe it as not so much a sway bar as it is a stiffening of the torsion axle beam to disallow flexing. To me, as a BSME, a true sway bar mounts to the chassis and to the axle as a seperate, twisting, resistive component of the suspension system.
Theenica: What sway bar design did you have in mind?
Theenica: What sway bar design did you have in mind?
theenico
New member
From your description, the Saab 9-3 sounds similar to the old Rabbits. It took me a while to find a decent photo, but here is what a rear sway bar for an old Rabbit looks like (thanks Google images):
The blocks/saddles are on the horizontal portion of the axle and the ends mount to the shock bolts. Since the axle already works like a sway bar, mounting the bar directly to it is not a problem. You are effectively "supplementing" its existing roll stiffness. This is basically how I was going to do it on the Sonic. Because of the exhaust, shape of the floor pan, etc., it would be very difficult to mount the horizontal portion of the bar to the body. Another possible design is a nested straight bar that gets bolted or welded into the beam itself.
Sway bars don't necessarily even need any body mounting. On a fox body Mustang, the rear bar is only attached to the lower trailing arms and "floats" under the rear axle. It doesn't fall or rotate down because each arm on the bar is nested in the trailing arms and attached with 2 bolts spaced about 3" apart.
The blocks/saddles are on the horizontal portion of the axle and the ends mount to the shock bolts. Since the axle already works like a sway bar, mounting the bar directly to it is not a problem. You are effectively "supplementing" its existing roll stiffness. This is basically how I was going to do it on the Sonic. Because of the exhaust, shape of the floor pan, etc., it would be very difficult to mount the horizontal portion of the bar to the body. Another possible design is a nested straight bar that gets bolted or welded into the beam itself.
Sway bars don't necessarily even need any body mounting. On a fox body Mustang, the rear bar is only attached to the lower trailing arms and "floats" under the rear axle. It doesn't fall or rotate down because each arm on the bar is nested in the trailing arms and attached with 2 bolts spaced about 3" apart.
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theenico
New member
I was doing some research today for work and stumbled upon the "contribution of rall rate" spec for the Sonic axle. The spec is checked/measured with the axle mounted in a fixture (at the bushings just like it mounts in the car) and one arm held solid. The free arm is then pushed down at the location where the spindle/bearing assembly is attached. The spec is it must take 450Nm +/- 25 to move the free arm 4.55 degrees. Unfortunately, it is in degrees so there is not an easy linear conversion to translate this into a common wheel rate measurement such as lbs/in.
98.9 newton-meters per degree = 72.96 foot-pounds per degree
98.9 newton-meters per degree = 72.96 foot-pounds per degree
SteveSonic
New member
That's a GREAT data find. I think if we measure the distance from the axle centerline to the spindle centerline - that is, the moment arm of the axle rotation under bending load - then we can convert the 73 ft-lbs per degree to pound-inch of axle rotation (axle 'spring rate'). I'll double-check that idea during lunch time today. I'm supposed to be "working" on other things right now ...
SteveSonic
New member
From your description, the Saab 9-3 sounds similar to the old Rabbits. It took me a while to find a decent photo, but here is what a rear sway bar for an old Rabbit looks like (thanks Google images):
The blocks/saddles are on the horizontal portion of the axle and the ends mount to the shock bolts. Since the axle already works like a sway bar, mounting the bar directly to it is not a problem. You are effectively "supplementing" its existing roll stiffness. This is basically how I was going to do it on the Sonic. Because of the exhaust, shape of the floor pan, etc., it would be very difficult to mount the horizontal portion of the bar to the body. Another possible design is a nested straight bar that gets bolted or welded into the beam itself.
OK, I'm following you. The bolt used for the shock bottom mount would be the attachment point for the bar end links in the Sonic, with heim joints for free rotation.
But I'm hoping to design an adjustable bar. That would require an intermediate link between the bar, which would have several mounting holes along it's arm, and a mount point on the body (w/heim joints on both ends of the intermediate link). If the bar could bend upward inside/near the spring cavity before projecting rearward, then the intermediate link could attach from there downward to the shock mount. The adjustment points along the end of the bar would, unfortunately, be up inside the cavity between the shock and the spring. Is there room up in there?
Thanks for putting your mind to this.
SteveSonic
New member
So much for working while in the office ...
OK, so a quick google search found this: Installing a Neuspeed rear sway bar on a VW GTI 337 1.8T
That's a Neuspeed install on a Golf IV/GTI/337 chassis. That's a 28mm, somewhat long-armed bar on that chassis, with no reference to installing lowering springs, coilovers, shocks, or a front bar at the same time as this modification.
Most importantly is the Neuspeed adjustable link on this setup. However, the addition of an adjustment link causes the bar to hang below the shock lower mount. This idea might not be so smart because the bar and linkage are vulnerable to damage.
OK, so a quick google search found this: Installing a Neuspeed rear sway bar on a VW GTI 337 1.8T
That's a Neuspeed install on a Golf IV/GTI/337 chassis. That's a 28mm, somewhat long-armed bar on that chassis, with no reference to installing lowering springs, coilovers, shocks, or a front bar at the same time as this modification.
Most importantly is the Neuspeed adjustable link on this setup. However, the addition of an adjustment link causes the bar to hang below the shock lower mount. This idea might not be so smart because the bar and linkage are vulnerable to damage.
SteveSonic
New member
Another link to another VW rear bar configuration:
VW MKIV Autotech Rear Sway Install
This Autotech bar design is like what I installed in my racing Sonett, although the sliding heim joints of my Sonett bar are mounted to the floor pan/chassis versus to the rear axle. Therefore, my bar imparts a significantly higher roll rate increase to the rear suspension verses mounting to the axle and supplementing the axle bend stiffness. Note also that this Autotech bar offers no adjustibility. In my Sonett, I drilled several mounting holes in the floor for the sliding heim joints, but I installed my joints in the "middle" hole and never moved it.
VW MKIV Autotech Rear Sway Install
This Autotech bar design is like what I installed in my racing Sonett, although the sliding heim joints of my Sonett bar are mounted to the floor pan/chassis versus to the rear axle. Therefore, my bar imparts a significantly higher roll rate increase to the rear suspension verses mounting to the axle and supplementing the axle bend stiffness. Note also that this Autotech bar offers no adjustibility. In my Sonett, I drilled several mounting holes in the floor for the sliding heim joints, but I installed my joints in the "middle" hole and never moved it.
SteveSonic
New member
I'm just trying to wrap my head around your bar setup on the Sonett. I got that the arms are attached via links to the chassis. What is the center/horizontal portion of the bar mounted to?
Is this what your rear suspension looks like?
Yes. My sway bar is attached to the underside of the axle in two metal (!) mounts outboard, just inside the two bends, using heavy duty exhaust clamps. It bends inside of and parallels the stock axle trailing arms. The ends then slide within heim joints that are mounted to the underside of the trunk floor. The I.D. of metal blocks are just over the O.D. of the bar, of course. The heim joints in which the bar ends slide are very large and are actually the joints that the home-grown circle track guys use for their steering shaft supports.
Savage_383
New member
Here is a picture of my Sonic at the Autocross a few weekends ago.
If it wasn't for the crap stock tires giving up the fight so easily, I think the inside back tire would be off the ground. haha
EDIT: actually, looking at the picture more closely, I think the back tire IS barely off the ground.
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