Starting to Think about a Race Car Sized Rear Sway Bar

[Fusion Works]

So currently it looks like there are mostly 21-22mm bars available for our car. I am wanting something even stiffer. I am kicking around a couple of ideas. I have a tubing bender and can get nice chromoly tubing. I think I can bend some 1.00, 1.25, and should I go crazy 1.5in round tubing or bar.

I would think a 1.00in x .250 wall (would be about double the stiffness), 1.250 x .125 (almost triple) or .250 wall would be a good upgrade. The nice thing these are easy to change so testing would be quick and easy.

Need to figure out a holding fixture to test the Eibach bar I have and see what its actual rate is. Theoretically I can bolt it to the welding table, though not sure what the best way to fix a scale under it. It doesn't have normal poly bushings like a normal bar. Gonna need to think about this a bit.

 

[Crew Jones]

I know the guys who used to race the vw gti that have a very similar rear beam to our fiestas would weld plates across the rear beam (box them in) to keep it from flexing. That could be an option. If your after some more rotation you could also think about shimming the rear wheel bearings to play with the alignment as it’s a bit toe in from the factory. Remember that the sway bar is a spring of sorts so it if you do go down the road of making your own (sounds like fun) that you will want to use a material that has memory.
just a thought.

 

[Fusion Works]

I was debating boxing the beam, but currently don't have enough understanding of the complexities of the beam to make structural modifications to the beam.

The rear already has shims, camber is -2.25 and toe is .070 out.

I am currently thinking either 4140 or 1144 Stressproof. Price is minimal difference.

 

[Dialcaliper]

4140 is not great if you plan to weld end plates on it. Actual “Stressproof” 1144 is hard to find unless you trust your source - not all 1144 is treated in that way. If you plan something like a clamp/machined end bracket (no welding) either might work

But 4130 is probably your best bet as it welds well, has decent strength (less important for a spring/sway bar) and good fatigue resistance (more important) and isn’t expensive - probably cheaper than both those two options, and more common than either, especially in tubing.

 

[Fusion Works]

I was sorta staring at it the other day and thinking about running a pair of bolts straight through the bar itself. That would eliminate the need for welded plates and the potential for flex there.

I have a couple of reputable suppliers for all these materials. Stressproof would be preferable for the prototype as I can avoid heat treating it, but 4140/4130 could be acceptable if i needed to make more of these. Again, gonna have to work up a procedure to make this work.

 

[Fish Freak]

So currently it looks like there are mostly 21-22mm bars available for our car. I am wanting something even stiffer. I am kicking around a couple of ideas. I have a tubing bender and can get nice chromoly tubing. I think I can bend some 1.00, 1.25, and should I go crazy 1.5in round tubing or bar.

I would think a 1.00in x .250 wall (would be about double the stiffness), 1.250 x .125 (almost triple) or .250 wall would be a good upgrade. The nice thing these are easy to change so testing would be quick and easy.

Need to figure out a holding fixture to test the Eibach bar I have and see what its actual rate is. Theoretically I can bolt it to the welding table, though not sure what the best way to fix a scale under it. It doesn't have normal poly bushings like a normal bar. Gonna need to think about this a bit.

I think I've got the same rear Eibach sway bar you have, it bolts to a plate with two holes on either end and suspends in the air with no bushings shadowing the torsion beam right?


You running anything else? Asking because I bought my sway bar from a FiST guy that ALSO ran one of the torsion stiffeners like they sell on Woosh, looks like this and basically reduces the twist of the torsion member between the trailing arms, does that make sense? He sold me the sway bar because together they were too much and gave it a tendency to snap oversteer mid corner. Just a thought...

 

[Fusion Works]

The VW guys use something like this bar, but they bolt between the two legs of the beam. I can't see how this really stiffens the beam. You are kinda relying on the stiffness of the bolt in bending and that seems insufficient to see measurable gains.

I have a piece of 1in 4140 that just showed up. Am going to bend it and see how it feels.

 

[Woods247]

The VW guys use something like this bar, but they bolt between the two legs of the beam. I can't see how this really stiffens the beam. You are kinda relying on the stiffness of the bolt in bending and that seems insufficient to see measurable gains.

I have a piece of 1in 4140 that just showed up. Am going to bend it and see how it feels.

I have the Pierce beam brace and the rear Eibach bar. Have you checked out the Pierce beam brace. I had the TB Performance one before and like everything TB makes I can’t tell a difference in how my car performs with those products installed. Pierce stuff is obvious from the moment you install it.

 

[Fusion Works]

I am not totally sold on the beam needing to be stiffer, but I am also not sure I can use a BTCC approach to roll stiffness and make the car work correctly.

I haven't looked into any of the add on monkey bars as I think they are a placebo at best. If Ferd could have stiffened the car even more with three bolt on beams, you think they wouldn't throw $5 worth of sheetmetal into the body/subframe/beam? (yes they did increase the beam stiffness)

 

[Fish Freak]

I have the Pierce beam brace and the rear Eibach bar. Have you checked out the Pierce beam brace. I had the TB Performance one before and like everything TB makes I can’t tell a difference in how my car performs with those products installed. Pierce stuff is obvious from the moment you install it.

Oh yea here you go, the Pierce bar Woods247 is using overcomes the bolt limitation Fusion Works mentioned by adding inner 90 degree bracing! This pic shows it. Are those inner braces nutted to the torsion beam? This pic shows my Eibach sway bar perfectly too. Stiffen that torsion beam from twisting and it'll have a dramatic effect on anti-sway.

Hey Woods, can you easily get oversteer with both rear bars? This was all to just help the OP from doing too much with his homemade experimental race sway bar.

 

[Fusion Works]

So it doesn't actually bolt laterally? Those are just delrin braces? It kinda wedges up into the beam?

 

[Fish Freak]

So it doesn't actually bolt laterally? Those are just delrin braces? It kinda wedges up into the beam?

Yes so Pierce says because of those white machined delrin caps, cross bolting those lateral supports is unnecessary and could also compromise the beam strength. They also said it's not flat up top, so where it bolts in, there's a radius that matches the torsion beam. Quite a bit of engineering into their parts, super strong and light 4130 chromoly steel, AND they're CHEAP! Dam you guys I just added some Pierce bars to my shopping cart....

 

[Woods247]

So it doesn't actually bolt laterally? Those are just delrin braces? It kinda wedges up into the beam?

It wedges in. Definitely works. I can rotate whenever I want as long as I don’t get on throttle too early. The rear of my car is usually sliding unless I’m over 80mph then the wing takes effect and calms it down.

I should’ve kept the stock front swaybar though and not changed to the Eibach.

 

[Fusion Works]

I don't get it, my car is not that loose even though I am running toe out on the rear with 600+lb springs on the back and the Eibach rear bar.

 

[Dialcaliper]

As you’re noticing, the sway bars dominate the roll stiffness on this car (which is actually quite high, even in stock trim). The primary spring rates don’t actually contribute very much - especially the rears which are mounted inboard of the wheels and so contribute even less in roll than they do in ride (front/rear stiffness/frequency).

So it’s not very effective to tune understeer/oversteer on this car with just springs.

The Pierce/TB braces just work by bolting to the torsion beam and twisting the added tube as the torsion beam also twists. The TB relies solely on the bolts, which seems like a poor design. The Pierce Delrin snubbers add a second leverage point to keep the tube ends centered in the torsion beam - slightly better design, but still relying on the bolts in shear.

 

[Fish Freak]

I don't get it, my car is not that loose even though I am running toe out on the rear with 600+lb springs on the back and the Eibach rear bar.

Do you really want it that tail happy?

My car's party trick is turning in as nearly hard as is physically possible and it just knifes through the corner. Blows passenger's minds, and this is with stock S springs and shocks, ST 17" wheels, Nitto's, front 21 mm bar, rear Eibach bar. Loose isn't fast.

 

[Erick_V]

I don't get it, my car is not that loose even though I am running toe out on the rear with 600+lb springs on the back and the Eibach rear bar.

That's odd. I have BC Coils (5k/3k), Pierce brace (same as above), camber plates, and even on warmed-up RT660's I can still get the rear to rotate easily with either trail braking or just lifting mid-corner. I usually run 2/3 stiffness in front and around 1/2 stiffness in rear. I don't recall the pressures exactly but I believe I was around 34-36psi hot in the rear. My alignment showed -0.05 LR and -0.25 RR toe and -1.8 LR and -2.0 RR camber when I had it corner-balanced a while ago.

 

[Woods247]

I don't get it, my car is not that loose even though I am running toe out on the rear with 600+lb springs on the back and the Eibach rear bar.

I should drive your car and you should drive mine. My car is probably a couple hundred pounds lighter than yours since I only have a driver seat. My BCBRs have 8k front and 6k rear springs (linear Swift). I typically run the front +10 clicks (from open) and rear +17 clicks (from open) at Barber. Sometimes at Barber I’ll run +20 rear if it’s hot out and +10 if it’s cold. I rarely touch the front. Once I feel the front bounce off the track and spin the tires I’ll pit and soften the clicks (one click at a time) until it has full traction then just leave it alone.

My rear tire pressure is usually between 2-4 psi (hot) higher than the front. 1psi can make a difference on my car (this is with RT660s). Without the aero my car would be uncomfortably sketchy over 80mph for my driving style. The rear end is all over the place until the wing plants it over 85ish mph.

 

[Fusion Works]

I am completely happy to swap cars and see what you think. The car isn't as loose as I prefer for a track car. The car is fine for a street car, there is a huge window in comfortable street setups. My car doesn't burn the inside tire off any more. HAHA

You are never going to be running at the speeds and slip angles on the street you are running on the track with hot sticky track tires, aero, and smooth tracks with minimal bumps. I also want maximum durability on the front tires. The "front stiff" setup that most people and OEMs run on street FWD cars is fine for two or three laps. The tires come up quick and the car does pretty well, but if you want a truly fast track/race setup that can lay down consistent laps for a 20 lap race or 20hr race front stiff ain't where its at for a FWD car.

My setup at Barber last month was:
Front Camber -2.25
Front Toe 0
Front Caster 5.5+
Rear camber -2.5
Rear toe .070 out.

Tire pressures end up at 32-34psi front and 34-36 rear.
Front springs 450lbs
Rear springs started the weekend at 550lbs and ended the weekend in the 650lbs range
Eibach rear bar
Stock front bar. (I think it was connected, LOL. I disconnected it in June)
LF 901
RF 899
LR 624
RR 512
Car is not on the bumpstops, its at the factory ride height.

Splitter was 3in off the deck and 5in out the front of the car. Rear Wang angle was reduced from 2deg down to 0 early on Sat.

 

[Fish Freak]

I am completely happy to swap cars and see what you think. The car isn't as loose as I prefer for a track car. The car is fine for a street car, there is a huge window in comfortable street setups. My car doesn't burn the inside tire off any more. HAHA

You are never going to be running at the speeds and slip angles on the street you are running on the track with hot sticky track tires, aero, and smooth tracks with minimal bumps. I also want maximum durability on the front tires. The "front stiff" setup that most people and OEMs run on street FWD cars is fine for two or three laps. The tires come up quick and the car does pretty well, but if you want a truly fast track/race setup that can lay down consistent laps for a 20 lap race or 20hr race front stiff ain't where its at for a FWD car.

My setup at Barber last month was:
Front Camber -2.25
Front Toe 0
Front Caster 5.5+
Rear camber -2.5
Rear toe .070 out.

Tire pressures end up at 32-34psi front and 34-36 rear.
Front springs 450lbs
Rear springs started the weekend at 550lbs and ended the weekend in the 650lbs range
Eibach rear bar
Stock front bar. (I think it was connected, LOL. I disconnected it in June)
LF 901
RF 899
LR 624
RR 512
Car is not on the bumpstops, its at the factory ride height.

Splitter was 3in off the deck and 5in out the front of the car. Rear Wang angle was reduced from 2deg down to 0 early on Sat.

Clearly you guys are doing this at a different level than I imagined. Sounds like you're havin' a ball out there! We should have a 'race suspension' thread cuz you're so right, on the street I'll never see the extended conditions you're experiencing, Fusion Works. Got any race vids we could check out?