sway (anti-roll) bars

Joebob

Goblin Guru
I would avoid 4140 if you plan on welding anyting to it as you would have to preheat the part prior to welding and post weld stress relieve after before going to final heat treatment for strength. We are talking hours at 1100F which is not sharetree type stuff. I would stick to low carbon steel.
 

ah.b.normal

Goblin Guru
I'm just a by stander and overall curious guy here. My question, how will you make the sway bar ends and how will you attach them to the bar? Splines? a hole?(I believe Tilton makes a "fits all" with straight tube and splined alloy "lever" ends.)
I am NOT metallurgist, got a little metallurgy learning in 10th grade chemistry class. But I believe that if you drill, weld or spline a piece of annealed steel you will have to re-temper it?(not correct?) Obviously that can be done with a big oven and thermometers.
I've never really looked hard at how to make a sway bar. Just curious how YOU will make a sway bar and want to see your methods and results! Don't worry, I have faith in you!:)
 

mike_sno

Goblin Guru
I would avoid 4140 if you plan on welding anyting to it as you would have to preheat the part prior to welding and post weld stress relieve after before going to final heat treatment for strength. We are talking hours at 1100F which is not sharetree type stuff. I would stick to low carbon steel.
Wasn't planing on welding, but can you recommend a material which would be better?
 

Ross

Goblin Guru
I would use 3/4" tube, as it is available in various wall thicknesses. That way if you want to swap out different sway bars, you don't have to replace the bushings mounts.

Search engine had this to say:
Steel Used in Sway Bars:

  • 4140 Chromoly Steel: This is a popular choice due to its high strength and ability to withstand torsional stress. It is often heat-treated to enhance its properties further.
  • 5160 Steel: Another alloy used in the manufacturing of anti-sway bars, known for its strength and suitability for demanding applications.
  • 4340 Steel: This alloy is also used, particularly in high-performance vehicles, for its excellent strength and toughness.
  • 4130 Steel: Often used in aftermarket parts, this alloy provides a good balance of strength and machinability.
Heat treatment is a crucial process in manufacturing anti-sway bars, as it increases the tensile strength of the steel while maintaining its toughness and ductility. This process is essential for ensuring the bars can withstand the stresses encountered during vehicle operation.
 

Joebob

Goblin Guru
In the oil industry we use 4130, 4140 and 4340 steels for their great strength and through hardenability. The issue is welding. Without precise controls, they crack at the fusion line or heat affected zone. They make great sway bar material due to their very high yield strength prior to plastically deforming which makes them great for springs. Like springs, the sway bars are hot forge formed into shape and then heat treated to strength. Something that can't be done DIY.

I would also suggest hollow section tube as the majority of the torsional soring rate is dictated by the square of the diameter so the inside core does very little work. Save weight and increase adjustability with going hollow section.
 

Chubbs

Well-Known Member
I haven't been very active on these forums lately, but I thought I'd check in with my sway bar experience over the last two autoX seasons.

I removed my rear sway bar at the end of last season. With a rear bar (I used the "comfort" cobalt sway bar) the car was tail happy and unpredictable. I could not get the rear to stay planted, even with the rear dampers super-soft and the front cranked up hard. I did not alter spring rates, just the damping rates. Even with a staggered tire fitment (255 rear, 225 front) the rear would step out on corner entry under braking, mid corner, and under power. It was a handful. At AutoX speeds below 60 mph this is fun, but at race track speeds of 100+ it's terrifying.

I removed the sway bar for the last couple autoX events last year, and it was much better. Body roll is still minimal simply because the car is so low and light. It's now very nuetral, though lift-off snap oversteer is still a thing with any mid engine car. It's no longer treacherous to drive, and I've been able to increase damping rates on the rear to better control things back there without it stepping out of line constantly.

Bottom line, if you're going to do a sway bar at all, I think you do the front one first. Doing just the one in the rear is playing with fire. I think most people will be happiest leaving it well enough alone, and balancing things with spring/damping adjustments.
 

Rttoys

Goblin Guru
I liked mine when I had it on the stock setup, at least for autocross. I remember doing a practice day right after I installed it. I removed it that day and ran .5 second slower. Reattached it and got the .5 second back. Maybe it’s my driving style, but I like how it feels. I miss it with the tubular frame setup and trying to make one for it. See what happens.
 

ah.b.normal

Goblin Guru
Wasn't planing on welding, but can you recommend a material which would be better?
I would think your best bet would be the simple pre-made tubular, adjustable type sway bar on the front. On our 04 MR2, IIRC, it had about a 14-20mm front sway bar and the rear almost seemed like a joke at about 8mm??! But it had a nearly full size spare tire stashed in the front too, so it was surely heaver than a Goblin front end. From what I remember seeing on this forum most that run a sway bar on the back of their Goblin run a very weak bar.
I would see if you could get Adam/Lonny to share on this question.
 

mike_sno

Goblin Guru
When I installed the rear anti roll bar I noticed the car is a lot more stable when I start from 0mph with spinning wheels.

The car always had a tendency to oversteer just with too much input from the steering wheel. I tested it and pushed it pretty hard and did not really see a change in that behavior. I have to test it again without the anti roll bar to see the difference. I wanna say highspeed stability did not change for me.
 
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