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Tracking / Autocross / HPDE / Drifting What these cars were built for!


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Old 07-21-2020, 02:21 PM   #575
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Why not? It's just a spring.
If you don't have adjustable end links you'll likely put preload on the bar which may cause some thing wonky, but even then I doubt it would be super noticeable.
If the other end of the sway bar was tied to a fixed point, I would agree, it act just like a spring. But it's fixed to the other side of the suspension, and force the spring on the other wheel to move.
By changing the setting on one side, you effectively have different arms length on your 'lever". Meaning when turning on one side, you will require a bigger amount of suspension travel to compress a small amount the other spring. When turning the other side, a smaller movement will be required to try to move the other spring a bigger amount (because the difference in lever arms length is reversed).
That's how I see it, but I may be wrong, that's a bit confusing.
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Old 07-21-2020, 05:12 PM   #576
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If the other end of the sway bar was tied to a fixed point, I would agree, it act just like a spring. But it's fixed to the other side of the suspension, and force the spring on the other wheel to move.
By changing the setting on one side, you effectively have different arms length on your 'lever". Meaning when turning on one side, you will require a bigger amount of suspension travel to compress a small amount the other spring. When turning the other side, a smaller movement will be required to try to move the other spring a bigger amount (because the difference in lever arms length is reversed).
That's how I see it, but I may be wrong, that's a bit confusing.
Since your rotating/compressing the spring relative to the strut positions the bar applies an equal force to both struts, a lever arm difference left to right is imperceivable to the physics of the car since each strut is seeing the cumulative force of the spring/bar.
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Old 07-31-2020, 02:07 AM   #577
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Since your rotating/compressing the spring relative to the strut positions the bar applies an equal force to both struts, a lever arm difference left to right is imperceivable to the physics of the car since each strut is seeing the cumulative force of the spring/bar.

I've just read a little bit on the subject, and I'm now 99% sure that having different adjustment side to side on the sway bar will result in a slightly different handling turning left or right. I've also read that nascar teams use asymmetrical sway bar adjustment on cambered round track to induce handling characteristic favourable to one side.
The difference is not in the resistance of the bar itself which will be the same either turning left or right, but the thing is that a sway bar is not just a spring in itself. It also compress the shocks it's tied to.

Take this great example I've read:
You're under heavy braking in a straight line. The front suspension compress by 2 inches on both sides. But the sway bar adjustment is not the same on both side, this means that one arm of the sway bar is slightly longer than the other (because of using different holes). It's the motion of the struts that induce the rotation of the sway bar. On one side, the 2 inch compression result in 20 degrees of sway bar rotation, but on the other side, since the lever arm is longer, the same 2 inches strut compression result in a 15 degree rotation. So the sway bar is now loaded on one side (by 5 degrees) even if you're braking in straight line. This result in one of the struts to be slightly more loaded/compressed. Now you're starting to turn after braking, but depending on the side you're turning, you either have a sway bar that's pre-loaded, or one that need to become neutral before becoming loaded again. That's not good.
I'm not sure if this effect is going to be very noticeable (probably not a lot), but it's there and it's enough of a difference to be used in Nascar.
@CSG Mike, can you chime in? We're talking about adjusting a sway bar asymmetrically (ex: left soft, right hard), to have a third intermediate setting.
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Old 07-31-2020, 10:54 AM   #578
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The swaybar rotates freely in it's bushings, in your braking scenario there is no difference in swaybar angle left to right, it is not loaded at all since the the left and right suspensions are moving equally.

Different arm lengths is not the same as preloading the bar.
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Old 08-02-2020, 10:03 PM   #579
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The swaybar rotates freely in it's bushings, in your braking scenario there is no difference in swaybar angle left to right, it is not loaded at all since the the left and right suspensions are moving equally.

Different arm lengths is not the same as preloading the bar.

I don't think you understand my point. Yes the suspension are moving equally, but the longitudinal movement of the suspension is transferred to a rotation movement of the sway bar by the arms of the sway bar. If the sway bar arms are not the same length, then the angle of rotation will not be the same on each side, thus loading the bar.
Take an extreme example: a 3 foot lever, that you move up by 1 feet. That cause a rotation of maybe 45deg. But a 1 feet lever than you move up the same 1 feet, then you end up with a 90 deg rotation (in practice the ball joint will not allow that), but that would be a massive 45deg of torsion on the bar.
The different arms length causes a difference of rotation on each side with the same amount of suspension travel, thus loading the bar under braking (or cornering for that matter).
I don't see how I can explain it any better, sorry. Take 2 sticks of different lengths, and try moving them around an imaginary axis by the same height, and see for yourself that the angle of rotation is different.
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Old 08-02-2020, 11:49 PM   #580
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It's not two sticks it's one stick.

For every action there's an equal and opposite reaction. The bar applies it's spring force to the suspension arms equally left to right regardless of arm length.
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Old 08-03-2020, 01:30 AM   #581
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It's not two sticks it's one stick.

For every action there's an equal and opposite reaction. The bar applies it's spring force to the suspension arms equally left to right regardless of arm length.

The sticks do not represent the bar, they represent the "arms" on each side of the bar (where the holes are). There are 2 of them (one on each side), and they are of different length (thus 2 sticks). During braking, the bar DOES NOT apply force to the suspension, it's the other way around, the suspension movement rotate the bar, and since each arms (the 2 sticks) have different length, the rotation applied to each side is not the same angle (thus loading the bar).
Sorry, but you do not seem to understand properly how the physic is working here.
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Old 08-03-2020, 01:44 AM   #582
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During braking, the bar DOES NOT apply force to the suspension, it's the other way around, the suspension movement rotate the bar, and since each arms (the 2 sticks) have different length, the rotation applied to each side is not the same angle (thus loading the bar).
Go back to the stick example, you've got a U, pick a low point on the left and a high point on the right, use your right hand to twist it, how much force do you feel on your left hand? Call it X.

Mirror that hand arrangement, high point on the left, low point on the right, twist the stick with your right hand, how much force does your left hand feel now?

F=kx
x is the degrees off nominal your bar has rotated
k is your spring stiffness which is a function of the bars geometry and the two arm lengths chosen

The spring force doesn't care if A is longer than B, it'll be the same spring force whether it's left or right.
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Old 08-03-2020, 02:00 AM   #583
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Go back to the stick example, you've got a U, pick a low point on the left and a high point on the right, use your right hand to twist it, how much force do you feel on your left hand? Call it X.

Mirror that hand arrangement, high point on the left, low point on the right, twist the stick with your right hand, how much force does your left hand feel now?

F=kx
x is the degrees off nominal your bar has rotated
k is your spring stiffness which is a function of the bars geometry and the two arm lengths chosen

The spring force doesn't care if A is longer than B, it'll be the same spring force whether it's left or right.

What you're describing is what happens when the bar is already loaded (or pre-loaded). The same force happens on each end, yes. You're basically describing the effect of the bar on the suspension, but it's not one-way. The suspension is also affecting the bar (twisting it).

So the force is dependent on the amount of rotation of the bar (or "twist"). And on an asymmetrical bar setup, the angle of "twist" of the bar will be different depending if your turning right or left. And again, on a straight line, the bar will "load", because one side of the bar will try to turn more than the other.
I suggest you read on the subject. You can start here, in the middle of the page, paragraph named "Sway Bar Asymmetry":
https://www.iracing.com/commodores-g...nti-roll-bars/
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Old 08-15-2020, 02:02 PM   #584
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Hey all, looking to get into d-street: not a ton of wheels in 17x7 for our cars unfortunately. Not a big fan of the rpf1, k4r, or motegis looks-wise, though I could put up with any lightweight wheel just based on the performance benefits.

Anything obvious that I'm missing out on, or any recommendations? Thanks

Edit: 17x7 is the move, right? No one is running 16x7 or 18x7?
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Old 08-19-2020, 10:46 AM   #585
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Hey all, looking to get into d-street: not a ton of wheels in 17x7 for our cars unfortunately. Not a big fan of the rpf1, k4r, or motegis looks-wise, though I could put up with any lightweight wheel just based on the performance benefits.

Anything obvious that I'm missing out on, or any recommendations? Thanks

Edit: 17x7 is the move, right? No one is running 16x7 or 18x7?

Yes, 17x7 is the best choice. Make sure you have the correct offset to be legal in street class. You can have an offset a couple of mm different from OEM (I don't remember the exact deviation allowed).
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Old 08-19-2020, 10:52 PM   #586
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Yes, 17x7 is the best choice. Make sure you have the correct offset to be legal in street class. You can have an offset a couple of mm different from OEM (I don't remember the exact deviation allowed).
A +/- 7mm offset change is allowed in street class.
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Old 08-27-2020, 02:46 PM   #587
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I'm planning a DS build for 2021. I went about two dozen pages deep into this thread and yielded not a whole lot of helpful information when it comes to upgrades to yield measurable gains.



What's the deal with shocks/struts? The two obvious options are Koni Yellows (I'm aware about the washer needed) or Bilsteins (B6 or B8). What are you guys doing here?



There's also the one bar mod. I believe the consensus leans towards a thicc front bar but does anybody do differently? I run in Ontario so our courses are often smaller and slower. I'm considering not touching my bars.


Lastly, intake & exhaust. I don't see much of a point in either... Exhaust can yield some weight loss but it's likely as negligible as the "power" increase from an air filter or cat-back.


I'm more interested in making the right strut choice. Furthermore, would Koni Yellows (for DS) work with appropriate lowering springs when comes the time for me to go STX build?



I'm 100% confident in my driver mod. I'm looking for mechanical advantages that give me measurable results.
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Old 08-27-2020, 04:19 PM   #588
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Bang on as far as I'm aware.
Koni yellows so you can adjust to conditions. I'd stick with front bar, you can get as much rotation as you need by playing with rear toe, added responsiveness from front bar pays off in slaloms and slightly better grip due to lack of camber. When STX comes just go to coilovers, no lowering spring package is stiff enough to be competitive and you won't save any money by putting sleeves + springs + revalving the yellows + camber plates, at that point might as well spend the $2k on a decent autox coilover.

You could buy the SSC compatible yellows which might be a little easier to resell, no major changes in valving vs ots, just slightly tighter QC. Make sure to install the washer on the yellows so you're not cheating on camber.
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