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Old 06-12-2019, 11:18 AM   #1
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Rear Sway bar only upgrade?

Opinions, please.

I recently got a set of M030 sway bars for my 986S. A local shop recommended installing only the rear and see how that affected the handling of the car before deciding to install the front. The car is a DD and used for AX and DE's. Should I install just the rear or should I install both?

Thanks for your thoughts.
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Old 06-12-2019, 12:10 PM   #2
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start with rear. It takes about 15 min to install. A stiffer front bar tends to increase understeer.
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Old 06-13-2019, 06:20 AM   #3
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Originally Posted by bbiela View Post
Opinions, please.

I recently got a set of M030 sway bars for my 986S. A local shop recommended installing only the rear and see how that affected the handling of the car before deciding to install the front. The car is a DD and used for AX and DE's. Should I install just the rear or should I install both?

Thanks for your thoughts.
This is what I did on my 986. It reduces understeer a bit and allows the car to rotate more easily without getting too slap-happy. Depending on the exact tire sizes and compounds you run it may be the right move. I ran mostly 225/245 NT-01 and balance was good.
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Old 06-13-2019, 07:39 AM   #4
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This is what I did on my 986. It reduces understeer a bit and allows the car to rotate more easily without getting too slap-happy. Depending on the exact tire sizes and compounds you run it may be the right move. I ran mostly 225/245 NT-01 and balance was good.
Can you help me to understand this concept, please? (I'm still a little green on some of this)

I think I understand how upgrading the rear bar can reduce understeer. no problem there.
But I'm not following how it helps the car to rotate. Maybe I'm calling rotation something DIFFERENT from what rotation really IS?
When I enter a corner, there's a moment where the weight transfers in the rear and it helps turn the car. Occasionally there's a small slide associated, but it's usually just the weight moving to the outside. I think I'm typically (maybe always?) still trail-braking as this occurs, and so the weight goes especially to the outside-front tire, which then hooks /bites / turns.

It seems like the "looser" the rear is, the easier that weight transfers? It seems like stiffening the rear bar would decrease the roll, decreasing the weight that gets transferred, decreasing the rotation. It seems almost like it would oversteer a little more easily.

So, am I thinking of "rotation" incorrectly? or am I misunderstanding the dynamics of how it happens?
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Old 06-13-2019, 08:03 AM   #5
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Can you help me to understand this concept, please? (I'm still a little green on some of this)

I think I understand how upgrading the rear bar can reduce understeer. no problem there.
But I'm not following how it helps the car to rotate. Maybe I'm calling rotation something DIFFERENT from what rotation really IS?
When I enter a corner, there's a moment where the weight transfers in the rear and it helps turn the car. Occasionally there's a small slide associated, but it's usually just the weight moving to the outside. I think I'm typically (maybe always?) still trail-braking as this occurs, and so the weight goes especially to the outside-front tire, which then hooks /bites / turns.

It seems like the "looser" the rear is, the easier that weight transfers? It seems like stiffening the rear bar would decrease the roll, decreasing the weight that gets transferred, decreasing the rotation. It seems almost like it would oversteer a little more easily.

So, am I thinking of "rotation" incorrectly? or am I misunderstanding the dynamics of how it happens?
I'm with you on this and the reason for my post. My understanding is a stiffer sway bar will cause that end of the car to be flatter and to lose grip sooner, hence allowing it to rotate better. My concern was that the car would then be tail happy. Correct me if my understanding is incorrect

I'm going to install it this weekend, I have a DE next weekend and can let you know.
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Old 06-13-2019, 08:11 AM   #6
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Can you help me to understand this concept, please? (I'm still a little green on some of this)

I think I understand how upgrading the rear bar can reduce understeer. no problem there.
But I'm not following how it helps the car to rotate. Maybe I'm calling rotation something DIFFERENT from what rotation really IS?
When I enter a corner, there's a moment where the weight transfers in the rear and it helps turn the car. Occasionally there's a small slide associated, but it's usually just the weight moving to the outside. I think I'm typically (maybe always?) still trail-braking as this occurs, and so the weight goes especially to the outside-front tire, which then hooks /bites / turns.

It seems like the "looser" the rear is, the easier that weight transfers? It seems like stiffening the rear bar would decrease the roll, decreasing the weight that gets transferred, decreasing the rotation. It seems almost like it would oversteer a little more easily.

So, am I thinking of "rotation" incorrectly? or am I misunderstanding the dynamics of how it happens?
I'm with you on this and the reason for my post. My understanding is a stiffer sway bar will cause that end of the car to be flatter and to lose grip sooner, hence allowing it to rotate better. My concern was that the car would then be tail happy. Correct me if my understanding is incorrect

I'm going to install it this weekend, I have a DE next weekend and can let you know.
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Old 06-13-2019, 08:24 AM   #7
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....My understanding is a stiffer sway bar will cause that end of the car to be flatter and to lose grip sooner, hence allowing it to rotate better.
See, if that's what "rotation" is, then I'm calling rotation the wrong thing. You're talking about oversteer, which can be useful in a higher HP car (you can "square-off" a corner that way) but seems counter-productive on a momentum car like the Boxster.

There are some great resources here, with some really knowledgeable guys.... hopefully they'll chime-in on this and set me straight, haha.
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Old 06-13-2019, 08:59 AM   #8
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yes, a stiffer bar will tend to have the car more prone to oversteer, which helps the car to rotate. That said, there are various parts of the turn and corner entry oversteer is pretty rare unless you are trail braking it hard. My car, even with various setups, was always pretty neutral on turn in, and pushes a bit on corner exit. Some prefer to have a car that oversteers on corner exit, but for a less experienced driver, push is better as you can drive out of it with less throttle whereas oversteer can be a bit more tricky to manage.

The reality is that the stiffer rear bar is just a small part of the package and the way you drive can be just as important as how its step up (and there is obviously lots of correlation there).

The best way to get rid of front end push on corner exit is a square set up, but then you'll want a softer rear bar.
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Old 06-13-2019, 09:19 AM   #9
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.... for a less experienced driver, push is better as you can drive out of it with less throttle whereas oversteer can be a bit more tricky to manage.
oh that is SO ME right now. I mean, I've been told I have "Really Good Car Control", but it's SOOO much easier for me to back-off the throttle a bit to reel the front end back, than it is to steer into the back-end's path and keep them movin' the same direction.

(My first few laps of each session I always leave the PSM ON, so that I can test the limits of the rear-end traction in "relative" comfort, before I turn it off and start controlling it myself. )
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Old 06-13-2019, 03:00 PM   #10
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For me, rotation means that when I enter a corner, I may lift off the gas, which gets the rear to step out slightly, allowing me to point the car into the turn quicker, so I can then get on the gas sooner. That "rotation" is different than oversteer, which would be the rear of the car stepping out in a constant cornering mode. This behavior is what makes a mid-engine car so wonderful, you can steer the car with the throttle to a degree.

Now that I think about it, it's not so much that the back end steps out, but that it's the combination of the rear stepping out every so slightly and the front end getting a really good bite to get the car pointed into the turn.

This corner entry lift is brief, just enough to get the car to rotate (there it is again!), and then I'm back on the gas. Getting on the gas doesn't necessarily mean full throttle. Normally, you want to be at least maintaining throttle or accelerating in a turn once you are done with your corner entry. Coasting in a turn should be a rare occurrence, like on a cool-down lap.

Rotating the car doesn't work in all corners, mostly just ones where a change of direction is pretty quick. You wouldn't try this in a high speed sweeper, for instance, but you certainly would going into a chicane.

I hope this makes sense.
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Old 06-13-2019, 06:47 PM   #11
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For me, rotation means that when I enter a corner, I may lift off the gas, which gets the rear to step out slightly, allowing me to point the car into the turn quicker, so I can then get on the gas sooner. That "rotation" is different than oversteer, which would be the rear of the car stepping out in a constant cornering mode. This behavior is what makes a mid-engine car so wonderful, you can steer the car with the throttle to a degree.



Now that I think about it, it's not so much that the back end steps out, but that it's the combination of the rear stepping out every so slightly and the front end getting a really good bite to get the car pointed into the turn.



This corner entry lift is brief, just enough to get the car to rotate (there it is again!), and then I'm back on the gas. Getting on the gas doesn't necessarily mean full throttle. Normally, you want to be at least maintaining throttle or accelerating in a turn once you are done with your corner entry. Coasting in a turn should be a rare occurrence, like on a cool-down lap.



Rotating the car doesn't work in all corners, mostly just ones where a change of direction is pretty quick. You wouldn't try this in a high speed sweeper, for instance, but you certainly would going into a chicane.



I hope this makes sense.
This describes precisely what I'm calling rotation. Sometimes I'm trail braking, not lifting, but either way it's loading the front and then shifting the weight in the rear: rotation.

So now that you and I agree: how does a stiffer bar in the rear improve this? I'm not yet grasping that concept.

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Old 06-13-2019, 09:04 PM   #12
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A stiffer rear bar puts more loading on the outside rear tire, so if you lift in a turn, it will transfer the weight to the front, and that loaded outside rear tire will step out slightly. It's not a dramatic loss of adhesion with tons of tire squealing, the rear just briefly describes a slightly wider arc than the front (how is that for some technical jargon?). But it helps to point the car into the turn.

BTW, this winter I replaced both front and rear sway bars with ROW M030 bars, and I've noticed that the car doesn't rotate as well as before; it feels less "lively". I've got 20mm wheel spacers at all four corners, so I may go with 15mm spacers in the rear to see if that makes any difference. If not, I'll switch back to the stock spec front bar. The rear bar is incredibly easy to change, unfortunately the front is a bit of a project to replace.
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Old 06-14-2019, 04:25 AM   #13
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A stiffer rear bar puts more loading on the outside rear tire, so if you lift in a turn, it will transfer the weight to the front, and that loaded outside rear tire will step out slightly. It's not a dramatic loss of adhesion with tons of tire squealing, the rear just briefly describes a slightly wider arc than the front (how is that for some technical jargon?). But it helps to point the car into the turn.
Are we talking about this: (starts at about 0:10)
https://youtu.be/qn8gJrx2gVc

This wasn't elegant, cuz I had the PSM on... doh.... and it "saved" me from myself, so I had to add steering input when the rotation was interrupted.

But is this what we're talking about?

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Old 06-14-2019, 07:40 AM   #14
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I'd say that is an extreme example of what I was talking about. To me that looked like the car was oversteering on corner entry.

You shouldn't have to correct it with steering. If any correction is made, it's with the throttle. The car should rotate, or "pivot" into the turn, and off you go.
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Old 06-16-2019, 08:18 AM   #15
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Sorry I missed this.

Yes a stiffer rear bar allows for a quicker weight transfer forward when you lift. This allows the front tires to set quickly and increase the rear slip angle so the car will point towards the apex. Now you can begin to unwind the wheel and roll on the gas early, being at or near full throttle at the apex. This is the fastest way around a tight corner IMO.

A perfectly balanced Boxster likes to prescribe a nice constant radius arc in a corner. This is what we all want on those fast 3rd gear sweepers. By stiffening the rear just a bit we can alter that arc as needed for a quick turn-in on tighter corners and get the car pointed where we want it to go.

The devil is in the details and the "stiffer rear bar" works best on a car running 225/255 stagger. If you run square with a stiffer rear bar, the rear gets slap-happy and tends to step out at 85 mph on those fast sweepers. Been there, done that... and not doing that is better.

Getting the car balance right for your local tracks and your driving style is a process and is not the same for everyone. This is why dedicated race cars run adjustable sways so they can adapt to changing conditions and changing tire setups. For a dual purpose car running staggered setup, I like the M030 rear sway a lot to put the car where I want it to go without getting too extreme.

I see some guys doing their own setup and they put heavy springs and a very stiff rear sway on the car. Now the car skips like a stone on corner entry and they get a lot of wheel spin on corner exit. They can't understand why with all of their "upgrades" the car is turning slower laps. The answer is simple: Wheel spin is slow.

Happy hunting!
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Old 06-18-2019, 07:41 PM   #16
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I'm still figuring out suspension setup, but I'm quite happy with stock front/ non-S M030 rear sway bars with Bilstein B8's/ H&R red sport springs for my spirited street driving, my tail never came around me (okay except once on very wet road when I was pushing it stupidly on worn rear tires... replaced them on the next day!)

I still have stock size 205/255 tires on 17-in wheels, and planning to go 225 fronts when they wear out and then maybe step up to beefier from sway bar, standard S or S-spec M030. I'm a less is more guy, going for a simple, light weight car that can be daily driven, and will definitely keep 17-in wheels for their weight as well as cushion to tolerate sub-par Michigan road. Wondering if I can squeeze more fun out of my 2.5 around street corners quicker with more 'rotation' with this bigger tire/ sway bar change up front.
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Old 06-19-2019, 05:32 AM   #17
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Wondering if I can squeeze more fun out of my 2.5 around street corners quicker with more 'rotation' with this bigger tire/ sway bar change up front.
Huh.....
Glad you don't live in MY neighborhood. Hahaha

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Old 06-27-2019, 07:44 PM   #18
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Who has gone 225 up front from 205 stock, and if you have, any appreciable benefits or downsides?

Also with added traction with 225, did you also have to upsize front sway bar to counter oversteering?
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Old 06-27-2019, 08:48 PM   #19
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Who has gone 225 up front from 205 stock, and if you have, any appreciable benefits or downsides?

Also with added traction with 225, did you also have to upsize front sway bar to counter oversteering?
I went through about 20 sets of tires in the 225/255 stagger and that was my favorite setup. It gives you a bit more grip forward so better cornering and braking. No need for a sway bar change.

I also experimented with a 255 square setup, and it was good but not quite as quick on my local tracks according to the data. Different drivers have different experiences with this.
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Old 06-28-2019, 02:37 PM   #20
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I went through about 20 sets of tires in the 225/255 stagger and that was my favorite setup. It gives you a bit more grip forward so better cornering and braking. No need for a sway bar change.

I also experimented with a 255 square setup, and it was good but not quite as quick on my local tracks according to the data. Different drivers have different experiences with this.
Thanks for feedback, was not expecting better braking but make sense. Canít wait to get a pair of 225 up front soon!
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