Sway bar differences - adjustable vs. non-adjustable
 

Just for fun...

In an effort to reduce the inherent understeer that I experience on the track, I decided to replace my "stock" 20 mm NON-adjustable rear sway bar with a 19mm adjustable sway bar (AJ-USA). But when I went to remove the "stock" sway bar, I found that the previous owner had already installed a larger rear sway bar - a 21mm NON-adjustable rear sway bar (964.333.701.07 Carrera 2 -90 M481).

So, I wondered...

Would a 19mm adjustable rear sway bar set to max firmness be more firm than the larger 21mm NON-adjustable?

Well, it took longer than I expected test them, but I finally had an opportunity to compare the two sway bar set-ups last weekend.

Because I didn't know what to expect, I thought it would be fun to take a poll to see what YOU would expect. I'll post my observations, for what they're worth, later...

Erick

I'm guessing the AJUSA 19mm bar reduced the understeer more than the 21mm bar because of the additional pre-load you get with an adjustable bar set at firm.

Ahhhhh. I didn't consider this distinction.... probably because I didn't understand the distinction. SO, when I say "firmness", I really mean "ability to reduce understeer". Thanks for the clarification.

Erick

When I put the strut bar (after having bought the Bilstein sport suspension kit), I was suffuring too much understeering. Therefore I made the same modification on the rear sway bar (RS adjustable sway bar)... it's not the same car now... and I'm so happy about the result! Especially on the track, the car is soooooo efficient and easy to drive now! The front turns (yes, before the car was not turning...) and the rear follows easily. The car is really neutral, I like that.

Sooner I think I'll test the front adjustable sway, but as I'm happy now I think I should not change... Using a harder sway bar on the front would lead to the come back of understeering...

PS: my car is a C4

NTTY

I'm wit Joey on dis one. :)

Adjustability does A LOT for dialing in your suspension...the VERY reason why I do NOT understand the RUF design swaybars for the 964. My only guess is that RUF wanted to create a bolt-on package for owners that don't want to fuss with adjustments, they just want a decent balanced package - which indicates to me that they would want to purchase the WHOLE setup.

NO intention of starting a debate, but I will always vote for adjustability! :thumbsup:

AFTER posting, I had a realization: I had the same debate (with myself) over the same issue with front swaybars...as I was going from a 22mm RSA NON-adjustable bar to an adjustable 25mm.

You see, the 25mm bar (if I remember correctly) on it's FIRMEST setting has the holes where they would compare with the location of the ONLY set of holes on the NON-adjustable 22mm RSA bar...I keep the front 25mm bar on it's LOOSEST setting, which seems to be okay.

SO, if one wanted to reduce understeer, they have two options regarding the adjustability of swaybars:

1) loosen the front
2) tighten the rear

Given these parameters, and Erick's question, I'm going to vote for "no noticeable difference" just for the point of debate...Erick, you need to lay the 21mm non-adjustable unit on the ground, with the new adjustable 19mm over it. Compare the location of the holes on the non-adjustable 21mm with the tightest setting on the adjustable 19mm...are they in the same location...to clarify, are the holes the same distance from the 90 deg. bends in the bar??

...if so, then the 21mm would be stiffer than the 19mm on it's FIRMEST adjustment, thus NOT solving your understeer issues! :grr:

The thickness of a swaybar only comes into play after the 90 deg. bends, on the straight section that runs laterally underneath the car...so the swaybar is effectively used as a TORSION bar.

The adjustment holes allow you to adjust the "leverage" under load, for lack of a better explanation (I'm not a Rocket Scientist...but close to it) ;)

Hopefully this helps - Erick, my vote is that you may be peddling backwards...send that bar back for a 22mm adjustable and have TRG send you their adjustable 25mm kit for up front - it's a STELLAR deal and comes with some nice clamps/bushings, not a Porsche part, an aftermarket wonder for half the price! :D

was it the TRG bar that you managed to break JC?:D

I'm with Jeff- you're making the understeer worse by softening the rear with a smaller sway bar. Get a different bar - the 19 likely won't help unless your existing bar is worn out (if that's even possible!).

:)

Well, as I posted elsewhere, it is possible that a 19mm bar may be stiffer than a 22mm bar, depending on where the holes are (which changes the length of the lever arm).

The math to calculate the bar's stiffness can be found in Fred Puhn's book "How to make your car handle", and some of the books from Carroll Smith.

IIRC, I never was able to make the numbers work right, which is probably more a reflection on my math skills than any inaccuracy in the formulas.

BGL

BGL you are definitely correct that because a sway bar is a lever, you can move the "work arm" further from the fulcrum and you'll get a "softer" bar - BUT most sway bars have a similar mounting range of the drop links, limited by the space under the car as well as the angle that the drop links can properly function. So most sway bars mount in a similar range (keeping the work arm fairly similar).

It would be possible to make a 19 like a 22, but you'd risk popping off the drop links (if they are pop-off type) - so in most cases a 19 would run softer than a 22 other than at the extremes of the mounting points.

Just some thoughts...

I'm sure that the suspense has been torturous, so here are my results:

The 19mm adjustable sway bar set to 'firm' reduced the understeer that I was experiencing with the 20mm non-adjustable sway bar!

Actually, it took me a while to get comfortable and confident with the balance of the car. It seems like the car is much more willing to 'rotate', and in the higher speed corners I had to slowly creep up on the limits to convince myself that the rear end would stay put. Reducing the rear tire pressures seemed to help, but I still need to play around a little bit to feel completely comfortable in the faster turns.

On the other hand, it was very easy to feel the difference in the slower corners. Where I was previously having a hard time getting on the gas early because of heavy understeer, I could now get on the gas much earlier and still have the car turn. Ahhh. Much better. Much less frustrating.

Okay, now someone can tell me why...

It appears to me that the 21mm non-adjustable bar has the mounting holes located at what would be the 'loosest' setting on the adjustable 19mm bar.

I still don't have a good understanding of how the sway bar functions. I have a significant amount of body 'roll' in the corners, but suspect that this is mostly a function of weak springs. But with that being said, I am now confused about the benefits of the 25mm front/22mm rear adjustable sway bar set from TRG. What would be the benefits of this setup if I'm already at neutral/slight oversteer?

Thanks for the insight.

Erick

Erick: I'm happy to hear the 19 mm bar was better!

I would expect that increasing the size of both bars will make for a stiffer car. With the bigger bar in the rear you will reduce the ability to lift the front wheel in a turn. However, as you put a bigger bar in the rear, you need a bigger bar in the front to maintain the "balance" of the car and not create a car that oversteers.

My take on this is that the primary reason to change your front bar is to gain adjustability on that end of the car. I have the 25/22 TRG bars and currently have the front set at the softest setting while the rear is at maximum firm. I'm not sure, though, that the 25mm bar at full soft provides better front end bite than the stock bar so in terms of understeer reduction, the 25mm front bar may not be the right choice.

Now, my setup is a little different than yours with AWD, firmer rear springs (308f/508r) and 8" wheels up front. I would say the handling is neutral but the tail will step out if I have some engine braking going on deep in a turn or if I'm a little aggressive with the throttle on corner exit.

That looseness wasn't evident until after I adjusted the bars to their current settings but it's not excessive and easily controlled with the throttle. Prior to that, the car's primary tendency was still towards understeer. So for my car, the 25/22 bar combo seems to be a good fit.

No offense, Tom, but I'd recommend that Erick run his car for a few events to see how he likes the new setup. Unlike our cars, I believe he's still using spring rates which are virtually the same front and rear, so adding stiffness up front may bring back that dreaded plough.

Joey, I agree with you.

I guess my point would have been better stated as: If you are happy with the existing setup, there is no compelling reason to change to bigger bars. With soft springs, I'm not sure big bars would be a good match. I would want to know if there is an issue with motoring around sweepers on 3 wheels, then bigger bars should help.

I suspect that a firmer front bar could bring me back to understeer characteristics, so I'd only add a 25mm adjustable front in conjunction with the bigger 22mm adjustable rear. My wish is to get rid of the prominent body roll, but I may be going about it the wrong way with sway bars considering that I'm still using the soft and progressive H&R 965 springs.

Still, it was fun to drive the car on the track for the first time without understeer. Right now, I'm pretty happy with the car. :thumbup:

Springs are always the place to start - as I've been told and from my own experience - start with springs, then fine tune with sway bars. If your car rolls a lot, or lifts a wheel, get harder springs, then fine tune the sway bars from there! I would not get harder sway bars before getting harder springs. That's my 5 cents... (already gave two....)