Torsion bars vs Sway Bars?

[autobonrun]

I upgraded my front torsion bars from 19 to 21 and will be upgrading my rears from 24 to 26. My question is what does changing the sway bars do that increased torsion bar diameter does not? Functionally, don't they perform a similar function; limit roll.

With larger torsion bars and Bilstein Sports on all 4 corners, is it even worth increasing the size of the sway bars on my 79SC?

My car gets some track use but primarily street driving.

[marcesq]

Auto:

I am running 21/26 torsion bars on my car with the stock 20mm front/18mm rear sway bars. I do not track the car at all (wife would leave me if I did).

The torsion bars reduced the amount of squat when accelerating, and also improved the tire to road contact.

I believe that going to larger sway bars would help reduce the side to side pitch of the car body when cornering.

The larger you go, however, the less "streetable" the car becomes because of reduced ride comfort.

For what its worth.

[Jack Olsen]

I would go to 27s in the rear, with 21s up front.

I'll leave the explanation of the different functions of the two components to guys who know more than me, but the simple take on it would be that torsion bars primarily allow the car to absorb and adapt to uneven surfaces (bumps) and secondarily work to reduce body roll. If you were trying to do all the roll reduction with only torsion bars, you'd have a very uncomfortable car.

I would get adjustable swaybars, front and rear, so you can fine tune your car's handling.

[autobonrun]

Thanks, I'll consider the 27 rear over the 26. The adjustable sway bars may be a little to expensive for me to handle however.

This winter had better end soon. I can't afford to keep my car up on stands. There are just too many projects that can be done when everything is within reach.

[masraum]

Torsion bars are the 911 equivalent to springs. They are primarily to suspend the car and absorb the irregularities of the road as Jack said. They may resist roll to an extent because the outside springs don't want to compress, but at the same time the inside springs want to extend. So while one side is trying to stay flat the other side is actually fighting it somewhat.
Anti-roll bars actually resist rotation around the middle longitudinal axis of the car. When the outside tire/hub compresses the spring and is pushed up into the wheel well the end of the sway bar on that side is rotated up with the wheel. Since the bar extends over to the other side of the car that side, the inside, will also try to rotate up which is the opposite of what the spring is trying to do to the inside wheel. So the anti-roll bar is actually trying to lift the inside wheel and compress that inside spring. Since the weight of the car and the inside spring are resisting that rotation it will also be resisted on the outside wheel. The anti-roll bars are actually trying to keep the car flat while each spring doesn't really car what the other springs are doing as long as he gets to extend as much as he is able.

I'm certainly no expert, but from what I've heard and read I would go with the new torsion bars, drive the car a while like that, and then once you are really comfortable with the new torsion bars then change out the sway bars. Gradual changes instead of everything all at once.

[Graham Archer]

IMHO, as delivered your car is already set up for street use (with some track time). I would suggect that you simply renew the wear components (bushings and shocks (HD)) and only beef up the torsion and sway bars in response to a specific issue on the track.

[jluetjen]

A couple of things to remember about springs (AKA Torsion bars) and sway-bars:

1) The job of springs is to hold the car up. If they are too soft the car will bottom out. If they are too stiff they will cause a really harsh ride. To stiff will also require a corresponding increase in stiffness for the shocks which can actually result in a reduction in traction if the result is the wheels coming off of the ground over rough surfaces. They can also be used to control roll, but doing so will often result in the springs being too stiff for the road surface.

2) Sway-bars (AKA anti-roll bars) affect the balance front/rear during steady state cornering. It is also important to remember that sway bars affect the handling of the opposite end of the car. So a rear bar will affect the handling of the front end and vice versa. Simply put, by putting on a stiffer rear roll bar you will transfer more weight across the back of the car during a corner then without. This will give the outside front tire some relief and hopefully allow it to provide more grip (thus reducing understeer). If you go "over the top" with the rear bar you can cause the outside rear tire to be overloaded which will cause oversteer and an overall reduction in cornering force.

Sway bars and/or springs can also be used as a crutch to cover up poor suspension design. For example, some suspension designs (such as McPhearson struts) work great in the center of their range but lose a lot of camber in compression, and body lean will make it even worse. Using stiff springs or shocks will prop the car up so that the suspension stays closer to it's "sweet spot".

Ideally you want a car's to suspension to be as soft as possible without it bottoming out. This should provide a pleasant ride and forgiving handling. Cars which are too stiff will often handle as if they are on a knife's edge. This sort of handling is difficult to manage for maximum speed and consistancy during a race.

That being said, the suspension design of the 911 is very good in general for most uses, especially road use. There shouldn't be a whole lot of reason to change it unless one of the parameters has changed. The reason why track and race cars have stiffer suspensions is because they are running stickier tires. As the grip of the tires goes up, the car will start to lean/dive/and squat out of the suspension's sweet spot. The fix to this problem is stiffer springs and swaybars. It's interesting to note that when it rains, race teams try to make the cars as soft as possible (softer springs, disconnecting sway bars) in order to maximize the car's use of the limited traction.

I may have been long winded, but I hope that it might clarify when you might want to change springs or bars.

[autobonrun]

Thanks for all the replies. This is just what I wanted to know. I did a search and most of the threads were on how to do the install, not on the dynamics of when to use thicker sway bars or how they work. I had only considered side to side impact of sway bars, not front to rear and vs versa.

[bento]

any thoughts on the cheapest place to buy torsion bars?

db

[RarlyL8]

If you are running an SC engine (AKA 3.0L) and the primary use is street I would opt for the 26mm units in the rear. This is what I put on mine and they are right on the edge of jarring my gizzard.
Your rear weight is not high enough to require a more aggressive rate for the street.

Theory of torsion and anti-sway is all nice, but the real world fact is that stiffer t-bars in a 911 reduce sway. With new shocks and low profile rubber you may just be where you want. Check your suspension out real good to see that there are no worn out parts that might mask any improvements.
Don't change the sways until you try out the t-bars first. Everyone is different - some like it rough.