[Shad Laws]

Hello-

I need some more explanations now.

Okay :-).


Why do most modern cars not use torsion bar setups then if it is as good and cheaper?

Most modern cars don't have torsion bar tubes and torsion bar tube supports, either. If you eliminate the entire torsion bar system (not just the torsion bar itself) and replace it with a coilover, you save weight.

What we were talking about was modifying an existing semi-trailing arm system with torsion bars to coilovers. If the page is blank, and you can do what you want, then starting over completely from something else lends itself to different solutions.

Why do the 911 and 944 guys upgrade their cars to coilovers?

Ah! Now this is applicable.

They do it for the reasons I said above:
- add easy adjustability
- add a highly-progressive spring rate
- add more simple linear spring rate

Also, the labor cost of adding stiff torsion bars vs. coilovers is much higher. This is important when you figure that many Porsche people have other people work on their cars for them :-).


Why did Porsche change the suspension with the 964?

The 964 saw a removal of the torsion bars, but the MacPherson strut front and semi-trailing arm rear basic designs stayed in place.

The rears has to go to make room for a long transmission (hey Wally - here's your application :-) and the fronts for a pair of new axles for 4WD. Plus, it allowed a less labor-intensive flexibility of adjustment and modification for different applications (i.e. racing).


If you consider buying shocks as well you can add some money to the entire rear setup.....not only the 200$ for other torsion bars.
If you are serious about your cars performance you will have to add bracing to the rear to eliminate wheel hop. This ties in the top shock mount so there is nothing to worry there.

Yes, but what about the lower shock mount? After 30 years of "normal" use, many VW trailing arms are bent, leading to excessive negative camber in the rear that really can't be adjusted out. Putting the entire suspension load on a stock trailing arm at that point will just make it worse. Now, if you already have more rigid trailing arms, then it's a different story :-).

Alex - I'm not saying that coilover systems suck. I'm not saying they don't work. All I was trying to do was give a very specific analysis of _why_ you would want to use them.

It seemed like many people just wanted them "because they're better," but they couldn't pinpoint why the torsion bars were inferior in this regard, except for that it is "common knowledge" that they suck. They want to bolt them on with little other consideration for the big picture (like the trailing arm problem, for example). I was trying to give some perspective - unfounded opinions of "sucky" and "cool" are a bad idea to design a car by :-).

BTW, the prevailing thought of "torsion bars suck and coilovers are better," without any further analysis, is also another major reason why 911 and 944 people do it :-).

For example, let's compare the following configurations:
CONFIGURATION A:
- aftermarket torsion bars
- adjustable gas shocks
- 944 adjustable spring plates
CONFIGURATION B:
- stock torsion bars, relaxed
- coilover shocks (constant spring rate springs, but gas-filled shocks)
CONFIGURATION C:
- the Eagle Products' setup
- coilover shocks (constant spring rate springs, but gas-filled shocks)

All three can be configured to give basically the same springing characteristics.

Configuration C may have a problem with isolation mounting. Configuration B and C require stronger trailing arms. Configuration A is slightly lighter in weight (not by a whole heck of a lot, but it's there). Configuration B and C consume more space (Oil coolers can get close to rear shocks...). But these are all minor points - there's no huge benefit to A, B, or C.

However, it is the common opinion that A is the worst, B is next, and C is the best, and difference between these three is substantial. While this may look better on a spec card for bragging rights, from a performance standpoint, this is false.

Take care,