Trailing arms? Nuts!

I am amazed at how well my 911s handle, but I the geometry of trailing arms suck. Think about it. When the cars leans in a curve, the wheels do not even come close to staying parallel to the ground as they would in wishbone, de dion, or even a rigid axle. Oh, it sure beats swing axles, but it is still a horrible approach. This is the one thing that I have never been able to justify, even knowing the packaging problems with the rear engine boxer layout. Can anybody justify this engineering? Other than a rigid rear suspension, is there an economical way to get proper geometry? If it weren't for the shape, the sound, reliability, galvanized, etc., I'd never have a car with this ridiculous set up.

Justify it! How can the ill effects of this be ELIMINATED? Then, my 911s will be perfect again.

Dan

[This message has been edited by diverdan (edited 01-09-2001).]

Good excuse?? I think you named them. Packaging, weight, and cost. But also, handling. While you may feel that the trailing arm is inferior, there are a few other 'notable' sports cars that had them. 240/260/280/300Z/ZX, IRS RX-7's, 914, even the old Datsun 510's (IMHO one of the best handling, predictable, and fogiving cars made). So I don't think a total discount of the philosophy is warranted.
If my memory serves me correclty, the mounting points of the spring plate and trailing arm are very close both in Front/back and height positioning. If equal, they would provide no increase in neg camber as a side is loaded (thus providing more bite to the outboard rear wheel) as in cornering. The 911 does provide for this. The mounting points can also be easily tuned to add or subtract bump steer (toe-in/out) which could make the car unmanageable, but also very benign (aka 87-88 rx-7 toe adjusting rear end).

So, surely it is not as capable as a full U/L A-arm set-up for pure racing, but it is very sturdy, light, and allows us to install those SSI's ourselves!!!!!!

What's the cause of your beef dan?? trying to corner balance or align??

Actually they are "semi" trailing arms. They are a nice compromise between trailing arms which have no camber compensation, and swing axles, which have way too much camber change and that dreaded "jacking" under hard cornering. Really they are an excellent all around set-up that are simple, lightweight, and above all, nearly indestructable. thats how porsche has won so many brutal endurance races. They also provide some anti-squat and anti-dive. The anti-squat diminishes with lowering however. The only real drawback, actually, is the absence of toe correction. That is a plus in my book however because I like to do the correction with my right foot and the gas pedal.

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Tyson Schmidt
72 911 Cabriolet

The geometry of the rear suspension is the achilles heel of the 911, and something that even Porsche engineers have been dying to fix for decades. Unfortunatly the rear engine has been blamed for all of the 911 handling "uniqueness".

The LSA rear suspension of the 993 has corrected all of this and brought the 911 evolution into the modern age. To me the only way to overcome the 911 rear is to get a 993 and never turn back. But then again, we love our 911's...

Also Scott, don't forget 2002, various Mercedes Benz, 924,944 and too many other BMWs to name. It survived in the 911 until 94 and in my opinion, only changed to save the ass of unskilled drivers. And the cars also were getting more and more tail-heavy. (well just heavy period)

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Tyson Schmidt
72 911 Cabriolet

I have seen early 911 race cars with the 993 rear suspension. It is doable.

I think Brain hit a point here on ruggedness. In a race, I'll take durable over precise anyday. Not to be a Porsche blow-hard here, but the 962 whooped up on Nissan, Toyota, Ford Probe GTP, Corvette GTP, etc.. it just outlasted them.

I fail to see any glaring design brainfarts on this. Geometrically, this suspension does not result in much alignment change when "loaded." Just a tiny bit.

But I have to say, that banana thing is the goofiest looking trailing arm I have ever seen.

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'83 SC

Guys: Thanks for your input. I guess that on my long freeway drives I think of crazy things like this. My first 911 back in the early 70s really impressed me with the way it could put power down on a rough surface. Cornering at the limit never felt as good as the little Alfas with the solid axle, you know, the one that diced with the BMW 2002s. But, the 911 was a whole lot more car than those simple Alfas.

Well, I looked at some cutaways of the 935, one of the most successful race cars of all time and they retained the trailing arm set up. The 917s did not.

That 993 set up on the 911 sounds interesting. Where did you see that Rarly?

I guess that Maserati used solid axels in its front engined cars until at least the end of the big quatroporte. Alfa didn't get de dion until 1975. I did have a 57 Maserati that had a transaxle with de dion, but it was crude and that car was anything but reliable throughout its race history.

I would certainly rather have the semi trailing arms than the solid rear axle setup or swing axels. Also, you are right regarding the loaded side preserving perpendicular to the road profile. The opposite tire is of much less consequence. I guess that the trailing arm is one of the design features that was not so far ahead of its time as the other features that I dearly love.

Superman, I always thought that it was goofy looking too, but I do appreciate that the large diameter really combines strength and light weight. It reminds you that the interior portions of the nice aluminum A-arms or links are really rather worthless when it comes to structural strength.

Thanks guys, I realize that while not perfect, it really isn't that bad and definitely better than most alternatives.

Dan