GP-Winning Racing Front Suspension

[FJCamper]

Above: An Auto Union C-Type in action. Your Type 1 front suspension was born on the race track.

Dr. Porsche invented the what we all know as the Type 1 front supension for his series of pre-war Gran Prix winning supercars ... most of which also happened to have swing axles, but that's another story.

The point of this post is to make you consider very carefully before you change your own front suspension.

The Auto Union front axle only has the torsion bars in the lower tube. The top "tube" is actually just mounts for the old style adjustable friction shocks.

Everything geometrically about the Auto Union front suspension and our Type 1 is the same. The question is why did Porsche design this suspension, how does it work as a racing suspension, and why did he think highly enough of it to continue it in the VW and Porsche cars?

The physical design was very light and compact, and used Mother Nature (or maybe Father Physics) to its advantage. As the body rolled from side to side, the torsion bar tubes did too. That made the tires lean, breaking adhesion, and inducing understeer.

The relationship between lean and understeer is direct and predictable.

To get caster to help the tires track straight, the bottom tube was tilted forward just a bit relative to the chassis.

The most important thing was the duty of handling in general was designed into the front end. It had the roll stiffness. The rear end (swing axle in particular) was just along for the ride.

Porsche knew the swing axles were going to tend to break grip, and the geometry of the front end worked in unison to break grip gracefully as well. Competing against the Mercedes W163's, Porsche constantly tinkered with the swing axles on the Auto Unions, finally replacing them with a deDion type rear suspension in the D models, and the over-powered Auto Unions keep winning races.

Look at the ground clearance between the lower torsion tube and the track in the photo above. Looks a lot like your stock VW, doesn't it? Lowering the ride height dramatically changes your geometry a lot and makes your car handle poorly.

That's why I recommend a two-inch drop at maximum. With extra caster shims.

Give the good Doctor his due. He knew what he was doing and had a house full of trophies and awards to prove it.

FJC

[david58]

As usual a great post thanks FJCamper nice to have you give us another history lesson. That pic really starts that post out with some interest.

[doc]

Pretty interesting! Lots of sex appeal in big drops though. Can poor handling be overcome with air bagging front and rear, thereby dropping the whole car?

doc

[FJCamper]

Hi Doc,

I know extreme lowering looks good to many if not most people. If the car is mostly show and little go, extreme lowering and the handling side affects it has can be tolerated.

An air-bagged VW is another animal entirely from original design intent. All geometry is changed for the worst, and the car becomes an oddity, like one of the East LA lowriders. A rolling cartoon.

I'm not advocating that every one set up like a race car, or drive like on a race track. I'm really talking to the guy who is modifying his daily ride so he knows the risks.

There's room for everybody in this hobby. I'd like to hear from those who have air-bagged or otherwise extremely lowered their car and still drive it everyday, and their experiences.

FJC

[Jadewombat]

Hi Doc,

I know extreme lowering looks good to many if not most people. If the car is mostly show and little go, extreme lowering and the handling side affects it has can be tolerated.

An air-bagged VW is another animal entirely from original design intent. All geometry is changed for the worst, and the car becomes an oddity, like one of the East LA lowriders. A rolling cartoon.

I'm not advocating that every one set up like a race car, or drive like on a race track. I'm really talking to the guy who is modifying his daily ride so he knows the risks.

There's room for everybody in this hobby. I'd like to hear from those who have air-bagged or otherwise extremely lowered their car and still drive it everyday, and their experiences.

FJC

This line of thinking about racing with airbag susp. or that they can handle is a bit outdated. Ten years ago this was the norm. Regular autocrossers run individual lines to each wheel with an expansion tank to compensate for the roll and bumps. The old 'put more air in, bag inflates, car goes up, everything stiffer-higher, softer-lower' just isn't true anymore. I'm not an expert, but the racing air suspension setups keep up just as well nowadays as shocks and springs and sway bars, if not better in some cases.

A google search churned up:

http://www.maxchevy.com/events/2006/ima ... esults.doc
http://www.ridetech.com/more/street-challenge-archive/

[DutchBug]

As a dummy the next question.
When I look at the picture I see the arms lying horizontal.
Is this the limit of lowering?
So drop untll the arms are horizontal.

[FJCamper]

Hi Jadewombat,

For the VW's, I was actually talking about the air bag lowering kits that have their own suspension geometry. At one time, I considered taking one of their front end arrangements and springing it conventionally.

Active or adjustable suspension systems, air or hydraulic, have been with us for ages. Consider the Citroen!

What I'd like is for guys with extremely low systems to tell us about their daily life with their cars.

FJC

[DutchBug]

I have a 1303 with Mac Pherson. So that is another story perhaps.
Anyway, it drives really well. This is totally different than a torsion bar susp. but just like to ad my 2cnts.
The only problem I have is the speed bumps which we have at about every 100 meters or less in my town. And I hit the road when driving to fast over holes in the road. I know most holes in my town but on strange roads I often get surprised. On the highway it drives just fantastic. It is the best steering bug I have ever driven. (I had about 7 myself from 64 to 73).
The wheels are 14". In this picture you can see how low it is. But it looks higher than it is in real life. Don't know why.

[doc]

I was really thinking about 2 things. First, the appearance aspect. Lower is pretty cool. And, second, lowering the center of gravity which should help handling characteristics. F1 cars have virtually zero ground clearance, eh. Probably not too good on speedbumps but clearly some parts of lowering create stability and better handling.

Same seems true of widening the track. Notwithistanding keeping everything under stock wheel wells, wider should be better. Same for wider tires.

I also would be interested in experience comments from lowered car users. I bought a Yukon last year - real smart -and it came with 20" wheels. Looked great - rode like a garbage truck. I traded down to the 17" wheels and the ride quality improved dramatically.

VWs handle reasonable well with stock setup, especially the newer cars with McPherson front end. But what can be done to get the cool look and great handling?

doc

[FJCamper]

Above: Rear roll, front roll, CG, & Roll Couple

Hi Doc;

If the center of gravity, roll centers, etc., were all unrelated, lowering alone would help handling.

Lowering the center of gravity is in itself a good thing. But the side effects of changing the suspension geometry that lowering causes creates troubles somewhere else.

For instance, front roll is calculated by drawing a line from the front axle through the angularity of the trailing arm to the ground. The car is going to try and lean left or right off the centerline from the front axle to the rear...the roll couple.

When we drastically change the trailing arm angularity in lowering, we change the front roll center, which changes the roll couple, which changes the limits at which the front and rear suspensions work together and cause controlled breakaway.

The center of gravity improvement gets negated.

Our Type 1 cars have that low front roll center (for very little roll) and high rear roll center (for roll) that lets the rear load the front.

This is not just textbook handling physics I'm showing you here. Knowing all this and using it at the racetrack is what lets us whomp the people who don't.

FJC

[doc]

So, to be clear, since what you've provided is quite over my head, does this mean that the stock setup is optimal? Would lowering front and rear (via airbags to maintain wheel alignment) not lower the overall COG (decreasing slope of line in center illustration), thereby improving overall handling?

In other threads you have mentioned benefits by adding antisway bars. Is this a positive in all setups? Does widening track width help? Are there caster/camber adjustments that help?

I want lower and better? I love the look of the East LA "bomb" cars but want to speed too!!

Tell us more.

doc

[brookester]

What if you lowered the front with dropped spindles and equally lowered the rear using a tranny raise kit?

[FJCamper]

Hi Doc,

The stock setup, meaning the ride height, is not optimal for the best handling of the system Dr. Porsche gave us.

An approximate 2-inch drop front and rear is best, because that has the least bad side effects on bump steer, and suspension geometry.

If we had a different suspension system, we'd be talking about something else. The design of our system causes trouble if we don't keep the same suspension geometry relationships no matter what the ride height.

"Same relationships" means trailing arm and axle angles so that the front end does most of the cornering work, there is enough suspension travel to allow weight transfer to make the roll centers work, and we stay off the bump stops.

Once you hit the bump stops and stay there, you are on the verge of losing control of the car, as suspension action has ceased.

Example, at the Barber Motorsports track outside Birmingham, there is a dip on a high speed slightly downhill straight that marks the spot where you start slightly uphill.

That dips scares hell out of the drivers in poorly setup cars -- BMW's usually, because they buy the whole lowered spring kit and set up their shocks too hard because they think that's "racy." They almost come off the road as their suspension bottoms out, and they bounce.

And so it is a simple Karmann Ghia with adequate suspension travel and moderate shock settings can blow right past them in that dip as they go into long term pucker.

There is what looks good, and what works.

FJC

Watch this clip again, www.youtube.com/watch?v=yowKsYDy4UU and see this happen. At tape count 0.1.46 you'll see our car slingshot a 6-cyl Bimmer as the guy lifts off in anticipation of the dip!

[turbobaja]

What if you lowered the front with dropped spindles and equally lowered the rear using a tranny raise kit?

I'd say this is the way to go. Swing axle, I would assume? This would truely keep all the suspension geometry intact and give a good drop in CG. Good ground clearance (acceptable at least) and still maintains a good amount of suspension travel before bottoming out.

Have you raised the trans in your bug, brookester? Sounds like a cool project. I've seen a lot of the drag racers use big trans raises (5-6") to really get low and maintain a nice contact patch with swingaxles and slicks. 2" would be just right for daily use with performance in mind.

Karl

[raygreenwood]

To reinforce what FJcamper is saying....and many people miss this entirely.....the front suspension of the beetle..and most cars for that matter...was designed for the wheelbase, tire height, weight etc....with a specific geometry in mind to wrok optimally for the range of motion of that suspension.
Does this mean that for handling Dr. Porsches design is optimal....no.
It means for general usage within the design parameters of the car....the suspension operates with the least bad habits and most longevity.

When you change the angles within which any of these components operate (by lowering, lower profile tires, weight distribution, or actual general usage of the vehicle), you change leverage equations and either the lifespan of some components or the behavior can change radically.

You can get away with a certain range of mods before you violate enough designed in abilities of the components. For example: just lowering the front end alone....to far...can change the operating angles and leverage much farther than a certain range of lowering across the board both front and back. Within a limited amount of change....at least front to rear proportionality can be maintained.

The mentioned example earlier of the SB strut suspension is a classic example of how one change violates to many design parameters and can quickly cause problems. The front SB suspension is based around experiences from the 411. It has some of teh same issues and it gets ugly quick.

Example:
Lets hypothetically lower the front of the SB by 2". You can do that by cutting coils (not recommended) or by swapping in shorter springs.

To be correctly done, these springs must be stiffer to arrest compression dives in a shorter amount of stroke. It is the springs that do this ...not the gas or oil cartridge. The cartridge simply "damps" the rate of speed of both compression and rebound.

BUT.....adding stiffer and shorter springs changes two things (a) the strut piston is now residing in a different position within the tube. It has a different range of time and pressure against what is otherwise stock valving.
This valving was designed for a longer stroke. It will not generate the same pressures in a shorter stroke. You now find that the struts cannot slow the rate of arrest and rebound as it could before. This makes the suspension harmonic choppy and rough and makes it harder to maintain tire contact to pavement.
(b) So you need to find a strut cartridge that has revalved pressures for lowering and stiffer less progressive springs. What this causes.....is an entirely stiffer unit of both spring and shock...above the ball joint. What quickly happens is that the compression arrest rate builds so rapidly that teh only "safety" valve is the ball joint spring. Its common to overcompress them on bumps and crack the spring.

So...the ball joint spring must also become stiffer.

The next thing to go south in this equation...is that strut bushing durometer and angle is designed for what arresting rate the struts came with. The bonded bushings typically wear out and tear faster on lowered strut suspension.

Lastly, the control arm bushings are designed to operate originally within a specific range of angle. Lowering decreases the angle and loads a different area with leverage. You usually must change to urethane contorl arm mounts ...to control.....the transfer of leverage to teh bonded rubber idler arm mount....which is the FIRST thing to go...because its not designed for the generation of sideloads now applied to it by the lower angle of incidence of the control arms. The centerlink bushings wear faster as well.

I'm sure some of the same issues apply to torsion bar suspension geomtry. Ray