Lowering For Handling

[redhot]

Hi again,

What I wondered is what made the suspension so stiff when lowered. It seems to me, based on your answer, that the force x arm is reduced, since the arm gets shorter as the torsion arms move upwards. The supension is progressive in its nature, and it`s logical that VW designed it to be soft around it neutral position, and stiffer when it gets more compressed.

Next follow up: for a balljoint car: at what lowering does the ball joints bind? Easiest to check on a car with no torsion leaves attached, only the complete torsion arms and wheel. A picture would say much, with the wheel present, and removed.

And there is a issue of lowering coupled with aerodynamics. The "How to hotrod" book says that VW in fact raised the front end to get more lift to the front vs rear in an effort to reduce the jacking effect.

I find great joy in these topics, as for me the suspension is a fascinating issue.

[FJCamper]

Hi Redhot,

Yes, the front torsion leaves are progressive in that the farther you twist them the greater the resistance.

What makes the front end feel so stiff (once lowered) is you have so little suspension travel and go to bumpstops so quickly that you have no front suspension. The driver feels this as extreme stiffness -- the frame has become the spring.

Not to mention that some felt stiffness is in the ball joints themselves.

Standard ball joints begin to bind at full deflection after just two inches of lowering, and at three inches are in the danger zone of breaking. The special "lowered joints" allow some margin in the three-inch drop zone. And some guys are running that low.

You mentioned VW (from Fisher's book How to Hotrod Your VW?) raised the front suspension slightly in relation to the rear. That's true, and applies to swing axles. Lift is trying to rotate the car up with the rear axle as the pivot.

Beetles have a lot of lift at 75 to 100 mph. And more lift at the rear than front! The insider's handling trick is to run the rear end a half inch lower or so than the front.

The old Bonneville salt flat trick for everybody else was to rake a car, and run it nose down, to try for a better angle of attack into the wind. This became the "hot rod" look, and even some of our VW guys fell for it. Monkey see ... monkey do.

On a high-speed straight-line swing axle VW, you lower it as much as possible, but let the rear ride that slight bit lower. And I mean a Bonneville or super speedway (think Daytona) car, not a dragster. They have their own set of tricks.

You don't want cosmetics -- you want better lap times.

FJC

[Bruce2]

On a high-speed straight-line swing axle VW, you lower it as much as possible, but let the rear ride that slight bit lower. And I mean a Bonneville or super speedway (think Daytona) car,

One result of this is that the windshield gets raked back a tiny bit so the car is more aerodynamic.

[Ozzie]

You don't want cosmetics -- you want better lap times.
FJC

I'm going to the trophy shop. I'm going to have this engraved on a brass plaque. Then I'm going to glue it to my dash.

[david58]

You don't want cosmetics -- you want better lap times.
FJC

I'm going to the trophy shop. I'm going to have this engraved on a brass plaque. Then I'm going to glue it to my dash.

That will slow yer car down.

[redhot]

There aren`t any bumpstops on the balljoint models as far as I know, nothing like the bar between the tubes on the link-pin. So it must be the balljoints one feels?

[redhot]

Great article about handling of the Porsche, which is very similar to VW

http://www.spyderowners.com/reviews/tobin1.asp

[FJCamper]

Hi Redhot,

The bumpstop on the balljoint models is the top of the shock absorber!

And yes, great 356 suspension article you cited. Everything in it applies to our VW's. The author didn't attribute the intentional leaning front suspension design to the Auto Unions, or mention that all Porsche tweaks soon followed on into VW designs.

A well set up swing axle can still win.

FJC

[Lew]

I learned somethings reading this thread....I plan to drop the front end of my 72 Bug using Drop Spindles.....Would someone recommend where they purchased forged spindles, and if satisified with them. Also recommend a Disc Brake kit. I want to do Disc Brakes on the front and stay with drum brakes on the rear......There are many vendors that sell spindles. I am just looking for good quality parts and pricing!

Thanks!

[kdf]

The lowered rear end (on an IRS) begins to suffer axle angularity as the transaxle drops in relation to the centerline of the wheels. The axles are cocked upwards, adding stress (and robbing power at the CV joints) as they rotate.

How low should your rear end be? No more than what gives you straight axles at rest.

I remember a touring team testing CV joints. After they had played around with them, they found over 20 horsepower on a chassis dyno, which is almost 10% of the power of the specific car. The stock CV's are so rough, that when they wear the surface on the inside becomes better as time goes by. So they built a fixture to wear CV's that was basically an electric motor rotating the CV at a slight angle against a brake. They found out that the more they wore, the less power they robbed. The bad side this was that they only had nerves to run the CV's for one race because the sloppyness was starting to be scary.

I use new CV's and I'm not encouraging anyone else to run worn out CV's. I'm just trying to point out that the attention to details in racing cars is very high. Finding many small advantages here and there makes the difference.

[FJCamper]

Hi KDF-

You are onto one of our tricks.

I have a set of worn but periodically disassembled, inspected, cleaned and regreased CV's on our IRS road-race Ghia. They are prized items.

Our power output is limited by what the CV's can take. If you are not drag racing, the Porsche factory tested the VW-style joint at being good (street reliable) up to about 150hp.

They will take more than that, as VW tuners have discovered, but the factory was concered with street life.

FJC

[Project AX]

FJC in the picture that you posted at the very beginning of this thread, is the relation of the center of the spindle and the top torsion important? In the picture it shows them being level?

[FJCamper]

Hi AX,

The simplistic illustration at the start of the thread isn't meant to be precise, but just to show basic relationships.

Type 1 VW's set caster by shimming the lower axle tube out forward relative to the top tube, and that of course causes the lower trailing arm to move forward, creating a slight tilt backwards in the king pin or balljoint centers relationship.

Lowering can affect caster by tilting the trailing arms upwards more than they would be in the factory ride height, and this causes the strange stability problems those who have the front end "down in the weeds" often notice, especially when running over bumps and undulations in the road. This effect is worse if the rear end isn't lowered in relation to the front. The front axle should always be reshimmed to compensate after lowering.

Lowering also affects suspension travel, which for road courses isn't much hassel, but for lowering on the street it is a constant problem. The exception to the "smooth road course" rule is dips or banked tracks where your suspension goes to full deflection due to g-forces. Goodbye oil sump!

FJC

[Marc]

Bump steer is caused by the change in effective length of the tierods as they move through the arc of their normal range of travel. The tierod ends do not need to run out of travel in order for bump steer to take place - but if they do, that's even more dangerous since they're likely to break (or at least deform and develop excessive play).
On most cars it's possible to to design the front suspension so that the steering arms of the spindles also move in and out a corresponding amount as the suspension travels, but on the torsion-bar VW the wheels move straight up and down. The steering arms do move slightly fore & aft with suspension travel, however, so there's still some interaction with the relative lengths of the tierods. The change in effective length of the tierods and the control arms is minimized when they are both kept as near to horizontal as practical at rest position.

Drop spindles allow lowering the front of the car while maintaining the stock steering arm height relative to the chassis, so the geometry of the control arms and steering linkage all remains unchanged....but they do NOT eliminate the need for caster shims.

When the front of the chassis is lowered relative to the rear caster is lost. Steering effort is lightened, making it easier to turn the wheel at low speeds, but high-speed straight-line stability is lost since the weight of the car is no longer working to keep the front tires pointed ahead. Doesn't matter what caused the forward rake - drop spindles, or even smaller front tires, still cause a loss of camber unless the rear of the chassis is lowered by the same amount.

The effect of caster is not unique to VWs, all cars react in a similar fashion. When my pickup truck is empty it demands full concentration to keep it centered in the lane at highway speeds - but add ~¾ ton of load and the chassis levels so it tracks nice and straight.

[Project AX]

Thanks FJC

Okay so now I have another question. In referring to your "about two inches" for the recommended lowering, would a 2.5" drop spindle + 2" drop from adjusters = 4.5" still equal your "about to inches" because the drop spindle is not effecting the geometry? In short would the lowest possible ride hight be 4.5" and still have room to adjust for camber, etc.?

Reason I'm asking is because I'm going from the world of "as low as possible" to "performance first" as I am building a car for soloII.