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Possible Problem with VW Stock Steering Geometry

FM Former Member
I just analyzed the heck out of the steering on my 356 Replica and have come to a conclusion that a great deal of the slight bump steering problem I have is due to the steering geomtery not being exactly corrrect.

Car steering geomtetry is based on the Ackerman geometry steering principle. This geomtry is accomplished by the angling of the steering arms so that they coincide with an imaginary line that is drawn between both the king-pin/ball-joints and steering arm pivot points intersects with the center line along the rear swing-axle/IRS-axles.

This geomtry prevents both the wheels from turning the by the same amount and as a result inducing the inside wheel to inneffectively slide sideway which in turn reduces the effectiveness of the steering because of tires resisting each other. This negative effect is reduced or eliminated by turning the inside wheel at a greater angle than the outside one. The Ackerman Steering Geometry does this.

Unfortuantely, the stock VW steering is designed for the length of the Beetle. When we shorten the pan for our vehicles, the Ackerman Geometry is negatively influenced and is somewhat affected. It moves closer to what is termed as "carriage parallel steering". Not that the steering is completely wrong, it is just affected to some degree of which I am not completely sure unless I do a tedious geometrical analysis on my car.

To back this, I dissasembled my front brakes down to the bare spindles and compared the spindles to a pair of 356 spindles. At first, they look exactly like my VW and to my surprise, well not really too surprised, I noticed that the markings on my 356 spindles were the same as my VW spindles down to the numbers and even the VW insignias! After measuring the steering arms, that is when I noticed a significant difference. The arms on the 356 spindles are angled more and extend toward the center of the pan by something like 3/4" or more! I guess that the commonality of part usage Dr. Porsche's employed between his Beetles and 356 cars is exemplified by this finding. The parts are the same parts and they are just produced slightly different by varying the arm angle to set up and tune for the Ackerman Steering Geometry for the shorter 356 cars.

I am going to swap my VW spindles with my 356 spindles. My 356 spindles are even reinforced with webs for racing. I guess this should work. I've tried everything to rid my steering from that slight problem and I guess I know why now. ;^)





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FM Former Member
I just analyzed the heck out of the steering on my 356 Replica and have come to a conclusion that a great deal of the slight bump steering problem I have is due to the steering geomtery not being exactly corrrect.

Car steering geomtetry is based on the Ackerman geometry steering principle. This geomtry is accomplished by the angling of the steering arms so that they coincide with an imaginary line that is drawn between both the king-pin/ball-joints and steering arm pivot points intersects with the center line along the rear swing-axle/IRS-axles.

This geomtry prevents both the wheels from turning the by the same amount and as a result inducing the inside wheel to inneffectively slide sideway which in turn reduces the effectiveness of the steering because of tires resisting each other. This negative effect is reduced or eliminated by turning the inside wheel at a greater angle than the outside one. The Ackerman Steering Geometry does this.

Unfortuantely, the stock VW steering is designed for the length of the Beetle. When we shorten the pan for our vehicles, the Ackerman Geometry is negatively influenced and is somewhat affected. It moves closer to what is termed as "carriage parallel steering". Not that the steering is completely wrong, it is just affected to some degree of which I am not completely sure unless I do a tedious geometrical analysis on my car.

To back this, I dissasembled my front brakes down to the bare spindles and compared the spindles to a pair of 356 spindles. At first, they look exactly like my VW and to my surprise, well not really too surprised, I noticed that the markings on my 356 spindles were the same as my VW spindles down to the numbers and even the VW insignias! After measuring the steering arms, that is when I noticed a significant difference. The arms on the 356 spindles are angled more and extend toward the center of the pan by something like 3/4" or more! I guess that the commonality of part usage Dr. Porsche's employed between his Beetles and 356 cars is exemplified by this finding. The parts are the same parts and they are just produced slightly different by varying the arm angle to set up and tune for the Ackerman Steering Geometry for the shorter 356 cars.

I am going to swap my VW spindles with my 356 spindles. My 356 spindles are even reinforced with webs for racing. I guess this should work. I've tried everything to rid my steering from that slight problem and I guess I know why now. ;^)





oldyeleroldyeler
The ackerman is a direct reference to how the car tracks ,in a varity of stearing wheel postions .

Why are you doing donuts? OH boy

A center line at the rear axle is used with a spindle centerline to place the tie rod end centers,so the front wheels can track true in any range of a true circle.

Im not sure it will help bumb stear, But it will help reduce front tire wear. Also if the tires all track a true circle when you have the stearing wheel turn in a curve, traction is improved.
FM Former Member
If you want to eliminate bump steer, you have to have both the left and right steering arms pivot in exactly the same "plane" as the suspension pivot points. On a VW chassis that is simply impossible. Then to make one steering arm three times longer than the other is simply to ignore bump steer in the design of the suspension (sorry Dr Porsche). Then you lower the front end and now your unequal length steering arms are not even parallel with the ground.

One obvious answer is to have a very stiff chassis, and a huge anti-sway bar up front (3/4 inch)to simply eliminate any body roll. That will at least reduce roll-induced bump steer (and it keeps the camber more better) to keep the rubber on the ground. That and try flipping the steering arms to the top of the spindles. They sell bushings for that.

As they say, the only reason the front suspension works at all is because the rear suspension is so bad.
FM Former Member
What I noticed is that my rod angles plus the noncompensated spindle arm-to-rod pivot location is most likely cause the bump steer and the also affecting the overall steering geometry. The suspension travel and geometry affects the steering geomtry and vice versa. In other words, the steering geometry links and suspension geomtry links are basically two four-bar-linkages that are influencing each other by a shared link. You limit one and you reduce the influence to the motion dynamics of the other system. That is why when you extremely drop a front end you better check you alignment or you might end up with a real bad dangerously handling car that will also quickly eat up you tires too. Proper toe-end will also be needed.

I am going to raise my front end while also incorporating the 356 spindles. I will do one at a time and I will post the results. Also, I will try to measure the geometrical dimensions prior to after each change (if time allows me!).

Yes, Ackerman's principle has defintely helped not only the horseless caraiges but also our beloved antique and modern automobiles!
FM Former Member
David, your exactly right! I also have a 19-mm bar I'm installing along with the other changes. Like I said I will do one at a time starting with the bar first, then adjust ride height, and finally the 356 spindles. I will post the results. Oh yeah, and just for the heck of it, also a camber compensator after I do the spindles. Mmmm, maybe a rear stabilizer bar too.....
oldyeleroldyeler
If a pair of 356 Spindles can not be found it is possable to heat and bend the beetle ball joint arms inward the 3/4 needed. It can be gone.

I know a Alinement specialest whos son races VW sprintcars they bent me a pair of spindles for my car. He needed my wheelbase and track info. and that was all.

He said that the vw set up is crude like the early porsche. but there are things you can do to help it. re bending the spindles is a must. a good away bar, and of course the camber shims.
FM Former Member
There was a recent article in VWT that covered a mod done to the spindle arms to offset the steering angle to improve handling. The mod involved welding tabs with drilled holes. I guess the same can be done. As far as bending, the VW and 356 spindles I have are identical even the casted part numbers and VW insignias. My guess is that they did heat and bended them like you stated.
FM Former Member
UPDATE:
I installed one set of caster shims and it did help a little. My front does not have the same floating feeling as it used to and steering requires a little bit more effort but it does feel more natural (whatever that is!).
Next, I will install the 19-mm sway bar and I'll post the results.
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