Torsion bar suspension. Pros vs. cons?

[sugarwood]

No one uses this setup anymore. So, I assume there is some inherent negative. Is it like the Mustang's solid axle? Is that why 911 went to IRS in 1990? What are some pros and cons of torsion bar suspension compared to modern coil over strut suspensions?

[Canada Kev]

Yes, manufacturers still use torsion bars. The GM C/K trucks in the 1500 series and I think even the 2500 and 3500s currently use torsion bars on the front suspension. And while they're no longer in production, the Dodge Durangos and Dakotas used torsion bars in some cases. Others include the FWD Cadillac Eldorado, Olds Toronado, Chrysler K-cars, 4WD S-10 pickups and Astro vans, and others.

It is nothing like the Mustang or any other vehicle's solid axle.

The 911 has always been IRS since the very beginning when it was a 901.

[TimT]

Search

Why are torsion bars inherently inferior

Not sure if F1 still uses them, or they are on to some electro voodoo stuff

[RSTarga]

A spring is a spring, it is all about packaging.

[sugarwood]

Ok, So why did they change the packaging?

[manbridge 74]

You must remember the designer's original intent. Two guys and two golf bags amongst other things.

The 911 is not like an F16 fighter plane. It's more an F4 ground pounder.

[Canada Kev]

Originally Posted by sugarwood

Ok, So why did they change the packaging?

ABS, all wheel drive.

[manbridge 74]

Yes, the scrub radius had to be changed for ABS so there's that.

[Tremelune]

That thread is a good read.

I suspect it made building race cars easier to start with production coilovers...Plus, the later G50 got big and perhaps got in the way of the rear tube. More frunk space, too?

[patkeefe]

Because it was really a VW. Don't tell anyone. That's why it had torsion springs in the first place.

"Ferdinand Porsche had been working on various other cars for other manufacturers before the Volkswagen and incorporated some older designs within this new project. Other vehicle designs were utilized for this project, the backbone chassis and the idea of independent front and rear
suspension came from one and the torsion bar front suspension patented by Porsche back in 1931.

The body styling dates back to 1931, to a car by Ferdinand Porsche for his personal transport".

[HorstP]

torsion bars are a linear spring. Coil springs can be made non-linear. And then, the torsion bar set-up needs extra space. The dampeners are already there, adding coil springs to them does not need a lot of extra space.

[chris_seven]

Originally Posted by sugarwood

Is that why 911 went to IRS in 1990?

Surely some mistake?

[sugarwood]

Originally Posted by chris_seven

Surely some mistake?

Yes, but not really the point of this thread

[Trakrat]

It's my understanding that as cars travelled faster and faster, the changes in the car's geometry happened at a much higher pace.
Torsion bars basically have to wind and unwind to work in controlling the suspension. This was too slow of a process for cars travelling in extreme speeds.
It also made it more difficult to make finer adjustments due to the limitations of the torsion bar's design in the way it 'mounts' to a hard point on the car. Meaning... the torsion bar is located at a fixed location on the car, and is adjusted from this fixed location.

At least that's what I would guess.

[wayner]

This yellow car is my favourite torsion bar Porsche

[wayner]

Originally Posted by Tremelune

That thread is a good read.

I suspect it made building race cars easier to start with production coilovers...Plus, the later G50 got big and perhaps got in the way of the rear tube. More frunk space, too?

In 73 the factory race team found that with the 73RSR, they had to go to coil overs in the rear since to get enough spring rate, the torsion bars would physically be too large, so instead coil over shocks were used and torsion bars removed

(See the coil packaging comment above )

(Remember the RSR had rear tires twice the width of stock, so that's a pretty substantial bump in the amount of force the suspension needed to cope with on the race car vs street car)

[chris_seven]

Originally Posted by Trakrat

It's my understanding that as cars travelled faster and faster, the changes in the car's geometry happened at a much higher pace.
Torsion bars basically have to wind and unwind to work in controlling the suspension. This was too slow of a process for cars travelling in extreme speeds.
It also made it more difficult to make finer adjustments due to the limitations of the torsion bar's design in the way it 'mounts' to a hard point on the car. Meaning... the torsion bar is located at a fixed location on the car, and is adjusted from this fixed location.

At least that's what I would guess.

A coil spring does, of course, operate in torsion and have to wind and unwind in just the same way as a linear bar.

The rate at which the wheel/damper combination will move is the limiting factor not the material.

Any metallic material being subjected to a disturbing force will initially, and in the case of a spring, will deform elastically.

Elastic waves will travel through a metal up to the speed of sound in the given material, hence listening to railway lines to hear approaching trains.

The mass and the spring rate are also important variables as they influence resonant behaviour.

I can't believe that the motion of a wheel and damper could ever be fast enough for the torsion bar to be unable to react and not move as this would imply an increase in stiffness with frequency and metallic materials just don't behave in this manner.

The modulus of metals are normally measured using ultrasonic techniques to provide the required degree of accuracy.

As far as I know the only materials which exhibit this type of behaviour are visco-elastic in nature.

I could believe, that if you eliminate spline wear, that a linear torsion bar provides a more 'pure' response to a disturbing force than a coil spring.

Coil springs that are co-axial with dampers generally create a bending moment that does influence the friction of the damper/piston arrangement.

Providing you can achieve the desired spring rate I don't really see why the difference in the two spring types would be very significant.

[v2rocket_aka944]

Torsion bar suspension is hard to keep a consistent tire contact patch when going hard and fast.
You set the static alignment and hope for the best. In the front of a 911 any movement of the wheel up or down changes the camber.

In the rear (since rear is mounted perpendicular to the front) a change in wheel position up/down turns the static camber into a TOE change.
Imagine going fast on a somewhat rough road knowing your rear tires are basically shimmying inwards and outwards with every bump...makes you nervous, right?

Only way to keep it consistent is to go with a VERY stiff bar which is 1) heavy and 2) beats the hell out of the driver.

It is very cheap to build such a system though, and they package very well to not intrude into the passenger/cargo areas too much.

Switching to multi-link lets them maintain a good contact patch/alignment by controlling the wheel's arc of motion under compression/rebound but letting you use a much softer spring for comfort...

[Tremelune]

Are coilovers a necessary component of a multi-link suspension?

[Canada Kev]

Originally Posted by v2rocket_aka944

Torsion bar suspension is hard to keep a consistent tire contact patch when going hard and fast.
You set the static alignment and hope for the best. In the front of a 911 any movement of the wheel up or down changes the camber.

In the rear (since rear is mounted perpendicular to the front) a change in wheel position up/down turns the static camber into a TOE change.
Imagine going fast on a somewhat rough road knowing your rear tires are basically shimmying inwards and outwards with every bump...makes you nervous, right?

Only way to keep it consistent is to go with a VERY stiff bar which is 1) heavy and 2) beats the hell out of the driver.

It is very cheap to build such a system though, and they package very well to not intrude into the passenger/cargo areas too much.

Switching to multi-link lets them maintain a good contact patch/alignment by controlling the wheel's arc of motion under compression/rebound but letting you use a much softer spring for comfort...

Yes, you are correct, but this is not spring dependent. Again, it's about the packaging.