There was a time when ‘Investigating Bars’ meant something entirely different and recently I found myself looking at picture of a 1932 Hot Rod convinced I must be drunk.
Surely, this push rod anti-roll bar set-up is impossible?
It took some head-scratching but I finally came around.
I love clever stuff…. Sorry this blog might get a little nerdie
In the above shot, it looks like a conventional Watts linkage between the two push rod actuated bell cranks. Surely, if one wheel moves up-wards, this linkage would also cause the other wheel to move up-wards by an equal amount? It can’t work any better than a cart axle? WRONG! VERY WRONG!
I was missing one crucial thing. The centre pivot of the Watt type linkage isn’t fixed, it is in fact attached to a pivot-able central torsional spring.
Push rod suspension systems; employing bell cranks; benefit from rising spring rates and many kit cars and hot rods use them. Yet only a few cars have ever hit the road with Le Mans or F1 style anti-roll systems. In fact Tomas Svenningsson ‘s 1932 Model B is the first I’ve seen.
These clever, seemingly complex systems are what the Le Mans boys and F1 guys have been experimenting with for a couple of decades. It’s very effective, light and mechanically far more balanced than the standard anti-roll bar you’d find on your hatch back. The great bit is; once you’ve got your brain around them; they aren’t that complex at all!
I’ve found several systems that share similar design aspects. They must have been a major breakthrough.
Spring Blade Anti-Roll Bar
Peugeot 908 Sebring
The shot above shows the 2007 Peugeot 908 Sebring race car. The central pivot is mounted on a T shaped arm attached to a single central anti-roll blade spring. This central leaf spring bows left or right, allowing the central Watts style linkage to move left or right under tension.
If you squint you can even see various potentiometers mounted on the pivots to measure and record suspension movement. You’ll also be able to see that there is provision for a second spring between the two pivots; this would be for particularly bendy circuits.
Push Rod Torsion Anti Roll Bar
There are several manufacturers with essentially very similar designs. The first car in this article has probably got a similar set-up to these. This type of anti-roll bar system has more in common with the type of system you’d find on a family saloon, but with fewer weaknesses.
Peugeot 905 Evo 1 Bis 1992 – 1993
In the centre of the above shot, you can see that the underside of the central Watt style crank, is mounted on top of an L shaped silver torsion bar (about 6-8 inches long). The top side of the watts linkage is steadied by a short, rose jointed link.
This Peugeot system is slightly more conventional in that it employs two coil-over shock absorbers.
My car will have an upside down pull rod version of this system.
Red Bull F1 2004
This system is pure genius. One central coil-over and two smaller dampers for roll.
Let me try to explain:
One wheel Bump
As the right wheel goes over the bump, the push rod moves up, rotating the right bell crank anti-clockwise. This in turn, pulls against the right arm of the central T crank. This slightly twists the central T cranks’ torsion bar and pivots the T crank towards the rear of the car. The central coil-over shock absorber compresses along with the right shock.
Two Wheel Bump
In a two wheel bump, the central torsion bar and crank do not twist. The T shaped torsion bar simply pivots towards the rear of the car on it’s bottom mount. The central coil-over and both external shock absorbers take the bump.
Roll To The Right
As the rolls to the right, the right push rod moves up, rotating the right bell crank anti-clockwise. Pre-load on the central shock pulls on the left bell crank rotating it anti-clockwise, pressing the left wheel down onto the ground. Body roll is resisted by the central T crank rotating; tensioning the torsion bar. The yellow arrows show the resistance to roll offered by the torsion bar. The external shock absorbers resist sharp roll movements and stabilise the car after roll.