Pushrod or pullrod, the difference as the name suggests is the whether the rod push up to the rocker or pull down to the rocker.
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Pull rods were first brought to Formula 1 by Gordon Murray with Brabham in the 70s but now all formula one teams make use of the push rods, as pull rods are quite hard to implement in a high nosed car. The advantages of a pull rod lie in the possibility to make the nose lower, assemble most suspension parts lower to the ground and thus lowering the height of the center of gravity.
Pull rod set up has a strut from the outer end of the upper wishbones that runs diagonally to the lower edge of the chassis and “pulls” a rocker to operate the spring\damper.
A pushrod is the opposite; the strut runs from the lower wish bone to the upper edge of the chassis.
Choice between the two is geometry and CoG (Centre of gravity). Also a pull rod will flex in droop (wheel going down) and push rod will flex with the wheel in bump (wheel going up) hence F1 push or pull rods are large carbon molding to withstand the flexing from the high wheel loads.
Most F1 cars now use push rods. The high nose makes it impossible to locate a rocker low enough in the chassis and still have the right geometry. Minardi and Arrows used pull rods with low noses to lower the centre of gravity. These two teams are a last two to use this concept.
Pullrod suspension has been ignored because of the installation problems with high nose cars. The critical geometry in spring\damper layouts is the installation angle of the push\pullrod. In the picture of Minardi PS1 below, the pullrod has an angle of around 35-degrees which is fairly steep. Notice how high on chassis is the the point where it meets the upper wishbones, on some cars these are now almost as low as the floor of the monocoque. Then the keel below the square section of the monocoque reaches down to pick up the lower wishbone, the space created below the nose is what allows the front wing to be so efficient as there is little to obstruct the wake forming. The keel is made to be as slender as possible to improve flow under the nose . Should the nose be made lower the aerodynamics would be crippled.
When pullrod suspension were adopted with a good installation angle, the rocker would need to be located near the keel (upsetting the aerodynamics) or appear pick up point of the pullrod would need to be located somewhere above the tire, clearly a upper wishbone mounted pullrod with a rocker inside the monocoque would never be able to work efficiently due to the poor installation angle.
Access problems used to be a common problem with pullrod suspensions: The removal of the dampers and rockers being hindered by their low location inside the monocoque
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In the typical torsion bar pushrod set up described below the torsion bars pass through the centre of the rockers and fix to the front of the chassis. The Rocker pivots on the torsion bar. The push rod pushed the rocker and twists the torsion bar to provide the spring in the suspension, the rocker then compresses the damper and operates the antiroll bar if the car is in roll.
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Black – Pushrod
Yellow – Rocker
Dark Yellow – Rocker splinted to Torsion bar
Light grey – torsion bar
Red – Damper
Blue – antiroll bar linkages
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Now is preseason testing for year 2009 and RedBull Racing with Adrian Newey like technical director and chief designer, brings pull-rod rear suspension back to Formula One for the first time after 10 years. The last pull rod dates from 2000 with the low nosed Arrows A20 which featured it.
With the diffuser moving rearwards under the revised 2009 regulations, the pullrod layout allows for cleaner aero packaging for rear suspension area. See circle for more common pushrod set-up witch normally occupy more space under the engine cover, preventing designers to make clean airflow toward rear wing because suspension rockers and dampers are positioned on the top of the gearbox.
Because of Red Bull’s choice to create very low sidepods at the back end, a pushrod did not make much sense as the suspension components would prevent a clean design. The pullrod version has allowed the designers to put more components close to the car’s floor, lowering its centre of gravity. The pullrod suspension is lighter and, along with a gearbox that is now 15cm lower, helps to improve handling. The top wishbone is a single piece and is attached very high at the rear of the car (see upper arrow), actually they connect above the car’s bodywork, in the most ideal position, forming a wing-like section that works together with the lower section of the rear wing. With some imagination, if you would turn the car upside down, the rear suspension is effectively connected at inverted single keel. The keel is here supporting both upper wishbones.
Also note the very low and rearward positioning of the exhausts (lover picture, right arrow), which exit just under the front arm of the rear wishbone, and the lack of a central pillar to the rear wing, which is instead mounted via the wing’s two large endplates, which attach directly to the diffuser. This concept will evolve next year (2010) to very successful blown diffuser, critical part in driver and constructor championship win by Red bull Racing
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