Pros and cons of pullrod suspension

[bernard]

I'm new to this foum so be gentle with me

As the heading might reveal, i am wondering what the pros and cons of pullrod suspension are, and exactly what is the reason why teams haven't adopted this design, despite the obvious CofG benefits.

[West]

Im sure that a pullrod would require a keel to be placed lower than usual and can therefore interupt airflow to the back; in other words, it screws up the idea of the raised nose.

[bernard]

but teams like mclaren don't have a raised nose, quite the opposite, and other teams haven't raced really high noses in years either.

[Guest]

Im sure that a pullrod would require a keel to be placed lower than usual

Why is this a bad thing? it allows the CofG to be placed lower, and especially the ballast. If the car was designed for the low nose/pullrod setup, then the aerodynamical disadvantages you mentioned would be minimal, and the CofG benefits massive, since the pullrods place the suspension weight already lower than pushrod, the low nose required places the weight even lower, and the ballast is very close to the ground. This gives phenomenal advantages.

[Monstrobolaxa]

Hummm....in recent years 2 teams used pull rod suspensions....Arrows in 2000 and Minardi in 2001. Like Benard mentioned there is a CofG advantage....but the main disadvantage is that with the diferent arrangment of the adjustable parts of the suspension there seems to make it very hard to make adjustments/suspension setup changes...

[f1techn1c1an]

with the diferent arrangment of the adjustable parts of the suspension there seems to make it very hard to make adjustments/suspension setup changes...

Why is it harder than in a pushrod setup? I don't mean to disagree with you, but a little insight would be nice

[Reca]

but teams like mclaren don't have a raised nose, quite the opposite, and other teams haven't raced really high noses in years either.

The problem isn’t the nose, it’s the chassis, if you look at the Mp4-18->19B the chassis, behind the nosecone, is pretty high, just like in all the recent years cars.
Furthermore the McLaren has a twin keel and that makes impossible to use a pullrod because it would mean to have rocker arm, torsion bars etc in a keel that has a very limited stiffness compared with the chassis.

The Dallara Irl3 has a pullrod at the front suspension, that’s because the rules impose a low nose/chassis hence there’s no aerodynamic disadvantage in using it, actually I remember Dallara guys claimed that they found an advantage in the reduced disturbance of the suspension arms.
From a structural point of view the pullrod is more efficient because it works in traction and not in compression, so it’s possible to make a slimmer and lighter arm.

[Monstrobolaxa]

f1techn1c1an

Sure...the thing with a pull rod suspension is that all the adjustable components are positioned at the bottom of the monocoque. While on a pull rod they're positioned on the top, and teams have an access hole on the top of the monocoque that enables/helps them to adjust the suspension. In a pull rod suspension there isn't a hole on the bottom of the chassis that lets them put their hand in and reach the suspension parts...pull rod teams might put a access port (hole) on the top of the chassis but the mechanics will have to put their hands further down in order to reach the parts.

[West]

Im sure that a pullrod would require a keel to be placed lower than usual

Why is this a bad thing? it allows the CofG to be placed lower, and especially the ballast. If the car was designed for the low nose/pullrod setup, then the aerodynamical disadvantages you mentioned would be minimal, and the CofG benefits massive, since the pullrods place the suspension weight already lower than pushrod, the low nose required places the weight even lower, and the ballast is very close to the ground. This gives phenomenal advantages.

No team runs the low nose though... and although nobody really use the "high nose" a variation is seen throughout the paddock... the emphasis on nose design is still clearing the flow underneath the nose.

[bernard]

okay, okay, very good points, all of you, but so far everybody has just talked about how it doesn't fit into the design of the cars racing this year. I didn't mean that some team would just all of sudden stick pullrod to their this years car, but that the whole car was designed keeping an eye on low nose and pullrod suspension combination. So that this would be the key factor of the car's design. That would be good, because everybody tries to get as good a CofG as possible, and this would simply take it to a whole another level

[Monstrobolaxa]

Well....the setup issue is a very important thing...in 2000 Arrows aledged that it was dropping the pull rod just because of the time it cost them in practise just to change the setup of the car!

[bernard]

Well....the setup issue is a very important thing...in 2000 Arrows aledged that it was dropping the pull rod just because of the time it cost them in practise just to change the setup of the car!

Well, if i'm not mistaken, then ferrari has only three different suspension setups per weekend to choose from. I don't remember where i red that. So then the time issue wouldn't be an issue at all.
though I don't remember where i have red that, so i could be mistaken.

[scarbs]

Pullrod suspension has been ignored becuase 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 digram below the pushrod has an angle of around 35-degrees which is failrly steep. Notice how high the chassis is at the point where it meets the upper wishbones, on some cars these are now almost as low as the floor of the moncoque. 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 uder the nose (twin keels clear the sapce under the nose completely). Should the nose be made lower the aerodynamics would be crippled.

The pushrod operates the rocker (Yellow) which in turn turn pivots on the torsion bar (white) and compresses the wheel damper (Orange), the third damper (Blue) and lastly the antiroll bar (Red).

If pullrod suspension were adopted with a good installation angle, the rocker woudl need to be located near the keel (upsetting the aerodynamics) or a the upper pick up point of the pullrod would need to be sites somewhere above the tyre (possible not allowed under the regulations), 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 be a common problem cited with pullrod suspensions, the removal of the dampers and rockers being hindered by their low location. Having seen the pull rod Minardi set up closely there appears to be as much access as for a pushrod set up which is equaly as difficult now.