Push vs Pull type rear suspensions... which is better?

[DaveW]

But correlation does not = causation. There's a reason why ONLY one manufacturer uses a pull rod setup. It's not like it's a new invention or anything... and all the teams know how critical aero is.

... & they might just be aware of the importance of c.g. height, which is why everybody copied them this year ...

Apologies, JT. I jest.. Not now, though:

With regard to pullrods being compliant... not sure if I believe that. Sure, you don't have to worry about buckling... but even a 0.500" OD x 0.035" wall x 24" long steel tube pullrod has a springrate of 64,000 pounds per inch if I did my quick dirty math right.

That's about as small a pullrod I can imagine... and that's not exactly what I'd call compliant given that it's well over an order of magnitude higher than the wheel rate.

I imagine your calcs are sound, but you haven't extracted your loads from the pull rods, yet.

The lowest front installation stiffness I have seen for an open wheeled carbon chassis vehicle was the Arrows A21 at < 1 KN/mm. The pull rod Dallara IRL is not much of an improvement (certainly not an order of magnitude greater than its "wheel rates"), & is a factor of 2 (roughly) down on its push rod predecessor.

p.s. If there is one thing you can be sure of, it is that every team on the grid did a detailed cost/benefit analysis of a rear pull rod layout when designing this year's cars. They clearly missed something, probably the freedom it offered to implement another performance enhancement.

[Jersey Tom]

I dunno. It's tempting to make the leap... Red Bulls are very quick this year... they also have a pullrod setup... you'd think maybe one has to do with the other either directly or indirectly.

On the other hand.. it IS still a leap. Soooo many more things could be major or minor contributors. Impossible for us to say. Probably impossible even for Red Bull to conclusively say where they leapfrogged the competition. They only know what they bring to the table rather than what everyone else is doing. Always a pleasant surprise when your solution is heads and shoulders above the rest!

[DaveW]

On the other hand.. it IS still a leap. Soooo many more things could be major or minor contributors. Impossible for us to say. Probably impossible even for Red Bull to conclusively say where they leapfrogged the competition. They only know what they bring to the table rather than what everyone else is doing. Always a pleasant surprise when your solution is heads and shoulders above the rest!

I don't disagree, JT. However, the ability to run a high speed corner flat a gear higher than the competition, whilst being ranked (almost) slowest through the speed trap at Barcelona suggests they have more raw down force. Probably not LH's "double", but significant nonetheless.

[Jersey Tom]

I don't necessarily disagree regarding RBR having higher DF... just a question of where it comes from.

[ringo]

The pull rods leave a cleaner surface area on the gearbox, free of bell crank mounts and spring mounts etc.
I could see how much better it is to have the suspension parts lower down.
Other than CG and aero, i don't see a sizable difference in the mechanical benefitis of either layout. If the rod is designed for the buckling load, and meets a certain requirement for buckling displacement, it should work as well as any pushrod.
Taking into account as well that the rod is not a circular cross section, it could be set in a way to have an advantageous Ixx in regard to buckling.

[marcush.]

The pull rods leave a cleaner surface area on the gearbox, free of bell crank mounts and spring mounts etc.
I could see how much better it is to have the suspension parts lower down.
Other than CG and aero, i don't see a sizable difference in the mechanical benefitis of either layout. If the rod is designed for the buckling load, and meets a certain requirement for buckling displacement, it should work as well as any pushrod.
Taking into account as well that the rod is not a circular cross section, it could be set in a way to have an advantageous Ixx in regard to buckling.

but you would always have to account for the additional uncertainty of excitations stemming from track input when using pushrod layout.So always the pullrod will have
an advantage in compression loads as the safety margin you have to allow for is considerably less .

[autogyro]

Adrian Newey has effected what I would call a 'ramp up' of design input.
Shortest wheelbase allows a closer couple of C of G and C of DF.
It also allows a more compact under floor design and diffuser.
Pull suspension places all the geometry low down and concealed which allows a much tighter and less draggy rear end.
Everything works much better together and works to allow further improvement.
By comparison IMO most of the other cars, apart perhaps for the lower runners like Lotus, have gone in one design direction that is now all but played out.
However it would be nice to be proven wrong.

[marcush.]

Adrian Newey has effected what I would call a 'ramp up' of design input.
Shortest wheelbase allows a closer couple of C of G and C of DF.
It also allows a more compact under floor design and diffuser.
Pull suspension places all the geometry low down and concealed which allows a much tighter and less draggy rear end.
Everything works much better together and works to allow further improvement.
By comparison IMO most of the other cars, apart perhaps for the lower runners like Lotus, have gone in one design direction that is now all but played out.
However it would be nice to be proven wrong.

to me car length is a tradeoff .
A longer wheelbase will net more underfloor surface so potentially more aero active area ,more downforce.
For the longer WB the change in attitude for a given wheeltravel will be less ,so pitch sensivity goes down
The longer car will be heavier as increase mass to elongate gerarbox or tub,the longer structure with the same crossection would be less stiff in bending or torsion so more material is needed to counter this.

[Belatti]

I don't necessarily disagree regarding RBR having higher DF... just a question of where it comes from.

The wings?

[ringo]

The pull rods leave a cleaner surface area on the gearbox, free of bell crank mounts and spring mounts etc.
I could see how much better it is to have the suspension parts lower down.
Other than CG and aero, i don't see a sizable difference in the mechanical benefitis of either layout. If the rod is designed for the buckling load, and meets a certain requirement for buckling displacement, it should work as well as any pushrod.
Taking into account as well that the rod is not a circular cross section, it could be set in a way to have an advantageous Ixx in regard to buckling.

but you would always have to account for the additional uncertainty of excitations stemming from track input when using pushrod layout.So always the pullrod will have
an advantage in compression loads as the safety margin you have to allow for is considerably less .

The pullrod can be shorter since it's mounted on the upper wishbone, where the upright is ussually cambered as well, bringing it closer to the car.
That reduction in rod lenght can make a difference in the buckling designed cs area. The fact that the pull rods are mostly under tensile strees under load also gives them a design advantage. On the other hand a pushrod is under constant compression loads.