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

[marcush.]

The springforce added cannot be much ,as it would put considerable bending loads into the wishbones ?

as either push and pullrods are loaded as well in tension as in compression (with bump and rebound) the main advantage would be that a pullrod is the safer solution as the worst case load would be a severe bump and this would put the rod under tension whereas with common pushrods you got compression -and buckling - so you need to add a lot of margin with these.As Aero is everything ....the trade off in the front is the raised monocoque gaining more than a thinner rod .

[xpensive]

The springforce added cannot be much ,as it would put considerable bending loads into the wishbones ?

as either push and pullrods are loaded as well in tension as in compression (with bump and rebound) the main advantage would be that a pullrod is the safer solution as the worst case load would be a severe bump and this would put the rod under tension whereas with common pushrods you got compression -and buckling - so you need to add a lot of margin with these.As Aero is everything ....the trade off in the front is the raised monocoque gaining more than a thinner rod .

Mt sentiments precisely, besides, "Springs should be pushed, rods should be pulled", that's what I remember from university anyway.

[riff_raff]

"Springs should be pushed, rods should be pulled"

xpensive,

Actually, I believe most F1 cars use torsion springs. So technically the springs are twisted, not pushed.

The drawback with pull rods is that the rebound damping rates can be somewhat limited. Since this loading condition puts the slender pull rod into compression, where it has very little margin in buckling.

Another consideration is that current F1 suspension links are composite. Carbon fibers do very well in tension, but not so well in compression.

With regards to the contribution of flexures to the total suspension spring force, while each "cantilevered beam" may have a modest spring rate, there are usually four per wheel. So the total contribution might be more than you would first imagine.

riff_raff

[xpensive]

"Springs should be pushed, rods should be pulled"

xpensive,

Actually, I believe most F1 cars use torsion springs. So technically the springs are twisted, not pushed.
...
With regards to the contribution of flexures to the total suspension spring force, while each "cantilevered beam" may have a modest spring rate, there are usually four per wheel. So the total contribution might be more than you would first imagine.

riff_raff

The above saying was obviously in reference to coil springs, which I'm sure you understood anyway. Torsion bars are of course something else altogether, after pioneered(?) on the Lotus 72 in 1970, it's rather surprising they did not become de rigeur in F1 until the 00s?

Anyway, remember that a push-rod will induce pulling-loads on the a-arms, while a pull-rod will do the opposite?

But on the flextures supporting vertical load of any significance, yes, I'd be very surprised if that's the case.

[riff_raff]

Anyway, remember that a push-rod will induce pulling-loads on the a-arms, while a pull-rod will do the opposite?

xpensive,

I don't think that statement is true. Both pushrods and pullrods put their supporting a-arms in compression in bump, since pushrods are typically attached to the lower a-arm and pullrods are attached to the upper a-arm.



riff_raff

[Just_a_fan]

"Springs should be pushed, rods should be pulled"

xpensive,

Actually, I believe most F1 cars use torsion springs. So technically the springs are twisted, not pushed.

Technically coil springs are torsion springs it's just that they're wound in to a tight package for ease of, um, packaging.

[marcush.]

"Springs should be pushed, rods should be pulled"

xpensive,

Actually, I believe most F1 cars use torsion springs. So technically the springs are twisted, not pushed.

The drawback with pull rods is that the rebound damping rates can be somewhat limited. Since this loading condition puts the slender pull rod into compression, where it has very little margin in buckling.

Another consideration is that current F1 suspension links are composite. Carbon fibers do very well in tension, but not so well in compression.

With regards to the contribution of flexures to the total suspension spring force, while each "cantilevered beam" may have a modest spring rate, there are usually four per wheel. So the total contribution might be more than you would first imagine.

riff_raff

in all respect ,the main advantage here is that rebound forces can be defacto calculated very precisely ,whereas the bump forces are also depending on track profile -inputs ....so it is at least imaginable that fopr a pushrod bump loadcase the designer has to make allowances for freak shock load inputs (which go into the pushrod due to restrictions in transmissibility or even ariving at suspension travel limits....


Torsion bar springs ? look here:at least one coil over in the Merc ...heave spring?

http://www.motorsport-total.com/f1/bild ... 013&sort=1

[xpensive]

"Springs should be pushed, rods should be pulled"

xpensive,

Actually, I believe most F1 cars use torsion springs. So technically the springs are twisted, not pushed.

Technically coil springs are torsion springs it's just that they're wound in to a tight package for ease of, um, packaging.

I'm, not really so sure about this, when a coil-spring is really a long section of shear-force loaded wire,
what is a torsion bar?

[riff_raff]

Just_a_fan is correct. The wire in a helical coil compression spring is loaded mostly in torsion. There is only appreciable bending stress when the helix angle is steep. The resulting torsional shear stress in the wire is also not uniform about the section like a conventional torsion bar. This is due to the beam being curved along its axis rather than straight.

riff_raff

[RacingManiac]

To my understanding, the migration or corner spring from coils to torsion bar was driven primarily through packaging, with secondary benefit in reduced suspension hysteresis through the elimination of the coil binding on the spring seat(even with use of bearing or hydraulic seat(more complicated anyway)? Potentially stuff like heave spring can be made of torsion spring, and conversely ARB can be made of coil. But its just a case of what works best where....

[DaveW]

Push-rod for best mechanical control, pull-rod for best aero (clearly).

Straight torsion bar springs: length defines the minimum rate, I believe (although they can be "folded"). Difficult to incorporate accurately adjustable pre-load.

[Jersey Tom]

Push-rod for best mechanical control, pull-rod for best aero (clearly).

Reason being?

[DaveW]

Reason being?

Push rods have to be designed for buckling, & therefore tend to be stiff. Pull rods are (usually) designed for strength & therefore tend to be compliant. Doesn't have to be that way, of course, but just try & tell that to an F1 aerodynamicist....

The only pull-rod design in F1 has the best down force coefficient. Obviously the second is a consequence of the first, & the exhaust routing has nothing to do with anything....

[autogyro]

+1 Exhaust will have a very small effect.

[Jersey Tom]

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.

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.