The relative benefits of a pull rod suspension

[mith]

I'm not the expert, but I guess I understand it enough to explain it.



See that rod which is not aligned with other wishbones? It's a push rod. 'Push', because it's pushing nose up from the wheels.

Here's drawing grabbed from (great!) Scrabs blog:



On the left there's push rod and on the right pull rod.

[Crabbia]

The post actually seems to have been written by a Ferrari fan that does not really understand what he is talking about, but manages very well to do 'as if'...

i think thats probably the case. unless it was murray walker then its perfectly understandable...

also i wouldnt read too much into the laps = reliability arguement when it comes to ferrari...

if you remember ferrari had by far the most milage during winter testing 2010. Dont get me wrong the car itself was nearly bullet proof... but with all their high milage testing they did not see the pnuematic system giving problems which caused quite a few failures for them and sauber in particular.

Sure you could say it was an oversight with the new rules but regardless, they didnt pick it up.

[Onch]

I'm not the expert, but I guess I understand it enough to explain it.

Thanks mith.
I know the difference between push- and pull-rods, it is the bit saying that pullrods work better whith higher downforce that is puzzling me...

[SEBA_406]

Great topic and discusion guys!!! Thanks!!!

[PlatinumZealot]

I'm not the expert, but I guess I understand it enough to explain it.

Thanks mith.
I know the difference between push- and pull-rods, it is the bit saying that pullrods work better whith higher downforce that is puzzling me...

You are puzzling your self! The pull rod can give you better airflow over the gearbox. You can choose what you want to do with it.

As we are seeing right now, teams have switched to pullrod which was an improvement flow over the gearbox, but they are not using it well, with fins and gills, low beam wings, all putting it to waste.

Let me give you some insight though, IF ferrari (RBR copy) go to pullrod they might be as fast as redbull on all tracks. hehehe

[delacf]

Hi, have read that the pull rod system is more fragile. Is this true?

Metals work better traction. This allows us minor safety factors (no risk of buckling) and allows us to go to the limit but that does not mean that the pull rod system is more fragile, that meant that we have gone too the limit.

Regards,

delacf

[ringo]

I'm not the expert, but I guess I understand it enough to explain it.

Thanks mith.
I know the difference between push- and pull-rods, it is the bit saying that pullrods work better whith higher downforce that is puzzling me...

I am puzzled by that and the counter claim about push rods as well.

[bettonracing]

Hi, have read that the pull rod system is more fragile. Is this true?

Metals work better traction. This allows us minor safety factors (no risk of buckling) and allows us to go to the limit but that does not mean that the pull rod system is more fragile, that meant that we have gone too the limit.

Regards,

delacf

Perhaps the author was referring to pullrod flexibility while going over bumps/ kerbs when the wheel is in jounce (instantaneous upward acceleration putting the usually-thinner pullrod in compression, vs. pushrod in tension under the same condition), leading to split-second load cycling on the tires. Apparently the front pullrod suspensions of the ~2000 era suffered this problem (think: split-second unpredictable steering after hitting a kerb). One could expect an instantaneous loss of traction due to the same phenomenon on the rear tyres - but one would have to be jumping the kerbs with the rear tires, and the cyclic bouncing may not have that much of an effect on tire traction.

In faster corners (where the driver is less likely to jump a kerb, and downward loads are likely higher, due to the higher speeds), this is obviously not a problem, and therefore the pullrods retain the advantage of being in tension (vs. compression for pushrods).

With modern day material technology/ understanding, as well as all current pullrods being used on the rear, I suspect this is less of an issue nowadays.

Regards,
H. Kurt Betton

[Sayshina]

Fact: Pullrod came first, and was then abandoned in favor of pushrod, front and back. Either all F1 designers of that day were incompetant, or there was an advantage to be found in pushrod, which would seem to imply that pullrod is not in fact inherently superior to pushrod.

Fact: Newey stated in '09 that having the pullrod rear suspension restricted RBR's ability to implement a proper "double difuser", and compromised the design of the car in this area.

Fact: Newey stated at the begining of '10 that they were sticking with the pullrod rear suspension not because it was inherently superior but because it was already on the car, working well enough, and the rules were changing the next year anyway.

Fact: Whatever reason Ferrari have for using a pushrod rear suspension, fear certainly doesn't explain it. The fearful choice would clearly be to follow the herd and adopt a pullrod setup.

A few years ago someone asked a F1 designer why nobody was using pullrod suspension anymore. I can't remember exactly who as I've read comments from several, but I want to say Mike Gascoyne. At any rate, his response can be summarized as:

Pullrod vs. pushrod

Equal in compression (no advantage)

Inferior in rebound (reasons have been posted by others in this thread)

Potentially superior in C of G (he went on to say this advantage doesn't usually work out to much in the real world)

Inferior in access (ability to work on it, fix defects, change setup, ect).

He closed by making the observation that nobody was using pullrod currently, but given the reality of F1 he expected it would reappear sooner or later.

To the above list of drawbacks I think it would be fair to list a couple additional ones faced by Red Bulls installation. First, housing the dampers inside the transmission has got to make it harder to get heat out of them (traditionally one of the major issues in suspension design), and second sticking so much of that setup inside the transmission has got to have involved compromises to geometry, installation stiffness, and heat transfer, possibly for the transmission as well as the suspension.

So for the love of christ can we please, pretty please, stop claiming pullrod has no disadvantages?

On another note, a couple of you have claimed that the RB6 had the most downforce last year and that at least part of it can be contributed to the pullrod suspension. Neither of these claims is defendable. You have no factual information on the downforce produced on any formula 1 car on the grid. We still can't get clear factual numbers for the power outputs of F1 engines during the turbo era, but you claim to be in the know about last years cars? This is unlikely.

The RB6 has been observed to have been the fastest overall package over a majority of the tracks, given the weather conditions faced at those tracks last year. And that is as far as the facts will allow you to go. Period.


Finally, I have yet to see a single rear suspension picture this year that doesn't apear to the naked eye to involve massive geometry compromises, and I'm not at all sure how you go about comparing massivly compromised pushrod with massivly compromised pullrod and arrive at the conclusion that one is clearly superior to the other.

[PlatinumZealot]

The first pull rods were nothing compared to the ones today. Just google some photos. Similar to the first EBD's to todays. Very crude.

[Sayshina]

The first pull rods were nothing compared to the ones today. Just google some photos. Similar to the first EBD's to todays. Very crude.

Are you claiming that the current Pushrods are exactly the same as the first and haven't also benefitted from development?

And as for blowing the exhaust through the diffuser in an attempt to keep the flow attacked and avoid turbulance, this was always a dumb idea. You'd never want to do that on purpose, it's much better to run proper underbody venturies that increased in volume at a more gradual pace, producing the target downforce without the high angles of attack. You'd always rather avoid the serious compromises an EBD requires. That is, unless the rules precluded doing it right.

Both of these concepts have come, gone, and come again. There is nothing in the current implementations of either to indicate that either or both are now here to stay, and the smart money would clearly be on them, once again, going.

[PlatinumZealot]

Googled the photos of old pull rod suspension? Just look what I mean first before we talk about modern push-rods. Because all of the F1 cars today have modern push-rod suspension.

[ringo]

The first pull rods were nothing compared to the ones today. Just google some photos. Similar to the first EBD's to todays. Very crude.

Are you claiming that the current Pushrods are exactly the same as the first and haven't also benefitted from development?

The truth is that the push rod has hardly changed since its inception.
A push rod 20 years ago is just the same as it is today.
Parts inboard of the car on the gearbox. Maybe a coil spring or torsion bar.

We can't say the same for a pull rod.
Especially in the rear of the car.

I can bet you that you can't find a torsion bar pull rod suspension in the rear of the car, that is mounted inside a gear box.

If you can find that then you have a case.

[shelly]

I think that the higher freedom for aerodynamics that a pull-rod scheme grants has a decisive weight in the pros-cons of push vs pull-rod, such to overshadow every other issue.

What gets this a little blurry is the fact that in 2009 redbull adopted pull, which was a disadvantage with double decker diffusers: but the pull rod choice had been made with a single deck diffuser in mind. They kept it 2010 for the above mentioned reasons, and now that single deck has become mandatory, pull rod is more advantageous from an aerodynamic point of view again.

It must also be noted that this year's ferrari has a very unconventional rear push rod assembly, with the "push" element moved forward in order to gain part of the aerodynamic freedom of a pull rod.

[myurr]

It must also be noted that this year's ferrari has a very unconventional rear push rod assembly, with the "push" element moved forward in order to gain part of the aerodynamic freedom of a pull rod.

That highlighted part of your statement is where I draw issue. Aerodynamically the push rod and pull rod are just different trade offs.

What you consider to be the "aerodynamic freedom of a pull rod" is in fact the aerodynamic freedom of lengthening the gearbox and mounting the suspension components inside the casing coupled to a pull rod. Ferrari's push rod solution similarly moves the suspension components forward and apparently down in a similar fashion, achieving a similar end result. Ferrari believe their solution gives the packaging advantages of the pull rod layout adopted by Red Bull and the other teams whilst still giving the benefits of the push rod.

The differences between these solutions is absolutely minimal compared to other aspects of the cars.