To Push or Pull in 2014

[Tim.Wright]

Yea actually, I wasn't completely clear on how you do it now. But now you cleared it up.

I just did a quick check in an FSAE suspension (in Adams) and added camber compliance in the form of a compliant wheel bearing. I didn't see any significant change in Fz/Fy in a lateral load test. Certainly not of the magnitude you mentioned earlier.

I'm thinking it might be something linked to the carbon flexure joints since their rotation axis w.r.t the chassis can change with load. So if the rotation axis is changing, its like having moving hardpoints on a traditional ball jointed suspension. In this case, I can imagine some movement of the roll centre due to load.

[munudeges]

The video is kinda BS y'know. As is how it goes with "things on the internet."

Ahhh, right - especially considering it's the topic of the article.

Push-rod, pull-rod, all the same stuff fundamentally. Crazy how worked up people get over it.

So you don't know basically? Great critique there.

[Jersey Tom]

The video is kinda BS y'know. As is how it goes with "things on the internet."

Ahhh, right - especially considering it's the topic of the article.

Push-rod, pull-rod, all the same stuff fundamentally. Crazy how worked up people get over it.

So you don't know basically? Great critique there.

Just because it's on topic doesn't mean it's right. If there are errors like mistakenly attributing all vertical force reaction by the push or pull rod.. it just really quickly diminishes any credibility. You have to be critical / questioning of everything with this stuff - even "well-known" names. Hell, especially well-known names - if only because otherwise the assumption is, "Oh well it's so-and-so they must be right."

In any event.. push vs. pull.. there's just no magic to it. No universal winner.

[munudeges]

The video and its explanation is pretty clear to understand. A pull-rod will raise the roll centre and will result in less control over what happens at the contact patch. The tyre sidewalls will have to do more work. Follow the loads and the forces. The push-rod is closer to the bottom of the tyre and the contact patch and that is extremely easy to understand in pure layman's terms. Anyone who doesn't understand that really has no credibility. It's the most basic, basic part of this to understand. That mechanical certainty is being given up with a pull-rod for a pretty tenuous aerodynamic gain. The fact that Ferrari is doing that with a low nose where they can't possibly get the volume of air they need to make that sacrifice work is extremely puzzling. They've handicapped themselves twice.

Simply coming up with a politically correct middle ground of statements that they are both equivalent is meaningless because natural selection and competition tells us that they aren't. The reason why push-rods have become ubiquitous over the past twenty years is because there has been a consensus, and there is a consensus because everyone has arrived at the better solution. The only reason to run a front pull-rod is if you lowered the front of the chassis and nose to the extent where a push just wouldn't geometrically work or you got a gain that was so enormous that it paid off, as Red Bull did aerodynamically at the rear.

I can't imagine Raikkonen enjoying this car, let's put it that way.

[Jersey Tom]

A pull-rod will raise the roll centre

Nope.

The tyre sidewalls will have to do more work. Follow the loads and the forces. The push-rod is closer to the bottom of the tyre and the contact patch and that is extremely easy to understand in pure layman's terms. Anyone who doesn't understand that really has no credibility.

Well, that doesn't make a shred of sense to me.

[thisisatest]

Where the rod is does not, in itself, change anything about the geometry, trajectory, etc, of the suspension or the wheels that are attached. The way the front pull rod suspensions have been implemented in f1 differs in roll center (and other characteristics) than their pushrod cousins. Look at the rear suspensions. There, push or pull, they keep the same arm layouts.

[Lycoming]

A pull-rod will raise the roll centre

Not necessarily, at least not with the kinematic roll center.

and will result in less control over what happens at the contact patch.

A high roll center does mean that more of the roll moment is taken up by the wishbones as opposed to the springs/ARBs. This means you have somewhat less scope to tune the car's lateral load transfer characteristics but unless but as I just stated, pullrod does not necessitate a higher roll center.

The tyre sidewalls will have to do more work.

Not if the effective vertical spring rate is the same, which you can do by taking into account the stiffness of the components in between the spring and the upright and the motion ratio of the pullrod and bellcrank. Note that you have to do all of those things with a pushrod suspension as well.

The tyre sidewalls will have to do more work. Follow the loads and the forces. The push-rod is closer to the bottom of the tyre and the contact patch and that is extremely easy to understand in pure layman's terms. Anyone who doesn't understand that really has no credibility.

Well, that doesn't make a shred of sense to me.

Well then clearly you have no credibility.

The push-rod is closer to the bottom of the tyre and the contact patch and that is extremely easy to understand in pure layman's terms.

That's true, but assuming the upright is stiff, what bearing does that have on anything?

The reason why push-rods have become ubiquitous over the past twenty years is because there has been a consensus, and there is a consensus because everyone has arrived at the better solution.

But they're not ubiquitous, and there is no consensus; many teams are running pullrod rears, and ferrari and mclaren either are running or have run pullrod fronts.

I can't imagine Raikkonen enjoying this car, let's put it that way.

Just because of the pullrod front? While I am personally of the opinion that pushrod is the way to go, I also believe that even in F1 terms, it doesn't make that much of a difference either way. To say nothing of the fact that they won races in both 2012 and 2013 with a pullrod front, somehow I suspect Raikonnen would prefer to be in the f14t than a caterham or marussia, but we will find out this weekend.

[Jersey Tom]

Where the rod is does not, in itself, change anything about the geometry, trajectory, etc, of the suspension or the wheels that are attached.

This. This is key. Effective jacking (forget about "kinematic" or "force based" roll center stuff and just go with the Matschinsky work balance approach, much clearer and complete approach IMO) is a function of the wheel kinematics and force/moment at hub. That's it. Push or pull rod has zero effect.

To draw up a "push rod" and "pull rod" suspension that have different control arm geometries would be very misleading.

[Tim.Wright]

Where the rod is does not, in itself, change anything about the geometry, trajectory, etc, of the suspension or the wheels that are attached.

This. This is key. Effective jacking (forget about "kinematic" or "force based" roll center stuff and just go with the Matschinsky work balance approach, much clearer and complete approach IMO) is a function of the wheel kinematics and force/moment at hub. That's it. Push or pull rod has zero effect.

To draw up a "push rod" and "pull rod" suspension that have different control arm geometries would be very misleading.

I'm going to agree here too. Don't forget also that even if packaging contraints cause a pull rod to have a higher force and worse motion ratio, the spring rate anyway is suitably chosen such that the desired wheel rate is met.

Even a layman can see that right?

[Krispy]

I saw this during the warm up of last weekend's race and couldn't identify why it was done.



The screen grabs I have in the picture above show the Williams driven by Bottas during the second formation lap before the start. He is weaving back and forth (cleaning/heating the tires I suppose) while the suspension is unloaded the pushrod extends, while loaded it compresses to a "normal" state.

Can anyone explain why they would do this?

This may be old news but it is the first time I have ever noticed it.