The relative benefits of a pull rod suspension

[ringo]

Ringo, was pullrod automatically better on the 75% of cars ferrari beat?is t worse now that ferrari use it? The reason peopl trust ferrari over you is because they've won more world championships than you

By the way I don't think anyone should be trusting team pedigree or journalists, or me. Best to use your judgement or the judgement of the majority of teams after a couple recent years based on evidence, performance and trends.
Based on the trends it was a no brainer that Ferrari were slow to react in 2011. They simply were too conservative. The push rod was not the best choice for them.
If we put aside their pedigree, it becomes easier to see they were behind.

Now that Ferrari is switching their suspension, what does that say about their choice in 2011?
The engines are the same, someone said earlier ferrari couldn't fit a pull rod because their packaging etc. etc. When we had a ferrari powered car, the STR using pullrod with the same engine. What has changed?

Now Ferrari themselves are exploiting the benefits, even splitting their radiator in 2 parts and placing the smaller part where the old push rod bits used to be.

Are we still on about one layout is better than the other because of the layout, not the reason of why it is used?

If only designing a system is so easy....

Difficulty is not the question. An f1 car is designed to make full use of the regulations to extract as much performance as possible.
The comparison between layouts is not so much the layout itself. It's really what the layout permits. A push rod layout does not carry as much benefit as the pull rod.
This thread is over a year old, and it's been a very good discussion; aside from the fact that we didn't really see any advantages of the pushrod stated.

The next question is if pushrods are extinct. Will we see any in the rear on any car this year?
If so, we can look at why they choose it.

[DaveW]

.... The next question is if pushrods are extinct. Will we see any in the rear on any car this year?
If so, we can look at why they choose it.

I don't think that is quite accurate, ringo, & I hate the thought of closing this topic without a balancing comment.

Let's see, looking beyond the confines of F1, push rods are used in RWS, GP2, GP3, F2, F3, Indy, FAltantic, FRenault, etc. In fact, F1 is pretty much unique in employing a pull rod rear layout. Not quite the same I know, but even LMP vehicles use push rod layouts.

At a very "pure" mechanical level, even FFord use push rods. A couple of years ago (I recall) one designer concluded that the CG height reduction offered by a pull rod layout would be a "winning design". I don't know what happened to the idea, but I haven't noticed FFord grids full of pull rod cars.

So, what are the advantages of a push rod layout? It makes the suspension components accessible, for a start, so damper settings & spring changes become a matter of a few moments work, but the main benefit (from my observations) is that, relative to a pull rod layout, it offers increased "installation" stiffness. I'm not completely sure why that should be (although I have unconfirmed ideas).

Some 10 years ago, the company I work with carried trials using a FRenault buck where we tested the effect of adding a spring mounted in series with the (rear) dampers. We discovered that dropping the rate to much less than 1 KN/mm caused a drop in vehicle performance. Sprung mass control could be recovered by increasing damper settings, but very quickly that caused a loss in control of the unsprung masses. In other words, decreasing the installation stiffness caused a loss of control of the vehicle, for which the only solution was to decrease the spring stiffness - the parameter that mattered was the ratio of installation/suspension stiffness.

With that as background, I conclude that a layout that caused a reduction in installation stiffness is not a brilliant idea, not mechanically, anyway.

My observations (via rig tests) suggest that pull rod suspensions reduce installation stiffness. In one case, for a rear pull rod design, I estimated values as a low as 600 N/mm. It is easy to believe that a stiffness that low (less that the top mount of a good road car) would have a catastrophic effect on vehicle mechanical control.

It, of course, possible to design a pull rod suspension with a poor installation stiffness. The rest of my argument involves several assumptions that I will not voice here, suffice it to say that it is perfectly possible to see how an F1 team might conclude that suspension characteristics had no effect on the mechanical performance of a vehicle, & the only thing that matters is aero....

I would simply add (as others have done) that the 2011 Ferrari (with its push rod layout) did, in fact, out perform nine of its pull rod competitors. Why the change in 2012? It might, of course, be the correct decision, but my guess would be that it had lot to with the people & organization involved coupled with a superficial understanding of the technical issues.

[shelly]

@davew: I appreciate your knowledge, but I do not understand your last sentence - when and where does superficiality come into play?

[rejeesh]

.... The next question is if pushrods are extinct. Will we see any in the rear on any car this year?
If so, we can look at why they choose it.

I don't think that is quite accurate, ringo, & I hate the thought of closing this topic without a balancing comment.

Let's see, looking beyond the confines of F1, push rods are used in RWS, GP2, GP3, F2, F3, Indy, FAltantic, FRenault, etc. In fact, F1 is pretty much unique in employing a pull rod rear layout. Not quite the same I know, but even LMP vehicles use push rod layouts.

At a very "pure" mechanical level, even FFord use push rods. A couple of years ago (I recall) one designer concluded that the CG height reduction offered by a pull rod layout would be a "winning design". I don't know what happened to the idea, but I haven't noticed FFord grids full of pull rod cars.

So, what are the advantages of a push rod layout? It makes the suspension components accessible, for a start, so damper settings & spring changes become a matter of a few moments work, but the main benefit (from my observations) is that, relative to a pull rod layout, it offers increased "installation" stiffness. I'm not completely sure why that should be (although I have unconfirmed ideas).

Some 10 years ago, the company I work with carried trials using a FRenault buck where we tested the effect of adding a spring mounted in series with the (rear) dampers. We discovered that dropping the rate to much less than 1 KN/mm caused a drop in vehicle performance. Sprung mass control could be recovered by increasing damper settings, but very quickly that caused a loss in control of the unsprung masses. In other words, decreasing the installation stiffness caused a loss of control of the vehicle, for which the only solution was to decrease the spring stiffness - the parameter that mattered was the ratio of installation/suspension stiffness.

With that as background, I conclude that a layout that caused a reduction in installation stiffness is not a brilliant idea, not mechanically, anyway.

My observations (via rig tests) suggest that pull rod suspensions reduce installation stiffness. In one case, for a rear pull rod design, I estimated values as a low as 600 N/mm. It is easy to believe that a stiffness that low (less that the top mount of a good road car) would have a catastrophic effect on vehicle mechanical control.

It, of course, possible to design a pull rod suspension with a poor installation stiffness. The rest of my argument involves several assumptions that I will not voice here, suffice it to say that it is perfectly possible to see how an F1 team might conclude that suspension characteristics had no effect on the mechanical performance of a vehicle, & the only thing that matters is aero....

I would simply add (as others have done) that the 2011 Ferrari (with its push rod layout) did, in fact, out perform nine of its pull rod competitors. Why the change in 2012? It might, of course, be the correct decision, but my guess would be that it had lot to with the people & organization involved coupled with a superficial understanding of the technical issues.

it depends on the design philosophy. a push rode in 2011 was conserving tires in f 150 at a cost of less qualifying speed. after a season with pirelli they understand qualifying and start of race is more important than tires. So pull rode will give them a better CoG to extract maximum 4m single lap

[Pierce89]

Ringo, was pullrod automatically better on the 75% of cars ferrari beat?is t worse now that ferrari use it? The reason peopl trust ferrari over you is because they've won more world championships than you

By the way I don't think anyone should be trusting team pedigree or journalists, or me. Best to use your judgement or the judgement of the majority of teams after a couple recent years based on evidence, performance and trends.
Based on the trends it was a no brainer that Ferrari were slow to react in 2011. They simply were too conservative. The push rod was not the best choice for them.
If we put aside their pedigree, it becomes easier to see they were behind.

Now that Ferrari is switching their suspension, what does that say about their choice in 2011?
The engines are the same, someone said earlier ferrari couldn't fit a pull rod because their packaging etc. etc. When we had a ferrari powered car, the STR using pullrod with the same engine. What has changed?

Now Ferrari themselves are exploiting the benefits, even splitting their radiator in 2 parts and placing the smaller part where the old push rod bits used to be.

Are we still on about one layout is better than the other because of the layout, not the reason of why it is used?

If only designing a system is so easy....

Difficulty is not the question. An f1 car is designed to make full use of the regulations to extract as much performance as possible.
The comparison between layouts is not so much the layout itself. It's really what the layout permits. A push rod layout does not carry as much benefit as the pull rod.
This thread is over a year old, and it's been a very good discussion; aside from the fact that we didn't really see any advantages of the pushrod stated.

The next question is if pushrods are extinct. Will we see any in the rear on any car this year?
If so, we can look at why they choose it.

You can't honestly believe a pull-rod suspension would have fixed the F150. it's problems were in producing DF. Ferrari have stated that in the design process for the F150 they tried both, and objectively decided on push rods. Maybe pull-rods are only better with a particular aero config. Your blanket statement that pull rods are automatically superior is unbased. You never give solid engineering principles for your assertions.

[myurr]

You can't honestly believe a pull-rod suspension would have fixed the F150. it's problems were in producing DF. Ferrari have stated that in the design process for the F150 they tried both, and objectively decided on push rods. Maybe pull-rods are only better with a particular aero config. Your blanket statement that pull rods are automatically superior is unbased. You never give solid engineering principles for your assertions.

This.

Plus the fact that they've changed to pullrod this year doesn't change anything about the choices they made last year or the relative benefits of the two systems. All it means is that within the set of compromises they've chosen for this years car they have evaluated that the pullrod is the better solution for them.

To predict the death of the pushrod is ridiculous. I will 100% guarantee that at some point in the future the pushrod will be back in F1. Neither solution provides such a clear cut advantage that the other will never find a place.

The current rules and packaging of F1 cars may mean that most teams, or even all teams, believe the pullrod to be the better compromise. But then the rules will be changing in 2014 and it will all be evaluated all over again.

If Ferrari win this year will you be predicting the end of the pushrod at the front?

[Pierce89]

You can't honestly believe a pull-rod suspension would have fixed the F150. it's problems were in producing DF. Ferrari have stated that in the design process for the F150 they tried both, and objectively decided on push rods. Maybe pull-rods are only better with a particular aero config. Your blanket statement that pull rods are automatically superior is unbased. You never give solid engineering principles for your assertions.

This.

Plus the fact that they've changed to pullrod this year doesn't change anything about the choices they made last year or the relative benefits of the two systems. All it means is that within the set of compromises they've chosen for this years car they have evaluated that the pullrod is the better solution for them.

To predict the death of the pushrod is ridiculous. I will 100% guarantee that at some point in the future the pushrod will be back in F1. Neither solution provides such a clear cut advantage that the other will never find a place.

The current rules and packaging of F1 cars may mean that most teams, or even all teams, believe the pullrod to be the better compromise. But then the rules will be changing in 2014 and it will all be evaluated all over again.

If Ferrari win this year will you be predicting the end of the pushrod at the front?

you restated everything I said but in a different way. I don't see the disagreement, or am I misreading the tone? Are you agreeing with me?

[raymondu999]

myurr's agreeing with you mate

[Pierce89]

myurr's agreeing with you mate

oh thanks, I couldn't tell

Facepalm on myself
and apologies to Myurr

[raymondu999]

Yup. He's referencing your point to direct an argument to ringo.

[myurr]

No worries

[xpensive]

You can't honestly believe a pull-rod suspension would have fixed the F150. it's problems were in producing DF. Ferrari have stated that in the design process for the F150 they tried both, and objectively decided on push rods. Maybe pull-rods are only better with a particular aero config. Your blanket statement that pull rods are automatically superior is unbased. You never give solid engineering principles for your assertions.

This.

Plus the fact that they've changed to pullrod this year doesn't change anything about the choices they made last year or the relative benefits of the two systems. All it means is that within the set of compromises they've chosen for this years car they have evaluated that the pullrod is the better solution for them.

To predict the death of the pushrod is ridiculous. I will 100% guarantee that at some point in the future the pushrod will be back in F1. Neither solution provides such a clear cut advantage that the other will never find a place.

The current rules and packaging of F1 cars may mean that most teams, or even all teams, believe the pullrod to be the better compromise. But then the rules will be changing in 2014 and it will all be evaluated all over again.

If Ferrari win this year will you be predicting the end of the pushrod at the front?

Truer words never spoken.

[munudeges]

At the risk of pouring a little oil on the fire in the name of speculation, does anyone want to bet that Ferrari will be doing the reverse, at least for the front of the car, in switching back to push-rod?

The push-rod is most certainly not dead because I believe you have to have a pretty solid reason and a big gain in performance to go against it.

[Crucial_Xtreme]

At the risk of pouring a little oil on the fire in the name of speculation, does anyone want to bet that Ferrari will be doing the reverse, at least for the front of the car, in switching back to push-rod?

The push-rod is most certainly not dead because I believe you have to have a pretty solid reason and a big gain in performance to go against it.

There is absolutely no reason to think they're changing back to push-rod. Why would they? The current pull rod setup works well. The front suspension is not Ferrari's problem.

[ringo]

You can't honestly believe a pull-rod suspension would have fixed the F150. it's problems were in producing DF.

The two are connect. I already mentioned the bodywork in the rear cannot be as tight with the pushrod. That is related to downforce.

Ferrari have stated that in the design process for the F150 they tried both, and objectively decided on push rods.

They made a wrong choice. That is simple. Why cant we all agree a team can be wrong?
So easy to say renault were wrong with the FEE, yet we cant say ferarri made a bad choice.

Maybe pull-rods are only better with a particular aero config.

This is a blanket statement, and it makes no sense.

Your blanket statement that pull rods are automatically superior is unbased. You never give solid engineering principles for your assertions.

You got to be kidding.
read the whole thread. Seg and I were basically the only ones giving evidence. It's all there.
Now i have statistics in my corner. Zero teams using pushrod and the regs have been very stable. One is simply extinct becuase it is not the best choice.
Never was in 2011 either.

I want to see engineering principles on your part and also statistics to show why the push rod suspension is still viable today.

It's been a long haul but i saw this coming from 1 light year away. No brainer indeed.