Does front pullrod suspension cause understeer?

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AR3-GP
AR3-GP
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Does front pullrod suspension cause understeer?

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Does front Pullrod cause understeer and if so, why?

Some have suggested the Ferrari F1 car began to understeer when they switched to a front pullrod from 2012 to 2014. Mclaren ran in 2013. Was the understeer a coincidence related to other factors like aero balance or a trait of front pull rod suspensions? Why should the springing medium have any effect on balance?

Greg Locock
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Re: Does front pullrod suspension cause understeer?

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Pushrod vs pullrod is a red herring, either can be configured to any parabolic plot of damper travel vs wheel travel you want, kinematically. (That is, pick 3 points of damper length and wheel position and we can hit it, pick 4 and we'll try). You may not be able to package the resulting mechanism, and it may not be compliantly feasible. As usual in engineering it's all a compromise.

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Stu
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Re: Does front pullrod suspension cause understeer?

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AR3-GP wrote:
Mon Apr 18, 2022 3:31 pm
Does front Pullrod cause understeer and if so, why?

Some have suggested the Ferrari F1 car began to understeer when they switched to a front pullrod from 2012 to 2014. Mclaren ran in 2013. Was the understeer a coincidence related to other factors like aero balance or a trait of front pull rod suspensions? Why should the springing medium have any effect on balance?
In theory, if you had two suspension systems with the same linkage rate and the same relative motion between hub and rocker, you would see no operational difference.

Much as with old-tech coil-over systems if you have a very low incidence angle in the suspension linkage there are costs to effectiveness; whether push-rod or pull-rod is used. The last Ferrari to use it had an almost horizontal pull-rod which would require a pretty weird rocker assembly to accurately control the suspension/platform.

One of the most successful cars of all time (McLaren MP4/4) had pull-rod suspension.
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AR3-GP
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Re: Does front pullrod suspension cause understeer?

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Stu wrote:
Mon Apr 18, 2022 7:16 pm
AR3-GP wrote:
Mon Apr 18, 2022 3:31 pm
Does front Pullrod cause understeer and if so, why?

Some have suggested the Ferrari F1 car began to understeer when they switched to a front pullrod from 2012 to 2014. Mclaren ran in 2013. Was the understeer a coincidence related to other factors like aero balance or a trait of front pull rod suspensions? Why should the springing medium have any effect on balance?
In theory, if you had two suspension systems with the same linkage rate and the same relative motion between hub and rocker, you would see no operational difference.

Much as with old-tech coil-over systems if you have a very low incidence angle in the suspension linkage there are costs to effectiveness; whether push-rod or pull-rod is used. The last Ferrari to use it had an almost horizontal pull-rod which would require a pretty weird rocker assembly to accurately control the suspension/platform.

One of the most successful cars of all time (McLaren MP4/4) had pull-rod suspension.
Interesting comment about the horizontal pull rod on the Ferrari.

As for everything else, I likewise don't see the difference in pull rod for push rod kinematically speaking. All of the control parameters of a suspension are tunable in both systems. I do not believe one could be more prone to understeer than another.

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Tim.Wright
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Re: Does front pullrod suspension cause understeer?

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Kinematically there is very little difference if any. The biggest differences are likely to be aerodynamic.

Regarding the Ferrari solution from 2012, the angle of the pushrod with respect to the other links is nothing special or extreme. This is my take on it from that time:
viewtopic.php?p=303124#p303124
Not the engineer at Force India

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Zynerji
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Re: Does front pullrod suspension cause understeer?

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Tim.Wright wrote:
Tue Apr 19, 2022 2:34 am
Kinematically there is very little difference if any. The biggest differences are likely to be aerodynamic.

Regarding the Ferrari solution from 2012, the angle of the pushrod with respect to the other links is nothing special or extreme. This is my take on it from that time:
viewtopic.php?p=303124#p303124
Would you rate the aero effect higher than the CoG effect of lower packaging?

Greg Locock
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Re: Does front pullrod suspension cause understeer?

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That is best answered with a lap sim, I doubt anybody can eyeball the tradeoff there!

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Tim.Wright
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Re: Does front pullrod suspension cause understeer?

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Zynerji wrote:
Tue Apr 19, 2022 4:43 am
Would you rate the aero effect higher than the CoG effect of lower packaging?
I have no idea at all about the aero effects. The CG effect these days is probably also nearly negligible since the cars are so heavy these days.
Not the engineer at Force India

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vorticism
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Re: Does front pullrod suspension cause understeer?

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I think one of the main changes that spurred this is the switch to 18" wheels. They offer more vertical space for the wheel upright, which means the arms can be spaced higher and lower, while the angle of the shock absorber rod can be placed more steeply relative to the chassis. Compare the RB and Ferrari front view. RB both have more widely spaced (vertically) arms, and their shock absorber rod is taking advantage of a higher outboard mounting point relative to wheel centerline (compared to what could be achieved with 13" uprights). Combined with fixed chassis dimensions that have more freedom to move the inboard parts down as opposed to up.

Compare to Ferrari who maintained both closely spaced arms and pushrods with a more shallow rod angle. The Ferrari members are likely heavier as a result. For them to get a similar rod angle to the RB they would have to push the outboard mounting point down below the lower A-arm; no one's doing that due to aero detriments, likely.

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Big Tea
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Re: Does front pullrod suspension cause understeer?

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Are there different effects from riding the kerb with pullrod to pushrod?
Would there possibly be a greater effect on the hub/wheel as there is (*) more unsupported weight?

*Wrong term I know, but more weight and more leverage higher up??? As if a 3rd class lever
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AR3-GP
AR3-GP
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Re: Does front pullrod suspension cause understeer?

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Zynerji wrote:
Tue Apr 19, 2022 4:43 am
Tim.Wright wrote:
Tue Apr 19, 2022 2:34 am
Kinematically there is very little difference if any. The biggest differences are likely to be aerodynamic.

Regarding the Ferrari solution from 2012, the angle of the pushrod with respect to the other links is nothing special or extreme. This is my take on it from that time:
viewtopic.php?p=303124#p303124
Would you rate the aero effect higher than the CoG effect of lower packaging?
The aero effect depends on your aero concept. If the push/pull rod is blockage in front of an important feature of your aero concept, then you will prefer one over the other.

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Honda Porsche fan
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Re: Does front pullrod suspension cause understeer?

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AR3-GP wrote:
Mon Apr 18, 2022 3:31 pm
Does front Pullrod cause understeer and if so, why?

Some have suggested the Ferrari F1 car began to understeer when they switched to a front pullrod from 2012 to 2014. Mclaren ran in 2013. Was the understeer a coincidence related to other factors like aero balance or a trait of front pull rod suspensions? Why should the springing medium have any effect on balance?
If I'm not mistaken, but weren't F1 teams using hydraulic reactive suspension in 2012 to 2014/16 ? I know Mercedes was.

Wouldn't the hydraulic reactive suspension help with correcting oversteer/understeer ?

feni_remmen
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Re: Does front pullrod suspension cause understeer?

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I think this is likely a by product of a mis-interpretation of car behaviour from the early 80’s. This is when teams finally made a definitive transition away from rocker beams to pushrod / pullrod rocker installations. Pullrods seemed to be associated with installation stiffness issues with the benefit of a low centre of gravity while pushrod seemed to be considered the opposite way. It was perhaps understandable, but I suspect many people associated car behaviour as inherent to the format rather than an underlying issue with the engineering on the whole platform of the car. I know when new cars debuted, details like pullrod or pushrod really produced enthusiastic discussion as if it really meant something. In truth, the characteristics of any cars were usually due to other underlying issues.

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Honda Porsche fan
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Re: Does front pullrod suspension cause understeer?

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Red Bull In 2019 and 2020 used a multi-link suspension...

In 2019 the RB15 featured a multi-link upper wishbone.

In 2020, the RB16 was using a multi-link lower wishbone instead with the rear leg mounted lower down than the front leg and it also seems to have a pullrod too..

Red Bull's innovative multi-link 2020 F1 front suspension design...

https://www.autosport.com/f1/news/red-b ... 6/4983946/

https://www.motorsportweek.com/2020/06/ ... ulls-rb16/

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coaster
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Re: Does front pullrod suspension cause understeer?

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I understand your gut feel on this, the 80's cars had pullrods almost as thin as 6mm, which is fine for pull type loads, not so for compressive rebound though.
I imagine all sorts of distortion on rebound, affecting wheel movement, those 80's cars would have felt very flimsy on rebound.