F1technical.net

What is the purpose of push rods on the suspension? I would think that having an exact 1:1 ratio from the wheel to the actual spring would be ideal, but perhaps not?

How do they determine what kind of rocker ratio would be ideal when designing the car? Lastly is there a computation formula for this?

As far as I can understand things, the benefits are inboard mounted spring/dampers for less un-sprung mass and air-resistance. Also the ability to create a progressive spring-ratio by simple geometrics.

Why would 1:1 be ideal? It's just a number. Spring and damper don't care how much they move relative to the wheel.

That said 1:1 is a decent goal for reasons of damper friction etc. The use of a pushrod, SLA system in general is because it is is minimum weight, gives you some nice packaging options, is relatively easy to analyze, and gives a good balance of kinematic control.

In terms of picking a ratio, depends on a lot. Packaging can be big, as can you desired rocker progression, available spring and damper rates, etc. End goal is to get the wheel rate progress you specify.

A typical modern racecar does not sport much in terms of wheel travel with given aeroconstraints ,especially flatbottom cars.
so putting the dampers springs on top of a wishbone will rob you again of some leverage .try as you might ,yau are stuck with a an unfavourable leverage plus digressive characteristic.
I doubt there´s much to find in terms of unsprung weight with rockerarm pushrod layout,considering a damper eye is basically nothing else than a pushrod ,it is quite a bit shorteras well,and of course not the whole spring is to be counted towards the unsprung weight.you also face a lot more bearings leading to some degree of possible bind /stickslip or end play ,all not really good things in suspension world.
I also doubt the aero gain is a big issue for most of the cars.

So the big advantage in rockerarm -pushrod suspension is you are able to tailor wheelmotion /dampermotion,springmotion to your needs be it a ratio of 1:1 or 1:2 ,digressive,progressive theres a lot of possibilities if you choose this arrangement. You may even get all the levers positioned giving you a linear
ratio over the whole travel if this was a desired feature...
The modern damper really is not so much dependant on its travel to create force but not so many years ago a damper really needed to travel over 10mm to build up damping force at all.so basically on a car with 10mm suspensiontravel it was not really working at all,without a proper mutiplication ratio.
bellcranks etc are there for a reason.But of course you would not make things more complicated just for the hell of it ,would you? in some cases I feel the air of doubt to be honest.

Regarding the weight aspect marcush, I can remember some years back when Arrows designer Sergio Rinland sort of re-introduced the pull-rod system, with the argument of lowering the car's CG by moving the torsion-bars from top to bottom.
Was that relevant in the context?

Where can i find more information that talks about this? RCVD, and Tune To Win? I own Engineer to Win, but i'm beginning to think tune to win is much better for learning how race cars work.

Jersey Tom wrote:Why would 1:1 be ideal? It's just a number. Spring and damper don't care how much they move relative to the wheel.

That said 1:1 is a decent goal for reasons of damper friction etc. The use of a pushrod, SLA system in general is because it is is minimum weight, gives you some nice packaging options, is relatively easy to analyze, and gives a good balance of kinematic control.

In terms of picking a ratio, depends on a lot. Packaging can be big, as can you desired rocker progression, available spring and damper rates, etc. End goal is to get the wheel rate progress you specify.

What is wheel rate?

fastback33 wrote:Where can i find more information that talks about this? RCVD, and Tune To Win? I own Engineer to Win, but i'm beginning to think tune to win is much better for learning how race cars work.

I bought RCVD when I was still a member of SAE... which was a few years ago. I am sure if you go to the SAE website you'll find out how to order it.

Which reminds me... I should continue reading it.

xpensive wrote:Regarding the weight aspect marcush, I can remember some years back when Arrows designer Sergio Rinland sort of re-introduced the pull-rod system, with the argument of lowering the car's CG by moving the torsion-bars from top to bottom.
Was that relevant in the context?

Here's a pullrod discussion we had years ago

viewtopic.php?p=5774

Thanx west, very educational that. All in all, as an Engineer I can see that the practical advantages with the pushrod outweighs most other arguments for a pull-rod system.

fastback33 wrote:

Jersey Tom wrote:Why would 1:1 be ideal? It's just a number. Spring and damper don't care how much they move relative to the wheel.

That said 1:1 is a decent goal for reasons of damper friction etc. The use of a pushrod, SLA system in general is because it is is minimum weight, gives you some nice packaging options, is relatively easy to analyze, and gives a good balance of kinematic control.

In terms of picking a ratio, depends on a lot. Packaging can be big, as can you desired rocker progression, available spring and damper rates, etc. End goal is to get the wheel rate progress you specify.

What is wheel rate?

http://letmegooglethatforyou.com/?q=%22wheel+rate%22

To good to pass up.

Actually, the displacement of the spring and dampener are important. The more fluid volume displaced in the dampener, the less critical the valving needs to be. The same with the spring. The greater the spring movement, whether helical coil or torsion type, the less critical the spring rate.

Consistency and repeatability are everything in suspension set-up.