Push Rod or Pull Rod for a front Suspension ?

[BK Jang (YNU_FSAE)]

Hey Guys.. Does anybody know what exactly different effects are between Push Rod and Pull Rod for the front Suspension of FSAE car?
Do they have just different position?
Please let me know what you guys have known already..
Thanks..

BK Jang
YNU_FSAE (the 1st Korean FSAE)
korea_fsae@hotmail.com
http://cmdm.yu.ac.kr
http://chunma.yu.ac.kr/~j8231524/ynu.jpg

[Angry Joe]

Pullrod suspension is designed so as the wheel goes into bump, the rod is pulled and it compresses the spring through a bellcrank. Aussuming both have been designed for equal performance, the advantages of a pullrod suspension over pushrod are:

- pullrods are in tension, so they can be lighter than an equivelent pushrod
- lower center of gravity
- less structure is generally needed to support the suspension

Disadvantages:
- packaging is tougher, frequently you must consider intruding on cockpit space or placing the shocks too close to the ground
- if you're not careful, the compromises you must make to accomodate suspension components could end up weighing more than what you saved in the first place



Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/~insae/formula)

[BK Jang (YNU_FSAE)]

Thanks for your answer.

May I ask one more question?

Now almost all or all F1 teams' suspension system are Push Rod..

However, according to the history records, Mclaren, Ferrari, and Benneton used Pull Rod for their front suspension in 1988.

Yah... I heard Pull Rod has little bit more advantage than Push Rod, but why all of them use Push Rod these days? Do you know or Can you figure out why?

In my opinion, they have limit space for mounting suspension stuff on base of frame because of Aerodydamic system, so they might use Push Rod instead of Pull Rod.

What is your opinion about?

I really thanks for your concern

Bye and happy new year. (Especially, today is the new year's day in Asia on the moon date^^.)

BK Jang
YNU_FSAE (the 1st Korean FSAE)
korea_fsae@hotmail.com
http://cmdm.yu.ac.kr

http://chunma.yu.ac.kr/~j8231524/ynu.jpg

[DJHache]

The suspension on an F1 is primarily designed to maintain the Aerodynamic platform at a constant height and angle of attack. In order to free up the airflow over the front wing, F1 teams have been raising the noses on their cars, preventing obstruction to the air. It's the same in the rear, where the suspension is optimized to allow the air to go around the tires and under the wing. This has led to teams adopting pushrod instead of pullrod. Keep in mind all of these improvements came in the wake of windtunnel testing, which is why the F1s had pull rod in the 80's. What's also interesting is the teams that ran rocker arm suspensions in the 80's

[vinHonda]

The push rods actuate torsion bars as dampers these days too. F1 cars require so little travel, the aero keeps them essentially 'hugg'n' the ground.

Vinh

University of Toronto Formula SAE Racing Team
www.fsae.utoronto.ca (http://www.fsae.utoronto.ca)

[karter]

In the early days of F1 ground effects, rocker arms were employed (look at the front end of a Lotus 78/79). This kept the air flow unobstructed but, the problem was the wheel rate was determined more by the rocker arm stifness than the spring/shock. Push/pull rod suspension got the spring/shock back into the picture. The advantages on an FSAE car are packaging, rising rate and adjustability. A well designed outboard spring system wouldn't look as cool but could be lighter and simpler.

[jack]

allthough djhache is probably right, i have read that f1 uses pushrods for a different reason. when cornering, the outside upper a-arm is in tension, while the lower is in compresion. due to high cornering loads from lots of down-force and huge tires, this lower a-arm gets lots of stress in an undesirable fasion (compression). now, if you use a pushrod, allmost half of that load is now disstributed to a traingulated member. thus, you dont have to have nearly as beefy of a lower a-arm (your pushrod will be a bit heaver than pull, but there is a net weight savings). anyway, i dont think aero is much better with pushrods rather than pull, because pushrods have to be thicker (higher drag). this is probably splitting hairs though, and i would say that the real aero advantage for pushrods in f1 is how you get to shape the underside of the nose in that area, now that you dont need shocks there.

what does this have to do with (relatively)slow FSAE cars with no aero? absolutely nothing. but f1 is so cool...

jack @ WWU
http://www.etec.wwu.edu/

[clausen]

Jack, I'd never thought about that. (the pushrod becoming a triangulating member) thats really interesting.

Regards

Paul Clausen
Uni of Adelaide

[Frank]

when it comes to packaging,

remember you want the push/pull rod to be at a fairly steep (say 30 deg to horizontal) angle, otherwise you have to package large rockers (to get some motion into your shocks, which is good)

our car was a "pushme-pullyou" hehe
pullrod front, pushrod rear

Frank

http://www.uq.edu.au/fsae/2003%20Photos/Comp/Dsc01200.jpg

[RiNaZ]

I was wondering what kind of suspension geometry is wollongong using? I saw their dampers were going horizontal at the bottom of the car

RiNaZ

[Travis Garrison]

...dampers at the bottom would mean pull rod....

[RiNaZ]

ohhh ... thanks. Clearly shows that i have to do extensive research on suspension geometry http://fsae.com/groupee_common/emoticons/icon_smile.gif. Thanks again travis

RiNaZ

[BK Jang (YNU_FSAE)]

Relly Thanks Guys.
Everything you guys said is interesting.
I got much new information about suspention..^^

Also it is nice car, Frank!!

Our team(YNU_FSAE) is still a Rookie, so we need a lot of help from you guys..

Please feel free to help us..!! http://fsae.com/groupee_common/emoticons/icon_smile.gif

Good Luck to you and your teams..

Thanks...

BK Jang
YNU_FSAE (the 1st Korean FSAE)
korea_fsae@hotmail.com
http://cmdm.yu.ac.kr

http://chunma.yu.ac.kr/~j8231524/ynu.jpg

[bahy]

Originally posted by Angry Joe:
Pullrod suspension is designed so as the wheel goes into bump, the rod is pulled and it compresses the spring through a bellcrank. Aussuming both have been designed for equal performance, the advantages of a pullrod suspension over pushrod are:

- pullrods are in tension, so they can be lighter than an equivelent pushrod
- lower center of gravity
- less structure is generally needed to support the suspension

Disadvantages:
- packaging is tougher, frequently you must consider intruding on cockpit space or placing the shocks too close to the ground
- if you're not careful, the compromises you must make to accomodate suspension components could end up weighing more than what you saved in the first place

And the upper arm will carry more load so it has to be stiffer

Lehigh Formula SAE Alumni
Team Captain 2002-2003

www.lehigh.edu/~insae/formula (http://www.lehigh.edu/%7Einsae/formula)

[M. Nader]

Just keep 1 thing in mind, although F1 is a source of inspiration it is very, very different from FSAE. so that means that what is good for them is not necessarily good for you, you will have to decide that and have a valid reason. Judges hate "it is in f1 so it must be good" and rightly so.

Another point that is somehow missing in this discussion is adjustability and tuning. by increasing the pushrod length ( by rod ends) you can increase ride height, Opposite in Pullrod so a problem may be caused by this that maybe your pull rod is as short as possible (rod end tightened fully). But then again in a push rod system you can't really push the rod end too much as this will cause the thread contact to be very weak. but it is quite hard to such tuning with an outboard system.


I noticed that you are a first year team, please let me tell you two pieces of advice (we were so last year).
1) work on adjustability.
2) finish the car AT LEAST 3-4 MONTHS BEFORE THE COMPETITION. no matter what the quality is, 3 months of testing can give your car more than 3 seconds of pace no matter how crappy it is (tuning the suspension and driver training can do that). so set yourself a deadline and whatever work that you have finished, it is your product even if it is crap.

[The AFX Master]

You just answered a 8yr old thread bumped by a spambot or a mute.

Seems to be they are no longer a first year team :P