Firm vs. soft suspension

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Post Fri Feb 23, 2007 1:51 pm

What are the pros and cons of having a firm suspension and a soft suspension?
Aside from the comfort of the soft suspension, does it have any effect on the performance of the car?

I'm interested in this because Mercedes tends to have softer suspension and Bmw tend to have harder suspension. But both cars can corner well
yayoyao
 
Joined: 20 Jan 2007

Post Sat Feb 24, 2007 5:05 pm

Yeah both can corner well if the electronic sh.. like ESP is on, turn it off and you´ll see the diference :D

In f1 if u run soft suspension there will be lots of body movement that will cause you underbody to be less eficient, u will have lots of oversteer and the car will be hard to controll.

Hard suspension on the other hand will minimize body movement but will give u understeer and your a.. will hurt after 5min in the car, so like everything else its a matter of finding the right setting for certain track :wink:
I have that Twitter -thingie now!
tomislavp4
 
Joined: 16 Jun 2006
Location: Sweden & The Republic of Macedonia

Post Sat Feb 24, 2007 5:11 pm

it also depends on the track.
take Monza for example, u have lots of high speed corners which require stiffer suspension. However, u have 2 chicanes and 1 s curve which require drivers to use the maximum track space available. Therefore, u don't want ur car to jump over the curves and spin on every chicane, so teams use something in between soft and stiff.
i don't know if i could explain the idea the right way :oops:
allan
 
Joined: 14 Jan 2006
Location: Waterloo, Canada

Post Sat Feb 24, 2007 6:36 pm

allan wrote:it also depends on the track.
take Monza for example, u have lots of high speed corners which require stiffer suspension. However, u have 2 chicanes and 1 s curve which require drivers to use the maximum track space available. Therefore, u don't want ur car to jump over the curves and spin on every chicane, so teams use something in between soft and stiff.
i don't know if i could explain the idea the right way :oops:


"The springs or torsion bars are the parts of the suspension that actually absorb the bumps. In simple terms, the softer the suspension on the car, the quicker it will travel through a corner. This has the adverse effect of making the car less sensitive to the drivers input, causing sloppy handling. A harder sprung car will have less mechanical grip through the corner, but the handling will be more sensitive and more direct, ideal for circuits such as Monaco where the drivers must be inch perfect between the barriers." Article in mechanics, F1 Technical

I need someone to comfirm which is right. According to the article i read, softer springs are faster through the corner. Can someone explain this.

Thanks for the responses, btw im new here
yayoyao
 
Joined: 20 Jan 2007

Post Sat Feb 24, 2007 9:20 pm

Welcome to the forum. Perhaps this may be useful:
In addition - refer to the "See Also" List

http://www.wikipedia.org/wiki/Car_handling
Carlos
 
Joined: 2 Sep 2006
Location: Canada

Post Sat Feb 24, 2007 11:56 pm

It's a huge topic you are addressing here. I'm not going to explain a lot but something I just read is bothering me.

Springs and torsionbars do NOT absorb bumps. Dampers absorb/dissipate bumps. Springs and torsionbars just store energy. It's a huge difference!

And yes, softer springs, by rule give beter mechanical grip. They allow the tire to follow the curves of the road better. But as said response becomes 'slow'.

Then there is the oversteer/understeer thing. Soft springs nor stiff springs will make the car oversteer or understeer. Yes, they do determine howmuch bodyroll there will be, but don't have oversteer or understeer as a characteristic. Oversteer and understeer are effects of the difference between the springstiffness of the front and the back. As you make the rear springs softer the more understeer you create and visa versa.

Furthermore springstiffness is relative. F1 cars run pretty stiff springs for aerodynamic reasons. This does not mean the springs are stiffer than the springs on a, for example, Maybach. Heavy cars need stiffer springs to have the same effect.

Dampers are a hole different ball part and there function is very hard to explain. But to keep it simple. The faster the wheel hits a bump the quicker the damper has to absorb the energy. Imagine the variety of speeds and bumps a road has and you will understand the complexity of there work/design.
Gmuze
 
Joined: 29 Sep 2006
Location: Delft

Post Sun Feb 25, 2007 4:16 am

Ahh, "Suspension 101", maybe the most complex part of racing, or even luxury cars. First off, I strongly suggest you get some good books, because this can become incredibly complicated.
Everything goes back to one fundamental, to keep the rubber on the track, to maintain as good a contact patch under all conditions the car encounters. Nothing else matters, anything to do with the suspension serves that one purpose. Of course I'm talking about performance, because at the opposite end of the spectrum, for, say, a luxury car, it's built to keep the driver nice and comfortable and happy, removing harsh bumps and all the other bothers of the ordinary world.
Please understand I will oversimplify, because suspensions interact and the more you look, the more complex it is. The chassis and location of the suspension pivots and different parts of the suspension such as the uprights and arms, are designed to keep the contact patch on the track under varying conditions, such as bumps, cornering, acceleration, and braking.
In a perfect world we would have track surfaces as level and smooth as a billiard table. But there are dips, bumps, curbs, changes of elevation, you name it, the track throws it at the car. A wheel and tire is a glorified beach ball, and if allow to do so, would bounce, and bounce, and bounce when it hits a bump. But every time it bounces, the tire lifts off the road surface, and traction is lost. Now when a tire moves up, it compresses, and when it goes down, rebounds. This is where the shocks come in, controlling the compression, and rebound. The forces are different in each direction, and the shocks are designed so the they resist compression with a certain force, and rebound with another level of resistance.
The springs? Well, basically all they do is hold the car up. That's it, they just hold the chassis in the air. Please remember I'm oversimplifying, because there actually are complex interrelationships between all the componenets, but trying right now would give me a headache and make this post about five hundred pages long.
There's also suspension travel, how far the wheels are allowed to travel up and down. In a Formula One car that spends it's life on relatively level and smooth surfaces, the wheel travel can be two, three inches. Almost a go-kart. But in the normal roads where curbs and bumps exist, the suspension must be allowed to deal with these hazards, else the suspension would bottom out, or the chassis would contact the ground. Very uncomfortable, and it would have an adverse affect on, yup, the holy grail, contact patch.
So a road car has a lot of travel and low compression and rebound on the shocks, because it is designed to travel the bumps and crap without the wife spilling her coffee. But in racing, driver comfort really doesn't matter, all that matters, here we go again, that magic contact patch.
Springs hold the chassis up, and the shocks control the compression and rebound of the wheels relative to the chassis.
DaveKillens
 
Joined: 20 Jan 2005

Post Sun Feb 25, 2007 11:52 am

And in terms of an F1 car a ride height adjustment of 0.5 (yes "half") a millimeter has a noticeable affect on car performance. A lot of the stiffness will be governed by aero requirements. (P.S. - I can't get my head around the idea that 0.5mm is important :shock: )

The aerodynamics are so dominant in the total performance around a track.

Is harder or softer quicker? Impossible to answer. Shall we throw in the tyres - what if harder or softer was not heating the tyres properly (too hot or too cold)? Then either could be slower simply because the tyres aren't being used well.

Remove ourselves from the perfect world of F1 cars and look at non-specialised racing cars (how about Historic saloons?). While, in theory softer should allow more grip - what if stiffer keeps the wheels at a better angle to the road. Then stiffer will be quicker again.

Race cars need to squat in order to go (like humans ;)) - what if the car was getting onto it's bump stops under acceleration - again (possibly) stiffer may be faster by keeping the rear end from bottoming out).

As Dave says - very complex.

I don't even know exactly how the springing/damping on an F1 car is configured these days - but it's not as simple as 1x damper & spring for each wheel. They are very secretive about keeping the suspension assembly covered up - not without good reason.

Again - I must agree with Dave - the springs are pretty much there to keep the whole mess from grinding itself away around the track. I seem to remember Carroll Smith saying that you need just enough spring to keep the car off the track and no more. With aero loads trying to squash the car into the road (and the fact they don't want to keep adding ride height) - then the springs have to be able to resist that force (I suppose the bump stops should be included in the definition of a spring :wink: )
RH1300S
 
Joined: 6 Jun 2005

Post Sun Feb 25, 2007 4:46 pm

Generally, if you're looking for performance, it's always been my understanding that you'd want the suspension to be as stiff as possible for the conditions you're going to be in. That's basically it.
bhall
 
Joined: 28 Feb 2006

Post Mon Feb 26, 2007 11:08 am

There's a bit of history involved too. Many years ago, sporty cars were a rarity, most were designed to carry the family on beach outings and all that jazz. But enthusiasts would take these vehicles and start to modify them for performance. Especially around the 50's, give or take a decade. These people found out that the stock suspensions were soft and an easy and common solution was to make the suspension harder. Shorter travel suspension, stiffer springs, and especially stiffer shocks. Because back then, just about anything would perform better if you stiffened it up.
Now let's change the subject and compare a long travel, softly sprung suspension against a shorter travel, harder suspension. You're driving down your favorite stretch of road, and enter a corner. You turn the wheel, and as the tires start to force the car in the desired direction, the chassis begins to roll because of the inertia. During this transition period before the car "sets", you really can't apply 100% cornering force because the chassis is still rolling. The suspension geometry has not reached the optimum position to give maximum contact patch, and you have to wait until it gets there. As well, the chassis roll is a form of energy, and the forces required to stop that roll transfer to the tires. You already have the tires working against the basic cornering inertia, and then you add the forces required to negate the roll. So basically, you can't reach 100% designed cornering performance until the chassis stops rolling and the suspension "sets".
If you have the softly sprung, soft suspension, that period of time could be a half second, or more. Do the same trick with a shorter travel, stiffer suspension and that period of time is lessened. Just look at a serious autocrosser, where you go from braking to acceleration, to left, to right one after the other, close together. That transition period is almost nil, because those puppies are stiffer than a sailor on shore leave. (bit of nautical humor there, lol)
DaveKillens
 
Joined: 20 Jan 2005


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