Hard v/s soft suspension set up

[ChassisSim]

This has been an age old question that I and many of my colleagues have debated endlessly. It's also one of my pet topics, hence my interest in contributing to this dicussion.

To give you a bit of background on myself I have worked as a race and data engineer in formulaes as diverse as F3000, F3, A1GP, V8 Supercars, Sportscar, FIA GT3 to name a few. Currently I run ChassisSim Technologies that produces transient race car simulation software used in fields as diverse as GP2, F3, V8 Supercars, the IRL, ALMS and many other categories. I also write for Racecar Engineering.

Tim I thought you gave a very good a detailed account of what's involved in the setup compromises.

However let me add the perspective of someone who has been there and done that. The Bottomline with soft vs stiff always boils down to the following two compromises.

*What do the tyres want. There are some tyres that must have load to bring them up to temperature. This requires a stiff setup. Conversely there are other tyres that will be positively cooked in no time.

*How much aero are you running and where you want the ride height envelope. The more downforce you are running the more of a deal breaker this is. Indeed as you go to F3 and above this combined with the tyres dictate what you can and can't do.

The other thing that throws the cat amongst the pigeons is your need to give the car some compliance as you going over kerbs and to manage your transients.

Unfortunately there are no hard and fast rules. It isn't that simple. It's why people like myself have a job. Sometimes part of me wish it wasn't so though!

For those of you who want to explore this in more detail this might help,

http://www.ebook.com/ebooks/All/The_Dyn ... _Car/16469

Let me be up front it's not free, but the free preview on tyres should give you all something to think about it.

Enjoy

Danny

[DaveW]

Agreed, Danny. In fact, the concept of "soft" vs "stiff" suspension set-up is best defined in terms of the ratio of spring to (dynamic) tyre stiffness, rather than spring stiffness in isolation. I would add a couple of thoughts (three, actually):

1. 747 introduced the idea of "driver preference". I think that is important for more than one reason. Arguably, it explains why some race drivers are more successful than others.

2. Regulations can influence suspension set-up significantly - particularly when they impose an artificial limit on static ride height.

3. For any "aero" vehicle, platform control (ride height & rake) will dominate performance at high airspeeds, whilst "mechanical" control will (or can) affect performance at low airspeeds. Mechanical control at low airspeeds can have a surprising impact on lap time at circuits where low speed corners precede long straights. For this reason there is often an overall performance gain to be had if a good "mechanical" (soft) set-up at low airspeeds can be married to a good "aero" (stiff) set-up at high airspeeds. In my experience, aero-dominated F1 teams tend to ignore that fact (or, perhaps, engineer their vehicles for aero reasons so that a mechanical set-up just doesn't "work"), whilst lower tier race series expend considerable effort to find a good track-dependent set-up compromise. That is one reason, I believe, that there is sometimes an overlap of F1 & GP2 grids....

[proutyc]

I find this topic very intriguing. We run mini sports cars (similiar to DSR) but using full length ground effect tunnels in our side pods.

From testing we're seeing some of these compromises but generally what appears to make the largest gains is control roll (or reducing it so to speak) What surprised me was this firmer roll setup has helped in lower speed corners too (80kph) where we have seen an increase in corner speed and also G.

I gather this comes back partially to driver being more comfortable with the car and also how important controlling the throat of the tunnel.

I'd really also appreciate anyone with experience in ground effects messaging me with any findings they saw and are willing to let me know. I'll test on the car at next track day.

[Tim.Wright]

This has been an age old question that I and many of my colleagues have debated endlessly. It's also one of my pet topics, hence my interest in contributing to this dicussion.

Its a small world Danny! I dont know if you'd remember me but we had a short discussion about engineering careers and simulation shortly before I left sleepy old Perth a couple of years ago.

This thread has actually turned out quite nice, I've learnt a few extra things and if anybody wanted to know the factors involved in hard vs soft setup, this thread nails the main points in 2 pages.

Compare this to the push/pull rod thread which is approaching 4e33 pages long and completely fruitless...

Tim

[RishiRajak]

That was helpful! thnks.

[Andres125sx]

I´m not sure about the reason you all see it that difficult, after this interesting read I got it in 2 minutes, you must go the softest you can handle the unintended consequences (pitch/rake/aero changes, car reaction delays, etc)

Easy









Now seriously, VERY interesting thread, upvoted several posts

[J.A.W.]

I´m not sure about the reason you all see it that difficult, after this interesting read I got it in 2 minutes, you must go the softest you can handle the unintended consequences (pitch/rake/aero changes, car reaction delays, etc)...

Agreed, super stiff set-up only works well on (rarely encountered) ultra smooth surfaces..

Look at Karts in which pneumatic give via tyres is the sole 'suspension' ( ok, with a bit of chassis flex too)..
..that primitive approach wears thin.. as quickly as mass increases..

[PhillipM]

Quite a lot of chassis flex in the top karts, they too like soft suspension, even if they don't have any