29 replies to this topic

[Freebird]

Current F1 cars are running a zero-keel suspension design to promote clean airflow below the monocoque. The result being the control arms are inclined upward ( Anhedral ) to join the monocoque. My question is, how do they make the kinematics of this layout work when the car is under side load?

They have a trick. What is it?

[gruntguru]

Current F1 cars are running a zero-keel suspension design to promote clean airflow below the monocoque. The result being the control arms are inclined upward ( Anhedral ) to join the monocoque. My question is, how do they make the kinematics of this layout work when the car is under side load?
They have a trick. What is it?

What are the upper A arms doing? What is the RC height? Can you post an indicative image?

[SteveCanyon]

I am sure it's because they have the centre of gravity so low in the cars now that they can run a high roll centre and get away with it. Because the car won't roll away from the direction of the corner they should be able to run them a little softer on the springs and a lot softer on the anti-roll bars.

[gruntguru]

I am sure it's because they have the centre of gravity so low in the cars now that they can run a high roll centre and get away with it. Because the car won't roll away from the direction of the corner they should be able to run them a little softer on the springs and a lot softer on the anti-roll bars.

The RC's must still be below the CG surely. Lateral grip would suffer severely otherwise.

[SteveCanyon]

Why?

[gruntguru]

Why?

Transient lateral loads (spikes) go directly into the tyres as opposed to sharing by suspension compliance.

Edited by gruntguru, 09 April 2010 - 00:27.

[SteveCanyon]

So how much of a problem is that going to be for an F1 car that has very small suspension travel and is running on a smooth track?

[gruntguru]

So how much of a problem is that going to be for an F1 car that has very small suspension travel and is running on a smooth track?

Not sure. Greg???

[Lukin]

I remember back when Toyota went to zero keel (TF105a to b maybe?), there was a comparison and the RC changes well over 100mm between one and the other. I think the moral of the story is aero rules and as Chapman said, any suspension will work if you don't let it move.

[Greg Locock]

I'm surprised Neil hasn't posted this, he found it http://www.vehicledy...15_lukianov.pdf

Ignore the suspension 101 bit at the front, look at the real data and comments.

Bear in mind that the internal geometry of the car has no effect on steady state load transfer.

[desmo]

"Any suspension- no matter how poorly designed- can be made to work reasonably well if you just stop it from moving." -Colin Chapman

[Fat Boy]

"Any suspension- no matter how poorly designed- can be made to work reasonably well if you just stop it from moving." -Colin Chapman

When Colin said this, I believe he was taking the piss out of people who over-spring their cars. It wasn't a design philosophy.

As far as the OP's question, I think what Greg posted has a lot of merit. They're looking for very quick steering response and low yaw damping. They can afford to run the front roll center quite high. Downforce is as such a premium that anything you can do to make more over-rules practically any other consideration.

[Greg Locock]

When Colin said this, I believe he was taking the piss out of people who over-spring their cars. It wasn't a design philosophy.

I am 90% sure he was commenting on the tendency to fit great fat sta bars and stiff springs to cars when they were 'upgraded' for handling, rather than sorting the fundamental kinematics out. When I was there at least the "Handling By Lotus" badge did not mean "chuck NVH and ride comfort out the window". In fact we often retuned the engine mounts as part of the R&H package.

Given the incredibly high wheel rates of the F1 cars I think the concept of a kinematic roll centre is a bit naive, if nothing else the compliance of the body and arms will alter its position substantially.

That's not to say that pointing the arms up won't affect things, of course. But I bet Lapsim says it makes no odds!

[DaveW]

I am 90% sure he was commenting on the tendency to fit great fat sta bars and stiff springs to cars when they were 'upgraded' for handling, rather than sorting the fundamental kinematics out. When I was there at least the "Handling By Lotus" badge did not mean "chuck NVH and ride comfort out the window". In fact we often retuned the engine mounts as part of the R&H package.

Good observation. Damped (& tuned) engine mounts & suspension bushes, especially damper "top mounts", have a significant effect on ride & handling, increasingly so as the ratio of power train weight to AUW increases. Tyres are also important, of course, again increasingly so as aspect ratios decrease.

Given the incredibly high wheel rates of the F1 cars I think the concept of a kinematic roll centre is a bit naive, if nothing else the compliance of the body and arms will alter its position substantially.

That's not to say that pointing the arms up won't affect things, of course. But I bet Lapsim says it makes no odds!

Not sure if Lapsim is sufficiently detailed, but I suspect that roll centre migration would be an issue with extreme geometries unless they were "fixed" by ultra-stiff springs.

(Mischievous note: Stiff front springs improve front ride height control, which allows more extreme aero solutions, helped by "aero-friendly" front geometries, which means that lower rate springs are no longer a viable option, leading to the inevitable conclusion that aero is the only thing that matters. Something like that. BTW, "kart" suspension solutions also have an observable effect on engine life....)

[desmo]

Looking at on-car video the front wheel travel in F1 is obviously minuscule today, even when they are bashing over curbs. If they move more than maybe 10mm total wheel travel I'd be surprised. I frankly can't see any travel at all but I'll assume there is some. It looks to me like the rear suspensions are allowed considerably more travel when you watch the in-car following another car as it clips a curb. Maybe they just let the rears move a bit to save the powertrains from getting bashed about and deformed in ways they weren't designed to.

How much difference can damping, ARB rate, suspension geometry etc. etc. really make at <10mm travel?

[Fat Boy]

How much difference can damping, ARB rate, suspension geometry etc. etc. really make at <10mm travel?

That's the F'd part of the whole thing. It's all still very important.

Super high downforce cars take some of the fun away for me. I like making some sort of mechanical / aero compromise. On some of these cars, there just isn't much of a compromise...Not sure why. I guess because it seems like there should be one. The aero just pretty much over-rides everything up to the point where the driver can't see because you're shaking the eye-balls out of his head on some cars, though.

[Ross Stonefeld]

That's easily sorted. Get the drivers together to complain about the track until they resurface it. Ideally you should air your grievances within 10 days prior to the start of the event.

[mariner]

I still think that Keith Duckworth in his wonderful logical style figured out the solution to downforce and no flex suspensions over 20 years ago.

He said just put rumble strips about 25 -50 mm high across the track and that would force people to raise ride height and introduce wheel movement thus destoying the ground effects.
It would cost about $200k or so per F1 track and would work even better today with the flat bottom/no skirts rules.

Watch the effects of very high roll centres then!

[desmo]

That's the F'd part of the whole thing. It's all still very important.

OK. Would damping, ARB rate, suspension geometry etc. still matter at 5mm of wheel travel? 2mm? 0.05mm? Zero?

[gruntguru]

OK. Would damping, ARB rate, suspension geometry etc. still matter at 5mm of wheel travel? 2mm? 0.05mm? Zero?

Diminishing wheel travel implies increasing wheel rates. As wheel deflection due to suspension compliance approaches wheel deflection due to chassis compliance, those things (damping, ARB rate, suspension geometry etc) become less relevent.

Of course tyre compliance is starting to dominate at the wheel travel values you mention.

Edited by gruntguru, 11 April 2010 - 22:52.

[Greg Locock]

Diminishing wheel travel implies increasing wheel rates. As wheel deflection due to suspension compliance approaches wheel deflection due to chassis compliance, those things (damping, ARB rate, suspension geometry etc) become less relevent.

Of course tyre compliance is starting to dominate at the wheel travel values you mention.

First of all I think you are exaggerating the lack of suspension motion. I think the Ferrari in 2000 had about 20mm of usable suspension travel at the front, and more at the rear. Not all of that was used in each race of course.

Seocndly, when you have 3 springs in a row, (tire, suspension, body) changing the damping in one of them will affect the overall transfer function across the system. And since it is the biggets wodge of damping, (tire is say 7% critical, body etc probably only 1% or less) vs shock at say 70-130%.

But I do agree, theoretical niceties like RCH are probably less important, until/unless you factor in tire stiffness and body stiffness.

[cheapracer]

OK. Would damping, ARB rate, suspension geometry etc. still matter at 5mm of wheel travel? 2mm? 0.05mm? Zero?

Yes. (except for zero!)

I remember seeing Alan Jones testing a Williams '80/'81? with no/solid suspension at the peak of downforce, didn't work and less grip, especially braking. Of course with F1 that means your driving on 4 big balloons, maybe different for low profile tyres?

Yeah I'm pro beam at the moment but I don't know why someone doesn't run a CF beam for aero reasons rather than the mess they have at the moment, rules maybe?

[SteveCanyon]

Yes. (except for zero!)

I remember seeing Alan Jones testing a Williams '80/'81? with no/solid suspension at the peak of downforce, didn't work and less grip, especially braking. Of course with F1 that means your driving on 4 big balloons, maybe different for low profile tyres?

I have a copy of that Horizon documentary, I still watch it every now and then as it has one of my favourite lines in it, when Jones is talking to Williams about how rough the ride is but the car has promise. Williams replies in his finest English accent, "perhaps you could sit on your wallet, Alan."

If I had to guess as to how much difference in the grip level would be with poor damping and even only 5mm of wheel travel, I'd say up to about 30% loss.

Yeah I'm pro beam at the moment but I don't know why someone doesn't run a CF beam for aero reasons rather than the mess they have at the moment, rules maybe?

DeDion FTW!

[cheapracer]

I have a copy of that Horizon documentary, I still watch it every now and then as it has one of my favourite lines in it, when Jones is talking to Williams about how rough the ride is but the car has promise. Williams replies in his finest English accent, "perhaps you could sit on your wallet, Alan."

I like when they first dropped the car off the jacks to the ground after putting solid struts in with Jones sitting in the car and he says "ooff"

[DaveW]

Yeah I'm pro beam at the moment but I don't know why someone doesn't run a CF beam for aero reasons rather than the mess they have at the moment, rules maybe?

No, stiffness (lack of).

I rig tested a venerable beam rocker F1 vehicle a few years ago. It had hub modes at both axles that coupled with beam bending having nodes at both the pivot & (close to) the spring/damper attachment point. Damping was 15% of critical with circa 140 N/mm wheel rate springs. Double the spring stiffness & the damping would be negligible....

It also had poor installation stiffness (<1 KN/mm at the wheels - about the same as a decent road car top mount) & fairly evil motion ratio of around 1.5. The MR would have to be ridiculously high to fit within a current F1 nose...

[Ben]

That's the F'd part of the whole thing. It's all still very important.

Super high downforce cars take some of the fun away for me. I like making some sort of mechanical / aero compromise. On some of these cars, there just isn't much of a compromise...Not sure why. I guess because it seems like there should be one. The aero just pretty much over-rides everything up to the point where the driver can't see because you're shaking the eye-balls out of his head on some cars, though.

I think anyone who saw the Strakka HPD car bouncing around like a mexican low rider at Ricard last Sunday would totally agree with you :-)

Ben

[DaveW]

I think anyone who saw the Strakka HPD car bouncing around like a mexican low rider at Ricard last Sunday would totally agree with you :-)

It doesn't have an extreme geometry - or a totally aero-biased suspension set-up. Nor was it slow. Care to elaborate, Ben?

[RDV]

DaveW-Mischievous note: Stiff front springs improve front ride height control, which allows more extreme aero solutions, helped by "aero-friendly" front geometries, which means that lower rate springs are no longer a viable option, leading to the inevitable conclusion that aero is the only thing that matters.

...indeed, and damping to control aero pitch sensitivity.

One can go over the top, though, is nice to run soft springing aided by bump-rubbers to reach a reasonable compromise, and never forget kerbs an integral part of racing lines at most circuits, specially low speed corners.
Personaly havent bothered with front geometry (apart steering and bump-steer) for a hell of along time, and suspect F1 even less prone to influence due to the ridiculous 13" rims against my usual 18"...rear is a bit different, still responds to geo. DaveWs' comment on migration very true, as have been bitten hard whenever I neglected it.
In GTs (FIA GT1) responds, in DTM and JPN GT just pro-forma, have never proved conclusively one way or the other, and although "correlation does not imply causation", it is directly proportional to aero forces...I.E., high downforce=geometry irrelevant.

Ben-I think anyone who saw the Strakka HPD car bouncing around like a mexican low rider at Ricard last Sunday would totally agree with you

Suspect they had some rather special Miches on, not on top of it yet, and the engine is a mother as soon as they start to pile the revs on..look at their and Lola Hpd top speeds, no way I could match it...drivers could follow them though corner six and accelerate earlier, only to be dropped mid-straight...one quote from my driver"..went away so fast I nearly got out to check why my engine had stopped."

Might change a bit on damping next couple of races, HTTT is a very smooth track, apart from unsetling bump just before Signes flat-out corner at end of straight.

Edited by RDV, 13 April 2010 - 10:29.

[mariner]

suspect F1 even less prone to influence due to the ridiculous 13" rims against my usual 18".

RDV -Does the fact that your cars running an 18" wheel with ( I assume) much lower aspect ratios than the F1 13" wheel mean you have better overall ride height control than F1 because the tyre will deflect less vertically? If true does this imply you could run a lower ride height than F1 if that is legal?

I have this sort of mental picture of the F1 car with the wheel rims almost motionless versus the chassis but still bouncing up and down as the relatively tall tyre walls flex whereas the 18" wheel stays more level with the track and the suspension/dampers do the height contolling.

[DaveW]

LMP tyres have around double the vertical stiffness of F1 tyres. I guess that the lateral stiffness ratio would be even higher. The rear/front vertical stiffness ratio of LMP tyres is better matched to the "natural" centre of gravity of a mid-engined vehicle. Against that, an LMP1 vehicle is around 50 percent heavier. I have read that F1 aero down force is the greater, but I have difficulty believing that given the plan areas of the two types of vehicle.

I leave it to tyre experts to predict the changes required to convert "endurance" tyres into "sprint" tyres, but I imagine they would become more compliant.

Suspension set-up strategies are also different. Aero changes to LMP vehicles are relatively infrequent, so teams tend to concentrate on optimizing suspension set-up to maximize performance whilst F1 teams seem to throw aero updates at their vehicles every race. The current ban on F1 track testing also appears to favour the wind manipulators.