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current F1 front suspension

current F1 front suspension

(OP)
newbie here,
current F1 front suspension layout would seem to indicate the front roll centre at perhaps ground level or lower. Is this the case, and if so would this not aggravate the "jacking effect". Have been out of the design loop for a long time am I missing something or is there a heavy "aero" package influence here that I am unaware of, any comments would be greatly appreciated from what appears to be very well informed panel.
with thanks.

RE: current F1 front suspension

In the interest of keeping ground clearance to an absolute minimum that they can get away with (see rulebook), F1 cars have extremely high spring rates and extremely high antiroll rates on top of that. There is very little suspension movement at all. In a situation like that, it almost doesn't matter how the camber changes with suspension movement, because there (almost) isn't any suspension movement to begin with.

On F1 cars, the upper and lower A-arms are pretty much horizontal at normal ride height. There's no jacking effect at all in that situation. The instant center is at infinity. Whatever slight jacking effect might be present, will be overwhelmed by the extremely high spring rates that don't let the suspension move.

RE: current F1 front suspension

(OP)
brian and greg , thank you for your response all points accepted. however can anyone explain to me why have the designers, possibly started by Williams, moved the front suspension points so that when viewed from the front the wishbones are parallel but sloping down to the outboard. I don,t have to put pencil to drawing board but this tells me that the roll centre is +- at ground level [all points made previously accepted] is there something that i am not aware of scrub, kpi, perhaps or some form of finite analysis [computer generated stuff that is beyond us oldtimers] previously it was accepted design philosophy that made the wishbone layout as unequal and nonconvergent dictating rollcentre migration and parameters that made sense [to me]. Brian with respect you said that the w/bones are near // at ride height it is very point that picqued my curiosity in the limited tv coverage we get to me the w/bones were not // when on track and at speed keeping in mind the huge influence of downforce, hence my question. I am now 70 and perhaps this is all beyond me but i did a stint with lotus and chevron in the uk in the late 60,s and am perhaps out of touch.
again with thanks golfpin





RE: current F1 front suspension

The inboard arm to body points are defined by aero, which defines where the body is, the outboard points on the spindle are defined by practicality. Everything else is an outcome.

The kinematics of double wishbones haven't changed.

I would say that geometric RCH gets less emphasis than it used to, force based RCH is easier to work with.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: current F1 front suspension

(OP)
Greg and panel,
thanks again for your replies. Greg could you elaborate on "force based RCH" please.
Would I be completely wrong in assuming that the position of some of the inboard points on current cars is dictated to more more from a packaging point, and perhaps getting the drivers feet and pedal assemblies into those "drop snoot" front ends, I have not been near an F1 for so long that trying to guage dimensions from pics. and tv is for me, impossible, hope this not to far out of the tech question frame.
with thanks,
Denzil Schultz RSA

RE: current F1 front suspension

FBRCH=d(Fz)/dFy*track

that is it is the height of the pivot of the equivalent beam axle with a single pivot on the centre line. In other other words it talks about weight transfer due to lateral forces at the contact patch.

Yes the inboard end locations are driven by packaging which is largely driven by aero.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: current F1 front suspension

(OP)
GREG THANKS AGAIN, MOSTLY UNDERSTOOD, PERHAPS I AM NOT SO FAR OUT OF THE LOOP AS I THOUGHT.
HAD AN ALL TO BRIEF A CHAT WITH MIKE PILBEAM A FEW MONTHS AGO, HE WAS OUR HERE IN RSA WITH ONE OF THE LMP CARS I TRIED TO GET TO GRIPS WITH THE DYNAMICS OF THE "HEAVE ANTI-HEAVE" LAYOUT ON THE CAR BUT THE TRACK NOISE AND MY FAILING HEARING DID NOT GO FAR TO CLARIFYING HOW IT WORKED! NOT EVEN A PHOTO!!TRUTH BE KNOWN COULD NOT GET CLOSE ENOUGH TO THE LAYOUT[BAD EYESIGHT]
APPRECIATE YOUR PATIENCE ,
UNTIL THE NEXT TIME
PS COULD I TROUBLE YOU FOR CLARITY ON FORMULA FBRCH=D etc I STILL US A SLIDE RULE SO AM A LITTLE LOST WITH MODERN DAY COMPUTER TYPE NOMENCLATURE


RE: current F1 front suspension

d is the differential - rate of change of the Fz compared to Fy.

RE: current F1 front suspension

I'm curious why you think modern F1 cars RCH's are at or below ground? This youtube video graphically shows them relatively high off the ground.

Jeff

RE: current F1 front suspension

(OP)
CASHMO.
THANKS FOR THE INFO I WILL NOW GO AND SIT IN THE CORNER AND WEEP AT MY STUPIDITY, BUT IN DEFENSE I DO NOT HAVE ANY CLEAR PICS OF F1 FRONT SUSPENSION SO I MADE AN ASSUMPTION, THAT HAS BROUGHT OUT A WONDERFUL BUNCH OF GUYS THAT ARE PREPARED TO SHARE THOUGHTS AND INFO, THANK YOU TO ALL.
GOLFPIN

RE: current F1 front suspension

Golfpin,

don't worry, no need to go sit in the corner and wheep. Your observations were more than valid and I am amazed on some of the comments I have seen here by people that actually have never seen an F1 car, let stand alone have designed one. No offence but an F1 car has got literally nothing to do with a road car. The simplest example of that is putting more front weight on the car if the car is understeering too much because the low mass causes not enough heat in the tire causing understeer. Try explaining that to a road car tire .....
Then, no designer of an Formula 1 car would be out of his mind to design an F1 car with a roll center that high as indicated in the youtube video. The jacking forces would multiply the vertical load by the friction coefficient of roughly 1,6 causing a horrible understeering and lifting car whilst cornering. Imagine a std road car with a CoG of approximately 550 mm with a roll center height of 100mm that "gets multiplied in its effect" by 1.6 (=160mm). That would be like going back to the dark ages of the worst handling cars of all times.... and now think of the same thing on a car with a CoG of 250 mmm ..... bloody hilarious ain't it ?
And as you did correctly see parallel links do more or less always result in a roll center height of 0mm. Considering this and the fact that F1 cars have always suffered from low speed understeer (and lately of extended tire wear) no designer with some sense of physics would go for a front high rollcenter. In fact it has been for more than a decade around -20/-40mm, at least kinematically. Due to camber compliance this value will inevitably go above 0mm (ALWAYS) but many teams have put a lot of effort into reducing camber compliance in order to keep it as low as possible (as they should since the laws of physics are valid for everyone - eliminating the part of load transfer due to RCH will produce higher lateral-g). During almost a decade in F1 and other racing series I have learned to put the appropriate attention to details. In F1 the old saying "aero, engine, tires" remains more than valid nowadays but that does NOT mean that the basic principles of good engineering are not valid. In fact the front rollcenters are positioned as low as possible and will be positioned as low as possible, independent of any aero constraints, so your observations were very correct Golfpin.

RE: current F1 front suspension

So your position is that the suspension below has a RCH at ground level? Could you show us how that geometry works vs the referenced video?

RE: current F1 front suspension

The video is assuming "strictly" parallel links (which is fair to assume and leads correctly to the "classical" conclusions as mentioned in the video), but what if the links are not strictly parallel ?. If the links would not be exactly parallel but the inner vertical spacing/distance of the two links at the chassis would be bigger than the vertical distance of the two outer joints the roll center would be forced down. I doubt whether one can see it with the bare eye since it the difference usually of a few mm is enough. At least that was how we did it. On top of that one can make the upper link length "longer" than the lower link (which would give theoretically positive camber gain, but who cares on 20mm of total travel at almost 0°/m gain). As you can see in the picture the upper link is quite long. Both instruments should give sufficient "design space" to control the lateral contact patch movement with jounce/rebound in such a way that the rollcenter becomes very low. Given the overall steep front view inclination of the two links in the picture and their relative length I doubt whether the kinematic roll center is here very much below zero but it is certainly lower than in the video. Then not to be forgotten, the camber compliance will certainly put it above ground. I made a picture for explanation of roll center height, hope that helps. As with many things in suspensions design the devil is the detail.

RE: current F1 front suspension

The geometric front roll centre of that Ferrari looks to be about 275mm high to me. Hardly catastrophic, but definitely not ground level.

Regards, Ian

RE: current F1 front suspension

Independent Suspension with Roll Center Height 275mm hardly Catastrophic ? You must be kidding ...... or joking

RE: current F1 front suspension

I had not seen the front view of the Ferrari before. To me, it looks like the upper link is more sloped than the lower one, which will place the instant center outboard and below ground level. If that observation is correct, that will reduce side-scrub of the contact patch a bit further than the angle of the arms might suggest and it will also send camber in the wrong direction in the case of body roll, and the roll center won't be quite as high but it's still going to be darn high.

I still maintain that these vehicles have extremely high spring and antiroll rates (by road car standards). You can make any suspension geometry work, if you don't let it move. Camber in the wrong direction? Doesn't matter, the suspension barely moves. Jacking effect? Doesn't matter, the high spring rates won't let it have any effect.

If this geometry works out better for aerodynamics and vehicle structure then the F1 engineers will find a way to make it work.

You do not want to design a road car with spring rates that normal people will tolerate with geometry like that.

RE: current F1 front suspension

@Brian, look at the picture I have attached in my previous mail and you will see that we are on the same line. The rates of a front suspension F1 car go from 150 N/mm to 400N/mm which is indeed very high but these usually ONLY act in heave motion. The roll rates are compared to the vertical rates however much lower in order maximize grip in the corner (so called 3rd spring suspension layout). So "jacking" DOES very well make a difference. Beyond that the front wing (Aeromap) is hugely sensitive to rideheight changes and creates more downforce the closer the wing is to the ground (groundeffect). Even just 1 mm front end raise due to jacking forces can make a significant difference in aero performance making or breaking the car's cornering performance.

RE: current F1 front suspension

Greg,

My estimate RCH would be as I said before around 0 mm.

As indicated in the picture I attached in a previous writing I think that the links in the front are NOT parallel but inclined "wrongly" in such a way that the instantaneous center of rotation is "outside"of the wheel . This in combination with a possibly longer upper-link than lower-link provides "in theory" sufficient room to create a geometry with 0mm or negative roll center height (I used always a "spacing difference" of 5mm - meaning the links are not parallel in front view but inclined "wrongly" to get a negative roll center height of -20mm to -40mm - and I presume that looking at the front view inclination of those two links the difference here must be around 15mm to get the roll center to the value that I am thinking where it is) The picture of the Ferrari is unfortunately not a design drawing so there will remain plenty of room for discussion.

In case none of the above would have been implemented by Ferrari and the links would all be "classically" arranged as was assumed in the video I would expect a RCH of around 70mm. But that again would not be so good.

Cheers,

Paul

RE: current F1 front suspension

Hi,

Sorry if I'm sticking my nose where it may be lopped off, but I have a question. If aero downforce is as dramatic as I am hearing, seeing the car at rest doesn't tell the whole story, as it would with, say, a Rolls Canardly. I suspect that the dynamic system, the car progressing around a circuit, loaded with driver and aero effect, would be a better starting point for discussion. "Static, in a Formula One car, then, might be taken as meaning at a given (average) velocity.

Once in motion, the reaction point would move further away from the CL of the car, and also up, slightly, correct? Therefore, the the roll center would move down. So, my question is: Why is "static" even considered in the same way for a production sedan as it is for a high downforce racing car? Wouldn't it make more sense to look at the vehicle at some steady state that is more representational of its "norm?" Maybe that normative value is the average velocity around a track, and has to be different from one track to the next?

Thanks in advance,to anyone willing to edify,
Bernard.

RE: current F1 front suspension

I think the instant centers would move up/out and with them the RCH. Between the stiff front springs and any built in anti-dive I don't think the front suspension compresses much. Another example from this years Lotus...





RE: current F1 front suspension

If you're tuning for track performance you should probably be looking at some combination(s) of roll and dive and calling that sort of a "steady state". I don't see why you'd ignore this completely is a road car with sporty handling intent.


Norm

RE: current F1 front suspension

Thanks.

Best,
B.

RE: current F1 front suspension

Quote (Cashmo)

I think the instant centers would move up/out and with them the RCH.

Given that the FVICs lie outboard of their respective wheels, are you suggesting that the FVICs and the GRC would both move upward with downward chassis travel?


Norm

RE: current F1 front suspension

(OP)
Ignorance at large, again please elucidate FVIC = FV?insant centre G?roll centre the acronyms have got me thanks Golfpin

RE: current F1 front suspension

FV = Front View.

There is also a Side View IC (associated with pitch rather than roll), so using "IC" by itself isn't a sufficiently descriptive term (unless you're talking to most drag racers, who don't much care about suspension behavior in front view).


Norm

RE: current F1 front suspension

That video posted by Cashmo was very informative. Back 10 years ago they had different priorities as is evident from this front view http://www.italiancar.net/site/news/06/0606/forSal...


"Simplicity is the ultimate sophistication." L. da Vinci
- Gian

RE: current F1 front suspension

Maybe this extra info could help you guys understand Suspension's better:

Just let go of all links and so on, just concentrate on the knuckle/upright. The "vertical" movement of the knuckle/upright can be seen as a rotation around an axis. This axis may be nearby or far away. This axis is called the Instantaneous Axis of Rotation of the suspension and where this axis "hits" the axle center line it is called the Instantaneous Front View Center and where the axis hits the Track Width Plane it is called the Instantaneous Side View Center. From the movement of the Wheel Center and The Contact Patch all suspension characteristics can be derived via vector algebra (the actual position of the links is completely irrelevant).

Now this "Instantaneous Axis of Rotation" has some very particular characteristics that allow a fundamental approach to define Suspension Types:

1) If the axis of rotation is more or less stable in space the suspension is called a "Plane Suspension" Plane revers to the fact that the suspension can be "easily" drawn "in plane" on a 2D drawing book. Typically SLA suspensions and McPherson Struts are "Plane" Suspensions and do not have many interactions between parameters. This means that their instantaneous FV & SV centers are quite well "tunable" and over wheel travel remains pretty much constant

2) If the axis of rotation moves BUT always goes through one specific point the suspension is called "Spherical Suspension" due to the fact that one point of the actual suspension is always acting as a spherical center for the instant axis of rotation (the axis "cones" around that joint). These type of suspensions are not so easily to be drawn on a 2D piece of paper and need the help of some 2,5D tricks in order to design them (on paper). Most famous representative of this type of Suspension is the BMW E36 (M3) or Toyota RAV4 where the "Spherical Joint" the trailing arm to Chassis Joint is On these suspensions you will always find a strong interaction between Toe, Camber and Roll Center Height. Due to the interaction of Toe Camber and Roll Center the FV instantaneous center can only be "tuned" marginally whereas the SV IC is almost always "fixed" next to the trailing arm. A computer program helps here a lot.

3) If the axis of rotation moves in space and is also characterized by a "thread movement" fore/aft along the axis the axis will be called "Momentary Screw Axis" and the suspension becomes a true fully 3 dimension multilink suspension. These suspensions cannot be calculated on a piece of paper and are characterized by a very significant interaction off all Parameters. Changing one point will change almost all characteristics. This means that the movement of FV IC and SV IC can be a lot and most of all change a lot over wheel travel. Without a computer and vector algebra one is completely lost.

I hope this helps understanding the FV & SV IC, I have btw started a new thread about my new suspension design tool. If you like have a look at it !

Cheers,
dynatune, www.dynatune-xl.com

RE: current F1 front suspension

(OP)
TO ALL YOU GUYS WHO HAVE TAKEN THE TROUBLE TO ADD,PROD,ARGUE, MAKE SAGE COMMENTS AND MAKE MY AGEING BRAIN TRY AND WORK AGAIN, A DEEP THANK YOU, CERTAINLY FOR YOUR PATIENCE IN YOUR REPLIES. I THINK THAT IN THIS WORLD OF TURMOIL THE DISSEMINATION OF KNOWLEDGE IS CRITICAL FOR ALL, MY THANKS AGAIN AND I HOPE NOT INAPPROPRIATE FOR THIS FORUM, TO WISH YOU ALL, AND YOUR LOVED ONES A GREAT FESTIVE SEASON AND WONDERFUL NEW YEAR..
YOURS IN ENGINEERING,
GOLFPIN

RE: current F1 front suspension

Cheers golfpin cheers


"Simplicity is the ultimate sophistication." L. da Vinci
- Gian

RE: current F1 front suspension

(OP)
Hi Dyanatune,
have just reread your last posting and wanted to thank you for a great effort. It helps enormously for people like myself who think they know a bit about suspension geometry to be updated so to speak, am out of the design loop by quite a few years but appreciate and enjoy the effort that people such as yourself, and many others, who give of their time to explain.

Thanks again and all the best for the coming new year.
Golfpin RSA

RE: current F1 front suspension

Golfpin,

Thank you for the kind words. As a "teacher" it does make a lot more fun to have "students" that are willing to learn smile ...

I have lived and breathed suspensions (and cars) now for more than 25 years and I had the fabulous opportunity when I was a starting engineer that I came to work for an "old" experienced engineer. Although the guy was close to retirement he was driven by passion for his job, he told me all his achievements and his biggest errors. I was amazed, like a baby in a candy shop. He was one of those people that wanted to share without "protecting" his position (not that anyone could be a danger) and I understood there that a pupil will always honor a good teacher and by now, I now that the greatest satisfaction for a good teacher is to see his pupil proceed into unknown territory. So this guy did for instance have a "library" of every article published on suspensions starting somewhere in the 50s of the last century and I was allowed to copy them all and read read read. What a time. He challenged me, making bets that for any question I could not answer I had to pay him a beer, for any question he could not answer I was offered a crate of beer .....needless to say that I did never win. From there on I did have the fortune to work on almost everything that had wheels on it, from a 40t 18 wheeler truck to an F1 car. So this little story is basically the main reason why you find sometimes replies here and why I did bother to write the dynatune software.

Cheers and a happy 2014 to all of you !!

Paul

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