current F1 front suspension

[golfpin]

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.

 

[GregLocock]

Aero totally dominates F1, and perhaps keeping the tread square to the road is next on their thoughts.Any notion of conventional suspension tuning is a nice to have.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BrianPetersen]

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.

 

[golfpin]

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

 

[GregLocock]

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

http://eng-tips.com/market.cfm?

 

[golfpin]

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

 

[GregLocock]

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

http://eng-tips.com/market.cfm?

 

[golfpin]

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

 

[loki3000]

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

 

[Cashmo]

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

 

[golfpin]

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

 

[dynatune]

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.

 

[Cashmo]

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?

 

[dynatune]

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.

 

[murpia]

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

 

[dynatune]

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

 

[BrianPetersen]

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.

 

[dynatune]

@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.

 

[GregLocock]

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

OK Paul, what is your estimate of the GRC of that suspension?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[dynatune]

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