Wierd F1 Suspension Geometry

[shiny side up!]

OK, in watching the race on Sunday, I saw some odd things going on with the front suspensions of some of the cars... namely the Jaguars, Renaults, and maybe Jordans? Anyway, what I noticed is that the upper A-arms on their front suspensions ran DOWNHILL to the tires... ie the opposite of a typical camber-gain design.

I was discussing it with another engineering friend, and he thought that maybe the kingpin inclination was so agressive that it was still possible to gain camber as the suspension compressed. I just don't see that as being feasible. At the same time, why would you want to LOSE camber as the suspension compresses as would happen with that geometry?

I don't really get it. A fairly wild theory for it is maybe with the actual amount of suspension travel you get on an F1 car (almost nil...), perhaps they are running a ton of camber so that down the straights there is less tire in contact with the road (less friction, more speed), but when you enter a corner and compress the suspension, you actually lose some of that excess camber and gain grip??? Farfetched, I know. Anybody have an idea what's going on here???

[MA2]

Camber gain can still be had, depending on the installation angle of the lower arm, but in any case, the jacking effect is thru the roof, Not sure just what they expect to gain with that so danged high.

It may also be in an attempt to offset some of the steering angle camber gain due to the kingpin inclination.

[KC]

Don't forget that many of them use a third damper to alter the caster angle of the suspension during compression and this might compensate for some bizaare angles.

[avsfan733]

When was this the caes running or sitting still? because if it is slight at a stop maybe it is meant to compress due to the aero downforce and creat the geometries they want to at speed

[shiny side up!]

The particular shots I saw were from qualifying, the cars were running at speed on the track. I'm still scratching my head on this one... I didn't really see anything else that was obviously different in the suspension.

KC... I wasn't aware that they use a third damper for castor control, how does that work??

[avsfan733]

I thought the third damper was for straightline reactions to bumps, Are you sure they were the suspension arms as opposed to the steering arms? Im goin back through all the stuff I can think of tryin to figure this one out

[Speck]

As far as I know, third dampers are for bump, and possibly some anti-squat/dive.

[shiny side up!]

Yes, there is no doubt that it was the upper wishbones. I never got a really good look at the lowers to see if they were doing anything funny... but I know it wasn't the steering rods...

As I understand the third damper, it is for straightline bump/ride height control, as you have said...

[avsfan733]

Based on the reading I have done (this has really been acking my brain) th downhill angle will act to sort of compound the increase in camber gained by the suspension movement, his is what they want because of the very small (relative) movements that the suspension pieces provide for. Imagine it as a trianglebased on the point of intersection of the arm and the upright drawing a horizontal line to which point it intersects with a vertical line drawn at the point in which the arm intersects the pushrod pivot assembly. ( I think this is what happens and seems to make sense but i am in no way an authority on this)

[Jukebox]

These are not your ordinary dampers....F1 dampers are designed to have different level of stiffness when blimp and rebound occurs.

On bumpy race circuits, whenever the cars goes through a corner...the outside wheels go into bump and the inside wheels go into rebound. Rebound dampers have about 2/3 times the strength of bump dampers forces.

[shiny side up!]

avsfan, I still don't get it... I can't see how the downhill angle to the upright does anything but LOSE camber as the suspension goes into bump... especially since the lower A-arms are so much longer than the uppers... errrr, what a head-scratcher! It is the upper and lower A-arms that determine the path of travel of the suspension assembly, and the pushrod only effects the rate of movement not the direction, so I don't get how your triangle described above works... perhaps I am simplifying it too much...

[Mackmot]

KC could be talking motorcycle language where I have heard the rake in the bike refered to as caster angle????

[MA2]

Juke:

On modern cars such as F1, the damping forces are quite often the same for bump & rebound.

[RWC]

I've heard that a few teams this year are working with 'constant contact patch' geometery or something.
Benneton was one i'm pretty certain of and i think ferrari was mentioned too..
I don't know if that has much to do with the acute whishbone angles.

[Jukebox]

MA2...

When the car turns, the weight moves to the outside front of the car. In the middle of the corner the weight ballances front to rear but moves to the outside tyres. As the car exits the corner and begins to accellerate the weight will shift to the outside rear then on to both rears as you straighten up.

That is why i said when the outside (load bearing) wheels are in bump the inside wheels will be in rebound.

[norman-normal]

This should clear things up about the 3rd spring-damper.

www.technical.com/article.php?sid=15


I hope this works, I'm better with cars than PC's

[eclectic]

All this just confirms my suspicions that there is NO chance that these cars will ever be run, even by VERY wealthy owners, in Histooric Racing in the future... wow even the suspension is almost impenetrable to the amateir enthusiast!

[norman-normal]

OOPS! excuse me ...for the third spring and dampener go to;

www.technicalf1.com/article.php?sid=15

[gttouring]

so the 3rd spring is like the AntiRoll-Antisway bar? if so NP i get it but the drastic upper arm angle could only be to prevent much movement of the tire up so it has the 'constant patch' and we have an unloaded side the length will keep these wheels pushed down on the track providing the most grip possible, the F1 cars now have such large side walls the tire itself can have some effect on suspension geometries- they should run with wheel of about 45- 50 cm plus the tire being about 35% high side wall (compared to the width) like touring cars with there 19 inch platter size rims...

[LandOfSnow]

If the lower wishbone is even more downhill than the upper there's nothing weird about it, the negative camber will increase as the supension loads up... as I don't know the case, it's another question if the lower one is more so?

[PhilThomas]

Originally posted by norman-normal
OOPS! excuse me ...for the third spring and dampener go to;

www.technicalf1.com/article.php?sid=15

This link does not work, is there an updated link somewhere? I'd really like to read that article in my attempt to understand 3rd spring/dampers. Thanks

[imull]

I am by no means an F1 fan so excuse me if this is all wrong.

Do the teams mention above use Michelin tyres? Michelin have a camber compensation system that was designed and has been run extensively in testing by an F1 team ( forget who). Possibly something to do with that?

[PhilThomas]

That's the OPT system, tested and maybe even used in races by Renault. Someone else will have better details about it though.

[Tobsc]

The 'downward pointing towards the wheel' angle of the top wishbone is purely a function of roll-centre design of the cars geometry, this is dependant on many other things...

if you imagine a line following the top and bottom wishbones, continuing though the wheel, off into a point in the distance, ( looking at the front of the car for simplicity to start with), at the point at which these two lines cross over each other, draw another line, back to to contact patch of the tyre on that side of the car, and continue it past the centre of the contact patch, and through the centre of the car.......now do this for both sides of the car, and the point at which they cross over each other (intersect), is known as the roll-centre,(this should be on the centre line of the chassis, if the vehicle is in steady state, and has symetrical geometry).

This is the point in space that the mass of the car is trying to pivot(or roll) around, when the car is cornering, (or transfering weight from one side to the other)

The height of this affects many other things, as you have noted the 'camber-gain in roll' of a given wheel, in the terms of the discussion that you were having, if this roll-centre point is very low, you will get more camber gain (take a look at the 88/89 McLarens), if it's higher (like most modern touring cars) you will get less camber change.

Also the higher that the centre of gravity, of the front of the car is,(relative to the roll-centre), the greater the leverage that it has, and thus the easier the car will roll.

Now, you have a point that the front is trying to roll around, you have to remember that you have one at the rear too......
and the line that joins these is the Roll axis, the line (front to rear) that the whole car is attempting to roll around mid-corner, so , depending on the height of the front and rear centre of gravity, If the front roll-centre is alot higher than the front, the whole handling characteristic of the car becomes more sensitive to rear anti-roll bar changes.

Trust me....

Poke a pencil through an empty cigarette packet,(using the packet as an imaginary car), with the packet held level ( or flat on the table), put the pencil in one end, but high at that end, and poke it out of the other end, right at the bottom, now, as you try and rotate the packet in an even roll situation,(as you imagine happens in your car and any race car mid-corner), you will find that it's forcing one end to roll more, and differently than the other(at the 'high end', the outside wheel is experiensing less bump travel than the inside is lifting), the end that moves more(the low end), will be more sensitive to 'externall trimming', or roll-bars, as know them, any is usually the lighter end of the car......

To get back to the original question, it may be, that jaguar, jordan and renault, have employed this 'high roll-centre' style of front suspension geometry, in conjuction with their not-visible rear geometry, to corespond with the centre of gravity height(front, rear and overall), desired pitch/squat characteristics, achievable torsional stiffness,Motion ratios, slip angles, camber gain requirements etc, etc... to suit their tyre choice/drivers style/engine-driveline configuration........

Tobsc@yahoo.com