28 replies to this topic

[perfectelise]

How low is the centre of mass in a state of the art F1 car - say relative to the wheel centres, is it below them?

[wegmann]

Yes. The best info I've seen puts the CG less than 25cm above the bottom of the car. So assuming the ride height is just a few cm, and the wheel center is about 32cm off the ground, it should be below it.

[Pioneer]

I'd venture to say that the ride height is less than a centimeter... but I think your statemen is likely valid in any case.

[Double Apex]

Originally posted by Pioneer
I'd venture to say that the ride height is less than a centimeter... but I think your statemen is likely valid in any case.

Less than a centimetre What about the plank then? I thought it was something like 4-5 centimetres?

[Pioneer]

More like milimeters.

[Double Apex]

Originally posted by Pioneer
More like milimeters.

Care to elaborate? I find that very hard to believe...

[mudsam]

It believe its more like 3-10 centimeters. If its below 1 centimeter you would have serious bottom plank issues. I don't remember the rules exactly but the allowed wear on the bottom plank is measured in millimeters.

I guess it depends on the track as well as how hard you need to ride the curbs.

[Double Apex]

As far as I know, the allowed plank wear is only 1 millimeter, with the plank itself being 10 millimeters thick.

A ride hight of only 4-5 millimeters would mean almost no suspension travel whatsoever, a couple of millimeters in the most extreme case. That doesn´t add up. Also, sometimes you get a low shot of a car when it´s just entering the straight where you can look underneath the car. It´s quite clear in those shots that there is some room between the plank and the road. At the very least a couple of centimeters. Even on a track like Magny Cours.

[JwS]

The ride height changes from low to high speed, so what you see at the entry to the straight is likely to be alot higher than the true ride height under full downforce. They were running as low as .050-.060 inches at the last race, because the smooth paving favors it
JwS

[robert dick]

Wouldn’t a centre of gravity located below the wheel centre mean that the car leans inward when rounding a corner?

[alexbiker]

No.

Irrespective of the centre of mass, it will always be thrown to the outside of the corner, compressing the outside suspension.

If ever this doesn't happen, look for roosters laying eggs, talking dogs etc, then build a nuclear shelter, as the end of the world is coming.

Alex

[robert dick]

Misunderstanding. Of course the centrifugal force is always pushing the car outward. But doesn't a centre of gravity located below the wheel centre generate a moment of force compressing the inner suspensions?

[alexbiker]

How could it? What's the mechanism?



Seems to be learning out to me.

Alex

[robert dick]

Imagine a simplified frame with rigid axles :
When the centre of gravity is above the axle, the moment of force compresses the outer suspension.
When the centre of gravity is below the axle, the situation is inverted, the moment of force compresses the inner suspension.
When the centre of gravity is exactly on axle level, there is no moment of force, inner and outer wheels are equally charged.

[WPT]

Both the front and rear suspension will have a roll center. The line joining these roll centers is the roll axis of the sprung mass. If the CG of the sprung mass is above the roll axis, then the sprung mass will roll to the outside in cornering. If the CG of the sprung mass is below the roll axis, then the sprung mass will roll to the inside in cornering. WPT

[JwS]

You can have 'reverse roll', the roll moment is developed by the 'centrifugal force' acting at the center of gravity, the axis it acts around is the instantaneous roll axis of the car which is determined by suspension geometry. So the lever arm part of the moment equation is the distance from the cg to the axis, and it could go either way, designers choice. I think in most cases the roll effect is in the expected direction because the roll axis is lower than the cg.
JwS

[BRIAN GLOVER]

Stage coaches' cabs were suspended in such a way that they would lean into a turn like motorcycles. This didnt prevent them from rolling over to the outside, though. Talk about unsprung mass. Didnt you hate it when you played Dinky Toys with your buddies and they leaned the their cars into the turn.? They became lawyers.

Originally posted by JwS
You can have 'reverse roll', the roll moment is developed by the 'centrifugal force' acting at the center of gravity, the axis it acts around is the instantaneous roll axis of the car which is determined by suspension geometry. So the lever arm part of the moment equation is the distance from the cg to the axis, and it could go either way, designers choice. I think in most cases the roll effect is in the expected direction because the roll axis is lower than the cg.
JwS

[Ursus]

What's magic about the wheel axle? The cornering force on the car ultimately acts where it touches the ground so cg. height over the ground is whats important.

Ofcourse you could get wheight transfer to the inside if say you were to run your vehicle on two elevated tracks with most of the mass suspended beneath.

[wawawa]

Originally posted by BRIAN GLOVER
Didnt you hate it when you played Dinky Toys with your buddies and they leaned the their cars into the turn.? They became lawyers.

[desmo]

Originally posted by wawawa

Beat me to it!

[Jow]

Then a (speed)boat rolls in to a turn, becauce the CG is under the water?

Jow

[JwS]

No, that is because the thrust is acting at an angle below the cg (I think)
JwS

[Ben]

You guys are confusing roll and load transfer.

As someone has mentioned, if the roll axis is above the CG the car will bank inwards into a turn.

The person who also said that we always get load transfer to the outside wheels is also correct.

Roll and load transfer are related but different things.

Ben

[JwS]

Explain that. As I see it, if the car rolls 'into' the corner that means the springs on the inside wheels compress (increasing tire load ) while the springs on the outside extend (decreasing tire load). if there is something changing tire load independant of the load seen by the spring I think we have got something!
JwS

[MclarenF1]

In order for a car to lean into the corner the roll center must be above the CG. But this does not mean that the amount of weight transferred is different. Weight transfer is defined by the (CG*F)/Track. This number can not change no matter what you do to suspension geometry, it is a physical impossibly (unless you have gyros but we won't get into that here). What does change is how the weight is transferred. There are three types of weight transfer. 1.) Unsprung mass (i.e. wheels, tires, outboard brakes, ect), 2.) Sprung Mass (everything that is not unsprung, chassis wings, driver, engine) and 3.) Transfer due to the roll center. It is this final type that is causing some confusion, as you increase your roll center height more and more weight is being transferred via the roll center and less by the sprung mass. So all having the car roll into the corner is doing is changing the distribution of wprung weight transfer and that due to the roll center, the total remains the same....(please excuse the gross simplification)

[robert dick]

Perhaps plausible if the two moments of forces are separated :

1) First moment of force = centrifugal force acting on centre of gravity/roll centre : responsible for the “inclination” of the chassis in relation to the wheels (CG can either be above or below RC).
This first moment of forces is active within the car.

2) Second moment of force = centrifugal force acting on centre of gravity/contact point of the outer wheel with the ground (simplified) : tends to turn over the entire car (always tends to turn over the car since the CG is always above the ground).
This second moment of forces concerns the entire car seen from the outside.

In principle these two moments of forces are active within two different systems (does not exclude that (1) and (2) are interacting).

[Yelnats]

Good stuff Bob Dick. And then to complicate things more there's the suspension jacking phenomenom exibited by some suspension where the ride height increases due to geometric deficiencies under cornering forces. The VW Beatle was an abject lesson in poorly designed suspension with a low roll cetre in front and a high one at the rear with wicked weight jacking at the rear and high G/G overall and a tail heavy weight distribution. No wonder it won car of the century in some polls.

[WPT]

There is an additional weight transfer term, that due to the CG of the sprung mass being offset to the outside from its static position when the sprung mass rolls. This term is very small for formula cars, but perhaps not small for Buicks. Obviously weight transfers to the outside tires during cornering regardless of the direction the sprung mass rolls. WPT

[mera308gtb]

The VW Beatle was an abject lesson in poorly designed suspension with a low roll cetre in front and a high one at the rear with wicked weight jacking at the rear and high G/G overall and a tail heavy weight distribution. No wonder it won car of the century in some polls.

I don't know much about Beetles, but I assume this is a swing-axle type suspension? I think the situation you are describing above relates to the roll center raising as the roll at the rear increases. Horrible stuff.

And I am sure Herbie has someting to do with the Beetle's popularity. He is just so cute despite the poor engineering.