Do we need suspension?

[hardingfv32]

Belatti

I wish to know why you propose to restrict the front suspension under braking.

1) If it is to control load transfer, is that possible?

2) How do you redistribute load transfer under straight line braking?

Brian

[Ciro Pabón]

By taking part of the load through torsion of A arms, is the method I've seen.

Of course that wouldn't work without a suspension, needed to dampen the forces created when you stop braking and the arms untwist, even in a perfectly flat track.

hardingfv, how if you teach us something about frequencies and harmonics in structural engineering?

I think Belatti (and others before him) have tried to point you in this direction.

It's hard for me to understand suspensions this way, where all that is accepted for analysis are static methods of analysis which I think are useful only in the extreme case presented initially in this thread, in a car with no vibrations at all, even from engine.

[DaveW]

Some longitudinal "weight transfer" examples here.

[hardingfv32]

It seems that the original thought for this thread has run its coarse.

Now we are talking about redistributing the load transfer from braking. How is this done?

Are you proposing this has something to to with requencies and harmonics in structural engineering?

Brian

[bill shoe]

I love the braking analysis videos from Turkey. I originally saw an HD version of this and it was clear the McLaren front pushrods were not moving in and out of the monocoque at all, it was pure tire bounce. Jensen Button needs an aspirin.

In street cars this kind of tire bounce with little or no suspnesion movement is sometimes called "boulevard jerk". Do race engineers have a different name for this?

DaveW, my original assumption with these videos was that the braking zone pavement profile had a subtle but significant oscillation that set off the front tire bouncing. However, you seem to imply the pavement profile has little or no contribution, and the bouncing gets started as a result of the abrupt weight transfer to the front end. Am I understanding this correctly?

It's often mentioned in these threads that the front end of a typical F1 car is almost locked in vertical motion but it can still be much softer in roll. It would be interesting to see the bouncier F1 cars go through the same braking zone while doing an early progressive turn-in into the corner. In this manner some roll damping might come into play to reduce bouncing. This would probably not be a faster way through the corner, but it would be interesting to see if there was a reduction in bouncing.

[747heavy]

In street cars this kind of tire bounce with little or no suspnesion movement is sometimes called "boulevard jerk".
Do race engineers have a different name for this?

different people (engineers) will perhaps use different terms.

some of the terms commonly used, to describe this phenomena are:
porpoising (this is mainly used in the context of an aerodynamic instability)
pumping
bouncing

(Mercedes DTM/GT1 cars had/have a tendency to do it)

[hardingfv32]

Could the wings have a dampening effect designed into them for this situation or are they the problem?

Brian

[DaveW]

Bill: No doubt the track did provide an input to initiate the instabilities, but the Lotus/RBR responses suggested that the track itself wasn't a complete disaster.

The instability is the result of coupled heave/pitch motion, causing variations in ride height, rake and their derivatives (ride velocity & rake velocity). These will cause the aero downforce to vary, which will modify the effective stiffness & damping of the whole vehicle (you might like to google "Wagner Function" & "wing flutter"). Usually, the damping is negative, which can cause a continuing oscillatory motion. The forces increase with airspeed (of course), & I think it is true that all aero race vehicles will porpoise if the airspeed is high enough. The "critical airspeed" can be increased most effectively by increasing vehicle sprung mass damping ratios (i.e. using the dampers properly). Stability will be recovered when the airspeed reduces below "critical". It is quite clear from the videos that McL & Merc were operating (initially) above their critical airspeeds, whilst the Lotus & RBR weren't.

The videos also illustrate a point that JT & I tried to make earlier. The "weight transfer" (pitch component of vertical force) in (some of) these clips was clearly not solely a function of longitudinal deceleration.

p.s. The Wikipedia entry trying to explain porpoising is plain wrong, I'm afraid.

[Belatti]

Belatti

I wish to know why you propose to restrict the front suspension under braking.

1) If it is to control load transfer, is that possible?

2) How do you redistribute load transfer under straight line braking?

Brian

I did not propose that. Re-read the thread, please.

[Belatti]

Now we are talking about redistributing the load transfer from braking. How is this done?

Brian

No one said nothing about redistributing load transfer under braking. There is a mix up in the thread between redistributing lateral load transfer and G sensitive dampers that change their characteristics under braking.

[DaveW]

It seems that the original thought for this thread has run its coarse.

Brian, I'm intrigued. Do you mean that the original thought has run its course, or this thread?

My understanding of your original thought is as follows: Is it possible to eliminate suspension if tracks, tyres & vehicles are all modified to suit? The consensus appears to be that the question isn't particularly useful or relevant. Robbobnob's comment was telling, I thought: "if they didnt need suspension they wouldnt have it....".

However, I would be interested to read about your views when you started the thread, & whether the thread has been useful to you in any way. Perhaps you think the thread might have been useful to Forum readers; if so, perhaps you could state how & why.

[Ciro Pabón]

... not to mention that tracks aren't flat by design, but I throw the towel long ago about explaining how that fact influences racing.

I can say from similar conversations that most people cannot distinguish circular curves from cubic curves. They don't realize what's going on in the horizontal direction, imagine explaining what's going on in the vertical!

In the former (circular, simple curves) you have to move the steering wheel up to 20 degrees opposite to the curve, to compensate for the sideslope you find in the straight, but most drivers don't realize they're actually doing it. You move your hands well over 20 cm but you don't notice!

Now, if that's unconscious, imagine if we have to delve into the different methods there are for side slope transitions and its influence on the car suspension.

[DaveW]

I once owned a road car with a similar characteristic, caused by compliance steer. Had been driving it for over a year when one of my GA friends commented on it. I didn't believe him until I watched what my hands were doing through corners....

[mep]

I can say from similar conversations that most people cannot distinguish circular curves from cubic curves. They don't realize what's going on in the horizontal direction, imagine explaining what's going on in the vertical!

Ah Ciro, I was asking you to explain that more detailed some months ago and still wait for a response.

[747heavy]

I can say from similar conversations that most people cannot distinguish circular curves from cubic curves. They don't realize what's going on in the horizontal direction, imagine explaining what's going on in the vertical!

Ah Ciro, I was asking you to explain that more detailed some months ago and still wait for a response.

I´m sure the Master will answer you,
in the meantime, perhaps this is providing some "food for thought"