Do we need suspension?

[hardingfv32]

PhillipM

'Smooth the driver inputs out, even on your perfectly flat glass track..."

Is your though that the movement of the car somehow extends the time that weight transfer takes place?

weight transfer = weight x cg height / wheel track x g. Where do you plug in the chassis movement into the formula?

You will notice there is no variable/input for time in the formula. When g (say, cornering force) is applied to the car you get WT. There is NO way to delay this.

Brian

[hardingfv32]

shamikaze

"That would mean that the weight (car-weight + Downforce at speed x), CoG and wheelbase + wheel-track are determining figures."

Determining figures for what?

Brian

[747heavy]

This is completely wrong:

"The ECU in overrun mode, retards timing so that the combustion efficiency and the Mean effective pressure is greatly reduced. The engine now puts out the required 200 hp. The other 400hp of air and fuel is sent out the exhaust pipe."

Let's discuss the logic of your proposal:

First, I am going to ASSUME that we are after some serious off throttle air and heat flow. I am also going to assume that we want the throttle open 100% during the off throttle mapping to accomplish that. You said that you want 200 hp. We will need an decent A/F mixture to get the mixture to light. Then we will use the ignition to develop the hp number you want. The goal of the retarded ignition is to limit the combustion pressures to develop only 200 hp. The combustion process will be allowed enough time to create 200 hp before the exhaust valves open effectively ending the combustion process. Combustion pressure = HP. Since you never reach maximum combustion pressure you are not going to get the big high energy exhaust flows that you are proposing.

There will be no 400 hp of exhaust to feed the diffuser.

Brian

Not sure, why, but I think we have two independent topics/discussions going on here.
Anyway:
You may simplifying things a little bit here hardingfv32.
It´s not only combustion pressure that matters, it´s the timing/position of the piston at which your pressure occurs, which will define the torque value of your engine. This in combination with the rpm will give you the power.
The pressure inside the cylinder is not instantenous, it builds up over time.
Imagine for a moment (hypothetical) that you have pressure x inside your cylinder
put your piston is perfectly at TDC.
The pessure you have multiplied by your piston area will give you a force at the conrod. But now, because you have only force, but no lever arm you have zero torque.

If you have the same pressure at 90° (past TDC) crankshaft angle, you have the same force multiplied by the max. leverarm -> ergo max. torque x given rpm = power at this rpm.
Now by timing the occurence and amount of pressure in relation to your piston/crank position, you can define how much of this pressure is turned into torque (mechanical energy). For a given amount of burned fuel, you can have more or less mechanical energy, the rest goes out the exhaust and into the water/oil as thermal energy.

The opening of the exhaust valves will not terminate the combustion process, it will just limit the increase in pressure, or will lead to an reduction of pressure inside the cylinder. If the combustion is not finished, still fuel there to burn, it will just keep burning while going through the exhaust. Putting higher termal stress on the exhaust valves and the exhaust system.

[DaveW]

You will notice there is no variable/input for time in the formula. When g (say, cornering force) is applied to the car you get WT. There is NO way to delay this.

Forgive me, Brian, but I think you have been unnecessarily bellicose in this thread.

Let's examine the statements quoted above. Your second sentence is perfectly correct, but the third is not, I'm afraid, because weight transfer, & hence cornering force, does not happen immediately a driver turns his steering wheel. It takes time to build up, depending upon suspension roll stiffness, damper characteristics & suspension geometry. It is true that drivers generally don't like a "lazy" turn-in transient. It is also true that a turn-in transient that is too short will generate transient understeer, because the tyres require some time to adjust to a change in load conditions. In fact, not allowing that time is a good way to destroy front tyres quickly.

Elsewhere you have (I think) suggested that a suspension is not required on a flat surface. That is again not quite correct, I'm afraid. Even on a perfectly flat surface the vehicle will be disturbed by driver inputs, & the energy generated by those disturbances must be dissipated. If the suspension is allowed to move, then the dampers can perform that function, otherwise not.

It is a widely held view that the front suspensions of F1 vehicles are effectively rigid. Now that might be (almost) the case vertically, but not necessarily in roll. In fact suspension roll stiffness distribution should be set to achieve a lateral mechanical balance. When that implies a low front roll stiffness, then front damper characteristics can be used to manage turn-in transients.

Overall, then, suspension set-up does affect cornering performance, even in F1 (though some appear to manage that rather better than others), and optimising suspension set-up is a fairly complex process.

I hope this helps a little.

[Jersey Tom]

Yes, a suspension is necessary.

The amount of false BS and handwaving in this thread thus far is astounding. May have to revisit this later tonight.

[hardingfv32]

"You may simplifying things a little bit here hardingfv32." Absolutely

You did a very good job filling in the details. I just wasn't sure anyone would appreciate them.

Do you think it is possible to get any meaningful extra exhaust full while at part throttle we such an odd mapping? Say the same exhaust flow that you might by properly producing 400 hp, BUT with only 200 hp actually making it to the flywheel (if there is one)?

Brian

[hardingfv32]

DaveW

Yes, very basic but I will try to defend my statements.

1) "but the third is not, I'm afraid, because weight transfer, & hence cornering force, does not happen immediately a driver turns his steering wheel."

I did not mean to imply max weight transfer. Weight transfer does vary with cornering force (g). BUT you cannot delay this relationship. Even when a car is actively rolling the weight transfer is still happening as stated by the formula.

2) "Even on a perfectly flat surface the vehicle will be disturbed by driver inputs, & the energy generated by those disturbances must be dissipated. If the suspension is allowed to move, then the dampers can perform that function, otherwise not."

Unless you stipulate otherwise I am going to assume that we are talking about some form of load transfer. There is no way to dissipate these load transfers. The formula says they will take place. Are we talking about the shocks dissipating a roll movement? No suspension, no roll, no movement. Why do I want roll?

Please articulate your disagreements.

Brian

[hardingfv32]

Jersey Tom

"The amount of false BS and handwaving in this thread thus far is astounding. May have to revisit this later tonight."

On a "dead smooth track" with no grip or tire flex factors... why do you need a suspension?

Please articulate your disagreements.

Brian

[Jersey Tom]

A few items in no particular order:

1) It's ridiculous to consider a track that is perfectly flat. No such thing. The amount of time spent doing 7-post testing by pro race teams should emphasize this point. Would be equally goofy to talk about cars with a CG height of 0.0 or some such shenanigans. Hell, even on the very smooth tracks you still have the kerbs to contend with.

2) Having the linkage there lets you do some trick stuff with roll centers and force coupling

3) With no suspension travel, you would have no damper travel, and lose one method of response tuning

4) Speaking of suspension travel, "locking out" a suspension means you can't do anything trick with chassis attitude control. Consider the straight line acceleration cases of a high downforce car with a very high front ride rate, and a soft rear ride rate. Get to do some interesting things by letting the rear squat down at speed, shedding drag by decreasing AoA of the aero elements of the car.

5) With no springs, bars, or tire rate, you have little to tune low speed balance with. Pretty much stuck with nose weight. Having some suspension travel engaging spring elements allows you to tune balance and response by varying load transfer distributions. Additionally, running an absurdly stiff (or solid / hard link) suspension would then make your load transfer splits purely dependent on compliances.

[DaveW]

Why do I want roll?

Please articulate your disagreements.

You don't, I guess, but having no suspension compliance in roll won't prevent roll - tyres will provide it. Now the problem is that F1 tyres are not efficient at dissipating energy, so the disturbance will continue because the tyres & vehicle mass will oscillate (interchanging kinetic & potential energy) with an accompanying reduction in grip. The problem can be increased if aero forces couple with that motion, effectively supplying negative damping. The same is true in pitch, & in this case the consequences of different set-up strategies are sometimes visible. The solution is to let dampers dissipate disturbance energy quickly (that is, after all, one of their primary functions), but they will be effective only if they are allowed to move. I hope that is sufficient articulation (with apologies).....

[hardingfv32]

The name of the thread is "Do we need suspension".

The key assumptions to narrow the discussion are:

1) Dead smooth track

2) No tire movements or grip issues.

Simply what does the suspension provide IF you exclude the above.

Jersey Tom... If you find these restriction hard to accept, don't participate in the thread. But I will answer your questions.

2) Why do I need moving RC or force couples, to change the balance of the car? If I have perfect balance with no suspension what is going to change if there is no suspension?

3) Why do I need response tuning? If I have perfect balance with no suspension what is going to response is going to need correction?

4) There could be some advantages to aero systems, but I am not sure the benefit would always out way the negatives. Do we see this in F1? Is RB rake set while at rest or does it develop only at speed?

5) Say I use camber to balance my no suspension car. Why would the balance change? Yes, things could happen between the front & rear tires, but this should be the same with or without suspension.

Brian

[Jersey Tom]

I'd love to hear where this intrinsically perfect balance comes from.

Or likewise, where this whole thought process is going as it is so side stepping between a a land of both shadow and substance, well, perhaps we should ask this man what he thinks:



What kind of assumption is no tire movement anyway? I could be running 60, 70, 80 psi tire pressure (4,1, 4,8, 5,5 bar for you European types) and tire deflection is significant.

Do we NEED suspension? I dunno need it for what? To move around? Perhaps not. Don't need pneumatic tires either. Could use wooden wagon wheels. But, given the opportunity, if I had to design and tune a racecar with a suspension to compete against an equivalent vehicle with rigid links, I'm fairly certain of being able to run circles around the competition.

[bill shoe]

This doesn't answer the overall question, but it may be a useful mental excercise.

Suppose we were talking about a three-wheel vehicle that was statically determinate (and determinate during steady-state cornering?). Go ahead and assume any weight distribution, tire size, track width, wheelbase, C.G. height etc. Also assume perfectly smooth/flat/consistent pavement.

Any need for suspension?

I think DaveW's recent concern would still be valid-- The tires would allow roll and pitch, so the addition of some suspension movement (with dampers) would actually increase the energy dissipation from these movements.

Other reasons for suspension in this Tron-like racing world?

[fastback33]

I'll refine my assumptions: Dead smooth track, no tire flex or grip issues/effects.

Sorry but, this question is a catch 22. If you have perfectly infinite grip you don't need suspension as that is what it is there for, tuning grip. Essentially you cant have one with out the other though. The question is, how do you plan to construct these "perfect" tires, or perfectly smooth track? ANything even at the microscopic level still has ridges and is rough.

Your question is flawed, nothing, no one, can ever be perfect. Interesting thought but has no end value.

[hardingfv32]

DaveW

No apologies necessary. This is just a fun thread to illustrate a simple premise.

1) Yes, the tires will cause roll, but I don't see it as a negative. The tires would need a fixed amount of camber to correct this. Is there going to be a lot of energy created with this compression of the tire in a corner? There is always the option to using a mass damper which would be part of the chassis.

2) Of what value is pitch? Isn't it just a by-product of having a suspension? The load transfer is the same regardless if there is a pitch or not.

"The best suspension is no suspension" is a famous Colin Chapman quote.

Brian