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Old 29th July 2003, 07:24 PM   #21 (permalink)
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Talking

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Old 29th July 2003, 07:24 PM   #22 (permalink)
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Quote:
Which confirms exactly what I have said!

Any graph that shows an angle of greater than 45deg. supports my statement.

Thank you.
Mycroft

Please tell me you're joking?

All an angle of 45 degrees means is that it increases to a greater degree (acording to the scale of that graph) than the x axis. Not that it more than doubles.

The fact that it is a curve that tails off, means that it the y axis LESS THAN DOUBLES, each time the X axis doubles.

Is it this misconception that you have derived you conclusions from?

All the best

Simon
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Old 29th July 2003, 07:26 PM   #23 (permalink)
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Sorry... "angle of MORE THAN 45 degrees", not "of 45 degrees"
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Old 29th July 2003, 07:55 PM   #24 (permalink)
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Now we have had sufficient pause to mourn the recent death of Simons ability to read both Graphs and posts correctly... shall we move on.
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Old 29th July 2003, 08:07 PM   #25 (permalink)
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Originally posted by Mycroft
Now we have had sufficient pause to mourn the recent death of Simons ability to read both Graphs and posts correctly... shall we move on.
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Old 29th July 2003, 08:08 PM   #26 (permalink)
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Laughable.
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Old 29th July 2003, 08:11 PM   #27 (permalink)
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Originally posted by Mycroft
Laughable.
Unfortunately, it seems it has reached that stage Mycroft.

If anyone has any further questions, please post.

All the best

Simon
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Old 29th July 2003, 09:03 PM   #28 (permalink)
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http://www.ubifhe.ac.uk/courses/gene...hs_for_beg.htm
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Old 29th July 2003, 10:15 PM   #29 (permalink)
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Ok well it seems yet again Mycroft resolves to just insulting anyone who posts contrary to his statements, while not actually being able to produce any proof to back up his claims. Disappointing.

Shame really, ruined what started out as an interesting thread.
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Old 29th July 2003, 10:22 PM   #30 (permalink)
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Originally posted by Thorin
Ok well it seems yet again Mycroft resolves to just insulting anyone who posts contrary to his statements.
TRANSLATION.

''Mycroft posts proofs, but it means I have to do some work getting to them, when all I want is to be spoonfed, and even when the simple proof is posted, I will ignore the evidence of my own eyes.''

Quote:
Originally posted by Thorin
Shame really, ruined what started out as an interesting thread.
Yes the first 3 posts were partcularly interesting I think.

Cheers.
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Old 29th July 2003, 10:24 PM   #31 (permalink)
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Yawn.
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Old 29th July 2003, 10:27 PM   #32 (permalink)
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Hi Thorin

Please don't let it ruin the thread. If there is more you would like me to elaborate on, please ask and I'll do my best.

All the best

Simon
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Old 29th July 2003, 10:30 PM   #33 (permalink)
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Thumbs up

Well said Simon.
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Old 29th July 2003, 11:27 PM   #34 (permalink)
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If anyone is confused about the graph issue, or questions the fact that the grip a tyre produces is less than doubled when you double the load on it, please let me know and I'll elaborate. Otherwise I'll assume that all (except maybe one ) can see this.

So I'll move on...

Is weight transfer a bad thing then??

Well in many ways yes, in that it reduces your grip, but the ability to balance the weight transfer around the 4 contact patches is what gives a car it's handling characteristics.

A car that transfers weight across the rear axle more than the front, will oversteer more than one which transfers more at the front.

The ways this is tuned comes in many forms.

Firstly things like the inherant characteristics of the sprung weight (basically - everything the body side of the suspension).

If you have a higher centre of gravity at the rear of the car than the front, there will be more weight transfer at the rear.

But if we assume we are stuck with that kind of thing, you can look at the suspension set-up.

There are two major states that chassis engineers look at when developing the suspension set-up.. steady state (which is a theoretical state that the car is in when no change in the forces acting on it occurs) and transient state (which is when the body of the car is rolling or pitching due to forces acting on it).

In the theoretical steady state (mid-bend - if you were able to make a car genuinely sit in steady state) the things that have the major effect on the weight transfer are the springs and bars. At this point, all they are really able to do is balance the amount of weight transfer as a ratio between front and rear.

In transient states (during the actual motion of the body rolling or pitching) the biggest contributers are the dampers (although the springs and bars do also affect this).

More bump damping creates more weight transfer when that corner of the car is being loaded up (pitching / rolling towards that corner - so the suspension is being compressed) and more rebound damping (meaning rebound of the suspesion if being resisted more) creates more weight transfer when that corner of the car is being unloaded (the suspension is in rebound / extending).

So chassis engineers are able to set the car up by tweaking these components to suit the desired effect.

As a side note, many race formulas (including - i believe - F1) use roll dampers also. This is a pretty cool way of being able to alter transient weight transfer during roll while not affecting the weight transfer whilst pitching.

All the best

Simon
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Old 29th July 2003, 11:55 PM   #35 (permalink)
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Originally posted by SDB
Is weight transfer a bad thing then??

Well in many ways yes, in that it reduces your grip, but the ability to balance the weight transfer around the 4 contact patches is what gives a car it's handling characteristics.

A car that transfers weight across the rear axle more than the front, will oversteer more than one which transfers more at the front.
Agreed, but I would say it's a bad thing only when it happens so that the car is compromised.

Are you aware of the term 'Lift-off oversteer'?

You drive into a corner, at near your maximum, you hesitate and feather the throttle, and the rear wheels go light?

Now if we look at your 'idea' that a lighter load will have more grip lift off oversteer can't happen can it!

Your 'idea' states that lighter load = more grip... the rear wheels have a lighter load, but they sure as hell dont have more grip!

For lift off over-steer to occur, the rear wheels are made lighter [due to weight transfer] and they lose the grip at a greater rate than they lose weight, hence lift off oversteer.

This again supports what I and many others know, until a certain point is reached in the Grip vs Load the graph shows in favour to the driver/car.

Exactly as I have stated previously.
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Old 30th July 2003, 12:21 AM   #36 (permalink)
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Originally posted by SDB
If you have a higher centre of gravity at the rear of the car than the front, there will be more weight transfer at the rear.
You are confusing COG with Roll Centre [RC] aren't you?

Never seen any car with more than Centre of Gravity!

Do we have a Left Side COG and a Right Side COG as well, or perhap a COG centred on the rear indicator just above the boot lock!
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Old 30th July 2003, 09:29 AM   #37 (permalink)
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Originally posted by Mycroft
Agreed, but I would say it's a bad thing only when it happens so that the car is compromised.

Are you aware of the term 'Lift-off oversteer'?

You drive into a corner, at near your maximum, you hesitate and feather the throttle, and the rear wheels go light?

Now if we look at your 'idea' that a lighter load will have more grip lift off oversteer can't happen can it!

Your 'idea' states that lighter load = more grip... the rear wheels have a lighter load, but they sure as hell dont have more grip!

For lift off over-steer to occur, the rear wheels are made lighter [due to weight transfer] and they lose the grip at a greater rate than they lose weight, hence lift off oversteer.

This again supports what I and many others know, until a certain point is reached in the Grip vs Load the graph shows in favour to the driver/car.

Exactly as I have stated previously.
I accept it can seem confusing at first, but it is quite straight forward once you get your head round it...

Firstly, everything I have said indicates that a tyre produces more grip the more load you put on it. Clearly this means that it produces less grip if you take load away from it.

When you transfer load from rear to front (as with lift-off oversteer) you take a load of grip away from the rear tyres, but the car still weighs exactly the same and therefore still needs to be resisted when turning, which the rear tyres are no longer as equiped to do.

Quote:
You are confusing COG with Roll Centre [RC] aren't you?

Never seen any car with more than Centre of Gravity!

Do we have a Left Side COG and a Right Side COG as well, or perhap a COG centred on the rear indicator just above the boot lock!
Nowadays, engineers are able to plot the c/g height along the entire length of the car like a wavy line. There is still a single centre of gravity (so I completely know what you're getting at), but this plot allows them to analyse the inherant characteristics of the chassis more accurately as the c/g being loaded up in a corner also creates a number of other "forces" that are rarely described in steady state physics.

Examples of these include a kind of twisting force (sorry I can't think of the name for it) which is created by a disparity between the c/g height at front an rear....

Imagine a car with ball joint connecting the front to the back so it was able to swivel freely. Bolt a 10m tall steel block on the rear, and nothing on the front. When you corner,the rear of the car will topple over, but the front will stay upright. This is the twisting effect.

All the best

Simon
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Old 30th July 2003, 09:31 AM   #38 (permalink)
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PS..

The same is true of the plan view of a car, you can plot the c/g position in the horizontal plain also.
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Old 30th July 2003, 11:17 AM   #39 (permalink)
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Originally posted by SDB
I accept it can seem confusing at first, but it is quite straight forward once you get your head round it...

Firstly, everything I have said indicates that a tyre produces more grip the more load you put on it. Clearly this means that it produces less grip if you take load away from it. [It does!]

When you transfer load from rear to front (as with lift-off oversteer) you take a load of grip away from the rear tyres, but the car still weighs exactly the same [But it weighs less at the rear!] and therefore still needs to be resisted when turning, which the rear tyres are no longer as equiped to do.
Isn't that a new paradox?

Kinetic energy will surley effect Centripetal motion otherwise none of this can happen, yet you are saying the exact opposite.

The same thing you see can happen in a straight line, where no centripetal force is present, if it were otherwise then we would not have the majority of braking imparted to the front!

We both know that one effect 'outpaces' the other, and so yet again, this points to the fact, that up to a certin point, tyres get more grip for the weigh imparted, at a point on that graph where a line at 45degrees passes thru that curved line, we know, that that point is the sweet spot, the point where the tyre and weight match perfectly, we both know also that there are at least 3 of those 'graphs' in every real world situation jostling for that sweet spot, in Formula racing much time is spent by tyre engineers trying to find a compound/carcass that is closes to that crossover on all three charts, that will win them the race.

Spend some money, buy the Milliken books, they are worth every penny.

I'll now show you why again... you have typed:-

''Nowadays, engineers are able to plot the c/g height along the entire length of the car like a wavy line.''

This line you describe is not some kind of elongated centre of gravity, that is just a joke, that line that starts high at the back and finishes some few feet in front of the car is actually the Longitudinal Roll Axis... COG? utter rot!


''Examples of these include a kind of twisting force (sorry I can't think of the name for it) which is created by a disparity between the c/g height at front an rear....''

Torque!

Buy the books!!!
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Old 30th July 2003, 12:38 PM   #40 (permalink)
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Oh dear.

You clearly have no idea what you're talking about. I will explain this for everyone so that they do not take the words you have typed as fact. If you choose to reply and spill more drivel on to this thread, you will have to forgive me for not responding, unless others (who would actually benefit from the information - as they do not think they know it all already) ask me to.

Firstly... you added the words "But it weighs less than the rear" to my quote. The rear of the car does not change in weight. The VERTICAL LOAD on the tyres reduces, but the "centrepetal acceleration" of the mass within the car does not change. Therefore they tyres are having to resist as much "centrepetal acceleration" with less available grip.

Quote:
We both know that one effect 'outpaces' the other, and so yet again, this points to the fact, that up to a certin point, tyres get more grip for the weigh imparted, at a point on that graph where a line at 45degrees passes thru that curved line, we know, that that point is the sweet spot, the point where the tyre and weight match perfectly, we both know also that there are at least 3 of those 'graphs' in every real world situation jostling for that sweet spot, in Formula racing much time is spent by tyre engineers trying to find a compound/carcass that is closes to that crossover on all three charts, that will win them the race.
This is (unfortunately) pure drivel, and doesn't really warrant a response. I will however endulge you purely for the benefit of others and to state exactly what *I* know, not what you perport me to know.

Unfortunately in doing so I have no choice but to make you look a completel fool.

You make comments about a graph having a 45 degree angle and that being the "sweet spot".

Firstly let's take the graph I drew for you on a previous page...



Notice at what approx point the 45 degree angle is at.

What if I had draw it at a different scale for the y axis?



Which one is correct, as they both show your sweet spot at different points?

Secondly.

It is unquestionable that doubling the load on a tyre less than doubles the grip it produces (we've all agreed this above). So why would race car designers want to pitch their car at a point where the additional grip in extra load even less than it would be at a lower load?

There is absolutely no way to answer the rest of that quote as you are simply talking nonsense.

Quote:
Spend some money, buy the Milliken books, they are worth every penny.
I bought milliken YEARS ago. It is basic reading for anyone interested in vehicle dynamics. Its *main* focus is on theoretical steady state physics which is used as a starting point for inexperienced chassis engineers to gain a base point understanding of vehicle dynamics.

It is a superb resource. You, sir, have clearly mis-understood it.

Quote:
This line you describe is not some kind of elongated centre of gravity, that is just a joke, that line that starts high at the back and finishes some few feet in front of the car is actually the Longitudinal Roll Axis... COG? utter rot!
Again we see lack of experience (in-fact probably zero) and a complete belief that everything you have read makes up the entire world of vehicle dynamics, plus your ability to draw hugely inaccurate conclusions from limited knowledge.

The Roll Axis is a completely different plot. It is a straight line, not a wavy one.

In addition to this, there is the Mass Distribution Axis (otherwise known as "principal axis of inertia"), which is a straight line average of the plot of cog height as mentioned above.

The importance of this Mass Distribution Axis is to allow engineers to design the roll axis in relation to it.

Just because you haven't heard of it Mycroft, does not mean it doesn't exist. For your own sake, why don't you try to actually learn something from these discussions rather than attempting to prove you know everything, which in-turn restricts the learning of others.

Quote:
''Examples of these include a kind of twisting force (sorry I can't think of the name for it) which is created by a disparity between the c/g height at front an rear....''

Torque!

Buy the books!!!
Are you really that simple? Do you really think it was the word "torque" I was searching for? It is the term for the torque acting on the tortion of the chassis (caused by the difference in cog height at front and rear) that I was searching for. Perhaps you could enlighten us, it is bound to be in one of your books.

I'll try to dig out a plot of the cog height for us all to see.

Again I must ask this.. as I really don't have the energy or interest in discussing this with mycroft alone. Is anyone actually interested in this. If so, please post so I know there would be some purpose to the time I'm spending on it.

All the best

Simon
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