ORCA General Discussion

[Marcus Garvey]

I didn't say anything about centrifugal force. The inertia(like that) of the mass acting upon the center of gravity causes the body roll.

Keep 'em coming.

 

[MC-Chase]

And while the front springs are compressed under braking, is there more weight/load on the tyre contact patch at the surface than when the car is sitting static in grid?

More load yes, more weight, no. More weight would imply it carried it's own momentum.

 

[Marcus Garvey]

Load is weight, son.

 

[MC-Chase]

I didn't say anything about centrifugal force. The inertia(like that) of the mass acting upon the center of gravity causes the body roll.

Keep 'em coming.

Apologies, mis-read. It's late here.

 

[MC-Chase]

Load is weight, son.

No, load describes a force exacted on a surface. Weight describes mass*gravity (have I mentioned that yet?)

 

[Marcus Garvey]

Yes, load is a force, and in this case that force is the inertia of the mass, of which mass can be expressed as weight because gravity is not a variable. It's a constant.

 

[MC-Chase]

Yes, load is a force, and in this case that force is the inertia of the mass, of which mass can be expressed as weight because gravity is not a variable. It's a constant.

You're missing that one point. *if* we consider what I am calling the inertia force a single downward compressive force on the spring then that explains why the spring compresses more under breaking in our hypothetical braking scenario. With you calling it weight you are implying that this downward force also carries with it a momentum force, which it doesn't, because it has no mass.

 

[OwensRacing]

http://www.turnfast.com/tech_handling/handling_weightxfr

Anytime you force something down you s
Applying more weight.

Your little gravity equation is about free falling objects or static objects. Once an outside force is applied the whole equation is useless.


So if I was to put a scale between the front tires and ground. Under braking would that scale read higher. Under accell would it read less. Answer is yes. Why cause weight is being transferred.

I'm done at this point. No more needs to be said. The facts have been set forth. It's up to a certain someone to either learn or continue being wrong.

As well stop trying to change the context to prove your right. You are wrong. Was wrong and will be until you admit weight is transferred when a car turns, brakes, or accelerates.

 

[Marcus Garvey]

Force is not mass, the force acts upon mass increasing the loading on the front tyres under braking. Let me ask a couple of questions directly.

If you had scales placed under the tyres of a car during braking(yes, not possible, but since we're far off into never never land at this point) would the scales under the front tyres read higher than they would with the car sitting static in grid?

The mass of my race car is equal to 2485 Earth pounds. Guess what it weighs?

 

[MC-Chase]

So if I was to put a scale between the front tires and ground. Under braking would that scale read higher. Under accell would it read less. Answer is yes. Why cause weight is being transferred.

I replied to you on this point before, you're confusing an additive scalar force along WITH weight to an increase in overall weight, and that simply isn't the case. If you don't want to continue discussing then that's fine, but there's no need to tell me to learn or be wrong - that's a bit unnecessary.

 

[Marcus Garvey]

You're discussing theoretical physics; we're having a conversation about practical applications.

Table. Legs.

 

[OwensRacing]

All that matters is where the rubber meets the road.

You know damn well under braking that a scale between the front tires and the road would indeed read higher. Aka more weight being applied.

I don't care how or what you think caused this. It's plain and simple. The weight is increased. A freaking SCALE dude. That measure weight. It increases. Seriously.

 

[MC-Chase]

Force is not mass, the force acts upon mass increasing the loading on the front tyres under braking. Let me ask a couple of questions directly.

If you had scales placed under the tyres of a car during braking(yes, not possible, but since we're far off into never never land at this point) would the scales under the front tyres read higher than they would with the car sitting static in grid?

The mass of my race car is equal to 2485 Earth pounds. Guess what it weighs?

Yes they would, we established this very early on!

You're missing the point of the inertia not holding any momentum all in on itself. I fail to see what more I can suggest to explain my point without going further into "never never land" as you put it. It's late here, but perhaps over the day tomorrow I can think of some scenarios that may help clarify what I mean.

 

[dsgerbc]

Whoa, a lot of post on something related to physics. I'll weigh in tomorrow, from work.
Nevermind:
I know several fast guys who think they know the physics of why they are fast, but are in fact badly confused about anything and are fast just because they are fast.

Marcus, apparently isn't one of them

The rest is semantics. When talking car physics one has to be real careful about the frame of reference. Automotive engineers tend to use the system of axis that is fixed to the car. In that one centrifugal forces are real, and a braking car (a non-inertial system of reference) is subject to a force acting forward, applied at the center of mass. I hate using it, but most of stuff written on vehicle dynamics uses it.

In the regular axis: sure, weight is a force applied at the center of mass. But the equivalent Earth's reaction force is applied at the wheels. And it's this earth's reaction force can be thought of as negative of 'weight' over that axle.

In this Earth axis, under braking there's braking force applied at the ground level, if there's no 'weight transfer' to counteract it, it will rotate the car around it's center of mass (think wheelie). And that's how it starts, the body starts rotating forward, springs compress and increase pressure on the ground in the front, reducing in the back. With this, earth's reaction force is higher in the front, lower in the back and that creates a rotational moment around CG, counteracting braking force (braking force also changes a bit). Enough 'weight transfer' - and earth's reaction force's moment equates moment of the braking force, and the rotation stops; you're doing steady-state braking.

So, listen to what Marcus is saying. If unclear - think again, still unclear ask (him).

 

[Marcus Garvey]

It's more of posts on terminology than physics. Physics is merely the context.

 

[MC-Chase]

Automotive engineers tend to use the system of axis that is fixed to the car. In that one centrifugal forces are real, and a braking car (a non-inertial system of reference) is subject to a force acting forward, applied at the center of mass. I hate using it, but most of stuff written on vehicle dynamics uses it.

I've absolutely never seen anything regarded to inertia shift in ANY field of engineering being referred to as 'weight', where on earth are you getting these from? Do you have any journals where this language is commonplace?

So, listen to what Marcus is saying. If unclear - think again, still unclear ask (him).

I did, I thanked him for his perspective on the matter, the terminology was/is wrong and in turn makes the descriptions incorrect. I am not in anyway unclear - indeed, perhaps when someone suggests reasons as to why this my be the case it might be a good idea to listen rather than instantly shoot them down for no adequate reason .

For the sake of Brandon's thread this will be my last message on this subject here - though if anyone wishes to add anything in terms of what they would consider corrections and/or further discussion then drop it here and I'll read it or throw it on my profile wall and I'll read it there and give it a response; I just don't want to drag the ORCA thread along with this anymore.

I considered ways of describing why weight and an inertial force were different and why it is important they are differentiated properly; I came up with this in the end.

It's plain and simple. The weight is increased. A freaking SCALE dude. That measure weight. It increases. Seriously.

Imagine a scale with a 300kg weight on it - the scale would measure 300kgs; this is 300kgs of weight. Now imagine a 1kg G-clamp, you put this G-clamp around the empty scales and tighten the clamp until the scale dial measures 300kgs; this is not weight, the clamp doesn't weigh 300kgs - it is exerting 300kgs of force upon the pressure plate of the scales.

Why is this important? As I have been trying to explain (albeit apparently badly) since the beginning is that the physical 300kg weight will have inertial properties under kinetic movement. The 300kg force exerted by the G-Clamp will not.

Allow me to throw in some more mental imaging. You have the same 300kg weight that was on the scales (let's say it's a rock in this instance) on a trolley, you can push the trolley about on the floor in any direction you please. Imagine an identical trolley which is holding the G-Clamp - you are also able to push this trolley about as you wish. If you push the rock away from you, allow it to roll, and then try and pull it back you will encounter a lot of resistance in getting the trolley to stop because of the momentum of the 300kg rock, you will not encounter this same level of momentum resistance from the G-Clamp on a trolley. This is why inertial forces are not adequately described as "weight" because weight is not in on-itself a force. It is merely capable of exacting a force.

I cannot explain this on any lower grounds of understanding, this is *far* from theoretical physics, this is correct application of some of the most established laws we have in classical physics and absolute entry level engineering application - correct units and very basic maths, no 3rd order Laplace transforms here.

 

[CC570]

inertia force

You're making up stuff here.

" Inertia is one of the primary manifestations of mass, which is a quantitative property of physical systems."
and
"In common usage the term "inertia" may refer to an object's "amount of resistance to change in velocity" (which is quantified by its mass), or sometimes to its momentum, depending on the context."

Both from the wiki article you linked. Regardless it is not a force.

 

[MC-Chase]

You're making up stuff here.

" Inertia is one of the primary manifestations of mass, which is a quantitative property of physical systems."
and
"In common usage the term "inertia" may refer to an object's "amount of resistance to change in velocity" (which is quantified by its mass), or sometimes to its momentum, depending on the context."

Both from the wiki article you linked. Regardless it is not a force.

"Moment of inertia is the mass property of a rigid body that defines the torque needed for a desired change in angular velocity about an axis of rotation."

I have no idea what you're implying with that final quote - that simply reinforces my point! But if you wish to quote definitions then;

Weight = mass*gravity,

yet everyone here seems to deny that the physical mass (that being physical atoms, molecules, matter, stuff, whatever you wish to call it) stays at the same point regardless of where the vehicle is moving. I'm finding it incredibly hard to see why this is so hard to understand.

Either way, as I said this is beyond the scope of the thread - my profile wall awaits.

 

[dsgerbc]

nevermind, PMs are better.

 

[RDAardvark]

My brain hurts.

 

[dsgerbc]

If it hurts, it means it's growing... like a muscle

 

[BrandonW77]

Yikes. I'm all for this kind of discussion guys but please keep it civil. From the bits that I know about vehicle dynamics and physics in general (and I'm not completely ignorant in either) I think there is simply a giant discrepancy in the terminology and how it's being used. In purely scientific realm I believe Chase is correct but vehicle dynamics tend to make science its bitch and behave in ways you don't always find elsewhere. His descriptions of mass/inertia/weight are correct to the empirical usages but when those are applied to cars it can get muddy and a lot of car people use these terms in different or incorrect ways. I also know Marcus well enough to respect every word he says about automobiles.

Does the force of a tire on the road change as the inertia changes? Of course it does. Does its mass change? No way, never. Where does "weight" fit into that equation? I don't know because weight is a variable measure and can/is influenced by environmental factors. Does a car weigh the same on the moon as it does on earth? Of course not. Does gravity even exist/function as we have historically understood it? Believe it or not there's some debate about that.


Is any of this accurately replicated in GT6 and worth debating? Probably not.

 

[dsgerbc]

It's all fun and games until someone's head explodes...

 

[BrandonW77]

http://gifsoup.com

Anyway, I plan to have a thread up this weekend for the new BMW GT Spec championship. We will use the same basic points structure from the last one we did, the Silvia Cup. 4 weeks, only the best 3 count, bonus point for pole position. There will be a Tuesday Championship and a Saturday Championship each with its own winner. Tuning prohibited, SS tires, 45 minute races (Daytona will stay at 1.24 hours in length) with a necessary pitstop, day/night transition when possible, might throw weather into the mix for one of them. Preseason race at Indy Road (pending test), first points race probably the second Tuesday in February. No aids but ABS, damage light, penalties off, yadda yadda. Hope some of you will be interested in participating. Just gonna start simple, if it goes well and we get good crowds I'll keep it going and think about ways to change/improve it.

 

[Marcus Garvey]

Well, this thread has delivered.

MC, don't get me wrong; I like you.

I'd also like to explain a bit of background. Everyone here is well into their 30s and 40s, most of us with higher degrees in the science and engineering fields and 15-20 years into successful carreers(have you seen our rigs, cars, houses, etc?). Most of us have been familiar with each other for over 3 years, and know each other's real names, where we live, our employers, etc. Some of us have run successful race teams for over 10 years.

Now, there was obviously a difference in perspective upon the frame of reference discussed as DSG and Brandon pointed out. That is the difference between theory and practice. From the perspective of a race engineer in practice, outside of the classroom; the car is the center of the universe. Everything that occurs, happens to the car.

That aside, I can understand your frustration with everyone in the conversation disagreeing with you. Your brief history here and elsewhere on the internet has produced a clear record of confrontational discussions, some on this very site and even related to this very topic. Your condescent of others in this discussion here is what brought about the tone in which the conversation turned and warranted a response. You proceeded to twist words, misrepresent others, and contradict your own statements many times.


You responded to this:

And while the front springs are compressed under braking, is there more weight/load on the tyre contact patch at the surface than when the car is sitting static in grid?

With this:

More load yes, more weight, no. More weight would imply it carried it's own momentum.

Then you responded to the same question:

If you had scales placed under the tyres of a car during braking(yes, not possible, but since we're far off into never never land at this point) would the scales under the front tyres read higher than they would with the car sitting static in grid?

With this:

Yes they would, we established this very early on!

Scales measure weight, you know; which in the reference of automotive engineering is referred to as load when applied to a tyre.

You refused to acknowledge that gravity is not a variable in the discussion, being a constant. You refused to reply to other's posts that pointed out that your own citations contradict your posts. You do realise that the internet is wide open, right? Your own history demonstrates that this behaviour is not isolated but a theme. You have caused several people to take a special interest in you.

Now, I'm going to ask you a couple of personal questions. Where are you from? I ask because your vernacular is purely American breadbasket. Your spelling is absolutely American English. Your tone, diction, and sentence construction has never demonstrated any British English. Even your own time refences on this very site suggest you are American. You state that you raced Karts with Lewis Hamilton and that the reason he is an F1 driver and you aren't is because he won a coin toss against you. Really?

Again, I like you. You've got balls. Let me know when you get a car and I'll help you set it up for your intended purpose.

 

[BrandonW77]

Enough. Take it to PM if you want to continue.


I plan on being online in about an hour to do some final testing for the BMW's, feel free to join.

 

[dsgerbc]

Again, I like you. You've got balls. Let me know when you get a car and I'll help you set it up for your intended purpose.

Marcus, I've shared a PDF of Milliken&Milliken with him, should contain enough info.

 

[BrandonW77]

If this is how you guys are going to treat all of our new drivers I don't think our grids are going to be very large.

 

[BrandonW77]

Anyway, I have a room open to do some BMW testing and practice if anyone is interested.

 

[dsgerbc]

Is the room still up? I finally have some time to turn some laps.