Do Flat Floors Slow You Down?

[nasanu]

Mass does not impact on top speed, but it impacts on acceleration.

So absolutely NOTHING impacts top speed then? Everything that moves a car or impacts on movement acts on acceleration, so what possibly in your view could effect top speed?

You are playing semantics and trapped yourself. The simple truth is that if something has mass then it can not by law reach the absolute speed limit, but something without mass can. Therefor it is blindingly obvious that mass impacts on top speed.

There is no air in space, it's a vacuum.

OMG... I cant stop laughing.

And yet making something immediately less "aerodynamic" makes it have lower drag, for a particular set of circumstances, which has also been said several times already. That's what adding dimples to a golf ball does. It's about effecting a regime change, one that isn't pertinent to cars at all.

You might what to read up on what aerodynamic means... Adding dimples to golf balls is almost the very definition of the word.

aerodynamic
"Designed to reduce or minimize the drag caused by air as an object moves though it or by wind that strikes and flows around an object."

Go correct the dictionary Griffith!

The question isn't whether they are "good", the question for the last few pages has been, do they work in Gran Turismo relative to the way they are modeled, as they would in real life? In other words, take a real car, slap a flat floor on it and nothing else, no diffusers or other aerodynamic aids, and will it increase or decrease drag/downforce/topspeed?

It does add a diffuser...

I recalled watching Best Motoring test ( driver was the respectable "Professor" Nakaya Akihiko ) on rear diffuser, and flat undertray that was used as factory standard fitment on R34 GTR Vspec II, they tested the car against another model : R34 GTR with no front flat undertray and rear diffuser, the one with undertray and diffuser was slower on the straight at Tsukuba by a few kmh, but able to corner more consistently and more stable with slightly higher exit ( Akihiko-san showed with onboard cam where he can apply full throttle a split second earlier ). Lap times were very close, with the R34 GTR equipped with flat front undertray and rear diffuser faster by a few tenths and has less tendency for oversteer on exit.

Sorry, but your memory is corrupt. They compared an R34 with an R33. Not valid data.

 

[Bo]

So absolutely NOTHING impacts top speed then? Everything that moves a car or impacts on movement acts on acceleration, so what possibly in your view could effect top speed?

You are playing semantics and trapped yourself. The simple truth is that if something has mass then it can not by law reach the absolute speed limit, but something without mass can. Therefor it is blindingly obvious that mass impacts on top speed.

He didn't say that nothing impacts on top speed, did he?

It does add a diffuser...

In some cars it does, others not, as seen here:

If so, can you point out the diffuser there please?

 

[Imari]

So absolutely NOTHING impacts top speed then? Everything that moves a car or impacts on movement acts on acceleration, so what possibly in your view could effect top speed?

You are playing semantics and trapped yourself. The simple truth is that if something has mass then it can not by law reach the absolute speed limit, but something without mass can. Therefor it is blindingly obvious that mass impacts on top speed.

Not really. Comparing speeds of mass and massless things isn't really that helpful. Light doesn't obey classical speed rules like anything else. If you put more energy into a classical object, it goes faster. If you put more energy into light, it goes exactly the same speed and changes frequency.

Using light to further your understanding of classical physics is a mistake. They're not compatible, which is why it took so long for the speed of light to be accepted as a constant. The information has been there that this could be the truth for a long time, and people were aware of the possibility, but they mostly assumed that the experiments they were doing simply weren't accurate enough, because the idea of something stuck at a single speed without a carrying medium like the aether just does not compute in the classical physics that was used at the time.


Do not treat light like it was a freight train. They are not the same.

In a situation with no drag, a car (or rocket or whatever) will simply keep accelerating forever, always getting a little bit faster.
Light is stuck at one speed which is entirely determined by the medium it's in. It can not accelerate or decelerate.

Comparing light to something that can accelerate is like saying Usain Bolt is a better runner than the Eiffel Tower. One of these things can't run.

 

[nasanu]

He didn't say that nothing impacts on top speed, did he?

He said it acts on acceleration to dismiss what I said about it acting on top speed. Therefor he is dismissing anything that acts on acceleration. So if everything that moves an object acts on acceleration then nothing can change top speed.

Not really. Comparing speeds of mass and massless things isn't really that helpful. Light doesn't obey classical speed rules like anything else. If you put more energy into a classical object, it goes faster. If you put more energy into light, it goes exactly the same speed and changes frequency.

Using light to further your understanding of classical physics is a mistake. They're not compatible, which is why it took so long for the speed of light to be accepted as a constant. The information has been there that this could be the truth for a long time, and people were aware of the possibility, but they mostly assumed that the experiments they were doing simply weren't accurate enough, because the idea of something stuck at a single speed without a carrying medium like the aether just does not compute in the classical physics that was used at the time.


Do not treat light like it was a freight train. They are not the same.

In a situation with no drag, a car (or rocket or whatever) will simply keep accelerating forever, always getting a little bit faster.
Light is stuck at one speed which is entirely determined by the medium it's in. It can not accelerate or decelerate.

Comparing light to something that can accelerate is like saying Usain Bolt is a better runner than the Eiffel Tower. One of these things can't run.

So?... Should I quote some lorem ipsum back at you? This is one of those games where you say something pointless, irrelevant and unrelated then I do so in return right?

 

[Ridox2JZGTE]

What if say a land speed record car capable of over 400kmh, with a weight of just over 1000kg, now if that car is 20,000kg in weight - made from material with more mass ( same shape, same drag coefficient etc ), would it hit even hit 10kmh with the same power ? Just curious that's all as some said weight do not really affect top speed, I am not good in this

 

[nasanu]

What if say a land speed record car capable of over 400kmh, with a weight of just over 1000kg, now if that car is 20,000kg in weight - made from material with more mass ( same shape, same drag coefficient etc ), would it hit even hit 10kmh with the same power ? Just curious that's all as some said weight do not really affect top speed, I am not good in this

It will go much faster because the weight does not effect top speed and the extra inertia will push the air particles out of the way more easily

 

[Imari]

So?... Should I quote some lorem ipsum back at you? This is one of those games where you say something pointless, irrelevant and unrelated then I do so in return right?

What?

You were using light as example that mass affects top speed. I was merely pointing out that mass doesn't affect top speed, and your example was a proof of nothing, because a classical object does not behave the same way light does and so comparing them is not sensible.

What if say a land speed record car capable of over 400kmh, with a weight of just over 1000kg, now if that car is 20,000kg in weight - made from material with more mass ( same shape, same drag coefficient etc ), would it hit even hit 10kmh with the same power ? Just curious that's all as some said weight do not really affect top speed, I am not good in this

All other things being equal, yes.

Except that it'd be really hard to get the rolling resistance and the like of a 20 ton car down to the levels of a 1 ton car. But if it could be done, that everything but the mass was equal, they'd get to the same top speed, just the heavy car would be slower to get there.

It will go much faster because the weight does not effect top speed and the extra inertia will push the air particles out of the way more easily

Not even sure if you're serious...

 

[LMSCorvetteGT2]

It will go much faster because the weight does not effect top speed and the extra inertia will push the air particles out of the way more easily

Now you've turned on his sarcasm

 

[Bopop4]

Not even sure if you're serious...

It's because of the extra weight of the air in space creating a venturi effect under the car.

 

[nasanu]

What?

You were using light as example that mass affects top speed. I was merely pointing out that mass doesn't affect top speed, and your example was a proof of nothing, because a classical object does not behave the same way light does and so comparing them is not sensible.

When did I mention a photon? I never did. There are a whole class of mass less particles (all leptons for example), not just light.

If you make a blanket statement that mass does not effect top speed then it should go for all cases. Don't cry when someone points out where your statement is very clearly incorrect.

 

[Imari]

When did I mention a photon? I never did. There are a whole class of mass less particles (all leptons for example), not just light.

My apologies then, you were talking about the speed of light, not photons specifically.

So reaching the speed of light is just a matter of time for any engine? Mass MUST impact on top speed, otherwise we could achieve light speed travel. From my understanding the reason why anything with mass can not reach the speed of light is that mass increases with velocity. But you are saying mass does not matter so I am confused as to why light speed travel is not achievable?...

If you make a blanket statement that mass does not effect top speed then it should go for all cases. Don't cry when someone points out where your statement is very clearly incorrect.

You'll have to point out what's incorrect though. My understanding was that all the massless particles moved at the speed of light. They still don't accelerate in the sense of changing speed, although they do change direction.

You're going to have to explain more carefully how mass affects top speed. There's nothing stopping anything with mass from reaching light speed other than the availability of energy. It's theoretically possible, just not practical. Throwing a divide by zero in with massless particles gets you directly to light speed, but that goes in perfectly with how the rest of the theory works. Mass affects acceleration, not speed. Zero mass means infinite acceleration, so the particle goes directly to the highest possible speed.

So tell me how mass affects the attainable top speed. I suggest that mass simply modifies the time taken to reach the given top speed, all other things being equal.

 

[nasanu]

There's nothing stopping anything with mass from reaching light speed other than the availability of energy. It's theoretically possible, just not practical.

Not its not possible even in theory. The energy requirements go up to infinity if a particle has mass. So I am not sure how you miss the point that mass limits speed?

You might want to say, well 'in the real world'... But then your examples would have to be in the real world also, and we all know the heavier something is the slower it goes because speed in practice is limited by acceleration and available space among many other things. On a track a heavier car will not reach the same top speed of a lighter car given the other parameters are equal. You can only be correct in a in between space where we discount the upper limits of speed and also discount the practical limits of our everyday existence. Its a Goldilocks theory.

 

[Imari]

Not its not possible even in theory. The energy requirements go up to infinity if a particle has mass. So I am not sure how you miss the point that mass limits speed?

But really, at any given speed for an object with mass, you can put more energy in and have it go faster, as long as it's below the speed of light. However close you think it can get to the speed of light, you can add more energy and get it closer.

There's not a limit, unless it's c. If you think that an object with mass has a speed limit that is lower than the speed of light, then please tell me what it is, or at least how to figure it out.

You might want to say, well 'in the real world'... But then your examples would have to be in the real world also, and we all know the heavier something is the slower it goes because speed in practice is limited by acceleration and available space among many other things. On a track a heavier car will not reach the same top speed of a lighter car given the other parameters are equal. You can only be correct in a in between space where we discount the upper limits of speed and also discount the practical limits of our everyday existence. Its a Goldilocks theory.

But that's not what we were talking about. I've stated from the first that mass slows the acceleration down. So in a given distance, the more massive vehicle will reach a lower speed. But that may not be the vehicle's top speed. We were specifically discussing top speed, which I understood to mean, "the maximum speed it is possible for a vehicle to reach under it's own power". We can quibble about this and that, but I'd hope that we both understand what the top speed of a vehicle means.

There's only a couple of places where a Veyron can actually reach it's top speed, but it doesn't mean that it's top speed is suddenly lower because the country in which it lives only has short, windy roads.


So if we're back to talking about real cars, given a Bonneville type situation where you've got as much dead flat "runway" to accelerate on as you like, and the cars are controlled so that rolling resistance and all variables other than mass are equal, what makes a more massive car hit a lower top speed?

P.S. Feel free to explain how massless particles of any sort are evidence that mass affects top speed while you're at it.

 

[Ridox2JZGTE]

Sorry, but your memory is corrupt. They compared an R34 with an R33. Not valid data.

Nope, I still have the video. You have no idea what you are talking about, the R34 Review Edition Best Motoring is very rare video, it also has comparison to R33 on a gymkhana track, driven by Nakaya Akihiko as well, you must have seen a part of it. The 1st part is full review by Dori Dori driving the Bay Side Blue R34 GTR Vspec.

 

[nasanu]

But really, at any given speed for an object with mass, you can put more energy in and have it go faster, as long as it's below the speed of light. However close you think it can get to the speed of light, you can add more energy and get it closer.

There's not a limit, unless it's c. If you think that an object with mass has a speed limit that is lower than the speed of light, then please tell me what it is, or at least how to figure it out.

From now on I shall call you Zeno.

But that's not what we were talking about. I've stated from the first that mass slows the acceleration down. So in a given distance, the more massive vehicle will reach a lower speed. But that may not be the vehicle's top speed. We were specifically discussing top speed, which I understood to mean, "the maximum speed it is possible for a vehicle to reach under it's own power". We can quibble about this and that, but I'd hope that we both understand what the top speed of a vehicle means.

There's only a couple of places where a Veyron can actually reach it's top speed, but it doesn't mean that it's top speed is suddenly lower because the country in which it lives only has short, windy roads.


So if we're back to talking about real cars, given a Bonneville type situation where you've got as much dead flat "runway" to accelerate on as you like, and the cars are controlled so that rolling resistance and all variables other than mass are equal, what makes a more massive car hit a lower top speed?

P.S. Feel free to explain how massless particles of any sort are evidence that mass affects top speed while you're at it.

We have gone over this. I don't think there is anything more to say really.
What would be helpful at this point would be to get back on topic. If anyone could find a real world test of identical spec cars with and without flat floors that would be a good start.

Nope, I still have the video. You have no idea what you are talking about, the R34 Review Edition Best Motoring is very rare video, it also has comparison to R33 on a gymkhana track, driven by Nakaya Akihiko as well, you must have seen a part of it. The 1st part is full review by Dori Dori driving the Bay Side Blue R34 GTR Vspec II.

 

[Imari]

From now on I shall call you Zeno.

Great, so now you're resorting to being an arse instead of addressing the point.

We have gone over this. I don't think there is anything more to say really.

There certainly is. You could start with what is the maximum speed for an object with mass.

Then you could explain why you think mass makes a vehicle ultimately more draggy.

You've expounded a hypothesis that is quite at odds with current scientific theory, namely that objects with mass have a top speed that is dependent to some extent on their mass. Any time you'd like to explain that using an actual example, where the variation in top speed isn't caused by increased drag or some other agency, that would be super.

 

[eran0004]

@eran0004 Most the downforce is actually created by the low pressure zone caused by the car being low to the ground. The diffuser essentially slows the air back down, causing it to return to normal speed and pressure. Otherwise the air would be forced to rapidly increase in pressure, causing lift at the rear and drag due to turbulence caused by the uneven air pressures.

Essentially the closer the car is to the ground, the lower the pressure. This is because a larger sum of air is trying to be forced into a small area. The air speeds up but in order to compensate for this the air has to decrease in pressure. The decrease in pressure underneath the car (with a high pressure zone above the car) creates a vacuum, pushing and pulling the car down.

You are correct though. More downforce also means more drag. I believe PD decided to model it based on "FlatFloor=Yes then Downforce=100 Drag=50" regardless of how they visually modeled it.

As you can tell I really, really like aerodynamics!

A large amount of air being forced into a small area (or volume) would increase rather than decrease pressure and if it occurs underneath the car it would produce lift rather than downforce.

The air does speed up underneath the car though, but the reason is not because there's a lot of air pushing to get in, it's because there's a shortage of air underneath the car - an effect created by the diffuser.

The reason why the diffuser creates downforce is because it collects the air that travels underneath the car and then forces it to expand by increasing the volume that the air has to cover. That causes the airflow to speed up (as it wants to fill in for the air that's missing in the greater volume) and that lowers the pressure and pulls the car down.

​

The lower the car is, the greater the difference in volume and the greater the effect of the diffuser.

I'm not hopping in to argue or anything. I'm just here to say that it's four times the effect on a car going 400KPH versus a car going 200KPH.

Speed and air drag have a quadratic relationship.

Yeah, I meant it was "punished" twice, rather than the effect being multiplied by two:

1. The diffuser makes a greater difference on a super streamlined body than on a less streamlined body.
2. The difference in speed also makes the effect greater on the faster car than on the slower.

 

[Griffith500]

LMSCorvetteGT2 on the subject of rake in F1, look here.

You might what to read up on what aerodynamic means... Adding dimples to golf balls is almost the very definition of the word.

aerodynamic
"Designed to reduce or minimize the drag caused by air as an object moves though it or by wind that strikes and flows around an object."

Go correct the dictionary Griffith!

There is more than one source of drag in fluid flows. Adding dimples increases one type of drag, but "stabilises" the flow (by causing a turbulent "boundary layer"), reducing another type of drag. That second type of drag dominates for golf balls, so there is a net improvement.

Doing the same on a car's underbody will only increase drag, because it is so far above that regime change already that the dominant drag type is the one caused by the dimples, because there is already a turbulent boundary layer. You can't take a special case and apply it generally.

In the general case, making something "less smooth", for typical length scales, will increase drag.

In one sentence flat floors reduce drag, in another sentence they increase it.

Get back to me when you're certain.

I never said that. Stop being obtuse. Venturis, diffusers and such are generally not "flat". A pure, simple flat floor shouldn't change the profile of the car, so it can only decrease drag over a floor that isn't flat. If it's adding other shapes to the underside, or anywhere else, it's not just a "flat floor" anymore. This is the crux of the discussion.

 

[Ridox2JZGTE]

Did you watch the video, the R34 with diffuser and without are tested at Tsukuba. The R34 vs R33 was compared at gymkhana track. Akihiko-san noted about the braking stability, less oversteer and quicker times on the car with diffuser.

I have most of 99 Best Motoring videos, including Altezza review, S2000 review and GTR Battle.

 

[eran0004]

So absolutely NOTHING impacts top speed then? Everything that moves a car or impacts on movement acts on acceleration, so what possibly in your view could effect top speed?

You are playing semantics and trapped yourself. The simple truth is that if something has mass then it can not by law reach the absolute speed limit, but something without mass can. Therefor it is blindingly obvious that mass impacts on top speed.

I've never said "nothing impacts on top speed", I don't know what kind of semantics you've been looking at. I said that mass does not impact on top speed, which is correct because it doesn't. A 2000 kg car and a 1000 kg car with the same engine and the same body will have the same top speed - the difference is the amount of time and distance required to reach it. Thus, acceleration suffers, top speed does not. What limits both cars is when the drag of the airflow becomes a greater force than what the engine is able to perform.

The simple truth is that if something has mass then it can not by law reach the absolute speed limit, but something without mass can. Therefor it is blindingly obvious that mass impacts on top speed.

That is all logic gone wrong. Yes, the property of HAVING MASS impacts on extreme top speed, because it means that it's impossible of reaching the speed of light (because it would take an infinite amount of energy to accelerate it there). But the AMOUNT OF MASS that an object has is completely irrelevant. An object weighing 1 gram will encounter the same issues when it comes to reaching lightspeed as an object weighing a billion tonnes. The 1 gram object will require a lot less energy to accelerate, though.

0.00001 * infinitiy = infinity
1000000 * infinity = infinity

 

[Firedragon]

Now that I've seen the picture of the Prius, I see that the term 'flat floor' is interpreted differently by us. There seems to be a distinction between these two meanings:

1) Literally a flat floor; flat plates cover the underside of the car. There are no splitters, diffusers or other geometric additions at all. The effect compared to a 'standard car' with bits and bobs 'sticking around' are this, like some people rightfully have said:

- Drag is decreased.
- Generally no downforce is generated.

See this graph (taken from Katz, Aerodynamics of race cars, http://strangeholiday.com/oops/stuff/annurev.fluid.38.050304.092016.pdf, page 50) where downforce (- C_l) and drag (C_d) are plotted against the ride height of a race car. The light blue line named 'plate' is the one mentioning a literally flat floor.


This is streamlining the car and some have interpreted that GT6 incorporates this, but because there is no downforce gain, this is not right type of 'flat floor'.

2) The second interpretation of 'flat floor' is what I first understood from reading the first few posts, where downforce is mentioned by a few members. This is of course talking about 'GT6's flat floor' and the only way of introducing a significant amount of downforce is by adding at least an air-accelerating device, like a diffuser at the back*. Maybe even other advanced aids like the vortex generators (VG) mentioned in the image above.

*Accelerating air through the first, flat part because there the flow area is narrower than at the diffuser, where air gets decelerated (Venturi). In that sense, a diffuser is there to substantially increase the downforce-generating efficiency of the 'literally flat floor'.

But whatever is added to the flat floor to create a 'GT6 flat floor' is not important, only the notion that the GT6 version does produce downforce and that this can only come from these additions like a diffuser or vortex generators.

This is more what GT6's flat floor can be interpreted like, with at least a diffuser at the back:

See also the first image, but now look at the other three lines, which represent a 'flat floor + air-accelerating addition'.
Also, this is from the report I mentioned, where the effect of an added diffuser is shown (drag and downforce plotted against diffuser angle):



From the images, it can be seen that the production of downforce always comes at a price of drag, well generally spoken.......except for the case of a very low diffuser angle. Because then, the situation is slightly different:

2.1) Now what this picture unfortunately doesn't show, is a diffuser with an even shallower angle of less than 5 degrees. In that case, the diffuser's effect would be so small that there is (almost) no downforce generated and then we almost have the 'literally flat floor' again. This is the case with the Nissan Leaf, where the diffuser is so shallow that it doesn't create extra drag nor downforce (http://www.autocar.co.uk/car-review/nissan/leaf/design). It does at the same time benefit greatly from the reduced drag of the 'literally flat floor' part of the undertray. The only desired effect of the diffuser part is there to match the outgoing air velocity with that of the free-stream velocity, reducing vortices behind the car and therefore actually reducing drag. This shows again how complicated the subject is, because in the case of the Nissan, a 'literally flat floor + very shallow diffuser' creates even less drag than purely a 'literally flat floor'.

The most important thing I want to give you is this: the subject of aerodynamics can't be simplified in a way that 'parameter x' is proportional to 'parameter y' (like saying a flat floor always creates more/less drag), because it fully depends on the actual geometry.

But back to the main question, the effects of GT6's flat floor should be as follows (flat floor + diffuser):

- Drag is increased
- Downforce is generated

The downforce comes from a diffuser or VGs or whatever, but it almost always comes at the price of drag. Since GT6's flat floor does produce a significant amount of downforce, I have always assumed that everyone was talking about this and all of my arguments for 'drag increases with increasing downforce' is true for GT6's type of flat floor.

Now what is untrue, is this: a 'flat floor' generates downforce and at the same reduces drag. The literally flat floor reduces drag, but generates lift/is neutral, while the flat floor + diffuser/any other aid does generate downforce, but at the cost of adding drag.

I hope stuff is more clear now.

 

[nasanu]

Great, so now you're resorting to being an arse instead of addressing the point.

No, there was a point there. You just haven't grasped it. I'll give you a hint then, add paradox to your name.

There certainly is. You could start with what is the maximum speed for an object with mass.

Then you could explain why you think mass makes a vehicle ultimately more draggy.

You've expounded a hypothesis that is quite at odds with current scientific theory, namely that objects with mass have a top speed that is dependent to some extent on their mass. Any time you'd like to explain that using an actual example, where the variation in top speed isn't caused by increased drag or some other agency, that would be super.

Now you are just making stuff up. But I guess that is the job description of a philosopher.

Did you watch the video, the R34 with diffuser and without are tested at Tsukuba. The R34 vs R33 was compared at gymkhana track. Akihiko-san noted about the braking stability, less oversteer and quicker times on the car with diffuser.

I have most of 99 Best Motoring videos, including Altezza review, S2000 review and GTR Battle.

Did YOU watch it? There is nothing on the video that matches what you are saying from what I have seen. All three parts are on youtube, can you find the bit you are talking about?

There is more than one source of drag in fluid flows. Adding dimples increases one type of drag, but "stabilises" the flow (by causing a turbulent "boundary layer"), reducing another type of drag. That second type of drag dominates for golf balls, so there is a net improvement.

Doing the same on a car's underbody will only increase drag, because it is so far above that regime change already that the dominant drag type is the one caused by the dimples, because there is already a turbulent boundary layer. You can't take a special case and apply it generally.

In the general case, making something "less smooth", for typical length scales, will increase drag.

Great paragraphs. None of them related to you saying making something more aerodynamic increases drag though. Care to take another shot at it where you actually address what I said without trying to redefine drag?

 

[Imari]

No, there was a point there. You just haven't grasped it. I'll give you a hint then, add paradox to your name.

I'm aware of Zeno's paradox. Or at least the one of halving halves that I assume you're referring to. Close, but it doesn't apply.

The speed limit for physical objects is the speed of light. They cannot go the speed of light, but if you name any speed less than the speed of light, they can go faster than it.

It's very similar to the 0.9 recurring = 1 argument. There is no infinitesimal that will fit between the actual reachable speed of an object with mass, and the speed of light.

Now you are just making stuff up. But I guess that is the job description of a philosopher.

Now you're just being insulting.

How about you stop being gnomic for two seconds and explain your point in clear English. I'm telling you what I understand your point to be. If I'm wrong, and it wouldn't be hard given the amount of space you dedicate to taking cheap shots rather than explaining yourself, then correct me.

If you make a blanket statement that mass does not effect top speed then it should go for all cases. Don't cry when someone points out where your statement is very clearly incorrect.

I took this to mean that you think that mass does affect top speed in all cases. Am I misunderstanding, and if so, how?

The simple truth is that if something has mass then it can not by law reach the absolute speed limit, but something without mass can. Therefor it is blindingly obvious that mass impacts on top speed.

This also seems to be indicating that you think the mass of an object is directly linked to it's top speed. You even spell it out in nearly as many words. What am I missing?

If mass affects top speed, how does it do so? What is the mechanism we're looking at here?

Bring it back to the real world situation I outlined above if you like. You have two otherwise identical cars at Bonneville, but one is substantially heavier than the other. Both have more than enough room to reach their aerodynamically limited top speeds. Does the heavier one go faster or slower, and why?

As I've said before, I think they both reach the same top speed, although the heavy one will require more distance to do so. If you disagree, I'd like to know your reasoning instead of you jerking me around with snappy one liners. If I'm wrong, I'd like to learn what is correct so that I can avoid making the same mistake again.

 

[Firedragon]

You guys are both right: mass does impact top speed...but at the same time doesn't.

Just read one of my old posts:
https://www.gtplanet.net/forum/threads/gt6-screenshots-videos.282212/page-235#post-9007830

So yes, strictly mass generates rolling resistance and limits top speed. But the relative magnitude of that is also pretty insignificant compared to the air resistance (1:20 or so), so in that way it doesn't limit top speed. It's all about interpretation.

 

[Johnnypenso]

1) Literally a flat floor; flat plates cover the underside of the car. There are no splitters, diffusers or other geometric additions at all. The effect compared to a 'standard car' with bits and bobs 'sticking around' are this, like some people rightfully have said:

- Drag is decreased.
- Generally no downforce is generated.

This is more what GT6's flat floor can be interpreted like, with at least a diffuser at the back:

My point all along has been that this "interpretation" of the GT6 flat floor does not jibe with what we actually see which is this:

This is the only clear, well lit picture I could find of a car upside down with a flat floor, that wasn't a race car. I'm sure there are others and maybe someone can post a couple, but I see no diffuser there. It's modelled as a simple flat floor.

 

[Imari]

You guys are both right: mass does impact top speed...but at the same time doesn't.

Just read one of my old posts:
https://www.gtplanet.net/forum/threads/gt6-screenshots-videos.282212/page-235#post-9007830

So yes, strictly mass generates rolling resistance and limits top speed. But the relative magnitude of that is also pretty insignificant compared to the air resistance (1:20 or so), so in that way it doesn't limit top speed. It's all about interpretation.

This is what I've been trying to point out.

Any variation in top speed is caused by effects at least one step downstream from the mass, not the mass itself. Rolling resistance is not purely a function of mass, it is affected by many other factors as well. Mass directly affects things like acceleration, but at best indirectly affects top speed. And were rolling resistance and other factors to be held constant, I would expect mass to have no effect on ultimate top speed at all.

And as you say, the magnitude of the effect is not large. Pretty cool that you actually calculated it out though.

 

[Firedragon]

My point all along has been that this "interpretation" of the GT6 flat floor does not jibe with what we actually see which is this:

This is the only clear, well lit picture I could find of a car upside down with a flat floor, that wasn't a race car. I'm sure there are others and maybe someone can post a couple, but I see no diffuser there. It's modelled as a simple flat floor.

Now you're just trying to find a way to prove that PD is wrong.

A flat floor like in your picture would give no downforce and reduce drag, yes, so PD is wrong in a literal sense. Although my guesstimation is that the drag reduction is not all that worthwhile at all, simply because macrosopically a car is already pretty flat at the bottom. In a game where the aerodynamics are simplified to a certain degree, I doubt that modeling this type of a flat floor would be significant in both effect and usefulness.

But as far as I'm concerned and aware, the 'GT6 flat floor' option is all about downforce and that will come at the cost of extra drag. The graphic representation and modeling may be wrong and that's not very relevant, but the relation between downforce and drag is correct.

It's either:
1) slightly lower drag and no downforce
2) more downforce and more drag

The second option is chosen and makes more sense, in my opinion. Furthermore because incorporating the drag reduction of the first option is far more detailed than the real-time CFD in GT6 can handle, so there's no point in giving that option.

So in a true sense, you're correct in saying that the modeling does not correspond real-life effects, but then I'd like to argue that only the second effect is relevant to the game from a 'racing game' perspective. Physically, there is a diffuser modeled at all times (I assume) while it doesn't have to be visible in the game. Technically it is wrong because it doesn't always match the underside of the car, but I personally welcome the game's one-size-fits-all, uniform effect on aerodynamics whenever the flat floor option is chosen. Having to flip a car everytime when installing the flat floor option to determine what the effects should be isn't really convenient.

 

[Johnnypenso]

So in a true sense, you're correct in saying that the modeling does not correspond real-life effects, but then I'd like to argue that only the second effect is relevant to the game from a 'racing game' perspective. Physically, there is a diffuser modeled at all times (I assume) while it doesn't have to be visible in the game.

We already know they chose more downforce and more drag, one only needs to install a flat floor and drive the car. I think PD modeling it wrong is relevant however, because it adds to the litany of shortcuts or mistakes they've made either in the physics of the game or it's visual representation. The diffuser is behaving differently than it should given it's visual representation. Ride height is the same, camber is the same, there are several parts of the game that are modeled visually correct and work incorrectly and vice versa. These things should be corrected for GT7 and we need to make PD aware that we know how these things are supposed to work and what they are supposed to look like and that we won't settle for half 🤬 anymore

 

[Firedragon]

We already know they chose more downforce and more drag, one only needs to install a flat floor and drive the car. I think PD modeling it wrong is relevant however, because it adds to the litany of shortcuts or mistakes they've made either in the physics of the game or it's visual representation. The diffuser is behaving differently than it should given it's visual representation. Ride height is the same, camber is the same, there are several parts of the game that are modeled visually correct and work incorrectly and vice versa. These things should be corrected for GT7 and we need to make PD aware that we know how these things are supposed to work and what they are supposed to look like and that we won't settle for half 🤬 anymore

Oh yes, certainly, since I believe that the physics modeling of most current 'simulators' only differ in the details rather than in general behaviour. The difference can more or less only be made in these little details.

In this particular case though, I'm not sure if it's worthwhile to have this detail corrected. Graphically modeling a diffuser would be a way to correct this, but I think that's not worth the time, since it only makes a difference in the appearance. Maybe in the future it's useful to model the diffuser, when the real-time CFD calculations are sophisticated enough to distinct between several diffuser shapes/angles.

On the other hand, they could simply reset a few numbers: remove downforce and slightly alter the coefficient of drag. But knowing that the real-time CFD can't be all that detailed, the impact on the overall car's behaviour would be very small at best, I reckon. It's easily doable, but then GT6 isn't really meant to be a hardcore simulator.

So from a practical point of view, I think this issue isn't that important at all. Stuff like the ride height and especially camber are more of an issue, I think. Although those faults can be significant, I still regard the physics modeling at this point pretty highly rather than half-assed, since overall behaviour (weight transfer, body movement characteristics) are pretty nice for a semi-casual/sim like this.

 

[nasanu]

This also seems to be indicating that you think the mass of an object is directly linked to it's top speed. You even spell it out in nearly as many words. What am I missing?

You are missing that simply having mass puts a limit on speed. This is a law of physics and nothing you can talk your way around. Sure is an absurdly high limit, but a limit. Why can't you accept that? Anyway I tire of this. Chose to believe what you will.