Will you fix the incorrect top speed physics?

Latest Patch: 1.14 - sadly, still not fixed. Shame on you PD !

 

I think this is to do with the downforce modelling, more than anything else.

Cars with added downforce have restricted top speeds, you can tell there's forces stopping them from going faster.

No downforce is different, it's like there's nothing stopping the car from going faster besides the power/transmission.

It should not be this way, every car should have a certain amount of natural downforce, even if it's minimal.

 

@Streeto that's sort of right. Theoretically any car's top speed is only limited by how long the gears are and the power to weight ratio. If a car has a static mass and the motor can overcome that mass the vehicle will accelerate until there are no more gears. Downforce essentially adds weight to the car as the car goes faster so if a car has no other outside forces acting on it will accelerate until it runs out of gears or the weight of the vehicle is so large due to the downforce that the car's motor will not be able to overcome the added weight. In the real world every car has outside forces acting on it; things like wind resistance, wake turbulence, negative downforce (or lift) at high speeds in the case of most road cars, etc. All of which add the equation and would need to be factored in to generate a realistic top speed for any particular vehicle.

I think the problem with GT6 is that they don't model fluid dynamics very well...or rather at all. Modeling something like grip, downforce and suspension travel (all be it complex) is linear and relatively simple to do compared to the complex mechanics of air traveling into, over, under and around multiple different surfaces and the turbulence caused in the wake of all of that. There is also a vacuum effect that can occur due to turbulence behind a vehicle which causes resistance.

So in reality a car can actually have negative downforce at certain speeds and still have a top speed. It has more to do with resistance than it does true downforce.

 

BTW, I did some direct comparisons with GT5 (same track, not SSRX, same car), doing standing start accelerations, comparing times and speeds at the same track points.

The difference becomes noticable above 125mph / 200 kph (in acceleration) and with it, the top speed at the end of the straight is higher as well.

Using stock, road cars, like Enzo.

I should test with race cars some day...it will be interesting to compare.

 

The higher you go in top speeds the more overwhelming wind resistance is to all other factors. I would think that by simply marrying drag coefficients to known real world data should be enough to be reasonably accurate. They were more accurate with GT5 so something went amiss with GT6. PC sims do this stuff quite well operating on budgets that are a tiny sliver of GT's so it's not like rocket surgery to get this right. Having top speeds off by 50+ km/h in a so-called "driving simulator" is ludicrous.

 

Could not agree more

 

Amazing thread! Thank you OP!

 

I have updated first post with more data about acceleration from high speed. Because of Motec Data export availability we can test acceleration quite accurately.

 

Reposted from the Motec Thread:

These results are even more startling when you pull out just the error portion, that is, how much faster each car is from 200-300km/h, real life vs. game.

LFA 200-300 km/h
Real - 38.6s
Game - 15.1s
That's less than half the time in game to go from 200-300 km/h!


Mercedes SLS AMG 200-300 km/h
Real - 30.5s
Game - 16.7s
Only slightly more than half the time.

McLaren MP4 12C
Real - 21.3s
Game - 12.6s
Again, only slightly more than half the time.

I knew it was off but I didn't know it was off by that much!! I wonder when the two really start to separate. It might be 210-250km/h depending on the car before the game car really takes off. Holy arcade physics Batman!

 

Knowing that air resistance is a geometric progression, to be able to achieve 400 km/h + instead of 360km/h (as per Enzo example), you need A LOT more power *. As such, this 'invisible power' gives a lot of advantage in acceleration as well....

Anyway, the first time I saw that stock SL55AMG does 360+ kph or E60 M5 - 350+, I was like 'wtf'..this is waaay off. Crazy.

* In my estimated guess, with Enzo body aerodynamics, you would need 1200+ hp or more instead of 600hp. That's how much of a boost this bug delivers

Also I think the point of miscalculation happens somewhere around 160-180km/h and upwards.. And above 220-230 you really start to feel the difference (between GT5 / Real Life and GT6)

 

It's definitely the fluid dynamics. Drag isn't a geometric progression, it's quite complicated. IRL there are factors such as "seperation" which is where much of the drag comes from at higher speed. By using drag data from low speeds and simply scaling it up to higher speeds a lot of information is missed.

 

Not going into details, it is something more similar to geometric progression, meaning that to go from 350 to 400km/h you need much more HP than from 250 to 300 km/h. I.e. it's not linear progression. That was my point. So those differences between correct (GT5) and incorrect (GT6) implementation are actually huge from the "power gain" point of view

 

Ok I have made one interesting test.

Question: How much more HP you need to make GT5 car achieve the same top speed as stock GT6 car?

Answer:




Actually I could not get to 410 with GT5 because I can't upgrade car engine any more Based on estimated calculation I would need about 910-920 HP for GT5 Enzo. However you can see the general idea

 

That's like a logarithmic progression, right?

 

That's like geometric progression

For example, if you increase speed 2 times, then drag force (resistance) will increase 4 times, so:

36 Kph -> 18 N
72 Kph -> 72 N
144 Kph -> 288 N
288 Kph -> 1152 N
576 Kph -> 4608 N

 

I know I'm wasting my breath in this thread so I'll state this as a possibility only, but the formulas for Aero are pretty simple, and there is no reason to have one that is not consistent across the board as I see it. Where as, for example, the tire model may (assuming Pacejka), have mathematical limits imposed and is designed to alter the "simulation" physics to get the equation to work, and so might cause issues with longitudinal slip when big numbers are involved... it was JohnnyP that questioned the over-rotation indicated in the Motec software thread... but looking at real world Motec data it's not uncommon for over-rotation to occur at speed. Perhaps the game is not allowing for enough over-rotation of the wheels thanks to overly grippy tyres.. a possibility that is also suggested by lower top speeds on comfort tyres.

Unlike the aero, which is a relatively simple calculation (assuming constants for Air Density), the Pacejka tyre model is waaaaay harder for any of us to double check. In the Motec thread I showed my graph for the Veyron which also includes Air resistance, and power required to overcome air resistance on a top speed run... it's pretty easy to do. On this run, it showed that in simple terms, the Veyron has enough power to overcome it's drag even at it's in game top speed. So another question worth asking is, if it's not just Aero limited, what are the other effects that could give it it's acceleration curve, and how do you know they are modelled correctly too?

*Plus lets not forget you're aiming for top speeds in environments not replicated in the game.

 

If it was the overly sticky tires causing this top speed issue, dropping down 1 or 2 tire grades should fix it but that isn't the case so there must be other factors at work. On the issue of over rotation I also think it's a little too simplistic to just say, "real cars over rotate and so does GT". It would be nice to know how much cars over rotate in real life and compare it to GT. I had the math worked out for GT but didn't find any hard numbers from real world data to compare it to. `

 

I have managed to 'break in' the GT5 Enzo and squeez more power from the engine, so I matched the GT6 speed with 'extra' 280 HP

 

I don't understand what you mean by "break in" the engine on GT5. Are you saying that now the two games top speeds DO match?

 

No. "Break-in the GT5 Enzo engine (motor)" means I bought a new Enzo and with all tuning upgrades I got 'only' 900 HP. But after 500 km of B-spec driving on Indy, engine power increased to 922 HP (after another oil change).

That's the 'feature' of the game, the more you drive your new car, the more power it will have until certain point when driving more will force power to decrease.

Thus with 'break-in' or 'running-in' I got enough power to match GT6 stock speed and calculate theoretical HP difference.

So 640 HP Enzo in GT6 has the same top speed as 920 HP Enzo in GT5

 

Wow! That is ridiculous!! And thank you for explaining the engine "break-in period" for me. I never played GT5 and I was unaware of that...

 

Question for testing:

Has this happened on ALL tracks, or just one?

 

Unrealistic acceleration and top speeds were noticed and confirmed on all (randomly selected) tracks, not just SSRX. However further tests were done on this track because of the convenience.

So to answer - no, it's not because of the track.

 

I had someone ask the following question, and it made me think, so I want to pose it here:

If the physics are wrong in the game, does it give any driver of any race in game an advantage?

Think about this. If everything is the same for everyone, then no one will be better unless they drive better.

How does an odd top speed affect this?

 

No. You are correct. Since everything is the same for everybody, it most certainly comes down to one person having to drive "better" than the other if he wants to win. That's not the point of the OP's argument, however. Gran Turismo touts itself as the "Real Driving Simulator" and therefore the way cars behave should be somewhat realistic. Otherwise, we can all just play Outrun! There are plenty of video games that can provide plenty of enjoyment without accurate physics and super accurate car models, etc... Gran Turismo is supposed to be above that - based on the creator's own words! Therefore, I would expect the cars in Gran Turismo to only achieve speeds similar to the real world counterparts.

 

If you compare times GT6 vs GT6 then there is no advantage. Everyone has the same physics engine.

The issue appears when you, for example, want to do some time-trials, compare car performance in game vs real life and when you try to apply some knowledge from the real life to the game (for example tuning, especially aero tuning, etc.)

This is about 'simulation' part of the game (not competition), and how accurately the reality is simulated. There are a lot of people who want reality to be simulated (they can't drive all those cars IRL but they can experience reality in the game. At least as much as possible). And it's part of the fun.

So when reality is simulated incorrectly - no fun to do tests and comparisons and playing with the tuning, etc.

 

Well, from THAT angle, I can understand. But, since I don't do compare time trials, it doesn't bother me....

 

You mean something like, "if the physics are wrong, does it give [insert ethnicity here] in game an advantage?"

All joking aside, top speed physics don't matter to you and that's ok of course, you're entitled to enjoy the game as is, as is everyone else. But some players want a higher level of realism and immersion and Kaz to be true to his word and have GT actually feel like the "simulator" it claims to be. I think quite a number of the hardcore sim drivers are coming to the realization that GT only pays lipservice to the word "simulator" and really has no intention other than to cover the broad strokes of simulation. Letting the top speed physics be so out of whack for an entire year, when they did get them correct in GT5 just fans those flames a little more, on top of the other myriad assortment of issues with the game physics. If one thinks of it as a casual game then who cares right? If one actually wants to recreate reality to the best of their ability, you really have to suspend disbelief in GT to do so.

 

Sure. There are gamers who like need for speed nonsence (a.k.a arcade stuff) and there are game developers who build games just for them. That's all fine. But then there are people who like real life and simulation of the real life. Different players - different needs.

I'd say there are 3 components in GT game: simulation, competition, fun factor. So if one of those components is clearly flawed, it should be fixed.