GT6 Top Speeds Are Not Realistic, Please Fix PD!

[TonyJZX]

Wont be fixed unless you think GT7 and a new console is a 'fix'... maybe.

Been playing these sims on console and PC for years and there's been instances where people love their overpowered, 300mph+ street cars... and perhaps made worse by the VGT "2035" SRT and Chapparal nonsense...

We want realism mostly but we also want a slice of the ridiculous. What other reason is there for Route X and "Like the Wind"?

I expect this kind of hyperbole and I dont expect them to change, nor do I care.

Its GT by PD. Even Forza has it to some degree.

 

[BrodieBoi94]

How do you explain GT5 was more accurate than GT6? Is the game devolving?

Could be that the aerodynamics physics devolved, while other physics like suspension, and tires evolved... it seems like suspension physics were definitely a main focus for this game.

Or aerodynamic resistance may have taken a hit while overall aerodynamics like downforce and such improved...

Considering that they supposedly redid/revamped the physics engine maybe they did some things better this time and some worse (like top speed/wind resistance).

I have been able to feel downforce difference much better than I remember being able to in GT5 at least.

 

[Voodoovaj]

Wont be fixed unless you think GT7 and a new console is a 'fix'... maybe.

Been playing these sims on console and PC for years and there's been instances where people love their overpowered, 300mph+ street cars... and perhaps made worse by the VGT "2035" SRT and Chapparal nonsense...

We want realism mostly but we also want a slice of the ridiculous. What other reason is there for Route X and "Like the Wind"?

I expect this kind of hyperbole and I dont expect them to change, nor do I care.

Its GT by PD. Even Forza has it to some degree.

Yup - All the tires are tuned to be ridiculously grippy and the stickiest of them all is the most popular. Let's face it, very, VERY few people are actually able to drive Senna's Lotus at anywhere near Senna's lap times. I don't think even the best in the world at the moment could really do it.

Keep in mind, these games are focus tested and in a focus test, the opinions of that group are worth far more than the opinions of people that want uber-realism. You go find a series that races 550+ on comfort tires and I'll retract my statement.

As far as the aero goes, to me it seems tuned to the perception of reality. 400pp cars are hitting 150 mph/240kph, and still people tend to think that they're boring and slow. They should be topping out at maybe 130mph/210kph and THAT is generous. a 500pp RX7 SHOULD really top out at about 260kph not 320+ and it should take longer for it to get there. And you know Ferrari HAD to have made a deal to get more out of their cars,and I'm sure others have as well. That's why some cars are accurate and others are WAY over performing.

Maybe they can change the "real" slipstream option to be a "real aero" option.

 

[TonyJZX]

I think its tradition now that PD will have a "Like the Wind Part III" challenge in GT7. There is a place for those 400mph+ things but on the other hand we will still see stuff like 500pp 5 lap Dristelen races where the cars barely reach 140mph.

I kinda think that Forza Mainstream has turned into quite a serious and dry sim and that GT has its moments of lightness and sillyness and thats these sorts of 1,200hp+ madness cars. I like that. I mean GT shouldnt be so dry.

I disappointed that Forza has gone so stale with 5 and hope they will lighten up.

 

[Voodoovaj]

Could be that the aerodynamics physics devolved, while other physics like suspension, and tires evolved... it seems like suspension physics were definitely a main focus for this game.

Or aerodynamic resistance may have taken a hit while overall aerodynamics like downforce and such improved...

Considering that they supposedly redid/revamped the physics engine maybe they did some things better this time and some worse (like top speed/wind resistance).

I have been able to feel downforce difference much better than I remember being able to in GT5 at least.

Also, posted tops speed in real life are a combination of estimates, ideal conditions, speed limiters, and tire limitations.

GT has no such limitations. Take pretty much any unlimited car and test it's top speed. Change the road surface, air temperature, altitude, etc, and the top speed will be different.

Real cars come from the factory with tires that are rated for road use (often, R, S, H, V, Z). The engine might be able to push the car into an H or even a V speed range, but the tires are only R or S, so the car is either limited to the tire's speed or they simply list the stop speed accordingly in their "estimated top speed". So, basically, take a printed top speed with a grain of salt. GT6's speeds are a bit on the high side, but I DO NOT IN ANY WAY want them limited to match reality. That would be a frustrating game top play.

 

[Johnnypenso]

Also, posted tops speed in real life are a combination of estimates, ideal conditions, speed limiters, and tire limitations.

GT has no such limitations. Take pretty much any unlimited car and test it's top speed. Change the road surface, air temperature, altitude, etc, and the top speed will be different.

Real cars come from the factory with tires that are rated for road use (often, R, S, H, V, Z). The engine might be able to push the car into an H or even a V speed range, but the tires are only R or S, so the car is either limited to the tire's speed or they simply list the stop speed accordingly in their "estimated top speed". So, basically, take a printed top speed with a grain of salt. GT6's speeds are a bit on the high side, but I DO NOT IN ANY WAY want them limited to match reality. That would be a frustrating game top play.

Which means nothing given the top speeds and rate of acceleration at high speed changed from GT5 to GT6. Things appeared to be more correct in GT5 and took a turn towards the arcade for GT6, which follows a similar trend for the AI and offline portion of the game, license tests etc.

 

[eran0004]

Which means nothing given the top speeds and rate of acceleration at high speed changed from GT5 to GT6. Things appeared to be more correct in GT5 and took a turn towards the arcade for GT6, which follows a similar trend for the AI and offline portion of the game, license tests etc.

It did not take a turn towards arcade

They implemented a new way of calculating the aerodynamics, that's all. There is a flaw in the simulation, but that doesn't make it arcade.

 

[Johnnypenso]

It did not take a turn towards arcade

They implemented a new way of calculating the aerodynamics, that's all. There is a flaw in the simulation, but that doesn't make it arcade.

I didn't say it made it arcade, I said it turned towards arcade, the former is a destination, the latter a direction. Higher top speeds and unrealistic high speed acceleration are hallmarks of aracde racers and GT clearly moved in that direction with GT6, as did the entire offline portion of the game with it's dramatically uncompetitive AI. Seems clear to me that this was a conscious choice on their part and is not an unforseen byproduct of a change in the aero model.

 

[eran0004]

I didn't say it made it arcade, I said it turned towards arcade, the former is a destination, the latter a direction. Higher top speeds and unrealistic high speed acceleration are hallmarks of aracde racers and GT clearly moved in that direction with GT6, as did the entire offline portion of the game with it's dramatically uncompetitive AI. Seems clear to me that this was a conscious choice on their part and is not an unforseen byproduct of a change in the aero model.

Why am I not surprised. And how many bugs in Project Cars do you think were intentional?

Higher top speeds and unrealistic high speed acceleration indicates that the force of aerodynamic drag is too low, nothing else.

 

[Johnnypenso]

Why am I not surprised. And how many bugs in Project Cars do you think were intentional?

Higher top speeds and unrealistic high speed acceleration indicates that the force of aerodynamic drag is too low, nothing else.

So it's an accident that it was more or less correct in GT5 but not in GT6? Someone transposed a number, they tested it for months and months and nobody noticed? Launched the game, been on the shelves for 18 months and no one noticed top speeds are up by 10%? That's your theory?

 

[Tornado]

Real Life numbers were taken from here:

5.6 seconds seems astonishingly slow. Aston themselves claimed 4.5 for 60, for what it's worth. There's surprisingly a dearth of tests for the original Vanquish, and I can't directly comment on the 0-200 or 0-300 tests, but Car and Driver's 0-60 test for the original netted a 4.4 second run for the Vanquish and a gearshift (which was an SMG regardless) doesn't come into play because first ends just before 60 anyway. Automobile Magazine did a test that basically was exactly like that one (but with a 911 Turbo instead of a GT2 and the 575M substituted for the 550), but the version of it that they have on the website doesn't have the test data. I'll have to see if I can dig out that issue.

 

[YZF]

I'm not an expert, and I don't know many equations about physics and such but I have a theory.

We all know the games can't perfectly replicate natural conditions, there will be imperfections.

PD has an engine for each element needed for a racing game(just stating the foundation).

With that said whatever their aerodynamics simulation engine allows is what they go with.

They don't put a code (or whatever) in place to make the cars go a specific speed but instead let the A.S.E (Aerodynamics Simulation Engine) be the sole influence on the cars, so that they really can say the game is a simulating.

They haven't got it down pat yet and have to continue working on their formula to get the most realistic results, therefore we have innacuracies.

Just a summary of an average joe's theory, feel free to debate.

You are wrong

 

[YZF]

GT6's speeds are a bit on the high side, but I DO NOT IN ANY WAY want them limited to match reality. That would be a frustrating game top play.

A bit? Look at this and tell me that the difference expressed as engine power increase, is 'a bit':

 

[eran0004]

So it's an accident that it was more or less correct in GT5 but not in GT6? Someone transposed a number, they tested it for months and months and nobody noticed? Launched the game, been on the shelves for 18 months and no one noticed top speeds are up by 10%? That's your theory?

No, they may very well have noticed. It may just be a hard problem to correct. Nobody "transposed a number", they implemented a whole new system of dealing with aerodynamics, it's now being calculated using computational fluid dynamics.

Top speeds are not up by 10% across the board. It's individual for each car. Based on YZF's comparisons drag is down by 25 - 35%.

 

[YZF]

5.6 seconds seems astonishingly slow. Aston themselves claimed 4.5 for 60, for what it's worth.

The 0-100km/h time ,for the first version of Vanquish, is 4.8sec... In this test it is 0.8sec slower...well maybe during the test they had issues with traction or shifting and it was not as perfect as manufacturer claims...

In any case, 0-100 acceleraton is not so much relevant here, as the main discrepancy is above 200km/h

 

[BrodieBoi94]

You are wrong

Explain.
Edit: I'm here to learn, so throw some knowledge my way if you can. "You are wrong" is not a valid answer.

 

[YZF]

Explain.
Edit: I'm here to learn, so throw some knowledge my way if you can. "You are wrong" is not a valid answer.

Yes, you are right, this is not 'proper' answer...but lets just say that I don't want to say more at the moment, I'll just say that 'there was a mistake made'. Human error. That's why we have this flaw. It was not intentional

And at the same time, if you look at GT5 and GT4, they all have proper top speed physics. Thus 'Aerodynamics Simulation Engine' is a code too...code which is created by typing

 

[BrodieBoi94]

Yes, you are right, this is not 'proper' answer...but lets just say that I don't want to say more at the moment, I'll just say that 'there was a mistake made'. Human error. That's why we have this flaw. It was not intentional

And at the same time, if you look at GT5 and GT4, they all have proper top speed physics. Thus 'Aerodynamics Simulation Engine' is a code too...code which is created by typing

I won't bug you for a more defined answer.

But what you replied gives me a better understanding.

 

[Neddo]

I think that speeds are faster because this game feels slow anyways

 

[YZF]

I think that speeds are faster because this game feels slow anyways

Did you try to drive TX5G-whatever ?

 

[Neddo]

Did you try to drive TX5G-whatever ?

No. But people who can't afford it should feel speed too.

Also has anyone tested Cerbera Speed 12?

 

[Exorcet]

No, they may very well have noticed. It may just be a hard problem to correct. Nobody "transposed a number", they implemented a whole new system of dealing with aerodynamics, it's now being calculated using computational fluid dynamics.

Top speeds are not up by 10% across the board. It's individual for each car. Based on YZF's comparisons drag is down by 25 - 35%.

Yes, even things that do seem simple to fix can be deep problems in coding. However if I'm honest, looking at things PD has done before I can't confidently say that it's just a tough bug.

When analyzing the aero simulation, it needs to be kept in mind that it's more than just drag. Past GT aero simulation went from OK to "not even close" when the car went from straight and level to crazy angles. Maybe GT6 tried to get edge of envelope performance right and this lead to less accuracy in normal conditions (I can't say, I don't have GT6).

Explain.
Edit: I'm here to learn, so throw some knowledge my way if you can. "You are wrong" is not a valid answer.

I wouldn't say that you were wrong, but your wording was strange.

This:

"They don't put a code (or whatever) in place to make the cars go a specific speed but instead let the A.S.E (Aerodynamics Simulation Engine) be the sole influence on the cars, so that they really can say the game is a simulating."

is basically spot on. Top speed doesn't appear to be hard coded, but calculated from parameters of the car and conditions the car is experiencing. Though it's not as impressive sounding as you put it, even some arcade games might do this.

As you said, something is off in this process. Either formulas or constants, and the result is a somewhat consistent error.

 

[BrodieBoi94]

Yes, even things that do seem simple to fix can be deep problems in coding. However if I'm honest, looking at things PD has done before I can't confidently say that it's just a tough bug.

When analyzing the aero simulation, it needs to be kept in mind that it's more than just drag. Past GT aero simulation went from OK to "not even close" when the car went from straight and level to crazy angles. Maybe GT6 tried to get edge of envelope performance right and this lead to less accuracy in normal conditions (I can't say, I don't have GT6).



I wouldn't say that you were wrong, but your wording was strange.

This:

"They don't put a code (or whatever) in place to make the cars go a specific speed but instead let the A.S.E (Aerodynamics Simulation Engine) be the sole influence on the cars, so that they really can say the game is a simulating."

is basically spot on. Top speed doesn't appear to be hard coded, but calculated from parameters of the car and conditions the car is experiencing. Though it's not as impressive sounding as you put it, even some arcade games might do this.

As you said, something is off in this process. Either formulas or constants, and the result is a somewhat consistent error.

I don't know exactly how videogames work so I kind of had to get creative. LOL

But what you described mirrors my feelings/thoughts.

 

[eran0004]

Yes, even things that do seem simple to fix can be deep problems in coding. However if I'm honest, looking at things PD has done before I can't confidently say that it's just a tough bug.

When analyzing the aero simulation, it needs to be kept in mind that it's more than just drag. Past GT aero simulation went from OK to "not even close" when the car went from straight and level to crazy angles. Maybe GT6 tried to get edge of envelope performance right and this lead to less accuracy in normal conditions (I can't say, I don't have GT6).

I haven't tested the crazy angles, so I can't say. But the impact of downforce on drag seems to be greater now.

 

[Patruck GT2]

I presume this is a bit of a there ad resurrection, However I have something to say about this.
Aero physics concerning high speed acceleration are pretty simple. Don't take me wrong, they're exceptionally complex to study, but the amount of force that pushes a car backwards for its whole speed operating range can be calculated with acceptable precision with a function which only depends on the squared speed.
And for decent precision I mean maybe 5% error at 200km/h. Which si high but better than GT6. The incredibile simpleness of the formula means that PD did that on purpose, with no doubt.
Either they associated with each car a low Cx or they lowered air density, but these data are so common and easy to get there is no way you can do it wrong if you don't want to.
Which is worrying, since this means that this game took, on purpose, a turn against the realism it says it's its first goal. There is nothing wrong in a realistic game with arcade gameplay. But when arcade knocks at physics' door, that's alarming.

 

[Polsixe]

Road & Track August 2007 Standing Mile Verification

R&T magazine ran 13 cars + 1 mc on a military airstrip in 2007 to record the standing mile times and mph. As R&T noted the standing mile is a true test of power.

The results :

CAR, seconds, mph, h*w in^2, HP, kilograms
Chevrolet Corvette C6 Z51, 32.700, 154.0, 3511, 400, 1445.00
Dodge Viper SRT-10, 31.400, 159.7, 3580, 500, 1550.00
Lamborghini Murcielago, 30.900, 168.0, 3621, 580, 1827.27
Ford GT, 29.900, 171.4, 3929, 550, 1584.09
HPA Audi TT, 30.100, 172.2, 3857, 542, 1561.82
Vortech Mustang GT, 30.400, 179.0, 3929, 575, 1750.00
Ruf R Turbo, 28.600, 180.2, 3657.6, 590, 1511.36
Pontiac-Riley Mk XI Daytona Prototype, 27.800, 180.3, , 500, 988.64
Jaguar XKR Trans-Am, 28.000, 180.5, , 630, 1159.09
Ruf CTR, 28.600, 185.8, 3437, 469, 1172.73
Lola-Ford Cosworth Champ Car, 24.200, 203.3, , 800, 709.09
Saleen S7 Twin Turbo, 25.900, 205.7, 3210, 750, 1340.91
Hennessey Venom 1000 TT Viper, 25.600, 210.2, 3580, 1000, 1559.09

Now the interesting thing is nine or 10 of these have equivalent models within GT6, where weight and horsepower can be adjusted to match the actual R&T test models. Then run these through @eran0004 's standing mile course as a stand-in to the air strip.

CAR, 1 mile secs, mph, PP, Tires, w*h, HP, cd, kg
Formula Gran Turismo, 22.823, 224.0, 826, RH, 3204, 800, 0.367, 709.09
Saleen S7 '02, 25.381, 217, 612, SH, 3210, 750, 0.377, 1340.91
Viper SRT10 Coupe '06 (Hennessy), 25.072, 214.0, 632, SH, 3580, 999, 0.470, 1559.09
Ruf CTR "Yellowbird" '87, 28.567, 185.0, 532, CS, 3437, 469, 0.356, 1172.73
Lamborghini Murcielago LP640, 29.011, 184.0, 535, CS, 3621, 580, 0.424, 1827.27
Ford Mustang GT '05, 30.757, 179.0, 542, CS, 3929, 575, 0.421, 1584.00
HPA Motorsports FT565 Audi TT '07, 29.237, 174.0, 538, CS, 3857, 542, 0.440, 1561.82
SRT Viper SRT10 Coupe '06, 30.418, 174.0, 533, CS, 3580, 500, 0.438, 1550.00
Corvette Z06 (C6) '06, 31.248, 172.0, 512, CS, 3749, 400, 0.346, 1445.00

The Formula GT is getting close but not really a match for the Lola champ Car.

The Yellowbird is almost a perfect match, Ford HP-boosted Mustang and HPA Audi TT very close.

Six cars need detuning in GT6 to match the R&T speed/mph results.

C6 Corvette needs only 290 HP not 400
'06 viper needs only 375 HP not 500
Murcielago needs only 440 HP not 580
Ford GT needs only 392 HP not 550
Saleen S7 needs only 635 HP not 750
'06 Viper Hennessy clone needs only 840 HP not 1000

So GT6 cars are going much faster than actual test results with the same Horsepower. Why? When 3/9 are right on?

Wind and other weather actual conditions may have and impact. Some cars may have inflated HP for marketing. Suspect the GT6 game drag coefficients Cd may not be correct.

The two '06 Viper Coupes used are a clue. They would have the same Cd in the game and both go much faster than actual with same HP.

So GT6 is a bit off in top speeds, if this sample size is representative than about 2/3 of the in game cars have inflated speeds. Doesn't mean the PP relationship is wrong only the drag coefficients.

In above Cd is calculated from simplified formula Cd = ((1.65e7)*HP/(width in.*height in.*MPH^3). In R&T test and GT6 it was observed some of the cars are still pulling or acclerating at the 1 mile point, this formula is most accurate if top speed is at max HP.

Something to fix for the next GT S and GT7 right PD?

 

[eran0004]

this formula is most accurate if top speed is at max HP.

If you use the power limiter you get a flat power curve. Makes it easier to tell how much power you've got when you reach top speed.

 

[Johnnypenso]

Road & Track August 2007 Standing Mile Verification

R&T magazine ran 13 cars + 1 mc on a military airstrip in 2007 to record the standing mile times and mph. As R&T noted the standing mile is a true test of power.

The results :

CAR, seconds, mph, h*w in^2, HP, kilograms
Chevrolet Corvette C6 Z51, 32.700, 154.0, 3511, 400, 1445.00
Dodge Viper SRT-10, 31.400, 159.7, 3580, 500, 1550.00
Lamborghini Murcielago, 30.900, 168.0, 3621, 580, 1827.27
Ford GT, 29.900, 171.4, 3929, 550, 1584.09
HPA Audi TT, 30.100, 172.2, 3857, 542, 1561.82
Vortech Mustang GT, 30.400, 179.0, 3929, 575, 1750.00
Ruf R Turbo, 28.600, 180.2, 3657.6, 590, 1511.36
Pontiac-Riley Mk XI Daytona Prototype, 27.800, 180.3, , 500, 988.64
Jaguar XKR Trans-Am, 28.000, 180.5, , 630, 1159.09
Ruf CTR, 28.600, 185.8, 3437, 469, 1172.73
Lola-Ford Cosworth Champ Car, 24.200, 203.3, , 800, 709.09
Saleen S7 Twin Turbo, 25.900, 205.7, 3210, 750, 1340.91
Hennessey Venom 1000 TT Viper, 25.600, 210.2, 3580, 1000, 1559.09

Now the interesting thing is nine or 10 of these have equivalent models within GT6, where weight and horsepower can be adjusted to match the actual R&T test models. Then run these through @eran0004 's standing mile course as a stand-in to the air strip.

CAR, 1 mile secs, mph, PP, Tires, w*h, HP, cd, kg
Formula Gran Turismo, 22.823, 224.0, 826, RH, 3204, 800, 0.367, 709.09
Saleen S7 '02, 25.381, 217, 612, SH, 3210, 750, 0.377, 1340.91
Viper SRT10 Coupe '06 (Hennessy), 25.072, 214.0, 632, SH, 3580, 999, 0.470, 1559.09
Ruf CTR "Yellowbird" '87, 28.567, 185.0, 532, CS, 3437, 469, 0.356, 1172.73
Lamborghini Murcielago LP640, 29.011, 184.0, 535, CS, 3621, 580, 0.424, 1827.27
Ford Mustang GT '05, 30.757, 179.0, 542, CS, 3929, 575, 0.421, 1584.00
HPA Motorsports FT565 Audi TT '07, 29.237, 174.0, 538, CS, 3857, 542, 0.440, 1561.82
SRT Viper SRT10 Coupe '06, 30.418, 174.0, 533, CS, 3580, 500, 0.438, 1550.00
Corvette Z06 (C6) '06, 31.248, 172.0, 512, CS, 3749, 400, 0.346, 1445.00

The Formula GT is getting close but not really a match for the Lola champ Car.

The Yellowbird is almost a perfect match, Ford HP-boosted Mustang and HPA Audi TT very close.

Six cars need detuning in GT6 to match the R&T speed/mph results.

C6 Corvette needs only 290 HP not 400
'06 viper needs only 375 HP not 500
Murcielago needs only 440 HP not 580
Ford GT needs only 392 HP not 550
Saleen S7 needs only 635 HP not 750
'06 Viper Hennessy clone needs only 840 HP not 1000

So GT6 cars are going much faster than actual test results with the same Horsepower. Why? When 3/9 are right on?

Wind and other weather actual conditions may have and impact. Some cars may have inflated HP for marketing. Suspect the GT6 game drag coefficients Cd may not be correct.

The two '06 Viper Coupes used are a clue. They would have the same Cd in the game and both go much faster than actual with same HP.

So GT6 is a bit off in top speeds, if this sample size is representative than about 2/3 of the in game cars have inflated speeds. Doesn't mean the PP relationship is wrong only the drag coefficients.

In above Cd is calculated from simplified formula Cd = ((1.65e7)*HP/(width in.*height in.*MPH^3). In R&T test and GT6 it was observed some of the cars are still pulling or acclerating at the 1 mile point, this formula is most accurate if top speed is at max HP.

Something to fix for the next GT S and GT7 right PD?

The standing mile isn't the best indicator of the issues with top speed and aero in GT6 because, from what I've read anyway, the 0-200 km/h times seem fairly accurate. It's the 200+km/h and especially 300+km/h acceleration where things seem to get a bit wacky.

 

[Ridox2JZGTE]

There's also a difference when running for top speed at SSRX to other tracks like SSR7 and La Sarthe No Chicane ( I prefer this track as it's closes to GT5 in terms of top speed - I compared R34 GTR top speed GT5 vs GT6 here ). I recently tried to reach 234mph at La Sarthe no Chicane with 900HP Shelby Mustang ( Need for Speed movie inspired project ), using Shelby real car data, the car could not reach 230mph, on 6th gear it's just loses acceleration somewhere around 220mph. Surprisingly, go to SSRX, and the car could reach 234mph on 6th gear with ease I used Shelby Mustang gear ratios ( 3.310 rear and optional 3.730 rear )

 

[MclarenGT]

Road & Track August 2007 Standing Mile Verification

R&T magazine ran 13 cars + 1 mc on a military airstrip in 2007 to record the standing mile times and mph. As R&T noted the standing mile is a true test of power.

The results :

CAR, seconds, mph, h*w in^2, HP, kilograms
Chevrolet Corvette C6 Z51, 32.700, 154.0, 3511, 400, 1445.00
Dodge Viper SRT-10, 31.400, 159.7, 3580, 500, 1550.00
Lamborghini Murcielago, 30.900, 168.0, 3621, 580, 1827.27
Ford GT, 29.900, 171.4, 3929, 550, 1584.09
HPA Audi TT, 30.100, 172.2, 3857, 542, 1561.82
Vortech Mustang GT, 30.400, 179.0, 3929, 575, 1750.00
Ruf R Turbo, 28.600, 180.2, 3657.6, 590, 1511.36
Pontiac-Riley Mk XI Daytona Prototype, 27.800, 180.3, , 500, 988.64
Jaguar XKR Trans-Am, 28.000, 180.5, , 630, 1159.09
Ruf CTR, 28.600, 185.8, 3437, 469, 1172.73
Lola-Ford Cosworth Champ Car, 24.200, 203.3, , 800, 709.09
Saleen S7 Twin Turbo, 25.900, 205.7, 3210, 750, 1340.91
Hennessey Venom 1000 TT Viper, 25.600, 210.2, 3580, 1000, 1559.09

Now the interesting thing is nine or 10 of these have equivalent models within GT6, where weight and horsepower can be adjusted to match the actual R&T test models. Then run these through @eran0004 's standing mile course as a stand-in to the air strip.

CAR, 1 mile secs, mph, PP, Tires, w*h, HP, cd, kg
Formula Gran Turismo, 22.823, 224.0, 826, RH, 3204, 800, 0.367, 709.09
Saleen S7 '02, 25.381, 217, 612, SH, 3210, 750, 0.377, 1340.91
Viper SRT10 Coupe '06 (Hennessy), 25.072, 214.0, 632, SH, 3580, 999, 0.470, 1559.09
Ruf CTR "Yellowbird" '87, 28.567, 185.0, 532, CS, 3437, 469, 0.356, 1172.73
Lamborghini Murcielago LP640, 29.011, 184.0, 535, CS, 3621, 580, 0.424, 1827.27
Ford Mustang GT '05, 30.757, 179.0, 542, CS, 3929, 575, 0.421, 1584.00
HPA Motorsports FT565 Audi TT '07, 29.237, 174.0, 538, CS, 3857, 542, 0.440, 1561.82
SRT Viper SRT10 Coupe '06, 30.418, 174.0, 533, CS, 3580, 500, 0.438, 1550.00
Corvette Z06 (C6) '06, 31.248, 172.0, 512, CS, 3749, 400, 0.346, 1445.00

The Formula GT is getting close but not really a match for the Lola champ Car.

The Yellowbird is almost a perfect match, Ford HP-boosted Mustang and HPA Audi TT very close.

Six cars need detuning in GT6 to match the R&T speed/mph results.

C6 Corvette needs only 290 HP not 400
'06 viper needs only 375 HP not 500
Murcielago needs only 440 HP not 580
Ford GT needs only 392 HP not 550
Saleen S7 needs only 635 HP not 750
'06 Viper Hennessy clone needs only 840 HP not 1000

So GT6 cars are going much faster than actual test results with the same Horsepower. Why? When 3/9 are right on?

Wind and other weather actual conditions may have and impact. Some cars may have inflated HP for marketing. Suspect the GT6 game drag coefficients Cd may not be correct.

The two '06 Viper Coupes used are a clue. They would have the same Cd in the game and both go much faster than actual with same HP.

So GT6 is a bit off in top speeds, if this sample size is representative than about 2/3 of the in game cars have inflated speeds. Doesn't mean the PP relationship is wrong only the drag coefficients.

In above Cd is calculated from simplified formula Cd = ((1.65e7)*HP/(width in.*height in.*MPH^3). In R&T test and GT6 it was observed some of the cars are still pulling or acclerating at the 1 mile point, this formula is most accurate if top speed is at max HP.

Something to fix for the next GT S and GT7 right PD?

Road and track tests are generally much slower than other magazine tests and also the cars tested are us spec which is significantly slower than european tests.
Mclaren F1 Autocar test

• 0–60 mph: 3.2 s
• 0–100 mph: 6.3 s
• 0–125mph: 9.4 s
• 0–150 mph: 12.8 s
• 0–200 mph : 28 s
• 0–400 m : 11.1 s at 138 mph
  
• Topspeed : 240 mph

Mclaren F1 R&T test

• 0-60 mph : 3.4 s
• 0-100 mph : 7.7 s
• 0-120 mph : 10.5 s
• 0-400 m : 11.6 s @ 125 mph
• Topspeed ; 217mph

Similarly for Enzo Ferrari best 0-60mph was 3.14s R&T one was 3.3s.