Corvette C7 Test Prototype ’13 DLC Out Now!

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To reach a speed you have to accelerate until this speed. Acceleration is a matter of torque which is related directly to the way a motor delivers its output. But: for every additional 50kgs of weight a motor carries, its output is 2% lower in result. All together, to change the kinetic condition of an object you need some more power than before to push it. If this power is reduced or the mass of the object increases, the speed will decrease. After all, when elevation comes, which factor is that decreases the speed? The weight applied to the car is increased depending to the angle of elevation. It is very simple guys.
 
So tell me,

1200hp Bugatti Veyron SS, 1900kg
1200hp SSC Aero, 1200kg...

Last time I checked, the SSC Aero wasnt faster?


And if we want to play the elevation game, the higher you go, the faster you can travel due to reduced air resistance.
 
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Nismo34
So tell me,

1200hp Bugatti Veyron SS, 1900kg
1200hp SSC Aero, 1200kg...

Last time I checked, the SSC Aero wasnt faster?


And if we want to play the elevation game, the higher you go, the faster you can travel due to reduced air resistance.
Click to expand...

For the above car comparison I have already said about the other factors that contribute to the top speed. And Cw was higher than weight in importance. 👍

By the way here it says about SSC Aero that the projected top speed is 273mph=440kph. We know Veyron SS reaches 258mph=415kph. Isn't there a huge difference which shows the considerable effect of their difference in weight? You might say that they haven't proved their saying yet but they are sure of it. Laws of physics are consistant in these levels.

Updated: Now I saw that Veyron SS reached 267mph=431kph. The difference exists although smaller.

Elevation angle is the one that I talked in my topic not elevation only. Sorry if I was not clear enough in this. :guilty: I hope you re-read my previous post. :)
 
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Rotorist
It is very simple guys.
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If it's so very simple, why have you changed your definition so many times?


First it was "this car is too fast because no other car has gone 200 with less than 500HP." After 4 such cars were pointed out that did, it changed to "no other car as heavy as the Corvette has gone 200 with less than 500HP." After a 5th was pointed out that was almost half a ton heavier than the Corvette, now it's "no car as heavy as the Corvette has gone 200 with less than 500HP unless it had lots more torque."



I also ran the numbers that you keep repeating:
Rotorist
But: for every additional 50kgs of weight a motor carries, its output is 2% lower in result.
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The original Diablo was 180 kgs heavier than the C7 is. According to this apparent formula and using the C7 as the baseline, that means it has 460 hp (with less torque).
The SL55 was 390 kg heavier than the C7 is. Depending on which HP number you use, that means it either had 427 hp or 406 hp.
The Porsche 959 weighed either 50kg less than the C7 or 22kg more, depending on whether you listen to Porsche's numbers or the numbers achieved when the car was actually tested. That means it either had 460 hp or 446 HP (with a lot less torque).



Even going by the logic you are giving for why it shouldn't, the Corvette going 200 MPH with the power and torque it has (nevermind what it has in the game after an oil change) makes perfect sense.


Rotorist
By the way here it says about SSC Aero that the projected top speed is 273mph=440kph. We know Veyron SS reaches 258mph=415kph. Isn't there a huge difference which shows the considerable effect of their difference in weight? You might say that they haven't proved their saying yet but they are sure of it. Laws of physics are consistant in these levels.

Updated: Now I saw that Veyron SS reached 267mph=431kph. The difference exists although smaller.
Click to expand...

No, the difference doesn't exist because of the weight difference:

  1. That's a claimed speed for the SSC, so it's completely irrelevant anyway.
  2. That particular car in that link with the 273 MPH claim has 100 more horsepower than the Veyron, which probably has something to do with it.
 
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It's all up to the "put the power on the road" thing... 1200hp are useless if the car don't have the grip to put it on the road. (of course combined with an excellent aerodynamic)
 
Rotorist
For the above car comparison I have already said about the other factors that contribute to the top speed. And Cw was higher than weight in importance. 👍

By the way here it says about SSC Aero that the projected top speed is 273mph=440kph. We know Veyron SS reaches 258mph=415kph. Isn't there a huge difference which shows the considerable effect of their difference in weight? You might say that they haven't proved their saying yet but they are sure of it. Laws of physics are consistant in these levels.
Click to expand...

Your logic gets thrown a bit more out of whack when we drag the Koenigsegg Agera R into the mix.

1140hp
1650kg full laden
proposed top speed? 440km/h,
same as the SSC's proposed top speed.

Cw= 0.37

SSC's Cw=0.35

Can we conclude that weight has very little to do with actual top speed?
 
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analog
Going into one direction at a constant speed (topspeed in this instance), mass doesn't play a huge role at all.
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this. mass matters more in getting the car moving = acceleration, once you're moving on a straight for instance the only thing moving the speedo up is more horsepower
 
It doesn't really surprise me, the slipstream model in GT5 is frankly awful. So many cars can reach ridiculous speeds that are not realistic, even with a slipstream.
 
The slipstream model is way out of realism. Every car in GT5 punches a hole in the air the size of an 18-wheeler, and the air just doesn't settle properly.
 
GTPorsche
The slipstream model is way out of realism. Every car in GT5 punches a hole in the air the size of an 18-wheeler, and the air just doesn't settle properly.
Click to expand...

Indeed, it also has a 'multiplier' effect so you can move from draft to draft and it increases further. Hence why so many cars can hit 300mph+ and you have the X1 going 700mph+.
 
I cannot persuade anyone I guess but the fact is that the "every 50kgs reduce the final result of output of a motor by 2%" rule is an engineers' rule. Search and find. I learned about this rule way before internet and google search was popular. Only this rule gives away enough about the importance of weight to the performance of a car. End of topic from my side.
 
I think weight has very little to do with top speed. The engine will still get to the car that speed, it will just take longer.

And grip isn't a factor in top speed runs.
 
Leave it to GTP to turn a thread from a C7 test proto to the real car to a beat-the-dead-horse argument about top speed and mass ... :rolleyes:

Unsubscribed.
 
Rotorist
I cannot persuade anyone I guess but the fact is that the "every 50kgs reduce the final result of output of a motor by 2%" rule is an engineers' rule. Search and find. I learned about this rule way before internet and google search was popular. Only this rule gives away enough about the importance of weight to the performance of a car. End of topic from my side.
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I'm an engineer and I've never heard about this rule.

As some already said, the weight of a car is quite irrelevant to a cars top speed. The power output of an engine can be recalculated to an actual force at the tire (Fw), which then is equated to the sum of various oppositely directed forces.

A simplified equation would be:

Fw = Fa + Ft + Fh

Fa = 0.5*p*cw*A*v^2

This is the main force stopping a car getting quicker, air resistance. p is the airtight, A the surface of the front of a car projected to a white wall, cw being the drag coefficient and v the actual speed...as we can see, it increases exponentially.

Two conclusions from that:

1: cw is quite irrelevant, if A is big. That's the main reason a normal saloon will have a higher top speed, than a suv with the same engine, even if the drag coefficient is the same.

2: because v increases exponentially, this force Fa gets indeed very big and is, as said before, the main reason stopping a car getting quicker...nice examples are your hand out of the window at 120 mph or the very high top speed of everything thats moving in a vacuum compared to it moving in normal air


Ft = µ*m*9.81*cos(β)

This is the the roll resistance of the tire (also very simplified) with µ being the rolling friction coefficient (something like 0.013 with a car on asphalt) and m being indeed the mass of the car. 9.81m/s^2 is the acceleration due to gravity (g).
This gets corrected by cos(β), with β being the angle of a possible slope

BUT because µ is so small you get something like 250N for a 2t saloon compared to 190N for a 1.5t hatchback on a level surface, which really is negligible compared to a few thousand caused by the air resistance.

Fh = m*9,81*cos(β)

The last main resistant force, which ONLY happens if the car is going uphill (or downhill, but then it's going on the other side of the main equation and helps you rather than being a resistance).

Now indeed the weight does make a notable difference, but again this entire part equals 0 if the road is level so TOP SPEED ON A LEVEL ROAD IS UNAFFECTED!



The weight plays a very notable difference while accelerating, as you pointed out. But it has to be said that the power output of the engine isn't affected at all, it's more a matter of an increased mass moment of inertia which than equals in a reduced driving force, from which the actual acceleration can be calculated, But then your into dynamics and, as its now past 3am where I live, i won't try in explaining this as well:sly:


There are of course many other resistances to consider, to calculate the real top speed of a car (tracking for instance) but I'd say, you should be able to get as close as 95% with this simplified version, provided you're knowing the driving force, which calculates itself from the real wheel horsepower.


By the way, I apologize if some of the technical tems are incorrect, English isn't my first language, we use logically the metrical system here (should someone be confused) and I wrote this down from memory which means I hope I haven't left anything crucial out (Considering the weight, I'm sure I haven't).
There are of course many other resistances to consider, to calculate the real top speed of a car (tracking for instance) but I'd say, you should be able to get as close as 95% with this simplified version, provided you're knowing the driving force, which calculates itself from the real wheel horsepower.


To get back on topic at the end: I also think the corvettes top speed is way too high, got mine up to 211 mph despite the sh**y gear ratios and only ~475hp
 
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DeadStig86
I'm an engineer and I've never heard about this rule.

As some already said, the weight of a car is quite irrelevant to a cars top speed. The power output of an engine can be recalculated to an actual force at the tire (Fw), which then is equated to the sum of various oppositely directed forces.

A simplified equation would be:

Fw = Fa + Ft + Fh

Fa = 0.5*p*cw*A*v^2

This is the main force stopping a car getting quicker, air resistance. p is the airtight, A the surface of the front of a car projected to a white wall, cw being the drag coefficient and v the actual speed...as we can see, it increases exponentially.

Two conclusions from that:

1: cw is quite irrelevant, if A is big. That's the main reason a normal saloon will have a higher top speed, than a suv with the same engine, even if the drag coefficient is the same.

2: because v increases exponentially, this force Fa gets indeed very big and is, as said before, the main reason stopping a car getting quicker...nice examples are your hand out of the window at 120 mph or the very high top speed of everything thats moving in a vacuum compared to it moving in normal air

Ft = µ*m*9.81*cos(β)

This is the the roll resistance of the tire (also very simplified) with µ being the rolling friction coefficient (something like 0.013 with a car on asphalt) and m being indeed the mass of the car. 9.81m/s^2 is the acceleration due to gravity (g).
This gets corrected by cos(β), with β being the angle of a possible slope

BUT because µ is so small you get something like 250N for a 2t saloon compared to 190N for a 1.5t hatchback on a level surface, which really is negligible compared to a few thousand caused by the air resistance.

Fh = m*9,81*cos(β)

The last main resistant force, which ONLY happens if the car is going uphill (or downhill, but then it's going on the other side of the main equation and helps you rather than being a resistance).

Now indeed the weight does make a notable difference, but again this entire part equals 0 if the road is level so TOP SPEED ON A LEVEL ROAD IS UNAFFECTED!

The weight plays a very notable difference while accelerating, as you pointed out. But it has to be said that the power output of the engine isn't affected at all, it's more a matter of an increased mass moment of inertia which than equals in a reduced driving force, from which the actual acceleration can be calculated, But then your into dynamics and, as its now past 3am where I live, i won't try in explaining this as well:sly:

There are of course many other resistances to consider, to calculate the real top speed of a car (tracking for instance) but I'd say, you should be able to get as close as 95% with this simplified version, provided you're knowing the driving force, which calculates itself from the real wheel horsepower.

By the way, I apologize if some of the technical tems are incorrect, English isn't my first language, we use logically the metrical system here (should someone be confused) and I wrote this down from memory which means I hope I haven't left anything crucial out (Considering the weight, I'm sure I haven't).
There are of course many other resistances to consider, to calculate the real top speed of a car (tracking for instance) but I'd say, you should be able to get as close as 95% with this simplified version, provided you're knowing the driving force, which calculates itself from the real wheel horsepower.

To get back on topic at the end: I also think the corvettes top speed is way too high, got mine up to 211 mph despite the sh**y gear ratios and only ~475hp
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I think I have a headache.
 
Well I just drove by the Corvette factory and guess what's sitting out in front of it with spot lights on them? Appears to be a red c7 and a silver c7. Now I'm gonna go drive them in gt 5. :P
 
ItsAllAboutWins
Well I just drove by the Corvette factory and guess what's sitting out in front of it with spot lights on them? Appears to be a red c7 and a silver c7. Now I'm gonna go drive them in gt 5. :P
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Jeslousy. Due to the insane price of gas, we haven't been able to to down south to visit family or a few years, since 2008. The Corvette Museum is a special place. 👍

Tomorrow night at Barrett-Jackson on SPEED should be fun :)
 
DSUjoeDirte9
Whats going on with Barrett-Jacksons?
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They'll be showing off the C7. The CEO put his own Vette up for auction tonight for a charity benefit.

Coverage starts at 2pm ET. The ORIGINAL BatMobile will be sold for the first time too!

Check Barrett-Jackson.com for current sales & schedule for Sat & Sun.
 

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