Image of Bugatti Chiron Super Sport 300+

Bugatti Chiron Super Sport 300+ specs

Car type Coupe
Curb weight 1978 kg (4361 lbs)
Introduced 2020
Origin country France
Views 3.1k
Submitted by lafars

Powertrain

Engine type quad-turbo W16
Displacement 8.0 l (488 ci)
Power 1622 ps (1600 bhp / 1193 kw) @ 7000 rpm
Power / liter 203 ps (200 hp)
Power / weight 820 ps (809 bhp) / t
Transmission 7-speed DCT
Layout middle engine, all wheel drive
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nats50  1d ago

Here is another site on how to calculate air density or rho under different temperature, pressure and humidity or dew point.

https://www.omnicalculator.com/physics/air-density


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nats50  1d ago

Here is another site on how to calculate air density or rho under different temperature, pressure and humidity or dew point. https://www.brisbanehotairballooning.com.au/calculate-air-density/


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nats50  2d ago

And here is a very useful site in getting the air density or density altitude, dyno correction factor, etc... Enjoy! https://wahiduddin.net/calc/index.htm


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nats50  2d ago

Here is the formula I now use for determining the coefficient of rolling resistance. The SAE suggested an empirical formula for the rolling resistance in dependence of inflation pressure pi [N/m^2], forward velocity v [m/s] and tire load Fz [N]:

Fr = K/1000(5.1 + 5.5 x 10^5 + 90 Fz/pi + 1100 + 0.0388Fz/pi)v^2 where the factor K is taken as 0.8 for radial tires and as 1 for non-radial tires.

Fr = Rolling resistance
Fz = Tire load in N = newtons
pi = Inflation or tire pressure in N/m^2
v = Velocity or speed in m/s
Cr = Coefficient of rolling resistance (unitless)
m = Mass in kilograms
g = Acceleration due to gravity = 9.80665

Hw = Wheel Horsepower
Af = Frontal area in sq ft
Cd = Coefficient of drag
S = Speed in mph
W = Weight of car and driver in pounds

Fr = Crmg

Hw = 0.0025565AfCdS^3/375 + CrSW/375 -> divide the result by a factor such as 0.80 for 20% power loss, 0.83 for 17%, 0.85 for 15%, 0.87 for 13%, and so on to get the crank or flywheel horsepower needed to attain the top speed. Convert the units as needed.


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nats50  2d ago

I've done this revised calculations on the top speed using my own version, with a twist, of known formulas and equations . It can be achieved if it meets these parameters. Of course, there are many possible combinations of frontal area and drag coefficient, not to mention power loss which can only be accurately determined by putting the car on a dyno. There are many formulas or equations on predicting accurately the theoretical top speed--from the simplest to the most complex. As you probably know, there are like 4 forces or resistance acting on a moving car that influence top speed--air resistance; rolling resistance; gradient resistance and inertia. The first two are the most prominent. The gradient is usually not included in the mix cause top speed is supposed to be run on a relatively flat road or track, and that is why two runs, from both directions, are needed to negate any possible slope, uphill and downhill, not to mention wind, and just average the two speeds. Inertia is also neglected or may be insignificant for some reason. Anyway, I've developed my own version and I came up with these results. As I said earlier, there are infinite number of combinations you can do to arrive at the same top speed theoretically. Before I forget, they are based on standard temperature, pressure and humidity of--59 F, 29.92 inHg and 0% humidity--rho at 1.225 kg/m^3 or 0.00237689 slug/ft^3. They all mean the same thing. There are formulas out there on how to determine rho exactly using different temperature, pressure or elevation, and humidity. That is why I use or the constant 0.0025565 is used to simplify. Also, it must be known that there are different types of top speed--gear limited and rev limited (not to be confused with governor or electronically), power or drag limited. Finally, the frequently neglected and "insignificant" rolling resistance seems to be the more problematic one. There are many formulas or equations on how to determine the rolling resistance value. It can be seen that tire pressure, weight and even speed affect rolling resistance and consequently top speed. The air resistance is pretty much straightforward and well known. Again, I came up with these results and here they are:

Hc = Crank or flywheel horsepower
Hw = Wheel horsepower
Af = Frontal area in square feet
Cd = Drag coefficient
Pl = Power loss in percent
Pi = Tire pressure in psi (44 is usually used)
Cr = Coefficient of rolling resistance
W = Curb weight of car plus driver (165 is normally used) in pounds
S = Speed in miles per hour

Bugatti Chiron Super Sport 300+

Hc = 1,600 bhp -> 1622ps
Hw = 1,373 whp (air resistance) + 35 whp (rolling resistance) = 1,408 whp
Af = 22.30 sq ft -> 2.072 sq m
Cd = 0.319
Pl = 12.0%
Pi = 44 psi
Cr = 0.0095
W = 4,526 (4,361 + 165) lbs
S = 304.77 mph

Koenigsegg Agera RS

Hc = 1,144 bhp -> 1,160ps
Hw = 973 whp (air resistance) + 23 whp (rolling resistance) = 996 whp
Af = 20.16 sq ft -> 1.873 sq m
Cd = 0.330
Pl = 12.9%
Pi = 44 psi
Cr = 0.0096
W = 3,243 (3,078 + 165) lbs
S = 277.87 mph

SSC Tuatara

Hc = 1,350 bhp -> 1,369 ps
Hw = 1,030 whp (air resistance) + 31 whp (rolling resistance) = 1,061 whp -> 21.4% power loss -> 0.013 -> 311.00 mph
Hw = 1,070 whp (air resistance) + 32 whp (rolling resistance) = 1,102 whp -> 18.4% power loss -> 0.013 -> 315.00 mph
Hw = 1,122 whp (air resistance) + 40 whp (rolling resistance) = 1,162 whp -> 13.9% power loss -> 0.014 -> 320.00 mph
Af = 18.00 sq ft -> 1.672 sq m
Cd = 0.279
Pl = 21.4%, 18.4%, 13.9%
Pi = 44 psi
Cr = 0.013, 0.013, 0.014
W = 2,915 (2,750 + 165) lbs
S = 311.00 mph, 315.00 mph, 320 mph -> calculated top speed?

 

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BR2+  2d ago

Good lord man..


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manone  2d ago

it is not clear what your claim is. are you saying that these values that you provide
would equate to the top speed measured for the listed cars if plugged in the formula? It seems almost impossible to me that chiron 300 dropped cd from 0.36 to 0.32.
The problem is quantifying rolling resistance. a guy in https://drivetribe.com/p/technical-analysis-of-a-high-speed-P7t71_CaSSOMFdALcj_CWg?iid=SFD9PBiSSr25Dl5sTA_ayw
provided a reference to a "quartic polynomial model" for rolling coefficient, but did not provide computations. he came up with a drag coefficient of 0.27 necessary for Chiron to reach 490kph with 1600hp. I think it's plain impossible that Chiron 300 even comes close to having a cd of 0.27, if Chiron has 0.36 as stated.


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SpeedKing  2d ago

The formula for the Koenigsegg top speed run suggesting that it only needs 1160 hp is unrealistic given that Koenigsegg claim that the Agera RS has 1360 hp which i believe it would need to achieve an average speed of 277 mph. In addition to that the 0% humidity that you've applied is impossible.


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nats50  2d ago @manone

Hahaha, you guys haven't been paying attention. I didn't say that Bugatti actually admitting that they dropped Bugatti's Cd from 0.36 to 0.32. I'm only showing that the 1600 hp Chiron CAN ONLY achieve that 304.77 mph top speed
IF the Cd is down to that level! Or, the frontal area is reduced. Hello? Are you reading between the lines ? Otherwise, the car has to have more than the stated 1,600 hp. Either the frontal area or the Cd is reduced, or better both! I'm not forcing anyone to believe the formulas I'm displaying. You can use your formulas if that suits you.


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nats50  2d ago @SpeedKing

Are you familiar with air density? I know 0% is almost unrealistic unless you live in the desert. But I didn't create or set STP--Stantard Temperature and Pressure to dry air or 0% humidity, or ISA and IUPAC. They are all set to standard 0% humidity. BUT OF COURSE, you can use different humidity level, temperature and pressure to reflect the real conditions and adjust the formulas and equations. Here, go to these VERY USEFUL AND INFORMATIVE website regarding air density or so-called density altitude, correction factors for dyno. . As I said to manone, I'm not forcing anyone to trust my formulas.
https://www.thoughtco.com/density-of-air-at-stp-607546
https://wahiduddin.net/calc/index.htm


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nats50  2d ago @SpeedKing

BHP WHPa WHPr WHP Cr Pl S

1,360 bhp 1,287 whp + 30 whp = 1,317 bhp 0.012 Cr 3.2% 305 mph

1,360 bhp 1,225 whp + 29 whp = 1,254 bhp 0.011 Cr 7.8% 300 mph

1,360 bhp 1,164 whp + 28 whp = 1,192 bhp 0.011 Cr 12.4% 295 mph

BHP = Brake, crank or flywheel horsepower of the car
WHP = Total wheel horsepower needed to attain the top speed
WHPa = Wheel horsepower needed to overcome air resistance
WHPr = Wheel horsepower needed to overcome rolling resistance
Cr = Coefficient of rolling resistance
Pl = Power loss in percent = 1 - (WHP/BHP)
S = Top speed at these parameters
W = Weight of car and driver (assuming 165 lbs) = 3,078 + 165 = 3,243 lbs
Af = Frontal area = 20.16 sq ft
Cd = Coefficient of drag = 0.33
Pi = Tire pressure in psi = 44 (44 is usually used cause above 150 mph, tire pressure gains up to 7.5 psi because of heat. Some even 50 or more depending on the situation.
F = Factor such as 0.80 for 20% power loss, 0.83 for 17%, 0.85 for 15%, 0.90 for 10%, 0.95 for 5%, or whatever.

1 - (1,317/1,360) = 0.032 = 3.2%
1 - (1,254/1,360) = 0.078 = 7.8%
1 - (1,192/1,360) = 0.124 = 12.4%

Now, look at the results. For the car to attain 305 mph, the power loss must be at no more than about 3.2% which is kind of ridiculous or unrealistic. With 300 mph, the same car with the same parameters such as frontal area, drag coefficient, weight, etc., the power loss must be no more than about 7.8%, which is getting to be more realistic and achievable, right? Power loss below 10% or close to it is not that impossible or unheard of as some cars have achieved it. With 295 mph, you can probably bet your life on it that it is where some cars sit around, 8%-13%. Based on my formula or calculation, the car can achieve that speed with these parameters or specs. Finally, let me be very clear. The formula or equation assumes a standard rho of 1.225 kg/m^3 or 0.00237689 slug/ft^3, which is the standard air density at 59 F, 29.92 inHg and dry air or 0% humidity. Of course, in real life, the condition is not always there, specially humidity. That is why there is this dyno correction factor to correct the readings and results using the actual temperature, pressure and humidity or dew point, not to mention elevation. In other words, the true horsepower could be more or less than what is being used, therefore affecting the true top speed. Refer to my previous posts regarding the equations I'm using. And again, if you guys don't trust my formulas, it's not going to be my problem. Thanks for your time.


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manone  2d ago @nats50

"I'm only showing that the 1600 hp Chiron CAN ONLY achieve that 304.77 mph top speed
IF the Cd is down to that level! Or, the frontal area is reduced."

that is exactly what i asked. the frontal area is not decreased obivously, because the frontal projection of the car is the same (they just changed the rear of the car), thus they need 0.32cd, which i do not believe chiron 300 has.

But again, you may be underestimating rolling coeff. big time, as the guy in the link of my post gets a cd=0.27 for chiron 300 to hit 490kmh with 1600hp.


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nats50  2d ago @manone

You see, his Cd of 0.27 is even much lower than 0.319 or 0.32 I'm using. As I have stated before, most people are too concentrated on the air resistance alone since it is widely believed that rolling resistance is really that insignificant or negligible, or that they don't have the formula or equation on hand. In fact, weight and speed affect it even if the rolling resistance amounts to only a few percent of the total resistance, but enough to screw the top speed result. Here is the formula I now use for determining the coefficient of rolling resistance. The SAE suggested an empirical formula for the rolling resistance in dependence of inflation pressure pi [N/m^2], forward velocity v [m/s] and tire load Fz [N]:

Fr = K/1000(5.1 + (5.5 x 10^5 + 90 Fz/pi) + (1100 + 0.0388Fz/pi)v^2 where the factor K is taken as 0.8 for radial tires and as 1 for non-radial tires.

Fr = Rolling resistance
Fz = Tire load in N = newtons
pi = Inflation or tire pressure in N/m^2
v = Velocity or speed in m/s
Cr = Coefficient of rolling resistance (unitless)
m = Mass in kilograms
g = Acceleration due to gravity = 9.80665

Hw = Wheel Horsepower
Af = Frontal area in sq ft
Cd = Coefficient of drag
S = Speed in mph
W = Weight of car and driver in pounds

Fr = Crmg

Hw = 0.0025565AfCdS^3/375 + CrSW/375 -> divide the result by a factor such as 0.80 for 20% power loss, 0.83 for 17%, 0.85 for 15%, 0.87 for 13%, and so on to get the crank or flywheel horsepower needed to attain the top speed. Convert the units as needed.


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manone  2d ago @SpeedKing

" In addition to that the 0% humidity that you've applied is impossible."

assuming 0% humidity, he is actually making the air denser (by the Avogardo Law) contrary to intuition, thus assuming an higher drag than there actually is. He should correct lowering the power figures he computes or increasing the speeds. Anyhow, i suspect he is hugely underestimating the tyres rolling
coefficient at speeds around 500kmh.


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manone  2d ago @nats50

"You see, his Cd of 0.27 is even much lower than 0.319 or 0.32 I'm using"

yes, indeed it is impossible chiron 300 has 0.27. that car probably needs north of 1800 crank hp to reach 490kmh.


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manone  2d ago @nats50

"The SAE suggested an empirical formula for the rolling resistance in dependence of inflation pressure pi [N/m^2], forward velocity v [m/s] and tire load Fz [N]:

Fr = K/1000(5.1 + (5.5 x 10^5 + 90 Fz/pi) + (1100 + 0.0388Fz/pi)v^2 where the factor K is taken as 0.8 for radial tires and as 1 for non-radial tires."

no it is definitely not quadratic in speed, as the graph in the link you posted days ago clearly shows. By the way, the expression you write is lacking a closing parenthesis.
Plus, there are no reliable models i know of for rolling res at 500kmh, simply because there are basically no tyres reaching that speed. i suspect the coeff blows up


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SpeedKing  2d ago @nats50

Arguing about formulas is a lost cause and i prefer hands on real world experience. The number of variables required to accurately determine max speed, theoretically, is problematic, particularly for the Chiron SS because we don't have an accurate drag coefficient for starters. I'm very familiar with DA and grains of water in the air coz of my decades of drag racing experience. The bottom line is that most formulae are very useful tools but the same cannot be said of the formula for maximum speed accuracy.

Re hp loses from the crankshaft to the wheels that is constantly argued based on misinformation and ignorance. The most accurate measure of engine horsepower is achieved by using an engine dyno..fact. Drivetrain loss can be anywhere from 12% to 30% depending on what type of chassis dyno is used. Mustang dyno losses are the highest and Dynojet the lowest. Conversion factors are also a problem because many disagree on what % figure to use for each dyno based on the drivetrain configuration. It's NOT an exact art due to, once again, shitload of variables, so at best it's an approximation.


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nats50  1d ago @manone

Yes, I did notice there was another parenthesis that I missed putting which makes an effect. I agree with you the equation the mechanical engineers probably wrote didn't expect cars would run 300 plus miles per hour. There are many rolling resistance equations that I've kept in my library, none of them agree with each other--some reading higher or lower than others even though the speed is the same. One equation would give a rolling resistance coefficient in the 80s, like 0.080, while others put it in the 20s like 0.020, while others are in between. You see, I've been experimenting different values that I think would truly reflect the speed given the power the car has. I have to admit the figures I wrote are now not entirely accurate due to the fact that I gave the rolling resistance coefficient too low probably because of the missing parenthesis that affected the equation. You see, as I said earlier, I use different equations from different sources regarding rolling resistance values. Another problem and cause of the wrong results is that the equation for rolling resistance coefficient was in the metric system, using meters per second for speed instead of miles per hour where I'm comfortable with, newtons instead of pounds, you get the idea. Now, I finally just converted the equation into the English system where it uses mph, lbs, psi and so on.
I'm sure you would agree with me that to determine the top speed of a car requires both the air resistance AND the rolling resistance. The air resistance determination is pretty much straightforward and not really problematic as the equation with rho is standard. It is the rolling resistance that has been the problem child. Also, regarding rho, it is true the value 1.225 or 0.00237689 or whatever system or value one uses is based on a "standard" temperature, pressure and humidity or dew point, at sea level. Yes, it was based on dry air or a humidity of 0 which is not realistic in the real world probably except useful only in the desert. I know how to determine the true value of rho under different environment using different temperature, pressure, humidity and even elevation included. Of course, the power of the car, and consequently, the top speed would vary--higher or lower than what I posted. But those calculations that I've been giving where obviously based on just standard conditions for demonstration purposes. I've saved dozens of sites on where to get values for air density, dyno correction factors which affects the performance of cars under different conditions. Here is another one that I use to determine rho using different temperature, pressure, and yes, not 0% humidity! https://www.brisbanehotairballooning.com.au/calculate-air-density/
Another one that you will definitely find very useful is this: https://wahiduddin.net/calc/cf.htm
I will try to post my final calculations later when I can. Since we use different equations and technique, I'm aware we would still have our discrepancies. No problem. And thanks for your time.


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nats50  1d ago @SpeedKing

Hi there. Yes, I agree with you regarding the difficulty of determining top speed theoretically or just mathematically. As I said on my numerous previous posts, those power or drive train loss are only true based on the other figures and if they were met, not necessarily that they are the ACTUAL power loss. Yes, and I also said it on my numerous previous posts, the only accurate way of determining the horsepower of a car is by way of the DYNAMOMETER! However, as you are probably aware, there are different types of dynos, and each gives different results, not to mention the lack of experience or technical knowledge and even honesty some dyno centers have. As I just told manone regarding the calculation results, I did screw up a bit because of the rolling resistance coefficient that I used. You see, that equation, probably written by mechanical engineers, are in the Metric system of newtons, meters per second, kilograms and so on instead of the English system of pounds, miles per hour, pounds per square inch and so on that I'm working and more familiar with, and I had to convert each and every one of the parameters! On top of that, I missed that missing parenthesis on the rolling resistance equation that blew up the rolling resistance coefficient, hence lowering the wheel horsepower loss. My bad. However, that doesn't change the fact that to accurately calculate the theoretical or mathematical top speed of a car is BOTH air resistance or drag and rolling resistance are needed, not just the aero most people use. The other two, gradient and inertia, can be neglected since top speed runs are based on flat roads or tracks. The difficulty is really on the determination of the value of rolling resistance in the true world or not just empirical. The air resistance part is pretty much straightforward and well know. Not to mention that there are different types of top speed--rev limited, not to be confused with governor or electronically limited, gear limited, power or drag limited. You know that. Also, all the calculations that I presented obviously were based on standard temperature, pressure and humidity of 59 F or 15 C, 29.92 inHg or 1013.25 mb and dry air or zero humidity. Regarding humidity, of course, in real world situations, that is only possible in the deserts, but you get the idea. Not to mention also the value of rho that they were based on--the value of 1.225 or 0.00237689 or whatever value and system one uses. Using numerous websites that I go to just to determine the actual value of rho under different conditions, I know how to adjust. Regarding the drivetrain loss, I don't entirely agree with you on the numbers, the 12% to 30% values. Numerous experts and also based on the calculations I'm getting, it varies between near 10 to only as high as about near 20, not as high as 30. Well, I'm not going to debate with you on that. We're on our own.

Finally, as I said to manone, I will readjust the numbers again when I have the time. Actually, my earliest calculations were better because I sticked to the one rolling resistance coefficient equation I was comfortable with, but I just experimented with another one from another source. Oh well. Again, thanks for your time and I hope you don't take these conversations or posts personal for I don't. Cheers.


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SpeedKing  1d ago @nats50

One can argue a position without getting personal. "I don't entirely agree with you on the numbers, the 12% to 30% values". Without going into intricate detail there are significant variations between inertia and load bearing chassis dynos which end up with different percentage losses through the drivetrain. On top of that FWD,RWD and AWD experience different powertrain losses so the 12-30% refers to all dyno types and vehicle drivetrain configurations.


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nats50  1w ago

https://www.facebook.com/watch/?t=10&v=191073695633737
A simple case of power to weight ratio win by Koenigsegg?


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nats50  1w ago

Want to know the approximate wheel horsepower loss at altitude? http://dgm2780.austinbroadhead.com/whpCalculator/


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HighGear  6m ago

Likely 1180 lb-ft, like the standard Chiron.


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HighGear  6m ago

Source: https://www.topgear.com/car-news/supercars/bugatti-chiron-super-sport-300-production-300mph-car

The power output is 1,578 hp (1,600 PS).
Price: 4.2 Million pounds (5.18 Million US dollars)
Top Speed: 304.77mph*
*https://www.topgear.com/car-news/bugatti-has-broken-300mph-barrier?fpn=1


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manone  6m ago

"Why can't it reach 490 kph with 1600 ps? What are those "engineering peeps" that are so convinced it can't? Have they studied the shape of the car?"

Ok, let's do few computations for Veyron SS. The formula relating power to CdA, speed v and air density rho is:

P = CdA * v^3 * rho/2.

Knowing V=431km/h=119.7 m/s, P=1200bhp=895kw and rho@15C=1.225 kg/m^3,
we get a CdA of 0.85.

Therefore, for the Veyron SS to reach 490km/h you need 1307kw=1753bhp for
overcoming the drag alone from 431kmh to 490kmh. Then you have to add:

Rolling friction term, which linear with speed, and dynamic rolling resistance term, quadratic with speed.

Back to the Chiron SS: the A factor of Cd*A is seemingly not less than the
Veyron SS's. How much they could have decreased the Cd from the Veyron SS to the Chiron SS, provided the extra front venting surfaces the latter has?


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lafars  6m ago

very informative video regarding this car:
https://www.youtube.com/watch?v=DFlUYWfwOUg


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FastestLaps  6m ago

You know what is the saddest part - we still don't have proper data for the original Chiron :D

Bugatti are basically pulling a Christian von Koenigsegg.

 

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lafars  6m ago

you can at least add top speed to the stats: 304,77mph


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SpeedKing  6m ago @lafars

The pre-production 304 mph run had mods and highly likely more than the 1578 bhp claimed by Bugatti so until the 300+ is independently tested, when released, i wouldn't be adding the 304.77 mph stat :)


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SpeedKing  6m ago @lafars

The general consensus by engineering physics peeps is that for Bugatti to reach 304.77 mph it would need a minimum of 1800 bhp so if Bugatti/VW had any integrity it would be truthful rather than making bullshit claims that it has 1578 bhp. Once again it suggests that you can't believe any turbo hp figures from car manufacturers pfft


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FastestLaps  6m ago @SpeedKing

Why can't it reach 490 kph with 1600 ps? What are those "engineering peeps" that are so convinced it can't? Have they studied the shape of the car?


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SpeedKing  6m ago @FastestLaps

The aero changes aren't as amazing as you may think because a shitload of air, more than the current model gets, needs to be channelled to the cooling system to prevent the engine from overheating and this effectively increases drag which to a significant extent offsets the improvements they've made to the aero.

In addition to that the acceleration difference from 300 to 400 km/h is huge ie. approx 11 secs for the prototype vs 16 secs for the current Chiron. It takes more than 100 hp and aero to be that much quicker.

Lastly coz Hennessey said so and he would know don't you think? lol


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lafars  6m ago @SpeedKing

while i can't say for certian how much 100hp and longtail would add up to there is one thing that was mentioned in the supercarblondie video:

the longtail gives a 40% reduction in drag over the standard Chiron


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manone  6m ago @lafars

if 40% is over the total car's drag, then it would need much less than 1600bhp to reach 490km/h.


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SpeedKing  6m ago @lafars

The current Chiron drag coefficient is 0.38 in EB (standard) mode, 0.40 in Handling, 0.35 in Top Speed and 0.59 when the air brake is active. So a 40% reduction equates to 0.21 in top speed mode which is unrealistic given it still needs huge amounts of air being diverted to the cooling ducts to stop the engine from overheating and shutting down. Anyway the speed is not recognised as a record given it's not a production car and it was only a single pass.


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SpeedKing  6m ago @lafars

"the longtail gives a 40% reduction in drag over the standard Chiron" they didn't say that in the video. What the Bugatti engineer said was that there was a 40% decrease in size of the rear tear off area which doesn't equate to 40% less downforce. Details are important :)


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lafars  6m ago @SpeedKing

can you calculate the drag area using an estimated tear size?


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SpeedKing  6m ago @lafars

No, only Bugatti have that information coz you'd need wind tunnel verification to unequivocally determine the benefit. My guess would be approx 10%??


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BTICronox  5m ago @SpeedKing

A little copypaste...

The Veyron SS has a cd of 0.35 and a front surface of 2.1m² according to this:
http://rc.opelgt.org/indexcw.php
That results in a combined cdA of 0.735

Additionally, i calculated air density with this site:
https://www.timeanddate.de/wetter/@2932872/rueckblick?month=9&year=2019
And the result was 1.205kg/m³

So if you take the front surface of the Veyron for the Chiron and the air density at that day, you'll come up with following result:

cd = 2P /( v³ * rho * A)

cd = (2 * 1176470W)/(136.1(m/s)³ * 1.205(kg/m³) * 2.1m² )

cd = 0.368

The Chiron already has a cd of 0.35 according to Bugatti, so this is very probably a little lower, 0.33 or so, but probably with a higher surface area (A) than the Veyron. 490km/h is completely realistic for the 1600hp to achieve.


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SpeedKing  5m ago @BTICronox

The problem with your formula and belief is the acceleration difference from 300 to 400 km/h between the current Chiron and the 300+ 16 secs vs 11 secs for the 300+. Do you really think that with an additional 100 hp and slightly improved aero( let's not forget the bigger air ducts on the 300+ needed for engine cooling) that it can be 5 secs quicker?? No chance in hell!


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Cocobe  5m ago @SpeedKing

Why did you bring “bigger air ducts” into question? Obviously the super sport is much more aero efficient.

Acceleration should be the (total power - drag) /weight.

If the Veyron with had 1000hp and only managed ~400kph. We can assume the drag at 400kph is nearly 1000hp. So an extra 100hp makes a huge difference at these speeds. Add the fact the car could be about 5-10% more slippery, which would account another 50-100hp.

And who says the engine can’t actually produce 1700hp but be rated at 1600, like most German manufacturers understating their hp. It’s only cheating if the other super sports don’t have the same hp.


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SpeedKing  5m ago @Cocobe

Simple, coz bigger air ducts swallow more air and slow it down. Therefore the longtail aero gains are negated. Far more importantly no one had addressed the radically different acceleration figures i've brought up. A 5 sec improvement between 300-400 km/h is HUGE and aero is a minor factor. The biggest factor is a significant increase in power which doesn't mean 100 hp FFS...


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dr. cosimo  5m ago @SpeedKing

yeah, why do you have to bring in logic into every conversation ?

this is fastestlaps, where bs german brand is allowed to cheat and piss all over lap time board, if it ain't part of the vw group then the times are not legit.

sponsored by............

im0om5lnb35s.jpg?550x800m


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manone  5m ago @dr. cosimo

ahahahahaahahaha


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SpeedKing  5m ago @dr. cosimo

Ha coz my BS detector goes off when i read something which is just rubbish :)


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dr. cosimo  5m ago @SpeedKing

the new generation ev kids around here always get pissed and all they can do is a thumbs down, lol

can't fight logic with logic, so all they try to do is hide your comment with their all new mass weapon of destruction :)

vw the car to own and here's proof lol

6i27nnh698ct.jpg?550x800m

a rebadge and over 140k in price difference, das auto lawl

e4ff018cei8g.jpg?550x800m

9dhlls0ithhj.jpg?550x800m


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SpeedKing  5m ago @dr. cosimo

Ha yeah the truth is out there and yet peeps who do not do their research would have you believe that EV cars could beat an ICE car in a 24 hour race lol


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aaayy  5m ago @SpeedKing

if you used supercapacitors, maybe. The most effective carbon-neutral tech for long distance racing is in my opinion, hydrogen fuel cells. They refuel just as fast, and they're lighter than batteries. Or you could cover the outside of an EV in solar cells, since they're getting smaller and lighter, and use those to charge the car.


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SpeedKing  5m ago @aaayy

Super or Ultracapacitors are a long way off as a sole power supply if in fact that is realistic but i guess you could maybe incorporate them with battery technology but that's still in its infancy to my knowledge so for the time being ICE cars rule in long distance races.


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nats50  2w ago @SpeedKing

According to my calculation, for the Bugatti to achieve the 304.773 speed, it has to have about 1,899 horsepower–1,583 to counteract air resistance, and another 316 for rolling resistance and other losses, assuming 22.30 square feet of frontal area and 0.355 drag coefficient and about 4,525 weight including a 165-pound driver. Weight still plays an impact however minute since load on the tires affect the rolling resistance which also consequently affect the speed. Contrary to popular belief, weight not only affects acceleration but speed or velocity as well however minute but not completely insignificant. The only way it can achieve that speed is either the horsepower is about 1,899 as I said, OR with only 1,578 horsepower, the drag coefficient must be lowered to about 0.293.


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SpeedKing  2w ago @nats50

Whether the Chiron 300+ had 1800 bhp or 1899 bhp is academic. What is undeniable is that 1600 bhp would not enable it to get to 304 mph. If someone has irrefutable proof to the contrary let's see it...


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Cocobe  2w ago @nats50

sorry man, you're wrong.
https://en.wikipedia.org/wiki/Rolling_resistance

F = C x N

In the formula of rolling resistance. the force of the rolling resistance doesn't change at all according to velocity.
For drag
F = (1/2)p(v^2)(Cd)(A)
drag increases v^2.

power = F x v. So for the power lost to rolling resistance increases by the factor of velocity.
power of Drag however increases to factor of v^3.
p = F x V = (1/2)p(v^2)(Cd)(A) x v

In many cars 50mph is about when drag matches rolling resistance.
So take 300mph. That is 6x 50mph. say the force of (drag at 50mph) = y
Then drag at 300mph = 6x6x6(y)
rolling resistance = 6 (y)

At 300mph, rolling resistance is 1/36 of what it is to drag. Assuming the Chiron SS needed 1600hp to reach 300mph, 43hp would be lost to rolling resistance, 1557hp lost to drag.

Had the Chiron been 1500kg instead, the difference would have been an additional power of 10.8hp. which would have given it 0.675% more power. Take 1.00675^(1/3) = 1.00225.

The new top speed would be 1.00225x 300mph = 300.673mph.

By removing 500kg you would gain only 0.6 to 0.7mph for top speed.


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nats50  2w ago @SpeedKing

Didn't you read what I said? The speed of 304 mph IS attainable even with only 1,578 crank or flywheel horsepower if either the drag coefficient is lowered to about 0.293 from the assumed 0.355, OR the frontal area is trimmed down to about 18.41 square feet (1.710 square meters). It's also a matter of juggling with either the frontal area or the drag coefficient, or both.


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SpeedKing  2w ago @nats50

Yes i read what you said however the Bugatti DID NOT have the required lower drag coefficient to enable it to attain 304 mph with their claimed hp figure so the point you made while theoretically possible does not apply in this case.


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nats50  2w ago @SpeedKing

So maybe, that's the figure Bugatti people didn't or hasn't divulge. Maybe the longtail and whatever else dramatically reduced the drag or the drag coefficient which would affect the whole calculation.


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Cocobe  2w ago @nats50

nats50, your math is wrong.

Take the Bugatti Veyron SS
It had a Cd of 0.36.
If we plug in the formula for drag and removed any variables like rolling resistance
drag = 0.5 x 1.225 x v^2 x 0.36 x 2.07msq
power = drag x v
power /(0.5x1.225x.36x2.07) = v^3 = 1933829
calculate v and you get 124,6m/s.
You get a top speed of 449.4kph for 1200hp, which is 279mph. Some 10mph faster than the real thing. Yes, because that assumes 1200hp to the wheels. Given there should be about 10% drive train loss, it should be 1080hp. Which recalculates to 433kph, which is 269mph, pretty much bang on with the actual 268 real world speed.

For the Chiron
Cd is 0.35 in top speed mode. I couldn’t find the frontal area of the Chiron, so lets assume it’s the same as a Veyron. Again, we should be using 90% of 1500hp, and that would calculate to 470.8kph / 292.6mph
So the Stock Chiron should be able to go to 292mph, perhaps 290mph if you account for rolling resistance.

Had they not changed ANY of the dimensions nor drag coefficient,
With 1600hp, with 90% of power going to the wheels,
Theoretical top speed would be 481kph, or 299mph, at least 5mph short of the actual record.

So yes, 1600hp would not achieve 304mph.

However they did change the shape of the car, so the Cd is definitely lower. How much? Who knows. It could be 0.33.

Then in that case, theoretical top speed is 490.6kph / 304.9mph
holy sh*t that worked out almost exactly. And lets assume Bugatti indeed are lying about the engine hp, say it's 30-40hp more than it should. Then it would have made up for the exact difference of the rolling resistance.

The Chiron does NOT need 1800hp as some of you say.... But it probably needs 1630-1650


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BR2+  2w ago @nats50

Did you ever see the Chiron that made the run? It was not stock in any way at all, The interior is gutted to all hell, Hell it barely has doors, Full cage new underbody, And who knows what they did to the engine, All in what you said is simply based on a stock fully truth telling Hp n weight Chiron, And as you will see.....It certainly is not, And that is not what customers are getting, Its nothing but a publicity stunt n super disrespectful to previous holders.


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SpeedKing  2w ago @nats50

The heat generated from an engine producing 1600+ bhp is phenomenal particularly when it's pushed to the limit for a considerable period of time and the only way to prevent overheating is by using bigger front ducts to trap more air which creates additional drag offsetting any advantage from the longtail configuration. As for all those formulas, they're great in theory, but the only way to prove the accuracy is to physically put the beast through its paces with independent testing to determine the veracity of Bugatti's claims re hp which is never gonna happen.


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nats50  2w ago @Cocobe

Where did my math go wrong? And why are you ignoring rolling resistance and weight or mass? Didn't you read what I said to SpeedKing? Look, the usual basic formula or equation is this: H = 0.0025565ACS^3 + CrSW/375. In the case of the Bugatti, an all-wheel drive, multiply the result by a factor of 1.20. Now, regarding power loss due to drive train and other factors, it is not accurate to say that usually 15% is the power loss for front-wheel drive and manual transmission, and 17% for rear-wheel drive and automatic. In fact, low-powered cars with say 150 hp has a higher overall power loss than a 500 hp car! Those are just rule of thumb. Here is where to get the factor. They are just very good approximates, but not exact.

H = Horsepower (crank or flywheel)
A = 22.30 = Frontal area in square feet
C = 0.355 = Drag coefficient
S = 304.77 = Speed in miles per hour
Cr = 0.015 = Coefficient of rolling resistance
W = 4,525 = Curb weight of car plus driver and whatever else in pounds

0.0025565ACS^3 + 0.015SW

H = 1.20(--------------------------------------------------)
375

(0.002556522.300.355304.77^3 + 0.015^304.774,525)/375, then multiplied by 1.20

Now, the standard number used for Cr is usually 0.015, but in reality or in the real world, it is not a fixed number and can be lower or higher, depending on speed and other factors. Numerous formulas and equations have been written about this parameter, and I have tried, used and compared them and applied as well just to see how they compare and how accurate each and every one of them when applied to real life testing of top speed and such. As you probably know, there are many types of top speed. Top speed can be power-limited, gear-limited or drag-limited, rev-limited or governor-limited. Now, some people confuse rev-limited with governor or electronically-limited top speed. Of course, they are not the same. Top speed can also be limited because of tire rating limitations specially with regard to speed.
*Substitute 0.293 for the drag coefficient, or 18.40 square feet for the frontal area and it will jive. Here is site for the factor: https://www.mk5cortinaestate.co.uk/calculator4.php


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nats50  2w ago @Cocobe

The browser doesn't support the format you intend. Anyway, the equation should read:

(0.0025565 x 22.30 x 0.355 x 304.77^3 + 0.015 x 304.77 x 4,525)/375, then multiplied by 1.20



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nats50  2w ago @SpeedKing

That's what I've been trying to explain here! That Bugatti can achieve that 304.77 mph ONLY if it has more than the stated 1,578 hp, unless the original drag coefficient of 0.355 has been lowered to something like 0.293, yes that low, OR the frontal area from the original 22.30 square feet down to something like 18.40, OR a combination of the two. OTHERWISE, that particular Bugatti has to have something like 1,899 or so. Either the Bugatti folks are understating the horsepower figure, or either the frontal area or the drag coefficient figure is now wrong, or something else. I'm not disputing about what they did to the body works. The known formulas are reliable and accurate but only if the they are fed with the correct figures. They don't lie. I don't know what else is not clear from everything I'm saying. I've done a lot of researches regarding top speed, which is my main interest. I just posted and added about a dozen websites regarding this matter a while ago. You may want to check them out. Thanks for your time.


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nats50  2w ago @Cocobe

This is a good site to know how top speed is usually calculated. You don't ignore weight or mass and rolling resistance.


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nats50  2w ago @Cocobe

http://www.mayfco.com/cobra.htm


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SpeedKing  2w ago @nats50

Ok how about you put your formula to the test and calculate how much hp the Koenigsegg Agera RS needed to max out at 284 mph?



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FastestLaps  2w ago @nats50

Bugatti can claim whatever they want. The only thing we care about is what they actually have achieved. They have more than one place in Germany where they could attempt to go well over 400 kph. Unless they do, the topspeed of Chiron SS remains unknown.


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nats50  2w ago @SpeedKing

Koenigsegg Agera RS

H = 1,160 hp
A = 20.16 square feet
C = 0.33
S = 277.87 mph
W = 3,078 + 165 = 3,243 lbs.

H = Crank or flywheel horsepower
A = Frontal area in square feet
C = Drag coefficient
S = Speed in miles per hour
W = Curb weight of car plus driver (165 pounds is normally used) in pounds

0.0025565ACS^3 + 0.015SW

H = (-----------------------------------------------)1.15
375

0.0025565x20.16x0.33x277.87^3 + 0.015x277.87x3,243

= (-------------------------------------------------------------------------------------------)1.15
375

364,901 + 13,517

= (------------------------------)1.15
375

= 1,009 x 1.15 = 1,160

https://www.koenigsegg.com/car/agera-rs/#aerodynamics
https://www.koenigsegg.com/car/agera-rs/#engine
https://www.koenigsegg.com/car/agera-rs/#dimensions
https://www.google.com/search?sxsrf=ACYBGNSKvxfQGDdyQzUfQvaJByIRFXgpJg%3A1581860992466&ei=gEhJXpiGHIq0sQXjuKKoBw&q=koenigsegg+agera+rs+drag+coefficient&oq=koenigsegg+agera+rs+drag+&gs_l=psy-ab.1.1.0l2j0i22i30l4.18632.21530..23523...0.2..0.324.1013.0j4j1j1......0....1..gws-wiz.......0i71j0i67j0i20i263.LJ9rp7PIi2Y#spf=1581866843603


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nats50  2w ago @SpeedKing

For the factor, I use this site: https://www.mk5cortinaestate.co.uk/calculator4.php As it says, it is only a guess, or rather, a good estimate of power loss. But so far it seems to be right there. Since there is no mid-engine included, I usually just use the front-engine category. The Koenigsegg is a mid-engine, rear wheel drive automatic. Since a mid-engine rear wheel drive is about identical to a front-engine front wheel drive, closer than a front engine, rear wheel drive, that's the one to use.


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nats50  2w ago @SpeedKing

Here is where I got the top speed. https://www.motor1.com/news/264738/ssc-tuatara-targa-considered/


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Cocobe  2w ago @nats50

(0.0025565 x 22.30 x 0.355 x 304.77^3 + 0.015 x 304.77 x 4,525)/375, then multiplied by 1.20

even according to your formula, the factor of drag vs rolling resistance is
572922 vs 20686. So Drag is 27.7x more a factor than weight. And that weight would have only used up 55hp. In other words, had they shaved a massive 500kg, they would have had 14 extra hp to work with... like I said, not a factor.

I didn't use approximate numbers. I used metric units. I used the air density at 15 degrees C, sea level. where the air density is 1.225kg/m^2.

However if If I used a more realistic 50m elevation, 25degrees C. air density becomes 1.174kg/m^2.
The chiron ss achieved 136.24m/s. Lets say it's 136, and .24 was aided by wind.

0.5 x 1.174 x 0.355 x 2.07 x 136^3 = 1085059 watts
divide by 735.5 = 1475PS.

Say we use your figure of 55hp of rolling drag. which combines to ~1530PS

But, we know OBVIOUSLY the Chiron SS is much more slippery than the regular Chiron. The front splitter only has 1 element instead of 2. The rear packaging has tightened up a lot more, so the Cd could drop as low as .33 for extreme case.

recalculate
0.5 x 1.174 x 0.33 x 2.07 x 136^3 = 1008646 watts
divide by 735.5 = 1371PS. Suddenly that's looking a lot more possible.

Now add your rolling resistance = 1426PS.

Now, it becomes tricky... how much is drivetrain loss adjustment? If it's 15%, then it's 1640PS. If it's 10%, 1569hp. If it's 20% then it's 1711PS, all within +/- 7% of claimed power.

Those numbers are close enough if you ask me. If a Mclaren 720S pumps out 689 wheel hp, at 15% adjusted = 792hp, which is MORE than 10% claimed.

So Bugatti isn't pulling out ridiculous claims. You'd be a fool to expect the engine had exactly the power they stated since almost no manufacture gives exact HP numbers, (mclaren, BMW, Porsche, Audi, Mercedes...) they all give more than stated, imo, it's to mask and compensate for the understated weight as well...


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lafars  2w ago @nats50

actually anyone who's done a little research on top speed will tell how small of a factor mass and rolling resistance makes

they're minute compared to drag

rolling resistance can be reduced by having less downforce in top speed mode and focusing on aero balance, Bloodhound SSC for instance is running as close to zero-lift/downforce as possible so they only gain stability with winglets

mass:

assuming no air resistance the ability continually push an object you'd reach light speed at some point in time regardless of mass, this is an explanation that physicists have used to exemplify how mass doesn't affect top speed


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lafars  2w ago @nats50

the main problem in your calculations is that you're using top speed mode REGULAR Chiron for drag coefficient

despite the fact that they managed to reduce the tear off behind the car by 40% because of the long-tail


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FastestLaps  2w ago @lafars

Rolling resistance is very interesting quantity. Tyre rolling resistance can actually reduce when you accelerate from somewhat slow speed to somewhat faster speed, because tyres become stiffer when they rotate quickly and less energy is absorbed in tyre flex.

I am not sure what happens when you go really fast (I bet the resistance goes up overall). But for slow speeds it means that on highway you probably have less rolling resistance losses than in city at 40 kph.

This effect is probably more pronounced for higher profile (or lower PSI) tyres. For fast cars with low profile tyres "rolling resistance" probably means other things - energy loss in hubs/bearings/driveshafts etc.

But of course, this is all not very relevant. The main thing for topspeed is simply dividing real power to the wheels by the real aero drag.


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SpeedKing  1w ago @nats50

According to Koenigsegg the Agera RS has 1360 hp which i don't dispute. The 284 mph it achieved in the first run was on the downhill stretch of the Nevada highway. On the return second pass it only managed 270 mph due to the uphill gradient and possible heat soak. I don't know how long they waited before doing that second pass because some heat soak was possibly an issue. So my problem with using formulas is that those factors are not part of the equation but it's clear they play a role in determining the outcome.


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nats50  1w ago @SpeedKing

And that is why they run in both directions to offset any downhill or uphill added or suppressed speed, not to mention the wind. So, the average between the two, 270 and 284, is just right there, 277-278. Sure, formulas and equations are just that, but they sure predict good results nonetheless. Being within a mile per hour or a few horses is satisfying enough. I have dozens of website regarding this matter, from the simplest math to the most complex. It sure makes your head spin. Nice chatting with you.


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SpeedKing  1w ago @nats50

If there's one thing i've learnt over time is that one should never take everything manufacturers claim as an absolute particularly when it comes to hp figures. The Chiron SS is a perfect example given the acceleration comparison to a stock Chiron. The Chiron SS took under 11 secs to get from 200 to 250 mph whereas a stock Chiron takes 16 sec. So would an additional 100 hp make a 5+ sec difference? No chance. As i've said previously the longtail on the SS definitely reduces drag but the larger air ducts in the frontal area of the SS consumes a lot more air(primarily for additional engine cooling) which obviously adds to drag and therefore negates the longtail effect by a considerable amount. Hence the question i raised revolved around how much horsepower did the SS really have and my belief is that it had a lot more than the 1600 bhp that Bugatti claimed.


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nats50  1w ago @Cocobe

You are getting to be amusing. That formula is as precise as you can get. It is nothing but a conversion of the rho equation you are familiar with. You usually just use 0.002377 for rho, but there I gave you more significant figures. And let me tell you about where I got those factors such as 1.15 or 1.20 or whatever I will use. If you really good in math, you will notice that the reciprocal of 1.15 is 0.86956...or 1 - 0.86956 is 0.13043..., which means 13.043% power loss was used. Or, take 1.20 which is nothing but the reciprocal of 0.83333...or 1 - 0.83333 is 0.16667..., which means 16.667% power loss if you will. Making sense to you? Go to this website I've been posting and see for yourself. Sorry to say, but I've been doing these sorts of calculations for more than a decade. I'd like to show the true forms of equations or formulas, but the browser doesn't support the format such as superscripts and subscripts, radicals and exponents. Hard to express it here.

0.5 times 0.002376984 times 88S/60 times 88S/60 times Cd times A = 0.0025565ACS^2 then multiply again one more V

rho = 0.002376894, yes at standard temperature of 59 F or 15 C, 29.92 pressure or 1013.25 mb, 0% humidity
V = 88S/60 or 1.46667S
1.225kg/m^2 is just the same as 0.002376894 which is in slugs
88S/60 = is the same as V converted from miles per hour to feet per second, or, 1.46667S instead of 88S/60. It doesn't matter cause they are the same. It doesn't matter whether you use English or Metric or Imperial system just a s long as they produce the same results. 1 kilogram is the same as 2.205 pounds, 60 miles per hour is still 88 feet per second or 26.82 meters per second, and so on, right? The most troublesome part of the drag formula is the rolling resistance section. I wish I could show you here the engineering equation for determining the rolling coefficient which is part of the drag equation and you can't just ignore it and just stick to the aero drag only. Also, the rolling resistance is not directly proportional to speed or velocity. Twice the speed is not going to produce twice the resistance. It doesn't work that way. In fact, there is also the gradient and inertia equation parts that are not included here or are usually ignored. The 0.15 that is used here is just the standard one used, but in practice and reality, it is not a fix value but changes with speed of the car. it varies anywhere between a low 0.006 to 0.050 and even up! Enough of this.

Koenigsegg Agera RS

H = 1,160 hp
A = 20.16 square feet
C = 0.33
S = 277.87 mph
W = 3,078 + 165 = 3,243 lbs

H = Crank or flywheel horsepower
A = Frontal area in square feet
C = Drag coefficient
S = Speed in miles per hour
W = Curb weight of car plus driver (165 pounds is normally used) in pounds

0.0025565ACS^3 + 0.015SW

H = (--------------------------)1.15
375

0.0025565x20.16x0.33x277.87^3 + 0.015x277.87x3,243

= (----------------------------------------------------)1.15
375

364,901 + 13,517

= (------------------)1.15
375

= 1,009 x 1.15 = 1,160

https://www.koenigsegg.com/car/agera-rs/#aerodynamics
https://www.koenigsegg.com/car/agera-rs/#engine
https://www.koenigsegg.com/car/agera-rs/#dimensions
https://www.google.com/search?sxsrf=ACYBGNSKvxfQGDdyQzUfQvaJByIRFXgpJg%3A1581860992466&ei=gEhJXpiGHIq0sQXjuKKoBw&q=koenigsegg+agera+rs+drag+coefficient&oq=koenigsegg+agera+rs+drag+&gs_l=psy-ab.1.1.0l2j0i22i30l4.18632.21530..23523...0.2..0.324.1013.0j4j1j1......0....1..gws-wiz.......0i71j0i67j0i20i263.LJ9rp7PIi2Y#spf=1581866843603




User avatar

manone  1w ago @lafars

"actually anyone who's done a little research on top speed will tell how small of a factor mass and rolling resistance makes

they're minute compared to drag"

it depends at what speed you are talking about. check figure 2.31 of the link
https://www.sciencedirect.com/topics/engineering/rolling-resistance
they derived the rolling resistence of few tyres experimentally up to 220kmh and you see the increase in function of speed. Very little is known about the coefficient at higher speeds as far as i know, but i suspect tyre centrifugal forces start to play a big role at higher speeds.

"rolling resistance can be reduced by having less downforce in top speed mode and focusing on aero balance, Bloodhound SSC for instance is running as close to zero-lift/downforce as possible so they only gain stability with winglets"

bloodhoud rolling resistance do not arise from wheels themselves regardless downforce, but just from the ground surface. Wheels' centrifugal forces become a key factor: https://www.youtube.com/watch?v=mPshhkYpCBY


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lafars  6m ago

maybe i should've added Super Sport 300+ to the model name, but then again @fastestlaps can reupload with proper changes