3 My Take On The VW Golf R

It's me again, the controversial gremlin...LOL! I came across this car on the internet which is already causing some controversies. I found out it has to do with its true horsepower. Nothing new really. You see, it's well known that certain car makers, with no exception, at times either underrate or overrate the horsepower figure for one. Often on the underrate side. Anyway, having gathered this information or specs of the car to the best of my ability and information available at hand, these are the specs:

Car -> 2021 VW Golf R
Horsepower -> 315 @6,500 rpm
Torque -> 310 @310 @5,350 rpm
Weight -> 3,585 lbs including driver; 1,626 kgs
Frontal area -> 23.80 sq ft; 2.23 sq mt
Drag coefficient -> 0.275
Air density -> 1.204 kg/m^3 = 0.0000067005

Now, having achieved the following speeds which I will show on paper and in the articles showing the video also, I will use the assumed horsepower of 340 for now and see the results. Using the basic and standard drag and rolling resistance equation, I'll save you guys the trouble by having already solved these examples using different drivetrain efficiencies — 0.90, 0.85, 0.80, with the "fixed and overused" coefficient of rolling resistance of 0.015, and standard air density of 1.204 kg/m^3.

340 (345 PS) horsepower = 253,538 watts times 0.90 = 228,184 watts -> 184.87 mph -> 82.64 meters per second
340 (345 PS) horsepower = 253,538 watts times 0.85 = 215,507 watts -> 181.17 mph -> 80.99 meters per second
340 (345 PS) horsepower = 253,538 watts times 0.80 = 202,830 watts -> 177.31 mph -> 79.26 meters per second

Pn=[0.5pCdAV^2+ Cr(M+Df)g]V

where:
P = Power in watts -> 253,538
n = Drivetrain efficiency or (1 - n = power loss) -> 0.90; 0.85; 0.80
p = Rho or air density in kg/m^3 -> 1.204
Cd = Drag coefficient -> 0.275
A = Frontal area in square meters -> 2.23
V = Velocity in meters per second -> 82.64; 80.99; 79.26
Cr = Coefficient of rolling resistance -> 0.015
M = Mass of the car in kilograms -> 1,626
Df = Downforce, if any, in kilograms
g = Acceleration due to gravity -> 9.8067

According to this article, the top speed of the car, assuming the 315 hp, should only be about 167 mph. However, the video showed the speedometer reaching 289 kph, or about 179.61 mph. Now, it's not likely that 315 hp can achieve that as my calculation using different drivetrain efficiencies or power loss with a constant 0.015 coefficient of rolling resistance! These are the sites:
https://www.motor1.com/news/498540/vw-golf-r-top-speed/
https://www.motor1.com/news/495522/vw-golf-r-dyno-pull/

NOW, using my OWN method and controversial equations: According to this site, https://tirepressure.com/volkswagen-golf-r-tire-pressure#2019, I'll use both 39.0 psi and 42.5 psi which is usually the maximum tire pressure used for street rated tires. As you can see, the higher tire pressure used, the higher top speed results.

Hc = (0.00000556517pAfCdS^3+ 0.0026667CrSWt)/Pf
Pf = 5,252Hc/EpTp

Where:
Hc = Horsepower 315 (319 PS)
p = 1.204 kg/m^3
Af = 23.80 sq ft
Cd = 0.275
S = 166.94 mph @39.0 psi; 167.82 mph @42.5 psi
Wt = 3,585 lbs including driver (165)
Pf = 0.82103
Ep = 6,500 rpm
Tp = 310 lb-ft
Cr = 0.0340 @39.0 psi; 0.0320 @42.5 psi

NOW AGAIN, using this time 340 hp:

Where:
Hc = Horsepower 340 (345 PS)
p = 1.204 kg/m^3
Af = 23.80 sq ft
Cd = 0.275
S = 176.00 mph @39.0 psi; 176.87 mph @42.5 psi
Wt = 3,585 lbs including driver (165)
Pf = 0.88619
Cr = 0.0370 @39.0 psi; 0.0347 @42.5 psi

Finally, it is well established that European cars' speedometers read high due to this European Union adherence to UN ECE Regulation 39
https://www.thrillist.com/cars/your-speedometer-is-wrong-speed-calibration-inaccuracy-in-german-american-and-japanese-cars. In summary and conclusion, if the GPS-verified speed of 172 mph is to be the judge, then it is likely the car had more than 315 hp BUT less than 340 hp as suspected, the speedometer overreading as noted in the article. Thanks for the time.

7m ago by NatsM
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Corvolet3  7m ago

More than 315 but less than 340? Yeah, I'd say we take the middle which would be ~328 hp which pretty much translates to 332 PS. That way it would be equal to an Audi S4 B8 from 2008-2015. Performance wise I think you can also compare it to the first gen Audi RS3 which is claimed to have 340 PS. Though I believe it has more power due to the fact it has a weaker transmission and more weight.


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NatsM  7m ago

However, on second thought, had I used the SAE J1349 standard air density of 1.157 (77 F; 29.235 inHg; 0% humidity) and 46.5 psi tire pressure, it's still possible for 315 hp to achieve a calculated top speed of about 170.54 mph, or 171 mph, in line with the GPS-verified speed of 172 mph. The slight difference may be either a 1 mph wind, or a slightly different air density during the run, or both. And in conclusion again, if it was really the 315 hp version, and the speedometer read 289 kph or almost 180 mph, it can only be the dreaded speedometer error common to European cars, specially German ones.


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NatsM  7m ago

Using my method and equations, for the 315 hp version, the article says the top speed is 167 mph — just the same as my results of 166.94 mph using 39.0 psi tire pressure, and 167.82 mph using 42.5 psi tire pressure!