# Speed/RPM/Gear overlay on TV

9 replies to this topic

### #1 Otaku

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Posted 23 September 2013 - 06:02

Hey guys, I was watching the video posted on the thread about the Alonso/Webber incident and something got my attention.

Here's the video:

The thing is, how accurate is that crap? Because you can see that when Alonso is cruising in 7th gear at around 10.000 rpm, the speed reads 131 km/h. Now a bit or simple math tells me that, by linearity, at 20.000 rpm the car should be doing 262 km/h so there's something clearly wrong as the car was doing about 295 when it hit the 18.000 rpm limiter. How is the data the overlay uses obtained? Directly from the car's telemetry? Is it just calculated analyzing the sound like in the old times? It's not just a bit off, it's complete bullsh1t.

Opinions? Am I missing something here?

Edited by Otaku, 25 September 2013 - 23:06.

### #2 Jejking

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Posted 23 September 2013 - 09:46

Hey guys, I was watching the video posted on the thread about the Alonso/Webber incident and something got my attention.

Here's the video:

The thing is, how accurate is that crap? Because you can see that when Alonso is cruising in 7th gear at around 10.000 rpm, the speed reads 131 km/h. Now a bit or simple math tells me that, by linearity, at 20.000 rpm the car should be doing 262 km/h so there's something clearly wrong as the car was doing about 295 when it hit the 18.000 rpm limiter. How is the data the overlay uses obtained? Directly from the car's telemetry? Is it just calculated analyzing the sone like in the old times? It's not just a bit off, it's complete bullsh1t.

Opinions? Am I missing something here?

There's your flaw. F1 engines power output and torque output are never linear. Combine that with several gears, and your theory goes to bust.

### #3 SenorSjon

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Posted 23 September 2013 - 10:08

Try it with your own car in a gear. It is not double RPM = double speed.

### #4 Oho

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Posted 23 September 2013 - 10:35

Try it with your own car in a gear. It is not double RPM = double speed.

No kidding, so you think F1's have slipping torque converters to separate engine crank from the driven wheels. I looked at the same discrepancy on revolution count vs speed and it seemed very odd indeed.

Edited by Oho, 23 September 2013 - 10:38.

### #5 Scotracer

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Posted 23 September 2013 - 10:53

Try it with your own car in a gear. It is not double RPM = double speed.

Of course it is! There is a fixed gear ratio in 7th. If you double the engine speed you HAVE to double the road speed. It's as simple as that.

The OP is correct - very odd.

### #6 Otaku

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Posted 25 September 2013 - 22:38

There's your flaw. F1 engines power output and torque output are never linear. Combine that with several gears, and your theory goes to bust.

Try it with your own car in a gear. It is not double RPM = double speed.

Lol x 2. Go study some mechanic principles and come back.

### #7 george1981

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Posted 26 September 2013 - 09:31

Doesn't the wind resistance come into it too? Even if the car did produce double the power at 20,000 rpm as it did at 10,000 rpm. The faster the car goes the more power it needs to go faster. I think its fair to say that approximately the wind resistance squares with velocity, i.e. wind resistance at 200kph ~ = (wind resistance at 100kph x 4).

### #8 matd81

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Posted 26 September 2013 - 09:41

Heard of a diff guys?

Suggest you brush up on your mechanical knowledge and google it and what it does....

### #9 JeePee

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Posted 26 September 2013 - 10:06

Heard of a diff guys?

Suggest you brush up on your mechanical knowledge and google it and what it does....

A diff also has a fixed ratio. Same as the gears and there is hardly any slip in the drivetrain. Only when there's wheelspin the double RMP = double Km/h formula does not count.

I haven't check the video, but Otaku is right in saying the RMP in relation to the speed of the car is linear when there are no gear changes and no wheelspin and no clutch slip.

The thing that also bothers me on the overlay is the 'brake' indicator. It's always 100% brakes or 0% brakes, nothing in between, whereas the throttle seems pretty accurate.

Edited by JeePee, 26 September 2013 - 10:13.

### #10 prty

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Posted 26 September 2013 - 10:38

I think they just analyze the sound frequency to come up with the RPM count that is displayed, so they might have caught an harmonic of the microphone noise frequency, as in 7th at low speeds the engine is not so loud, and the signal to noise ratio is worse.

Try it with your own car in a gear. It is not double RPM = double speed.

No kidding

Edited by prty, 26 September 2013 - 11:01.