Actual speed governer cut off?

[Miamiboyca]

Originally Posted by David1

The wheel speed sensors and sensors in the trans.

How is this different?

I'm not being difficult and genuinely trying to understand.

[Junkball]

You mean I actually wasn't going 166 mph????

There's no doubt the speedos read high, and it seems to be a safety/liability feature - I think the latter moreso, and have been noticing the trend of describing certain things as safety features when they're more like design compromises due to legal or other obligations.

Both the analog and digital speedos indicated 167 mph for me at one point but I have no doubt I was only going 155.

[CanAutM3]

Originally Posted by L3x

Atleast I have an advantage living in Europe, not many days I dont hit 200+ km/h

Anyway, all speedo's are slightly off. I believe it is even a law for car manufactures, atleast for
European cars. One of the reasons is that when your tyres wear down your speedo actually shows slower speeds compared to real speed. So they make the speedo show higher speeds, believe on average it is about 5 to 10%. Your speedo will be more accurate with worn out tyres, a manufacurer would get in serious trouble if a speedo will show a slower speed then the actual real speed with worn out tyres!

It is the other way around. The speedo is optimistic to start with. As the tires wear down, their diameters decrease and thry need to spin faster for the same road speed, hence the speedo becomes even more over optimistic.

[CanAutM3]

Originally Posted by evanevery

Sure, the computer knows EXACTLY what speed your car is going

That statement isn't EXACTLY true either .

Since the computer doesn't know the EXACT rolling radius of the tires installed on the car, it can only make a best guess based on wheel rotation speed and a default factory setting of the rolling radius.

[CanAutM3]

The speedo is surely optimistic, but likely not as much as some are suggesting.

In this road test, they seem to have achieved a GPS top speed of 262.7km/h (163.3mph) with an indicated 266km/h on the speedo.

http://www.truespeed.co.za/index.php...t=WyJibXciXQ==

Car And Driver have also documented 163mph GPS top speeds in their M3 and M4 road tests. They also show a 2mph error at 70mph.

http://media.caranddriver.com/files/...ented-test.pdf
http://media.caranddriver.com/files/...w-m4-coupe.pdf
http://media.caranddriver.com/files/...015-bmw-m4.pdf

[CanAutM3]

Originally Posted by Miamiboyca

... and adjusted in software for 18 vs 19 inch wheels.

There is no need for adjustment between the summer 18" and 19" wheels since the respective tires have essentially the same diameters.

However, when installing the BMW recommended winter tires, the speedo will be even more optimistic, since they have a smaller diameter. There is no software adjustment for that.

[Miamiboyca]

Originally Posted by CanAutM3

The speedo is surely optimistic, but likely not as much as some are suggesting.

In this road test, they seem to have achieved a GPS top speed of 262.7km/h (163.3mph) with an indicated 266km/h on the speedo.

http://www.truespeed.co.za/index.php...t=WyJibXciXQ==

Car And Driver have also documented 163mph GPS top speeds in their M3 and M4 road tests. They also show a 2mph error at 70mph.

http://media.caranddriver.com/files/...ented-test.pdf
http://media.caranddriver.com/files/...w-m4-coupe.pdf
http://media.caranddriver.com/files/...015-bmw-m4.pdf

So I guess I went 157.... Hahaha

[F83]

Originally Posted by Junkball

You mean I actually wasn't going 166 mph????

There's no doubt the speedos read high, and it seems to be a safety/liability feature - I think the latter moreso, and have been noticing the trend of describing certain things as safety features when they're more like design compromises due to legal or other obligations.

Both the analog and digital speedos indicated 167 mph for me at one point but I have no doubt I was only going 155.

To quote Marshawn Lynch on Conan O'Brien;

"Point blank and broad daylight"! You have cajones my friend.

[Miamiboyca]

Originally Posted by F83

To quote Marshawn Lynch on Conan O'Brien;

"Point blank and broad daylight"! You have cajones my friend.

Do and ED and you will see its not that uncommon in certain parts of the autobahn.

When I hit my speedo indicated 161 (whatever it actually was) I was in a pack with 3 other cars and I could tell they were locals. (2-audis and 1 "other"

[evanevery]

Originally Posted by CanAutM3

That statement isn't EXACTLY true either .

Since the computer doesn't know the EXACT rolling radius of the tires installed on the car, it can only make a best guess based on wheel rotation speed and a default factory setting of the rolling radius.

You are correct. Perhaps my EXACTLY could have been tempered a little. But the computer does calculate the speed as close as possible to what it actually should be.

Not the case with the speedo(s) - which are purposefully set a little high...

[L3x]

Originally Posted by CanAutM3

It is the other way around. The speedo is optimistic to start with. As the tires wear down, their diameters decrease and thry need to spin faster for the same road speed, hence the speedo becomes even more over optimistic.

No, that is not how it works!
When your tyres wear down, your tyre will "travel" less distance each revolution. To simplify, your car messures how long each revolution takes or even simpler the speed of the revolution to determen the vehicle speed. But worn out tyres is less distance each revolution. Meaning a car with New tyres will show a higher speed as a car with worn out tyres while their real speed is the same.

Tyre pressure is also a factor, manufactures are in fault when a speedo shows a slower speed as it actually is. So they make is that even a car with worn out tyres and slightly off tyres pressure still shows a speed that is above the actual, but it will be closer to the real actual speed! It has to be made idiotproof or they can get in trouble.

[CanAutM3]

Originally Posted by L3x

No, that is not how it works!
When your tyres wear down, your tyre will "travel" less distance each revolution. To simplify, your car messures how long each revolution takes or even simpler the speed of the revolution to determen the vehicle speed. But worn out tyres is less distance each revolution. Meaning a car with New tyres will show a higher speed as a car with worn out tyres while their real speed is the same.

Tyre pressure is also a factor, manufactures are in fault when a speedo shows a slower speed as it actually is. So they make is that even a car with worn out tyres and slightly off tyres pressure still shows a speed that is above the actual, but it will be closer to the real actual speed! It has to be made idiotproof or they can get in trouble.

Sorry bud, but you got it wrong; better check your physics

Think about it a little. For the speedo, a given wheel RPM equates to a given road speed. If the car travels less distance for each tire revolution, as you correctly stated, then the car is covering less ground than it believes for each revolution, hence traveling slower than the speedo indicates.

[wazzza]

Originally Posted by MGM4

Driving home late last night on a familiar stretch of highway, no other cars around, decided to push it right up to what I thought was a top (governed) speed of 155 mph. I stayed on it right up to 155, and to my surprise, it blows right past 155, next thing I know, the speedometer is reading 161 mph on my HUD...doesn't take very long at all to go from 155 to 160 btw

I had to brake (hard) for the upcoming exit ramp otherwise would have kept pushing it...obviously had way more room to explore if there was no governer there

So, just wondering what the actual governed speed is?? I am located in the USA

Get a Room! Umm, I meant, a Race Track!