Speedo calibration
10-01-2003, 10:36 AM
#17
Super Guru
Rennlist Member
Rennlist Member
Originally posted by Phil Raby
If you have a handheld GPS unit, you can use it to check the accuracy of your speedo - most will display the speed you're travelling...
Cheers
If you have a handheld GPS unit, you can use it to check the accuracy of your speedo - most will display the speed you're travelling...
Cheers
10-01-2003, 10:58 AM
#18
Addict
Rennlist Member
Rennlist Member
Originally posted by Ruairidh
John, I'd ask Paula to hold the GPS unit for you, given the speeds you get up to - one handed driving at 150mph ain't recommended in any Highway Code I've ever read!
John, I'd ask Paula to hold the GPS unit for you, given the speeds you get up to - one handed driving at 150mph ain't recommended in any Highway Code I've ever read!
A mate has a Garmin unit and it wedges neatly between the screen and dash top. I'll borrow it sometime to check my speedo.
I think it's reasonably to assume that any discrepancy will not be linear. In other words, a speedo could be 10% out at 30mph and 5% out at 100mph...
Phil
10-02-2003, 01:01 AM
#19
Racer
Join Date: Jan 2003
Location: Hong Kong
Posts: 289
Likes: 0
Received 0 Likes
on
0 Posts
Dear 964ers,
I have these problem which I did raise before. May be some one can help me with that ( Adrian ?)
As far as I understand, there are two common types of speed pick ups. The analog one using a Tachometer which generates an analogue voltage signal in relation to rotating speed. This is normally used to drive the analog meter with a dial. For the digital pick up, basically the common one is optical pick up either using absolute type or inceremental type which producing some kind of digital signals (BCD or gray code). They are noramlly used to input to the Engine Management ssytem and may be in Porsche's case for the digital display.
I do not know how 964 pick up the speed signal and the fact that I have found the analog display has a discreptancy with the digital display. I do not know which one is more accurate and may be both of them are off.
Any idea?
Eddie
I have these problem which I did raise before. May be some one can help me with that ( Adrian ?)
As far as I understand, there are two common types of speed pick ups. The analog one using a Tachometer which generates an analogue voltage signal in relation to rotating speed. This is normally used to drive the analog meter with a dial. For the digital pick up, basically the common one is optical pick up either using absolute type or inceremental type which producing some kind of digital signals (BCD or gray code). They are noramlly used to input to the Engine Management ssytem and may be in Porsche's case for the digital display.
I do not know how 964 pick up the speed signal and the fact that I have found the analog display has a discreptancy with the digital display. I do not know which one is more accurate and may be both of them are off.
Any idea?
Eddie
10-02-2003, 03:47 AM
#21
Addict
Rennlist Member
Rennlist Member
Originally posted by John Boggiano
Just for the record, Porsch-Apart can't do it.
Just for the record, Porsch-Apart can't do it.
Cheers
10-02-2003, 05:59 AM
#23
Addict
Rennlist Member
Rennlist Member
Originally posted by John Boggiano
I would have told them to back it off by 10% across the range, which seems right in my case.
I would have told them to back it off by 10% across the range, which seems right in my case.
How have you come to that figure?
Cheers
10-02-2003, 11:36 AM
#27
The thing you are talking about is a so called "safety margin".
In newest porsches (996, boxsters) there are two signals: "real speed" and "speed with safety margin".
In newest porsches (996, boxsters) there are two signals: "real speed" and "speed with safety margin".
