odometer over-reading
Discussion
I've long thought that my odometer isn't accurate, I'm sure what used to be just under a 40 mile journey in my last car is over 40 in the wedge.
With my new GPS, I've confirmed the the odometer shows 107 miles for every 100 miles the car travels.
I'm guessing this is as I have a slightly different circumferance of the wheels, as I have 16" wheels rather than the standard 15" (or as my dad says, due to too much wheelspin). Is there anything I can do to get it adjusted?
With my new GPS, I've confirmed the the odometer shows 107 miles for every 100 miles the car travels.
I'm guessing this is as I have a slightly different circumferance of the wheels, as I have 16" wheels rather than the standard 15" (or as my dad says, due to too much wheelspin). Is there anything I can do to get it adjusted?
cdt said:
I'm meaning the distance driven rather than the speedo, that's always been out on every car I've had.
The mileometer is driven by the speedometer. So if the speedo is out (and they all are, whatever the car, if only by a small percentage), then the mileage will be out too...All my different cars have over read on the speedo compared to the Sat Nav
BUT as someone said to me
"if your speedo was under reading and you kept getting speeding tickets
then you would soon be sueing the motor manufacturers"
It just means you can go faster than what your speedo says !!!!!
(but don't blame me if you get scameraed)
Rich
BUT as someone said to me
"if your speedo was under reading and you kept getting speeding tickets
then you would soon be sueing the motor manufacturers"
It just means you can go faster than what your speedo says !!!!!
(but don't blame me if you get scameraed)
Rich
It's not the size of the wheels that's important; it's the width and type of tyres. I have the same problem. We both have tyres with an overall rolling diameter slightly smaller than the factory calibrated value.
I have 235x45x17 tyres. 235x50x17 would be too large. 245x45x17 would be closer.
I have 235x45x17 tyres. 235x50x17 would be too large. 245x45x17 would be closer.
My last new Mondeo was worse for this, at 30 mph only 2 mph out, but at an indicated 120 (on a private track 
) I was only doing 105 on the GPS
I know how I got time to look at both speedo and gps whilst going round the track at such attrocious speeds is beyond comprehension
Speed kills they say, but it was answering the phone and sending a fax at the same time that got me
) I was only doing 105 on the GPSI know how I got time to look at both speedo and gps whilst going round the track at such attrocious speeds is beyond comprehension
Speed kills they say, but it was answering the phone and sending a fax at the same time that got me
If you have non standard wheels then the rolling diameter is going to change and that will put the speedo out. you would have to fit lower profile tires to reduce the rolling diameter or change to a digital dash. but as said all speedo miss read. when a car leaves the factory it can over read by 10% IIRC but not under read.
The only car that I have had that reads within 1% of the GPS is the Wedge. even at 90 MPH as tested on a track
car was 90 GPS was 89.
Will have a Digital dash in the BBWRC run off GPS and acceleration meters.
The only car that I have had that reads within 1% of the GPS is the Wedge. even at 90 MPH as tested on a track
car was 90 GPS was 89.Will have a Digital dash in the BBWRC run off GPS and acceleration meters.
[quote=TVRleigh(BBWR)] you would have to fit lower profile tires to reduce the rolling diameter.
[/quote]
Surely lower profile tyres and a reduced rolling diameter would mean the transmission has to do more turns to cover a set distance so the calibration of the speedometer, based on factory rolling diameter value, would indicate an even higher speed than real speed?
[/quote]
Surely lower profile tyres and a reduced rolling diameter would mean the transmission has to do more turns to cover a set distance so the calibration of the speedometer, based on factory rolling diameter value, would indicate an even higher speed than real speed?
driverrob said:
My TomTom 501 seems to do everything except display my speed. I keep reading of others that do. Is there a setting I've missed somewhere?
On the 710 you can get it to show on the display via:menu/change preferences/status bar preferences/ then select "speed."
(To get the staus bar preferences option to show for the first time:
menu/change preferences/show ALL menu options)
Not sure if it's the same on yours
Incidentally my V8S speedo, according to the TomTom, is the most accurate of any of the other "normal" cars I've had. It does mean that there's not much margin for error though.
Speedo is calibrated by 2 factors: gain and offset.
If the ofset is wrong (i.e. the needle is on the piss on the shaft), the misread'll be constant.
If the gain is out, the mis-read will be propertional to amplitude (speed).
Either way, the easy thing to do is understand what the error is and drive accordingly when in the evil stare of LTI20/20 / Truvelo / Gatso / SPECS.
Ed.
If the ofset is wrong (i.e. the needle is on the piss on the shaft), the misread'll be constant.
If the gain is out, the mis-read will be propertional to amplitude (speed).
Either way, the easy thing to do is understand what the error is and drive accordingly when in the evil stare of LTI20/20 / Truvelo / Gatso / SPECS.
Ed.
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