Speedo reading vs actual speed
Discussion
Started a new thread on the back of the b
h in the audi thread but also hear it mentioned quite a bit on here around the speado reading a few MPH less than you are actually doing, more so at higher speeds.
My car is 13 this year and can imagine it is somewhat out by quite a bit - dont have GPS/satnav to verify this but would imagine so.
Is it possible to take it to a garage to have synched/re callibrated and if so is it worth it from a cost perspective?
h in the audi thread but also hear it mentioned quite a bit on here around the speado reading a few MPH less than you are actually doing, more so at higher speeds. My car is 13 this year and can imagine it is somewhat out by quite a bit - dont have GPS/satnav to verify this but would imagine so.
Is it possible to take it to a garage to have synched/re callibrated and if so is it worth it from a cost perspective?
Most car speedos are usually out by about 7-8 mph at motorway speeds,4-5mph at lower speeds.I have noticed this on all the cars ive driven compared to a gps reading.
From what I have gathered they are set this way from the factory by the manufacturers mainly to stop any disputes over speeding convictions from drivers who might say their speedo was inaccurate.
From what I have gathered they are set this way from the factory by the manufacturers mainly to stop any disputes over speeding convictions from drivers who might say their speedo was inaccurate.
DaveH23 said:
Started a new thread on the back of the bh in the audi thread but also hear it mentioned quite a bit on here around the speado reading a few MPH less than you are actually doing, more so at higher speeds.
It would be quite unusual for a speedo to read less than the speed you're going at. Usually they over-read. h in the audi thread but also hear it mentioned quite a bit on here around the speado reading a few MPH less than you are actually doing, more so at higher speeds. The worst i've seen is a Nissan Micra, which through a combination of terrible dial design (spacing between lines too large) and over reading by miles, means that 30mph looks like 35mph! 30mph on the dial is actually more like 26mph.
The dial is also extremly slow to move around, particularly under deceleration.
The dial is also extremly slow to move around, particularly under deceleration.
GBDG said:
The worst i've seen is a Nissan Micra, which through a combination of terrible dial design (spacing between lines too large) and over reading by miles, means that 30mph looks like 35mph! 30mph on the dial is actually more like 26mph.
The dial is also extremly slow to move around, particularly under deceleration.
Worse one for me is a d40 navara! A good 6-7 miles out.The dial is also extremly slow to move around, particularly under deceleration.
Apart from that all my cars have been within 2-3 miles an hour.
I have the 'AwesomeHUD' (geeky and a bit sad I know, but it was free) app on the iphone, which obv uses gps data to figure out your speed and both that and the tomtom always read the real speed about 5-7 mph under with the differential increasing the faster I go. 70 on the speedo is about 64-65 on the gps devices.
kambites said:
It would be quite illegal for a speedo to read less than the speed you're going at. Usually they over-read.
EFAAs indicated above it is illegal for speedos to under-read or over-read by more than 10% so most are set for 2-7% over-reading. Only way to test is to sit at an indicated 60 mph on the motorway and get your passenger to time you between mile markers, the more the better. Take the time and calculate your real speed. GPS is not really that accurate as the distance measurement is +/- and also takes no account of corners.
Both my current cars are pretty accurate...
2000 Porsche 996 - 5 mph out at 80mph
2008 Mondeo 2.2TDCi - 3 mph out at 80mph
I borrowed a 2008 Golf GTI from our car pool to go to the South of France in a few years back and when I set the my Tom Tom to kmh the Golf speedo was miles out... >20kmh over reading at 180kmh.
2000 Porsche 996 - 5 mph out at 80mph
2008 Mondeo 2.2TDCi - 3 mph out at 80mph
I borrowed a 2008 Golf GTI from our car pool to go to the South of France in a few years back and when I set the my Tom Tom to kmh the Golf speedo was miles out... >20kmh over reading at 180kmh.
Remember that if your speedo is 10% out, so is your odometer and any trip computer you might have. However, it's not something that gets worse with age, so wether your car is brand new or 13 years old the difference would be the same.
Lots of people are saying 'mine is out by 'x' mph', however it is generally a proportional thing. E.g. rather than being out by 6mph at all speeds, it is more likely to be 6mph at 60 and 3 mph at 30. Remember it's illegal for it to over read by more than 10% at any speed.
Depending on the age of the car, re-calibrating may not be straight forward. On an older cable driven speedo your best bet is to tipex out the numbers and write new ones on with a pen
My 106 is spot on, the Volvo was out by about 5% and my 306 is about 10% out because I've put smaller wheels on it.
Lots of people are saying 'mine is out by 'x' mph', however it is generally a proportional thing. E.g. rather than being out by 6mph at all speeds, it is more likely to be 6mph at 60 and 3 mph at 30. Remember it's illegal for it to over read by more than 10% at any speed.
Depending on the age of the car, re-calibrating may not be straight forward. On an older cable driven speedo your best bet is to tipex out the numbers and write new ones on with a pen
My 106 is spot on, the Volvo was out by about 5% and my 306 is about 10% out because I've put smaller wheels on it.
Gassing Station | General Gassing | Top of Page | What's New | My Stuff