Speedo Calibration

[blackturbo]

Is it possible for a garage to re-calibrate a speedo or do you need a rolling road to do it?

Reason I ask is acording to my Sat Nav my speedo is UNDER reading by approx 5 mph which obviously is worse than over reading as im going faster than i think

 

[Tony 156]

sat navs are not accurate, your speedo will be more accurate so it is probally fine.

Just remember that wheel size does make i difference, at 30mph, with 17's you will be doing 32ish and with smaller wheels you will be doing less speed.

 

[David_smith_909]

sounds normal mate, when im doing 100mph (on my private track) my gps is showing 96/97mph

their never 100% and also changing wheels etc also affects it

Hope this helps

 

[blackturbo]

But my speedo isnt over reading its under reading which is unusual as most speedos tend to over read as you say David, 100 on the speedo and 96 on the gps whereas mine would be 96 on the speedo and 100 on the gps

 

[David_smith_909]

sorry mate, not too sure then

 

[blackturbo]

Well hopefully now that I have 17s on this will bring the speedo up to about right lol!

 

[flashbsd]

i was driving next to a C4 yesterday, she was showing 48 mph on the big display, i was at 50 on my speedo, and she was driving faster than me slightly. they are all designed to underread anyways.

Then she was doing 70 and it was clocked as 73 on mine!

 

[Wolves73]

You can recalibrate your speedo with vag com in group 17 display, I have adjusted mine because it was over reading compared to my GPS by 5mph (common on VW cars). I know GPS can be out slightly but on my previous car (a Citroen C5 2.2hdi) and a Peugeot 407 1.6hdi I have driven for work were within 1-2mph of the GPS.
All you need is a laptop and a vag-com lead & software from ebay (cost about £15)
I got mine from ebay seller weyri650

 

[Boo]

There is always a 5% difference on anything GPS based and your car speedo. When my speedo was faulty I used a talex speed camera detector to show me how fast I was going. I eventually found the cause of the broken speedo and still drove about with the talex out of habit. I found that when my speedo said I was doing around 30mph the talex said it was about 27mph. It just got confusing when it came to speed camera's as I didnt want to exceed the limit. Its not worth the risk to be fair.

 

[Wolves73]

GPS manufacturers quote 0.1 mph accuracy on flat ground speeds, readings will be different if going up or down hills and on bends and also the amount of satelites seen by the gps receiver will also have an effect.
Car speedometer always read above the actual speed unless the car has modified by changing the gearbox and by fitting larger wheels & tyres that increase the rolling diameter so its worth checking your speedo is not under reading if you do any of these modifications.

 

[__B3NNY__]

2 years old....

 

[andycupra]

sat navs are not accurate, your speedo will be more accurate so it is probally fine.

Just remember that wheel size does make i difference, at 30mph, with 17's you will be doing 32ish and with smaller wheels you will be doing less speed.

cant say i agree at all on this one!

Old thread also.

 

[RichN]

cant say i agree at all on this one!

Old thread also.

It's just plain old wrong

 

[Quikie]

speedos are normally 2.5% out, even from factory, as regards actual speed

If you read well into it you will find out the reasons why

 

[motorhead]

speedos are normally 2.5% out, even from factory, as regards actual speed

I used to work at Volvo plant, in the development and tech literature the accuracy was only to about + or - 6%, I would have thought all manufacturers would have to work within the same tolerances, although some will be more accurate

 

[Quikie]

I used to work at Volvo plant, in the development and tech literature the accuracy was only to about + or - 6%, I would have thought all manufacturers would have to work within the same tolerances, although some will be more accurate

yeah... i meant to say - tho