Speedometer inaccuracy

[Raistlin]

I was driving at what I thought was spot on the speed limit of 40 MPH the other day and went through one of those "Your Speed Is" tracking areas and I was somewhat surprised to have my speed registered as 46 MPH.

I managed to reduce the difference by re-setting the car's system so it knows I have 18" wheels but even so, I still seem to have a reasonably linear under-read of 3 MPH.

Now I don't mind the speedo over-reading because that means my speed is likely to be below that recorded but the other way, as it is now, is causing me concern.

Does anybody know a way to re-calibrate the speedo please?

[JOE-DOT-COM]

HI Paul

I'm sure you can change the wheel circumference in the diagnostic menus on the dash

that will alter the speed displayed

cheers

joe

[Raistlin]

Already did that Joe. Still way out though.

[JOE-DOT-COM]

hi

you can alter the circumference of the wheel in one of those settings

just alter it one way or the other till you get the desired effect

so if your speedo is reading slow decreasing the size, which  will give you a faster higher speed reading,if your speedo is reading fast increase the size which will give you slower lower speed reading, compare it to a sat nav, like a tomtom because using satelites should be more accurate speed reading.

never messed with it, but it should work

cheers

joe

 

[Raistlin]

Thanks Joe :)

[Botch]

just a thought, if you have 18" rims and a lower profile tyre the overall size will be the same?.

[JOE-DOT-COM]

HI

yes

you can check speed on the net like here

http://www.willtheyfit.com/index.php?width=205&aspect=55&diameter=16&wheelwidth=6.5&offset=40&width2=235&aspect2=40&wheel_size=17&wheel_width=9-5&offset2=20#isPage=1