Speedometer Over-Reads

(24-05-2012 04:24pm)evQ Wrote:  What model of garmin gps you are using ?
Not to hijack the thread as this is unrealted to speedometer, but I need to find a gps that works ( for navigation ) and would be nice to know what model you use.

Bought a Garmin 3790t last year for my wife's car and it's stunning (flogged the 540 Live TomTom on Ebay and felt guilty because it was so poor.). The 3790t does terrain mapping too - so shows all the hills as rendered graphics - its fast and accurate and portable so you can have hand held city guides too. You can get the Garmin lifetime map update software for about £50.

Phew !! now that's why I always escape speeding tickets.

Here is another better site to compare tyre size.....

http://www.1010tires.com/tiresizecalcula...t-emty-str

Here is a thought though - if your speedo is reading over actual speed by 10% it should follow that so will your mileage reading. If that's the case when your car gets to 100k it will actually have done 90k. On a down side, if the mileage is being over recorded then you are actually getting up to 10% less mpg than you thought!

Speedo "overreads" are required by law. They are intentionally built in - because the speedo can not show LESS then actual speed, it must show MORE. For this reason manufacturers deliberately calibrate it in this way,.... And it makes sense,....
BR : MM

(24-05-2012 09:24pm)BobM Wrote:  Here is a thought though - if your speedo is reading over actual speed by 10% it should follow that so will your mileage reading. If that's the case when your car gets to 100k it will actually have done 90k. On a down side, if the mileage is being over recorded then you are actually getting up to 10% less mpg than you thought!

This is not the case.

(25-05-2012 12:42am)ED209 Wrote:  This is not the case.

I don't understand. Why are you constantly a complete ar*ehole? You are continuously condescending, unhelpful, negative and arrogant in your responses and I am struggling to understand why. This isn't the first time I, and others for that matter, have seen it and you should know it doesn't make you look intelligent, knowledgable or superior at all. Quite the opposite.

You rubbish other people's opinions and posts constantly, and it's just rude; plain and simple.

(25-05-2012 12:42am)ED209 Wrote:  This is not the case.

Would you like to qualify your answer. Simple maths I would have thought ?

(25-05-2012 01:37am)BobM Wrote:  Would you like to qualify your answer. Simple maths I would have thought ?

The cars ecu will read the correct speed.

For example on the previous generation ford focus if you pressed the odo button in a certain way with the key in a certain position (cant remember exactly which) it put the cars trip computer into a workshop/diagnostic mode.

Then repeatedly pressing the button cycled through various different screens one of which was a digital speed reading. If you then drove off in this mode the digital speedo always displayed a slightly lower speed than the actual dials. Coincidentally this speed was the same as a GPS recorded speed.

Hence the cars dials were saying a slightly high speed but the cars brain was recording the correct speed and therfore the correct miles.

If your fancy gps has a trip computer function, try it and i am sure you will find 10miles GPS measured will be 10 miles on your cars odometer.

The purpose of my original post was not to query it as a fault but to show the actual error on my car, on my tyres. Your mileage, as they say in the US, may vary.

I've since tried 3 GPS devices in the car and they all show the same speed - a TomTom, a Road Angel and a SatMap walker's GPS.

evQ - Im using Garmin's nuvi 2465