How accurate is TT3 speedometer

[amcluesent]

I want to drive within the ACPO 'tolerance' bands for speed (i.e. nominal limit + 10% + 2mph). How accurate is the speed shown in TT3, assuming you are travelling at a constant speed on a straight, flat road)?

WHen TT3 is showing 77mph, my car speedo is showing about 82mph. They can't both be right

[lbendlin]

the GPS based speedo is accurate to 0.1 mph . the one in your car is intentionally set to a higher speed than you actually travel.
_________________
Lutz

Report Map Errors here:
TomTom/TeleAtlas NAVTEQ

[dlegros]

Although IIRC, the GPS specification states that velocity on a GPS is accurate to 5mps, which is approx 11mph.

Dom

[dlegros]

[RichXDA2]

I have a Toyota RAV4 and I have been told that the speedo on these cars intentionally read 7% high! When Tom Tom reads a speed of 75mph the cars speedo reads 80mph so this would suggest that Tom Tom is accurate!

[Dave]

All speedo's will read higher than they actually are, by law. GPS will be more accurate only if you are travelling at a constant speed on a flat surface. If you're going up a hill or down a hill speeding up slowing down, then it won't be as accurate.

[BrummyGit]

The law states that your speedo has to be accurate to within 10% and MUST NOT under-read, therefore as has been most manufacturers build in a tolerance of 5-10%

Just remember as well that the ACPO guidelines say that they will prosecute at 10%+2 and so you should stick to 10%+1 to avoid prosecution. Additionally as they are only guidelines you can be prosecuted for anything above the legal limit if an area is operating zero tolerance - Mr Brunstrom's lot???

[Robin2]

I was about to make the same point. I am happy enough to trust the GPS speed on the level and set my cruise control to 70mph GPS speed (about 75 mph on the car speedo). But since the ACPO guidelines are not followed by all forces, I don't push it beyond that
Robin

[MikeB]

[vlak]

Slightly OT...

I find it interesting to learn that car speedometers are intentionally boosted up. I have just taken a driving test (to upgrade from automatic to manual) and was failed for driving above the speed limit (about 34mph) in a 30mph zone.

I was furious! I was tempted to argue that the speedometer is not accurate and that I could plug in my PocketPC with TTN3 to prove it. But then again, what's the point.

Another £40 down the drain and a further 4 months wait. What annoys me the most is that I've had a driving license and been driving for nearly 20 years (both manual and automatic, in Canada) and if my current car was automatic, I'd be entitled to drive it without having to take a test. Now the examiner has failed me twice... the first time being for NOT overtaking a bus!!!

[BrianA]

Just FYI, my car (Audi A4) GPS consistently shows +_5mph less than speedo ...
_________________
Brian Abbott

Go 520 + Navcore 8
(was a happy PDA user until TT stopped updating the software)

[sn0rg]

Need to bear in mind that car speedo's can be influenced by a wide variety of variables -

Tyre pressure
Wheel size
Tyre wall size
Tyre wear
etc

All of these will affect the circumference (hence the number of revolutions per mile, hence the reading on the speedometer).

[MrT]

[technik]

I drove past one of those radar devices that shows your actual speed on a large board display, and my GPS speed was exactly the same as indicated by the radar device. ( No ticket on this occasion) :D

[Privateer]

Hi Vlak

We see you’re using an ad-blocker. We’re fine with that and won’t stop you visiting the site.
Have you considered making a donation towards website running costs?.
Or you could disable your ad-blocker for this site. We think you’ll find our adverts are not overbearing!