Tom Tom Accuracy

[tkdsteve08]

Hi All

Just got back from Amsterdam this morning,And wondered how accurate the TT's speed indicator is.

It is so different to my car Speedo.

[snoopstah]

In a straight line on a level road at a constant speed given sufficient time (several seconds) to settle, extremely.

[louismchuge]

Just to check the obvious, the Tom Tom wasn't set to KPH was it?

[The Hitman]

snoopstah said:

In a straight line on a level road at a constant speed given sufficient time (several seconds) to settle, extremely.

It tracks your movement via satellite, and can give very accurate readings, but on steep gradients you will see a difference as your movement reletive to the satellite tracking wont seem to be as fast, when in fact you will be travelling the same speed.

[tkdsteve08]

because at 100 mph the tt says 89 mph

[Austin.J]

tkdsteve08 said:

because at 100 mph the tt says 89 mph

That's about right, how old is your car? also unless its a prestige fancy one, it'll be out quite abit at speeds like that.

Edited by Austin.J on Tuesday 4th May 18:09

[MX7]

The speedometer in a car should always read higher than your real speed.

You're going 100mph, and your TT is saying you're doing 89mph?

[randlemarcus]

tkdsteve08 said:

because at 100 mph the tt says 89 mph

Nearly right. You meant at 89mph, the speedo says 100 mph

If it's your Civic Type R, and you havent changed wheels, I'd ask for Customer Services at reception. 3/5 mph out is OK, 11 isn't.

[Dick_Phallus]

tkdsteve08 said:

Hi All

Just got back from Amsterdam this morning,And wondered how accurate the TT's speed indicator is.

It is so different to my car Speedo.

More accurate than your speedo.

[inman999]

Sounds about right to me. They can't be over but can be under up to a certain percentage I think.

[Densai tikiwa]

if youve stuck aftermarket alloys on or gone to a lower profile trye , it can throw the rolling circumference of the wheel out, ergo....

[tkdsteve08]

what are your cars saying

[Martin_Hx]

I think if i remember rightly my Civic is doing about 75-76 ish when doing 80 indicated on the speedo so doing 89 @ 100 doesn't look to stupid !

[bigdods]

tkdsteve08 said:

what are your cars saying

TVR Bang on , speedo matches GPS
Omega GPS 60 , Speedo 63
Golf GPS 60, Speedo 62

[redtwin]

My Volvo reads a consistent 3MPH over the satnav speed, my motorcycle is about the same, but I have had bikes in the past that would show over 20MPH more on the speedo than the top speed test figures published by magazines etc.

[Whitean3]

Sounds to me like the speedo in your car is less accurate than it should be- at 89 mph (GPS) I's expect no more than 96, 97 mph on the speedo.

Could be a rolling radius problem, if you are not on original size wheels and tyres (this would be the most obvious explanation); or are your tyres worn down close to their limits? Does your car speedo read 0 mph when it is stationary- i.e. is the needle positioned where it should be?

[Le TVR]

IIRC the legal requirement is that the speedo error must be +0 to +10% max.
It is not permitted to under read ever.
Typically most cars achieve less than 5% error.

TVR Speedo 100 : GPS 95
Lotus Speedo 100 : GPS 100 (speedo can be calibrated)

[varsas]

Modern speedos can be between 0%-20% too slow (used to be +/- 10%), so 11mph at 100mph is pretty much bang on half way between the two limits you are allowed. My BMW is out by pretty much the same amount (maybe a little less), as was my old Vectra but both my '77 Stags have been absolutely accurate.

Unless you have changed your wheels/tyres from standard there's nothing to 'fix', it's how the car is supposed to be.

[bigdods]

varsas said:

Modern speedos can be between 0%-20% too slow

0% - 10% http://www.speed-trap.co.uk/Accused_Home/Rules_use...

[Fort Jefferson]

randlemarcus said:

tkdsteve08 said:

because at 100 mph the tt says 89 mph

Nearly right. You meant at 89mph, the speedo says 100 mph

Thats what he said?