ESH

Hi all,

I'm unsure whether this has been covered but I've got a Tom Tom I've set it up to let me know the speed I am travelling.

Is this more accurate than my in built speedometer?

Thanks in advance

ADILM

how come you setting one of those GPS things up, wouldn't it just be better to look at the 'normal' speedometer?

Prasius

iTrader: (1)

Yes, the GPS is more accurate. (short quick answer)

ESH

You pays your money and you use the functionality surely. The GPS seems to be reading about 8-10 mph slower even at 30mph.

scoobynutta555

So at 30 mph on the speedo it says 22 on the tomtom?

Prasius

iTrader: (1)

My tom-tom reads about 3mph slower on my '02 car at 30mph (the GPS speed being mirrored by the independent GPS on my Snooper).

Have to say I wouldn't have expected a speedo to be that far out at 30mph though, although mine over-reads by a good 10mph when around the 80mph mark on the GPS.

ESH

Precisely. Hence the question.

KiwiGTI

Different sized wheels/tyres could account for the difference

ESH

I've tried this in my daily (06 Seat Leon) and my Type R. The type R had a better reading with only up to 4/5 mph off the speedometer .

Avi

When the Speedo in my Civic shows 160, the GPS shows just over 145, so it;s way out at high speed.

KiwiGTI

My Civic overstates the speed by quite a bit too.

Avi

Just found this

So looks like mine is right at the limit running 10% fast, i'll check it again at 30mph

Chelspeed

One of those laws that came in 30 years ago and never been updated. At that time speedos were bits of bent steel pointer with spinning magnets dragging them round against a spring. It wasn't possible to mass produce them more accurately than +/-5% so the lawmakers said we'd rather have them reading fast than slow so they said -0%+10%.

Nowadays it's electronic pulses and stepper motor drives and they can probably make them +/-0.1%. So do the car buildrs set them at -0% +0.2%? Or do they set them +9.8% to +10% so their cars appear to go 10% faster and get them serviced 10% more often? Guess.

So believe the GPS or drive 10% faster than the speedo says and you won't go too far wrong.

Oh and press the lawmakers to update the law..... yeah right, like they have with the crossply tyre, drum brake 70mph safe maximum speed law.

Billgtt

My R5's speedo is spot on with my gps. My Mondeo however, is a different story.