GPS Vs Speedo

ironclaw

Hi Folks,

Been driving a Toyota Yaris (New and old model) for a year or so now. I've noticed the speedo on the old model seemed a tad off. So I compared it to a GPS readout of speed (From a SatNav, a GPS phone and a very accurate laptop model) and it was indeed off. It also seems to get worse at higher speed. At a reading on the speedo of steady 120km/ph, the GPS units would show a steady 110/115 km/ph with a tendency to the lower. I've checked it numerous times and I'm taking averages in different areas.

Would that be a common problem? I know speedo's have some tolerance but +/- 10km/ph is alot in my opinion. Anyway to get it checked?

ironclaw.

SV

I reckon the GPS is far more accurate...
it's about the same with mine actually


speedos always under read, they're meant to

ironclaw

SV wrote: »

I reckon the GPS is far more accurate...
it's about the same with mine actually


speedos always under read, they're meant to

I was thinking as much. It just seemed an awful lot to be off by.

Alanstrainor

ironclaw wrote: »

I was thinking as much. It just seemed an awful lot to be off by.

Well it will be off by a certain percentage generally, hence it appearing worse the faster you drive. My speedo is off by about the same the last time i checked. I know unkel had some stats on this the last time this discussion popped up.
It's worth noting that GPS will be most accurate on straight/level ground, as it's measuring a point to point speed. So if you're on a hill it will be off.

corktina

its common for speedos to be over-reading by 10% in my opinion
Hills make only a very tiny difference....do the trignometry on the angles from a satelite over a minute distance measured several times a second...its really a red herring..

Tragedy

My GPS reads 117km/h when my speedo reads 120km/h. When I had the wrong wheel size (225x40 instead of 230x40) it was around 112km/h when speedo read 120.

_Kaiser_

My Passat (with the correct 16" wheels/tyres) always over-reads by about 10% once you get over around 50/60 kmh.. it's normal.

Just feel safe that if you find yourself doing 105 kmh and you spot a garda with his camera out you're really only doing around 98/99 so you will be fine.

In reality I think most Gardai allow about 10% anyway in cases like that - I'd certainly dispute it if I was done for 102/3 in a 100 zone myself.

unkel

ironclaw wrote: »

Would that be a common problem?

It's not a problem, it's the law!

Speedos always show at least the real speed but mostly (a lot) more than the real speed. Legally:

real speed <= speedo speed <= real speed + 10% + 4km/h

That means that if the real speed is 160km/h, the speedo should read anything between 160km/h and 180km/h. Do a search here and you'll find previous posts, with links to the legislation (European directive) etc.

Tefral

Might be worth looking at this

http://www.boards.ie/vbulletin/showpost.php?p=65845017&postcount=4