speedo accuracy

[doddze]

A nice round trip of about 110 miles today but I am wondering if my speedo is accurate or maybe everyone else was driving slowly tonight. I was only cruising at about 80 (according to the speedo) but I seemed to be passing everything fairly quickly. Probably everyone else on a go slow.... will get someone to tail me and check it but what do you guys reckon.... are they accurate or a bit iffy?

[Psychobert]

Mines spot on, but only at about 60mph.. Testing with a GPS IIRC indicated 40 was actually about 36.. Its not great, but not too far off..

[NickP_S2]

If you have a dodgy battery the speedo goes awol, saying you are doing 100mph when you are doing 40mph and so on. Other than that mines been okay. No cameras flashed etc (he says as he touches his fake walnut dashboard)....

[heckler]

Hi doddze,

I find that sometimes you can be cruising at 80 and you're the slowest on the road (m'way). Othertimes at the same speed and you're permanently overtaking. Not sure why it happens, but the latter always has me worried that they know something I don't ... ie. BIB ahead. Maybe just the way it is?

pg.

[ukBoB]

In most cars, they are calibrated to read slightly higher than actual speed iirc. My GPS says 29 when speedo says 30.

[KentishS2]

Mine seems OK until I switch the heater blower on then I'm doing 40, errr no 60, no 40, errr now 60 and 40.

I find that I don't really look at it very often, I been driving enough years to be able to tell what speed I'm doing most of the time and if I'm aware of scameras I slow right down.

[deadboyfriend]

My GPS is always 3 mph slower than the speedo! No idea why but it's always spot on so i guess it's calibrated that way.

[ukBOB]

deadboyfriend said:

My GPS is always 3 mph slower than the speedo! No idea why but it's always spot on so i guess it's calibrated that way.

I heard (and its just what I 'heard') ... IF a speedo is incorrectly calibrated which they often are, undercalibration is the way to go by a small amount, which tends to keep owners of that brand safer re: points clocked up from speeding which affect insurance.

Just what I heard, iirc.

[kasio]

mine and her indoor's read about 3/4mph or about 10% (what ever's greater) above the speed shown on the GPS

once got told all car speedo's over-read ... something to do with the manufactuers risk of being sued