displayed speed accuracy

hgvman · Posted: Wed May 18, 2005 5:04 pm Post subject: displayed speed accuracy

can anyone tell me how accurate the displayed speed on the hp 1710 is, when travelling at 54 mph it says i am doing 50mph, does anyone know, maybe my speedo is out.

Privateer · Posted: Wed May 18, 2005 5:34 pm Post subject:

Hi hgvman,

Welcome

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Are you in Europe?
Please update your profile as it does help us to help you. Thumbs Up

It’s a requirement in the UK and I think for certain other countries in Europe that the speedometer over reads by as much as 10%, but it should never under read.

Your SatNav should display a much more accurate speed than your vehicle’s speedometer if:

You’re travelling at a constant speed and direction

You’re not travelling on an incline

You haven’t got a calibrated speedometer in your vehicle.

I would have though that your tachograph would read a very similar figure to that of your SatNav system.

Regards,
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transit · Posted: Wed May 18, 2005 11:15 pm Post subject:

yep same here my speedo reads about 5 mph more than my sat navs showing.
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MarkHewitt · Posted: Thu May 19, 2005 7:56 am Post subject:

Pretty much consistently 10% out on my car. I've tested it against those road side warning signs which display your speed and the sat nav proved to be the accurate one.

Many cars speedos overread, in a 30mph limit I often find myself behind people doing 25mph, presumably they think they are doing 30!

It's very useful to know this, because even when I'm not using the sat nav I know I can go up to 75mph on the speedo safe in the knowledge my real speed is not in excess of the limit.

hgvman · Posted: Thu May 19, 2005 4:07 pm Post subject:

well, i hope you are all right, cos i had the foot down on a dual carriageway doing 55 mph, (speed limit for hgv 50 mph), and didnt spot the safety camera van til it overtook me, thats when i checked speedo against sat nav so fingers crossed Wink

cyclopops · Occasional Visitor Joined: Mar 16, 2005 Posts: 28

are'nt HGV speedos calibrated for tachograph use? making HGV speedos accurate

kartracer · Posted: Sat May 21, 2005 11:20 am Post subject:

All standard vehicle speedometers give an estimate based upon the frequency with which the road wheels rotate. So unless you recalibrate very frequently the accuracy is bound to vary, with tyre wear amongst other things. As your tyres wear out your speedo will overestimate by a larger amount because your road wheels are rotating more often at any given road speed. Unless your GPS is faulty it should always give the more accurate reading on a straight and level road.
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