[AlanHo]

I have owned sat-navs for a few years now. They provide a simple and accurate means of checking how accurate your car speedo is.

My last 3 cars - all Audis - have had speedos that read slightly fast. For example - 44 mph on the speedo was actually 40 mph on the sat-nav. On all my previous cars the speedo was between 5% and 10% fast throughout the speed range.  I was under the illusion that motor manufacturers did this deliberately to allow for the different rolling radius for various load and speed conditions. Also to ensure that any error was on the right side of the law regarding speed limits.

I now have a new i30 and did a relatively long motorway journey today. To alleviate boredom I compared the speedo with the sat-nav and was most surprised to find that they matched exactly at all speeds up to 75mph (I didn't travel any faster). Thus there is no exaggeration on my car's speedo - hence I will have to be careful having got used to previously driving at an indicated speed slightly higher than the speed limit - knowing that I was legal.

It would be interesting to learn from members with sat-navs how accurate their speedo is.

[Dazzler]

Hi Alan this has been discussed b4 but not in a dedicated thread as far as I can remember.. Your post is interesting because the general concensus on here is between say 5 and 8 % over read for most members.

I know mine used to be around indicated 118kph at a GPS figure of 110 and about 64 indicated at a "true" 60kph on my Feb 2008 build CRDi 

[Lorian]

Mine matches up well to about (coughs) 85mph when it gets maybe 1mph over the satnav speed.

My old car always read 2 or 3mph fast.

[bumpkin]

Mine under-reads all the way to 75 by a couple of mph, 70 indicated=68 on the GPS.

I have put that down to the 18" rims

[Lorian]

I have 17s. I think the computer can probably be re-programmed to cope with rim changes.

[Shambles]

I always drive by GPS indication. It says 67mph - speedo (allowing for parallax) says 70mph - the given speed limit  8)

Yes it's been discussed many times but never in one place, so this is a good topic/thread

[asathorny]

Yep, mines 2/3 miles per hour faster than my sat nav....  which saved me from being nailed by a cop with a speed gun, I thought I was doing 34/5 when I saw the cop hiding up a side street and thought, Oh shit, I am gonna get busted.   Then some time later noticed the sat nav difference, which meant that I was probably just within the limit or so close so as not to be busted.  A happy ending, for me

A

[Surferdude]

This IS a good topic.
I don't have a satnav and have always worked on the 5% or so error on the side of safety. Hence I'm comfortable doing an indicated 110kph in a 100 zone. (5% for me + 5% for the radar).
The only points of comparison I have are

1/ Never been booked at said indicated speeds.

2/ There are 2 types of external warning signs in Oz. The first are those trailer mounted things at roadworks which I don't consider as accurate but I have concluded from many years experience they are at least fairly consistent. And on some freeways in NSW & Qld they have radars mounted up high and show your speed on one of those big overhead signs. Again, I've found them consistent with what my speedo says but always 5% or so under my speedo.

However, since I got the Hyundai, both these speed indicators signs are showing the same speed as my speedo.
So, like Alan, I'm re-adjusting my thinking a little.

[Lakes]

Mine is almost 10% faster @ 100kph Sat Nav it reads almost 110kph .

I think I'm seeing a trend. Those calibrated in MPH are more accurate than those in km/h. Maybe the error is just in the printing.

Mine's out by probably 5-10%. Don't have a good reference except those overhead indicators on highway/motorways and not sure how good they are either.

[Surferdude]

I think I'm seeing a trend. Those calibrated in MPH are more accurate than those in km/h. Maybe the error is just in the printing.

Except mine - it's in KPH and more accurate than any speedo I've ever had before.

[cafstar]

Mine reads a two kilometer an hour difference between the speedo and the gps, if the gps reads 102 the speedo is bang on 100.
My other Hyundai ('98 lantra sportswagon SE) has a speedo that will read either 10kms under, or if I go round a left hand corner too quickly, the speedo has been known to read 160kms/h. I bought a really cheap, dodgy gps for that car JUST for some kind of idea of my speed.

[Brew69]

spot on up to 110kph for me. most accurate speedo i have had.

[eye30]

Now I don't have sat nav as I don't venture out of my comfort zone.

Near me there are 3 roads with the warning signs that flash up to warn you of your speed.

2 on a 30mph roads flashes 30 mph when I'm doing 27 mph and 28 mph
The other on a 40 MPH road flashes up when I'm doing 33 mph.

The local rag has had many letters about this so I presume these letter writters have sat nav and have checked true speed and still the activation hasn't been altered.

Big brother is alive and well in my area!!!!

[Myowni30]

I'm on my second i30 1.4 petrol manual.

The first i30 was on 15" rims and at 40MPH showing on the sat nav the speedo read about 43MPH.

My second i30 has 16" rims and at 40MPH showing on the sat nav the speedo reads about 41MPH.

Need to watch out for the Safety Cameras (which in total all types number about 10,900) 

[simon@mgr]

Australian standard for speedos.

Tony Abbott, only joking or is that scaring.

+ 4 kph
+0%
-10%

Which means you may be travelling at 100 kph but your speedo will indicate 114kph

[agentr31]

i thought it could be +-10%...

[2i30s]

going by my scangauge the speedo is beetween 3 and 5kms out,in my favour.at 70kmh I'm actually only doing 67kmh.

[Dazzler]

going by my scangauge the speedo is beetween 3 and 5kms out,in my favour.at 70kmh I'm actually only doing 67kmh.

That's about normal for the Oz i30 .. (from a "distant" memory) my SLX was doing about 63 or 64 Kph on the speedo when the GPS said 60Kph

[2i30s]

and reamember dazz I'm running 8" wide low profile tyres. 

[agentr31]

you have rims?

[2i30s]

no,just tyres. fitted strait to the brake  disc rotors. 

[agentr31]

LOL 8'' wide brake rotors FTW!

[2i30s]

massive brakes.    no,my rims are 17x7.5. 

[agentr31]

ahhh *squints at avatar* i see!

[2i30s]

look in petrol pics,my hatch pics and mods Ian. 

[agentr31]

*goes there pronto*

[babis_xo]

With the factory 185/65 R15, actual speed is 6,5% less than the speedo's (p.e. speedo: 130 km/h, GPS: 122 km/h)

[eyecon]

My first i30 (my08) speedo was terrible,much like Dazzler's, and got worse as speed increased. On my second i30 (my10) the speedo is much better. At (GPS) 120kph my speedo would read no more than 2kph over.

[ozsnowman]

Testing against GPS, and roadside radars etc, I'm usually about 5km under indicated.