Speedo Accuracy

[Dave Jones]

Having finally got round to setting my Snooper up, I was surprised at how different the speed on the speedo vs. the Snooper GPS speed is. It is always over reading by at least 10% - 30 on car = 25 on Snooper, 70 = 62 etc. I know speedo's typically (are required?) to over read, but this is much further out than I have experienced before - my BM :shutit: was generally within a couple of mph. Even the MM system shows the speed as the same as the snooper. Is this right? How far out are yours?

[chandru]

Having finally got round to setting my Snooper up, I was surprised at how different the speed on the speedo vs. the Snooper GPS speed is. It is always over reading by at least 10% - 30 on car = 25 on Snooper, 70 = 62 etc. I know speedo's typically (are required?) to over read, but this is much further out than I have experienced before - my BM :shutit: was generally within a couple of mph. Even the MM system shows the speed as the same as the snooper. Is this right? How far out are yours?

how do u see the speed on the MM? so i can check mine?

[Scarlet Pimpernell]

I'd like to know how the MM can give you a speed display in real time too.

I checked mine, it was typically 5% out. I'd get the snooper checked out...over reading by more than 10% is a bit too safe...

[Dave Jones]

Go into service mode (Info button held in and lights off > on 3 times) then pick the nav check, then sensors - shows the speed on the right hand side - need to go into service mode with the engine on, otherwise kicks you out when you start the engine. Have tried with both my old snooper (from my BM) and my new one and both read the same. Only thing I could think was that it might be calibrated for 17" tyres (on the basis that most IS will have these) but mine has 16" as it is base model.

[Scarlet Pimpernell]

Go into service mode (Info button held in and lights off > on 3 times) then pick the nav check, then sensors - shows the speed on the right hand side - need to go into service mode with the engine on, otherwise kicks you out when you start the engine. Have tried with both my old snooper (from my BM) and my new one and both read the same. Only thing I could think was that it might be calibrated for 17" tyres (on the basis that most IS will have these) but mine has 16" as it is base model.

Nice one....

[maneesh]

speedos on new cars can up to 10% optimistic under EU law. However, the GPS figures themselves are not 100% accurate either.

[paulsmansfield]

My IS250 reads a lot over, about 10%, which is dissapointing. Our Honda Jazz reads spot on all the way up to 100mph (the most I've had out of it)

[lee_iceman]

When we went to Germany, Gords 330 was accurate to about 3 mph at 140mph, as was Raj's M3 at 160mph :)

[caspian sky]

82mph on speedo=75mph on tomtom

[IanB]

My GS speedo shows 70 mph when my Tom tom One shows 63 mph. However, we also have a Ford Galaxy, and that shows 70 mph speedo, 69 mph Tom tom. I tend to use the tomtom figures and it doesn't set off Gatsos.

IanB :D

[Scarlet Pimpernell]

On a flat road with cruise/constant MPH, I would say that a GPS will be extremely accurate. GPS accuracy suffers in stop start conditions or on A roads and the like where you speeding up/slowing down...

Having said that my Dell GPS knows when I'm crawling in traffic at 1mph!

My IS - Speedo 70mph, GPS 67mph so approx 5% o/reading

[shapa]

IS220D SE-L (17'' tyres) - 8-10% difference (70 on speedo - 63-64 real), for sure I'm checking this on straight flat road (otherwise GPS will be inaccurate)

This is usual situation for EU cars (not for US for example - i have seen maximum 1% difference between tomtom and speedometer)

[Crispy]

I also checked my speedo against my GPS and found the speedo error to be at least 10%. So 110 kmph indicated was required to cruise at 100 kmph (or get run over by trucks on the freeway). I complained at the 30,000km service and was told "they all do it". I decided to leave that battle for another day but as luck would have it, the tacho started playing up soon after. This required a whole new instrument cluster. Lexus advised that a fix for the speedo error had been done and they will kill two birds with one stone. After the fix I compared the new speedo with my GPS and found it is now within a couple of kmph of actual speed.

All I have to do now is remember not to travel at 10kmph above the posted speed anymore.

[Colm]

About 10% for me too.

My gps=120kph, speedo =134kph

[Giblet]

10% also on my GS.

as Jamboo says the GPS systems are extremely accurate, except for the lag when slowing and speeding up. But if you maintain a steady speed they will be closer than anything else.

i've found also if you reset your average speed on car computer, you will find that the first reading it gives should be close to your current speed (assuming you stay at same speed) and it also shows somewhere between the speedo speed and the GPS.

[Crispy]

It is interesting that the average speed always manages to come up with a reasonably accurate speed. I also tried resetting it while the cruise was engaged and found that it was close to the GS reading. Now the speedo has been fixed they all agree.

[markoose]

I hate to resurrect such an old thread but I've noticed mine doing this too, to the extent where I have been constantly harrassed by tailgaters and people overtaking me in dangerous situations. I've never had this in any other car and haven't changed my driving style. I've been sitting there wondering what the hell was going on as yet another person overtakes when I'm reading just over 60mph on a single carriageway I've been driving down for years. Have started thinking it's all because of the speedo overreading but I'm not sure by how much. I'm wondering if it could be over 10% based on how high my speed has to be to keep up with traffic on fast roads. Put it this way I was reading 64mph when behind a lorry that claimed to be limited to 55mph. I'm going to dig out my garmin shat nav and see what it has to say. Bit annoyed because I've been really stressed out due to harrassment while driving since I bought this car and couldn't figure it out. This problem couldn't cause the mile counter to go up quicker could it? I don't fancy putting an extra 1000 or so needless miles on the clock every 10000.

[Matus]

I have 10% on 16" winter tires and 5% on 17" summer...

[dgman]

as far as i know all car speedo's are over calibrated and not unique to lexus.your odo reading will be correct but check it against your satnav for peace of mind.

[PCIronmike]

gonna borrow my bruv's Tom Tom and check mine tonight , I'll let ya all know my readings .

[Wallace]

TomTom GPS and Gamin GPS show about 10% slower than the speedo. In Shropshire we have speed check displays by the roadside and if i approach at even 1MPH over the speed limit i get the warning display flash, so i would say my speedo is very accurate. Or the speed checks have a wide tollerance.

[adrian71]

mine is usually 5mph less on road angel than speedo shows, at any speed