dodgy speedo readings

[74TC]

i believe the speedo to be out as had 2 instances of believing it may be inaccurate , first when i over took pc plod at what i thought to be 70 and got pulled and told i was doing over 80 and second when plod following me again at 50 got pulled doing what they say was 60 though both times they were the nice guys,the type you want to pull you if you do get pulled as they both suggest speedo out and let me on my way , so as anyone else thought there speedo out and will the local dealer correct this under warranty ? i did run gps speed along side that did suggest it is out.

[SplatSpeed]

my speedo is spot on and i mean spot on

this can be verified by satnav

have you changed wheels and tyre combination from standard?????

[anonymous-user]

What he said ^^

Mine reads exactly the same as my Road Angel.

[74TC]

no all standard wheels just how it came from greens

[_AJ_]

I DO have this excact problem! Not been able to get to a dealer yet, but yes, at motorway speeds the needle under reads by about 10mph, and this drops to about 5 'ish at town speeds. Very annoying. (Also from Greens btw)

Edited by _AJ_ on Thursday 5th July 10:00

[crisisjez]

Prob just a coincidence but both you guy`s have VXR500`s.

[SplatSpeed]

what wheels and tyres are you running????

[74TC]

SplatSpeed said:

what wheels and tyres are you running????

standard vxr set up on pirellis

[SplatSpeed]

what tyres are you running?

[mackie1]

Get/borrow a satnav or gps unit and see if it's out or not.

Mine is very accurate and doesn't under or over read at all.

[74TC]

just tried that with tom tom and told me i was doing 83 at 70 on speedo , so i must have some points coming my way then as passed a few speed cameras lately

[SplatSpeed]

what are the actual size of the tyres

83 / 70 = 18.5 % over

i dont think tytres can do that as the tyre wheel size needs to be 18.5% bigger

ie roughly 20 + 18.5 % = 3.7 inches larger

take it back now

[_AJ_]

Standard tyres as far as I know for me too. Pirelli 245/35 19 all round.

Checked with Sat Nav also.

[crisisjez]

Interesting. Using gearcalc

Just entered 70mph @3.9 diff rpm = 2209

However 80mph @3.46 diff rpm = 2240

If speedo software was set up for a 3.9 diff this would give the speedo error you are experiencing.

Not saying that this is the problem but may be worth a look at.

[M8LC N]

Mine did this but the other way, Speedo too high compared to actual speed by a constant 10%. Fixed by Greens last week.

[greens vauxhall]

We have seen this on a couple of cars now (including Malcs), and it is a quick fix via Tech2.

[74TC]

greens vauxhall said:

We have seen this on a couple of cars now (including Malcs), and it is a quick fix via Tech2.

so this fix is only a quick fix if all dealers carry tech 2 !am i right in thinking that dealers do or is this a monaro only device which only you carry?

[greens vauxhall]

All dealers carry a tech2, but only monaro ones may have the awareness to adjust speedo.

[ringram]

You can also sort this out with efilive, fairly quick fix too, also allows you to do it exact or a little over and under for peace of mind.
Tech2 from dealer is your best bet if its free though

[Wolfracer]

gsxr750steve said:

What he said ^^

Mine reads exactly the same as my Road Angel.

and mine as my (ex - Robbing B@$t@rd$) TomTom - to the MPH at any speed.