GPS readout vs speedometer

[bornwild]

mine is commonly connected to 8 satelites but can have up to 12 or 16 i believe

yeah basically the question just came down to me wondering whether my car's speedo needed adjusting... from the posts it seems that is not the case

Nah you're on the safe side mate.

Another reason why your speedo reads out 100km/h at 96km/h is due to 60mph equalling 96.6km/h.

You'd have a problem only if you're speedo was actually reading lower than the GPS.

[bornwild]

i understand a margin for error, most cars have this etc...but what scared me was that at an indicated 100km/h a subaru (think it was an outback)...was doing 94km/h...that's a dangerous misrepresentation if you didn't know about it, cos you're either going to be going considerably slower than traffic, or consider yourself to be speeding...

Yeah well 94km/h is a bit too much of a difference. You'll find modern cars(our AHs) are sitting at about 98-99km/h at an indicated 100km/h.

And yeah outbacks would have off-road tyres, maybe the tyre pressure was too low etc.

[glider]

i understand a margin for error, most cars have this etc...but what scared me was that at an indicated 100km/h a subaru (think it was an outback)...was doing 94km/h...that's a dangerous misrepresentation if you didn't know about it, cos you're either going to be going considerably slower than traffic, or consider yourself to be speeding...

I always like to sit on speed limit on the motorways... always wondered why people were passing me (apart from the ones that were speeding) - i guess some cars just have less margin of error

[sooty]

Yeah well 94km/h is a bit too much of a difference. You'll find modern cars(our AHs) are sitting at about 98-99km/h at an indicated 100km/h.

And yeah outbacks would have off-road tyres, maybe the tyre pressure was too low etc.

mine's obviously not got factory wheels (225/40/R18 [same as SRi-T] makes my speedo apparently 0.8% too slow) but i sit at about 104-105 and through the speed checks on geelong road get bang on 100

[bornwild]

Yours are 18"s, yeah?? I guess Opel would have incorporated that into the error thing as 18" are optional on all astras over there

[Dave]

Agreed with all the above, my speedo is 4-5k out acording to my gps, Ive gone through lots of speed cameras sitting 5k over by my speedo and dead on according to my gps....... i gues i trust it now

[Tigra]

That's wrong there mate . Quite a few cases lately where people have defended themselves from fines using GPS'. Most famous one I can think of is the case that was presented on CA or TodayTonight couple months back.

GPS' are more accurate than your speedo, btw. Professionals use GPS' to measure quarter miles, 0-100 etc. without too much hassle.

Thanks for the feedback, will keep this one in mind.

[blueraven]

Yeah well 94km/h is a bit too much of a difference. You'll find modern cars(our AHs) are sitting at about 98-99km/h at an indicated 100km/h.

And yeah outbacks would have off-road tyres, maybe the tyre pressure was too low etc.

Nope, its a subrau thing, the speedo read 8-9% high on all of them.


You can however get the dealer to adjust it, which i will be doing on mine.

[Calibrated]

white cali is 8km out. 17's. Stock are 15's. Turbo cali is spot on all the way through to an undisclosed speed.

[Peety117]

GPS' are more accurate than your speedo, btw. Professionals use GPS' to measure quarter miles, 0-100 etc. without too much hassle.

The accuracy the professionals get would be archived a differential GPS set up, where you can get, sub-cm accuracy.

http://en.wikipedia.org/wiki/Differential_GPS

mine is commonly connected to 8 satellites but can have up to 12 or 16 i believe

There are only a maximum of 24 satellites working at any give time, 12 for each hemisphere, but its virtually impossible to pick up 12 satellites.

Standard GPS is precisely inaccurate.

http://en.wikipedia.org/wiki/Accuracy

I trust my GPS with the speeds it reads out +-2km/hr, given that i have a strong signal and the signal is not inhibited from trees and tall buildings (IE, Natio/City)