Speedo Accuracy

[NIGHTHAWK]

How accurate are the speedos in our cars. I was in a friends toyota corrolla 97 model i think, when she was pulled up for doing 100ks in a 90 zone (qld). Of course he protested a bit to the officer that he was doing the correct speed.... but to no avail.
On the weekend we went on the highway and did 100ks side by side, and the only difference was the front of his car was up to my xfs front door. Surely the radar gun must have been out. Any one knows how to accurately check these things?

[jzab]

Do you know anyone with a hand-held GPS. These normally have a speed readout and are quite accurate. It's what I use to check speedos.

jzab

[MO]

Maybe the cop whistled when taking the reading!!!!

[xyute]

Generaly the faster you go the more inaccurate the speedo will read, all depends on the condition of the speedo drive system, and the type of car you are drivng.. All these ppl who swear they have seen 240km/h in their POS cars are dreaming

[Teki04]

Most new cars are out by a few kmh, but always lower. Most cars are doing 97 when reading out 100

[xyute]

Not always lower, a mates magna reads high by 20k at 100k it shows 120k ( radar checked by the way ) Another mate swears he was diong 140ks when i passed him in a MK2 1600 Cortina and I was in 3rd gear at the time ( stock MK2 Cortina doing 140+ in 3rd, no way in hell )

[NIGHTHAWK]

The thing is there were other cars going past us in the right hand lane, all be it just a bit faster. I reckon it was just that we were in the lane closest to them.

[MITCHAY]

Yeah alot of cars are under or over by a bit. Also if you dont keep the rolling diameter of your stock wheels it will throw the speedo out therefore why there is low profile tyres. If you have a greater rolling diameter (aftermarket wheels and wrong tyres) than stock it will throw the speedo. Simarly if you have smaller profile tyres than what is needed to keep your stock rolling diameter it will read under. No probs there less chance of getting done for speeding.

[Rodp]

Originally Posted by NIGHTHAWK

How accurate are the speedos in our cars. I was in a friends toyota corrolla 97 model i think, when she was pulled up for doing 100ks in a 90 zone (qld). Of course he protested a bit to the officer that he was doing the correct speed.... but to no avail.
On the weekend we went on the highway and did 100ks side by side, and the only difference was the front of his car was up to my xfs front door. Surely the radar gun must have been out. Any one knows how to accurately check these things?

The radar gun changed her sex from female to male?!

Speedos *generally* read under, but if you haven't had the car from new then it's difficult to say what may have been done to the car to cause the calibration of the speedo to be out. I threw 3.91's in my last car that would have made the speedo read 10% faster than what I was actually doing. Was great for measuring 0-100. :P

If the radar gun had been out, provided it was used correctly, it wouldn't have been out by more than 1kph. How sure was he/she of their speed the moment the gun was targetted on the car. About 95% of speeding tickets are handed out to people who know they were going slower than the speed limit.

[Jamie XR6]

Originally Posted by Rodp

The radar gun changed her sex from female to male?!

Maybe She copped a high dose of radiation from it

As Rodp said, most read under from factory. I think from memory ADR allow +/- 10%, though I could be wrong.

I know mine reads spot on up to 175 kph, I haven't tested it over this speed (reading was done on a dyno) and I've also tested it with GPS to 120 kph.

I've actually talked my way out of a speeding fine by arguing that my speedo was correct. I think I just got a good copper.

I know in Victoria and now in NSW you can be booked for being 3 kph over.

[K_Man]

Dont forget you can also throw the speedo if you change your diff ratio _2:

[Mechan1k]

Have also read if you can get a logged readout from your travel in your GPS at the time you received a ticket ... you can use it in a court of law ... GPS are extremely accurate.

Also the Police Officers are meant to write GPS readings on the ticket as well .... also if they write the wrong cross street/suburb ... you can take it to court and get them for it as well.

One of the guys at work did it (was riding on his way to work) ... got the logging off of his GPS and took the cop to court and won it.

[GhiaEB]

My LTD speedo is out by at least 20 - 25 kays (reads 105 when doing 70-75) its all good...

Not going to get it fixed... as long as I know I'm under it doesn't matter as a rule anyway I just keep with the flow of the traffic...

I've also drivin trucks with out any guages other then air tanks...

Cheers

Ben

[T-rent]

I put the AU's speedo into diagnostic mode and switched it to number three (Revs and digital speed) and it is allways slower than it actually is on the needle. 60km/h on the needle is usually 57km/h on the diag reading.

[MO]

Originally Posted by T-rent

I put the AU's speedo into diagnostic mode and switched it to number three (Revs and digital speed) and it is allways slower than it actually is on the needle. 60km/h on the needle is usually 57km/h on the diag reading.

So how does one put an AU's speedo into diagnostic mode.?

[T-rent]

Originally Posted by John McMaster

So how does one put an AU's speedo into diagnostic mode.?

http://www.fordmods.com/forums/documents.php?doc=34

Follow all of these steps EXACTLY. I was one second out on some steps, enough for it not to work.

Also I leave it on all the time now, much more usefull than the usual computer display. When fuel gets low switch 7 and it shows you amount of fuel left in litres. I usually leave it on three... digital speed and rpmx1000

[MO]

Thanks for that.