Can speedometer be wrong?

[Walla Walla]

Originally Posted by Porsche

If you talk to the court, you can probably plead it down to a lower speed for a lesser fine and less damage to your driving record. That's common in the U.S., but I'm unfamiliar with Canada.

One of these days they're going to nail me for going 120 mph out in the country, and I'm going to be crying, too.

I could, and I should, but I wont.

130$ for the ticket. If I have it lowered, at around 85$... and lose at least 4h of work... wich is worth more....

And i could expose myself to the same amout (less what I earn) if they don't accept to lower my ticket (and i think that they add a court fee of 65$ if you loose)

Also, here in Quebec/Canada, not every insurance company ask for driver record/tickets, so it doesn't affect my premium... only my Driver license will cost a bit more for next 2 years (130$ at the place of 95$, if i remember correctly!

Still a bummer, i was driving at the same speed than the rest of the traffic.. but i will have to assume that my car is easier to target!

thanks for all the answers again!

[Freetime]

Or skip all the calculations and put a cellphone with a GPS speedometer in your car and test it. I'm stock and I tested mine the first day I got it. 80mph on the dash and on the phone. Spot on.

[mav1178]

Originally Posted by Porsche

I always calibrate my speedometer with new wheels and tires by heading out onto the Interstate with my stopwatch.

Originally Posted by Freetime

Or skip all the calculations and put a cellphone with a GPS speedometer in your car and test it. I'm stock and I tested mine the first day I got it. 80mph on the dash and on the phone. Spot on.

I do a combination of both:

- Calibrate with multiple radar speed sensors (to verify general accuracy of radar vs vehicle speed). I ran across about 10 of these from my CA > WY > CA drive a month ago, and all of them were consistently accurate to what my actual vehicle speed was
- Verify actual vehicle speed with GPS app. I use "GPS Status" which gives me very accurate speed readings as well as location/pitch/roll/acceleration/heading/orientation info

The factory speedometer on my car is dead-on for speed estimation purposes. Will re-verify once my new wheels are on.

As for OP: not sure what the laws are in Quebec, but there's ways of fighting traffic tickets in California that increase your chances of winning.

-alex

[Razz]

I think it's okay to protest this and tell the Judge it is impossible you were doing 80mph.
You were only doing 73mph because you had cruise control on.

Then he will agree and give you a fine for 73 in a 63.

And an additional fine for wasting his time.

[jeebus]

Definitely do a GPS Speedo test. My car read "slightly" optimistic when stock. Most cars read optimistic because it's better to think you're going too fast than the opposite. With my 245/40/17 tires my car speedo and GPS are exactly even.

[fistpoint]

Thanks for the better explanation. My method left out too many variables apparently.

[TheRipler]

As said, most cars will give you an optimistic reading on your speed, but another thing to note is that the ECU will probably read closer. This car is almost right on the digital speedo when at highway speeds (I measured with Time/Distance and 10Hz GPS; I was impressed!).

Going from "normal" cars with 5-7% optimism to one with a more exact reading could cause you to misjudge the "extra" that most officers will allow. Adding the tire diameter difference will squeeze that "extra" a little bit more.

You also have a nice looking car, and he might have more incentive to check it out. I know I've been pulled over a few times with no ticket (no front plate, no signal on turn), and I've never been lucky enough to get away without a ticket before.

[DoomsdayJesus]

Originally Posted by Freetime

Or skip all the calculations and put a cellphone with a GPS speedometer in your car and test it. I'm stock and I tested mine the first day I got it. 80mph on the dash and on the phone. Spot on.

Came to post this, both my dash GPS in my other car and my cellphone have it. The one on my cell measures down to 1/10ths of a MPH, although to eliminate any risk of error it's best to do it on a straight and level road. Some do not compensate perfectly for altitude changes despite displaying both elevation and speed. Elevation will always be correct, but GPS usually only measures ground speed, not actual speed.

[MurderousPandas]

Take it to court. Manning up is good, no matter what you were speeding, but that speed doesn't match. Police radars and tachs are meant to be calibrated and they keep logs. If it's not calibrated properly, you win.

"Chasing speed with patience"

[Walla Walla]

Holy thread revival!

ticket was paid 3 years ago

[MurderousPandas]

Originally Posted by Walla Walla

Holy thread revival!

ticket was paid 3 years ago

Lol my bad, saw this on my feed as recent

"Chasing speed with patience"