Car says I'm goin like 10mph over actual
 

So sometimes my car will tell me I'm going like 10 or 15 mph over what I actually am..Or under. I think the speed sensor is faulty? Where is this sensor and what also could it b? 2003 350z six speed on 20's

the fact that its on 20's messes up the speedo.

the circumference of the tires determine how far the car travels on each revolution, and that is what the speedometer (and odometer) is geared to

I returned the wheels to stock and its still messed up. The speed is off.

hmm maybe the ecu and speed sensor need to be reset.

have you disconnected the battery?

How do you know it's messed up? Timing or GPS?

What are the EXACT sizes of your tires? 255/30/20, etc....

What speed is it 10mph off, when you're going 20, 50, 100?

i thought wheel sizes didnt affect our speedometer??

Like lets say person A was driving 19 over and is trying to get out of a ticket. How would he mess with the speed sensor?

Speed sensors can only be broken, not adjusted.

Your argument won't hold water in court - ignorance of a violation is not a valid excuse. Unless you could prove it was a known factory defect.

Tire OD controls the accuracy of the speedo. The speedo is calibrated for X number of revolutions of the drivetrain for a known tire OD to be a known speed. If you vary the tires sizes from OEM, you can throw off your actual speed.

How did you arrive at this conclusion?

Police

I'd say he got a ticket for going 89 in a 70 and is trying to find a technical explanation to give to the judge.

really? i had 20's before on another car and it was only a 4mph difference,i checked everytime i passed one of those "approach only" radars that are set up on the side of the road, also got better gas mileage too

lol@this thread.

So if you speedo is reporting 10 mph over, does that mean when you going 0 mph (complete stop) the speedo says 10 mph? haha...if it does, then you definetly have a valid case ;)

i had the same problem in my 240sx,form 0-10mph it was fine but the faster i went the more mph it was off,but my excuse was..........its a 240 come on lol

Good luck with that...

Laser? Pretty damn accurate!

Damn I just wanna get outta this ticket. Oh well. I guess it isn't possible. I was thinking If I could somehow throw my speed sensor off. it was 64 in a 45 by the way..going up an on ramp