In my the city I work there are free standing carts with digital readouts that tells you how fast you are going. In effort to get people to slow down. I have passed it on several occassions and each time it reads at about 2-3 miles under what the 8 speedometer says. Now I understand that it is most likley that there clocker is the one at blam but has anybody had a problem with theres.
Just curious

 

It's widely understood that most cars overstate the mph, rather than understate it.

3 mph faster on your readout sounds about right.

 

I have the same thing where I live. I asked the cops about how often the radar is calibrated and they tell me once a week. On that basis, my speedo reads, consistantly, about 2 mph fast which is standard for most cars. As an aside, my wife drives this huge lump called a G500 Mercedes and it has both digital and analog. The analog reads 2 mph slow!!; and the digital is right on target.

 

at all speeds above 50mph it reads 1.6mph fast compared to a waas enabled gps. i am sure mazda rounds it up to 2. didnt look belowe 50mph.

beers
john stewart

 

Are there federal mandates for the accuracy of auto speedometers?

For example: measured speed = actual speed +/- 2mph or something like that?

 

no, it must read equal to or more than your actual speed. Ferrari speedos, for example, are way way out of whack.

 

From my experience, the speedo is off by 3 mph. Too high.

 

Car and Driver had a big article on this a while back. What I got from it was that you are allowed to be off a certain percentage in relation to the max number on the speedo. So a 160mph speedo can be off more than a 120mph, etc..

I'd rather have my speedo show more and not less. Nothing I would lose sleep about..

 

Every digital I had was 100 % accurate.

They have posted radar screens here in California.

I can tell you it is accurate from 30 to 45mph.

ahhhh...... I could speed to see if its accurate at 65mph.

But I don't think so not worth the ticket

 

Actually your dash speedometer is reporting the correct speed and so is the digital radar gun. It's due to the fact that the radar gun is usually not pointed directly at the front of the car but slightly off to the side. I wont go into the vector mathmatics here (since most probably don't care) but it's the reason that the cops tend to sit in the center of the freeway or right over a curve. If a cop sat on the side of a road and clocked you going perfectly perpendicular to his radar gun he would get a reading of zero. The closer you can get the radar gun to the direction the car is travelling the higher the value (and more accurate) it will read. Thus the radar gun will always report a value equal to or below the actual speed the driver was travelling. Radar guns mounted permanently up on a post (as ones in an intersection to catch drivers running read lights) can have the off axis error taken out mathmatically such that the camera is alligned properly. Maybe I can track down an image to better illustrate this.

 

Yea its the same with motor bikles LOL!. I seen a DYNO of a Harley Davidson from the factory on Orange County choppers and it was off by like 10mph .

 

I have a GPS in the car that seems to be perfectly accurate. It appears to me the speedometer always read 2 to 3 mph high.

My S2000 which had a digital speedo was always 2 - 3 mph high also.

My wife's 4Runner and my Acura are always right on.

I am wondering if it has to do with the digital speedo?

 

To put this prospective for myself now I understand that is is known that 2-3 miles over is the norm. When we get pulled over for speeding is it taken in consideration that we actualy were going 2-3 mph slower. I think that would make everything about getting a speeding ticket unjustly especialy, if you are say doing 11mph over and that is where the break in fine for a ticket is. You would get a larger fine at 11mpg say than 10mpg in my city.
Sounds screwy to me they sould be set = not this over crap I think?

 

Speedometers on most German cars are known for overstating speeds as EU regulations state that the speedometer must never, ever understate a car's actual speed, so they build in a bit of tolerance.

However, most Porsches and BMWs are egregious about it, overstating your speed by around 5-6 MPH at 60 MPH...

 

In order to get a speeding ticket reduced to defective equipment , my lawyer had me take my 8 to the local GM dealer to have the speedo calibrated. It was exactly 1 mph high at all speeds up to 80. Speedos will always read correct or a little over as federal law law dictates it cannot read low.

 

I had an Accord that read 2-3mph high (analog speedo), and my Jeep (also analog) is just about right on, just a litlte high. I have verified both of these with my GPS (WAAS) and with my friend who is a local cop. He clocked me from up ahead and read my speeds to be me over the cell phone while I was driving. My RX-8 seems to be dead-on judging by those little radar carts, but I haven't checked it with GPS yet. I don' t think it has anything to do with digital vs analog guages, it's just a matter of how good the calibration is on your particular car.