Well, by law, speedometers are allowed to be 5% incorrect of actual speed.

 

I was on vacation when this thread was started, so sorry that I just now found it. There are no bulletins issued by GM on new models for speedometer accuracy. Just some old old ones. If it is within 4% accurate most dealers aren't going to replace the cluster. But here is what GM states about odometers:

2007 Chevrolet HHR | HHR (VIN A) Service Manual | Document ID: 2073601
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#PIC3100B: Odometer Accuracy - keywords IPC speedometer - (Feb 27, 2008)


Subject: Odometer Accuracy


Models: 1995-2009 All GM Passenger Cars and Light Duty Trucks
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This PI was superseded to update model years. Please discard PIC3100A.
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The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
A customer may comment that their vehicle's odometer appears to be inaccurate relative to a known distance traveled. This known distance traveled is probably based on odometer readings from other vehicles the customer has driven.

Recommendation/Instructions:
Even though there is not a federal regulation pertaining to odometer accuracy, some states do have specific laws. Generally, a tolerance of plus or minus 4% is allowed, however, it is the responsibility of each dealer to be familiar with local requirements before attempting to verify the accuracy of a customer's odometer.

To verify the accuracy of the odometer, the dealer should obtain a hand-held GPS unit to test the odometer. While driving on a straight road, over a mile long, mark the waypoint on the GPS when the odometer (not the trip odometer) rolls over a digit. When it rolls to the next digit, take a reading and compare the two for actual distance traveled versus the odometer reading.

If a hand held GPS unit is not available, the only other option is to verify the miles traveled using a surveyor's wheel or a dynamometer. Do not compare with another vehicle. Do not compare with the trip odometer. Also, mileage markers on an expressway are typically not accurate enough to perform exact measurements.

Additionally, dealers should confirm that the original size tires and wheels are mounted on the vehicle and that the axle ratio is as specified per the SPID label and have not been modified. Dealers should insure that the vehicle calibration is for that tire size and axle ratio when applicable. If correct and the odometer is beyond the required limit, consideration should be given to the relationship between the VSS and the reluctor on the transmission output shaft. Close inspection should be made of the associated wiring and any connectors in the circuits. Finally, it may be necessary to exchange the IPC with a replacement unit.

 

from my experience almost every car i have ever been in has been 1-4 mph off from the GPS. They've all been slightly low. I've never seen one that hits it right now.

And for the original person who started it. I really doubt your dealer is going to take care of a discrepancy that slight. when you're buying a 20k-25k economy vehicle there is most likely going to be some chance it might be off a little bit.

just my thoughts.

 

I got my first ticket in 17 years on Monday 52 in a 35. Right when I saw the cop I looked down at the speedo and I feel sure I was going about 40-45 and had a car about 2 car lengths in front of me. I bought freaked out when he said 52!!!!!!

 

"Feel Sure I was going about 40-45" ?

That doesn't sound like you are 100% confident about your speed. You probably were going over 50.

It is my experience that if the radar was properly calibrated you are within 3 mph of the radar reading. Most departments are pretty good about keeping them in calibration since this challenge has been used a lot over the last 10 years.

If you are confident your speed was 40 MPH, go to court and challenge the "last calibration", but don't admit you were speeding at all. You'll likely get a continuance (if the officer shows), and at the next date, the officer will have to produce the calibration cert for the last calibration. If it is over 6 months old, the ticket will likely be thrown out. If the officer doesn't show at one of the court dates, the ticket will get thrown out.

 

Maybe it's changed but.....

We had to certify calibration EVERY TIME we checked the radar gun out. It was done with a special tuning fork.

The MANDATED calibration and maintenance was done twice a year by a certified facility.

 

For MANY years I have noticed, using mile markers on the expressways, that vehicles typically overread speed/mileage. Manufacturers do it intentionally. It cuts the amount of miles you get in your warranty and leases. It also makes you think you are getting better mileage than you are. They justify it by suggesting it keeps you driving a bit slower so causes a safety increase when it is just a bottom line increase. There are a lot of things people do not know about cars. Did you know all steering wheels/columns are mounted on an angle? Take a look. If the column kept going forward it would end up crossing the center of the vehicle.

 

That's your first mistake.

Get a GPS and check mile markers. I've seen them vary as much as 2-tenths of a mile from the correct mileage.

 

Well all I can say is when I looked at the speedo I saw the needle just past 40 and since our cars go in increments of 10 I was definately below 50. I'm gonna pay the ticket, no since in fighting with the laser......it's only $197.00!!!

 

only $197!?!?! that's a new sway bar right there and a couple of beers!