Well... I've not been 'round here a long time but I have been driving and participating in boards for various cars and trucks and motorcycles for years.

First off, it is a good idea to check the speedometer/odometer using a GPS. Civilian GPS does include a feature called "selective availability" that injects an error in the reading but as another poster noted that has been turned off. (I do not believe that the GPS satellites can triangulate on you - civilian or military - because they are receivers and do not transmit. But that is another issue and is only my belief.)

Second, this subject comes up once in a while on *all* vehicle related boards where said vehicle drives on public roads and has a speedometer. And all speedometers read a little high. Ok, there are exceptions, but in general they will read 3-5 mph high at 60 mph. I don't think that is because the manufacturer wants to inflate your impression of speed to make you think you you have better performance than you actually have. More likely they are concerned that if the speedo read low, you could get a speeding ticket without the speedo indicating that you are speeding. that would make the manufacturer liable for the ticket.

If you check the odometer with the GPS or mile markers on the road, you will typically find that it is more accurate than the speedo. And in any case, if you are just over the mileage limit on warranty, the dealer will submit the claim. IIRC, Ford will allow an additional 1000 miles over and still honor the claim. So no one is losing warranty claims due to faulty odometer readings.

 

Ford speedometers are notoriously inaccurate, to the high side. You're not traveling as fast as the gauge indicates. (Car & Driver did a test of major manufacturer's speedos about a year ago, and Ford's were off by the most, always on the high side.) Let's give Ford the benefit of the doubt and say they do it for our safety and drivers' licenses; this way, people are actually going slower than they think they are, and you'll be less likely to get a ticket from a police officer with a deadly-accurate radar.

 

Yeah I read that same article in car and driver. I have a 99 mazda 626 and a 04 f-150 and my garmin does the same. It reads 2-4 miles per hour slower than my speedometer in both vehicles. But of course the mazda was also made by ford too.

 

Hmmm, maybe the 10mph rule just increased to the 14mph rule lol. I typically do the 10 rule and so far so good, but at my university the campus police have those little speed box things set up all over the place that tell you your speed as you approach them. According to those boxes my speedo is dead on in my 97 at low mph 25-35 as I've checked both. I don't know, maybe this margin of error occurs above those speeds? However, my 2001 SD speedo is off by a little bit ~2-3mph according to those same speed boxes. Both trucks have factory tires and wheels.


My dad's police interceptor crown victoria says "certified calibration" in the center of the speedo. I guess ford makes sure the cops know their exact speed so when the radar/laser quits working they can pace our speeds??

 

I have a friend who has a 5.0 mustang and it was a ex state patrol. We got pulled over by a 5.0 one night and he said we were speading and my friend said that no we werent. The cop said that sometime speedometers are off. My friend said that this one is speedrated, should be the same as yours. The cop kind of looked at the car a seconed and then told him to be on his way.


I was in the passenger side laughing my *** off.

 

I recently checked my 04 F150 against my GPS and was off by 1-2 mph. On my 03 F250 it was off around the same. When I replaced the tires on the 03 265/75/16 with 305/70/16 the speedo and GPS were in perfect unison. Lower my gas mileage as well.

 

HankB, you made an assertion that vehicle manufacturers intentionally increase reported speedo numbers to avoid a situation that "would make the manufacturer responsible for speeding tickets ". That is such a croc (IMO). Since when do manufactuers worry about speeding fines and penalties that accrue to vehicle buyers/consumers. If you can cite legal precedent for manufacturers being held liable for speeding tickets, pls do so. There's a potential vested interest for manufactuers to inflate reported speed (aka mileage), and it isnt about whether the car manufacturer worries if you or i get a speeding ticket. If speedos consistently read on the high side, i still wonder if the Error isnt more about limiting warranty claims. It's interesting that several posts agree that speed/milage are overstated; the less important comments speculate as to why the mileage is overstated. This post is not directed specifically at Ford products but at all manufacturers.

 

I'd argue this point as President Clinton Ordered GPS Selective Availability Turned Off on May 1, 2000. My Garmin 60CS as referenced with a known surveyed marker has been within a few feet with less than a minute fix. If it SA were turned on, then how are surveryors able to conduct sub-centimeter surveys without "P" codes (encrpytion to decode the acurate gps signals). Its all in the cost of the GPS equipment and the DGPS equipment and WAS to assist the gps with higher accuracy position reporting. I just used my Droid 2 gps during a Search & Rescue training event and the phone was within 9 foot of were the person was found as referenced via the SPOT Emergency Beacon and topo maps.