I hit the speed limiter so many times and every time i did it stoped at 102

 

Thats what Ford has the speed limiter at. You need a programmer to up that.

 

My speedometer was off 2 mph from factory.

 

3-4 mph inaccuracy of the speedometer is perfectly normal.

A better question is, what the hell are you doing driving 5000+ lbs of 4x4 truck at 100 mph?

 

Police vehicles are the only ones that have a speedometer that is certified to be 100% accurate.

 

LOL, long story short. This guy was being a 'hey i have a car and you have a truck so im gonna show off to you since you cant go fast' sort of guy so I raced him and i had him untill i notice that it let off and my speedo was at 102 so bla. The guy beat me and yea, not a smart choice on my behalf but now I know my speedo is off by about 3mph

 

Mine is off by about 3mph from the factory.

 

You would think that trucks costing 37k would have a more accurate speedo. Mine reads +3mph. I have never owned a vehicle with the speedo off that much. Funny this one was the most costly too.

 

Does everyone's speedometer read slower or faster?

 

Mine read about 7% fast.

70mph read as 75 on the speedo.

The scanguage would read the correct speed from the truck computer however. Also confirmed with GPS.

I have slightly larger tires so now the speedo is closer to real.

 

My speedo was off about 7% overstated as well (reading faster than true speed), vs the GPS measured speed. I first noticed it on the freeway when the police installed one of those "Your speed is" signs.

I've since gone to larger tires and the difference is about 1.5% overstate now.

 

Kind of.

All they do is get them calibrated [somewhat] regularly. The tropers here in VA have them calibrated every quarterly.... as I'm sure every other state around the country has similar standards. From one calibration to another, I've been told, that speedometer can be a few miles off. This is why an officer saying they were tailing someone at a certain speed doesn't hold up in a court of law. Remember that the next time should this arrise . . .

Radar guns are a different story.

It's police officer's radar guns that is certified to be 100% accurate.... or pretty damn close. This is because radar guns very rarely, if ever, lose their accuracy. They usually just breakdown and stop walking altogether. Not only are the calibrated regularly [at least one time every 10 days here in VA by the State Police] but they are all put through a full service on a regualr basis.

I'm not law enforcement but have had this information told to me during the course of several State Police ride-alongs here in VA.

Safe driving.

 

Guess it depends on the state. When an Officer goes to court here, he has to have the card from the speedo shop to show the latest calibration.

Plus or minus 1 is ok. Most courts require the radars to also go through a calibration at least yearly.

 

Actually it is physically impossible for a mechanical (not GPS) speedometer to be always accurate.

No matter how closely it is set, and the cost of setting one precisely is a LOT, it will still be wrong.

Why?
Tires change size as you drive.
You can pick up 1-2% just from the tire warming up.
The warm air in the tire expands.
Law of physics.
The tire itself also gets warm and expands.

As you go faster the tire gets taller. Centripetal force (usually incorrectly called centrifugal force) expands the soft tire casing by up to 2% .

Tires are not 'standardized' to even 1% so when you rotate your tires the Speedo goes off again.
During the normal life of a tire it will decrease it's diameter about 3%, thus if it is correct today, it is wrong next month.
And even if you could somehow overcome all those items, the speedometer needle is subject to everything from vibration to temperature differences. The little motor that runs it is also 'less than perfect'.
I think that speedometers that are within 1 or 2 mph at cruising speed are actually pretty remarkable.
Of course since it is not perfect it is terrible, at least according to some…
Chris