Ok I have google maps and it shows me 2 mph slower than my cruise so which one is right doesn't google maps run off of GPS is there any way to get them the same or do i just live with it thanks

 

Google is probably closer and your truck is probably off. You could also try a dedicated speed app but will probably get the same result.

 

Just live with it.
Try a motorcycle, they are normally off at least 5 mph at highway speeds

 

Normal. Put some bigger tires on it.

 

On your next trip on the interstate, check it against the mile markers.
Easiest way is to choose a 100 mile long stretch that is only interstate, not turn offs, no stopping.

 

Just flip off a cop radaring on the side of the road as you go by.... He'll tell you how fast you were going.

 

Good comparison with motorcycles. With motorcycles it's usually on purpose and to a larger degree than other vehicles. Combining two pieces of advice here, a motorcycle will often be 5 or more mph off at 60mph right from the factory, almost always reading over the actual speed. The difference is the odometer will be dead on. Sometimes "car" manufacturers do the same thing. As Ltngdrvr suggested, checking mile markers is a great idea. You can usually tell within 3-5 miles on the highway. You can do the calculations to figure out what the odometer is off by and adjust in forscan. The other part of this story is your odometer will become more and more inaccurate as your tires wear. If your tires are worn quite a lot, it will make your speed read higher and your miles click by faster. Usually not to a large degree though. It's usually a couple factors coming together to create a noticeable difference. If the truck was bought used, you can check if the wheels/tires combination is oem spec. It's possible they used other wheels/tires and had it adjusted in the truck... A lot of possibilities.

If I'm honest, if the reading is off and under warranty, there's a certain percentage that's allowable by law, and also by the manufacturer. If it's within that threshold, the dealer may not help. I think it's around 10%. It should only read low, and not high. If it's something you want to deal with, you can figure it out and adjust it. Otherwise you could try a wheel/tire shop. They could probably fix it quickly.

Just ideas. Good luck.

 

Back when I had my 2012 F250, speedo was off by 3.5%, reading high, putting more miles on the odometer than it was actually running, so Ford got out of the warranty 3.5% early. And, when I took it in to the dealer they told me they couldn't/wouldn't do anything about it.

 

Yeah, they're slimy like that. It should only be allowed to be under and not over, but technically they're within the law they'd say... It's a pain for sure. I would almost try a wheel/tire shop first. One that does custom wheels rather than a Discount Tire or Walmart, or something like that. You want someone that would put tires on that are larger or smaller than OEM. Most of the major tire shops that are nationwide won't do those kinds of adjustments. They would have the tool to do that kind of stuff to a really good degree of accuracy. Last I recall they had something that would get the gps speed and adjust based on that. Probably depends on the shop.

 

After the warranty was up I put a tune on it and corrected the speedo.

 

I think it is the opposite, it should only read high.
If it read low, then the speedometer could say you were doing 58 when actually doing 60. This is not good for the driver from a speed enforcement standpoint.

 

I picked up my brand new F350 in June. I almost immediately put a dash cam on it after a guy drove across in front of me, and I still don't know how I missed him. The dash cam has its own gps and mapping, and displays the current speed all of the time. I soon noticed that at 50 or below, it reads 1 mph slower than the truck's speedometer. Above 50, it reads 2 mph slower than the truck's speedometer. (I have checked it against those roadside radar "your speed is" things. The dash cam is dead on.) I just set the cruise control at 72 if I want to drive 70.

 

My 450 was 2 MPH GPS and iDASH slower. My 24 350 is 1 MPH both IDASH and GPS. The trucks speed is dead on, the speedometer is NOT. Keep in mind the truck also has GPS for Nav and grabs speed from that as well. This "should" make the odometer dead on, but why is the speedometer 1-2 miles faster than actual?

 

We just mad a 3000 mile road trip, and was commenting to my wife how accurate the speedometer is on our truck..

Exactly the same on the digital speedometer, phone gps and those radar speed signs on the side of the road that display your speed.

I was thinking Ford got it worked out on these newer vehicles, but I guess mine is the oddball.