GPS speedos are always 2 ticks faster than actual ground speed. This is due to the fact that consumer level GPS is not as reliably accurate as an onboard reading and so to cover their butts the manufacturers set them this way. I learned this after tuning my car and having concerns about mph vs. kph since my tuner is in the USA and I am in Canada. Every test I did had the GPS 2km faster at cruise, so further research and consultation with service techs uncovered the GPS fact.

As for the radar gun I dunno, my only guess would be it might not have been calibrated or calibrated correctly. Hop into any other Focus and run the same test with GPS you'll get the same results, I'm willing to bet a dozen donuts on it.

 

GPS speedos are always 2 ticks faster than actual ground speed. This is due to the fact that consumer level GPS is not as reliably accurate as an onboard reading and so to cover their butts the manufacturers set them this way. I learned this after tuning my car and having concerns about mph vs. kph since my tuner is in the USA and I am in Canada. Every test I did had the GPS 2km faster at cruise, so further research and consultation with service techs uncovered the GPS fact.

As for the radar gun I dunno, my only guess would be it might not have been calibrated or calibrated correctly. Hop into any other Focus and run the same test with GPS you'll get the same results, I'm willing to bet a dozen donuts on it.

I've used 2 different Garmin GPS units as well as 2 cellphone GPS units and all showed 2MPH faster than what actual speed was.

Thinking that was an anomaly, I tried it in a Fusion, F150, and a Toyota. All of their speedometers read EXACTLY the same as each GPS device....

schrodingersbox You owe me a dozen donuts.

 

Can't say what adjustments the Dealer computer can do offhand, if they can the amount off at 60 might be a std. to work from.

Just for interest, what tire size came on the car? (odd thought)

 

Standard 16

 

My speedo is off by 2mph as well, I just compensate for it. If I want to do exactly 65, I set it at 63.

 

KamelReds Sure, I know to compensate for it, but it's an annoyance. Have you ever tried getting it fixed?

 

Is it a constant 2 mph across the range (i.e. x+2 @ x), or 2 @60, 1 @ 30, 0.5 @ 15, 4 @ 120?

 

Yes. Doesn't matter the speed, it's always 2MPH too slow.

 

Take apart the gauge cluster and move the needle a bit?

 

Speedo needle off doesn't account for digital off, even more so IF it's the same at all speeds.

 

[dunno]Damnit. If there's a delivery donut service where you live you just let me know and the donuts are yours.

 

If it's 2 high at all speeds, zero to 65 and beyond, I don't have an idea for a solution.

That's NOT a calibration error that might be adjusted, sounds more like a computer glitch tagging on the extra at all times.

Calibration varies with speed as a constant percentage difference, error going from zero on up as speed increases.

 

Ok. Did another test. At 35 mph it's about 1-1.2 mph too slow.

 

You need to verify that the tire size mounted on the car is the same tire size calibrated into the modules

 

Honestly never checked mine but if so, I nearly run 70 all the time haha. I always set my cruise at 67

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What tire size do you have? All foci should have same overall diameter tires from what I've seen. Can't say I haven't seen a car come with wrong size tires

 

I should add to my original post on that I have 18x8's and 245/40 tires. But the speedo was off before I did the tires.

 

Weren't OEM tire size supposed to be 235/40-18? If so, how did you get 245/40 size?

If so, that's probably 107% of your problem right there.

 

Mine are 215/55r16 stock... 245?? I wanna see what this looks like

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Your wish is my command!

[/QUOTE]

Niceeeee! Me gusto mucho

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Before it was off 1-2mph depending on speed, now it's off 2-3mph.

Like I said, it was off before now it's just more off. Also, I'm not OP. My issue is self made, not sure about his.

 

doh [unsure] yeah. Tire size is everything. Some cars have inherent speedometer issues (see ~09 toyota camry). My GFs 14 focus is right on the money though.

 

A bit late to the party but... This might help...

You can fix this yourself.... Using FoCCCus you can recalibrate your speedomenter, It is lines 51 (tire circumference) and line 70 (tire dimension) I have an S model which came originally with the 195/65R15's and I upgraded to the 215/50R17 and suddenly started getting speeding tickets. Once i got my GPS i figured out that my new tires threw my speedo off by about 4 MPH or so.. it would read 60 on the speedo and 64 on GPS. I went in with FoCCCus and reset the tire sizes to 1975mm since it didn't have the P215/50R17 listed (I hit autotrader.com and looked for a focus for sale that had the same wheels i have now and grabbed the VIN then pulled the as built data from Etis to find out what the calibration settings are for those wheels, then set mine to match.) After clicking "Write to BCM" and clearing the codes with Forscan, i did another GPS speed calibration test and now its dead on accurate between speedo and GPS. I saved the original configuration since i do use the original 15's in the winter so i can easily reset back to the factory specs for winter, then saved a copy of the 17 inch wheel settings for ease of loading when i swap to summer times after the snow is gone for the year.

In your case, if FoCCCus shows the same size tire as your car has on it, but still getting a 2 MPH difference, you may want to try dropping to the next lower tire size in FoCCCus, and see if it corrects your speedo (BACKUP YOUR ORIGINAL CONFIGURATION FIRST BEFORE CHANGING ANYTHING SO YOU CAN GO BACK IF IT DON'T WORK!) You have have to play with different sizes until you find the one that works assuming its a programming error in the firmware of one of your car's modules.

One Caveat.. On mine, changing the tire settings in the BCM did set a PCM P160 Calibration Error trouble code that wouldn't clear, however it never set a check engine light and i noticed no ill effects driving it, But at least the speedometer would actually agree with the GPS.

 

You can fix this yourself.... Using FoCCCus you can recalibrate your speedomenter, It is lines 51 (tire circumference) and line 70 (tire dimension) I have an S model which came originally with the 195/65R15's and I upgraded to the 215/50R17 and suddenly started getting speeding tickets. Once i got my GPS i figured out that my new tires threw my speedo off by about 4 MPH or so.. it would read 60 on the speedo and 64 on GPS. I went in with FoCCCus and reset the tire sizes to 1975mm since it didn't have the P215/50R17 listed (I hit autotrader.com and looked for a focus for sale that had the same wheels i have now and grabbed the VIN then pulled the as built data from Etis to find out what the calibration settings are for those wheels, then set mine to match.) After clicking "Write to BCM" and clearing the codes with Forscan, i did another GPS speed calibration test and now its dead on accurate between speedo and GPS. I saved the original configuration since i do use the original 15's in the winter so i can easily reset back to the factory specs for winter, then saved a copy of the 17 inch wheel settings for ease of loading when i swap to summer times after the snow is gone for the year.



In your case, if FoCCCus shows the same size tire as your car has on it, but still getting a 2 MPH difference, you may want to try dropping to the next lower tire size in FoCCCus, and see if it corrects your speedo (BACKUP YOUR ORIGINAL CONFIGURATION FIRST BEFORE CHANGING ANYTHING SO YOU CAN GO BACK IF IT DON'T WORK!) You have have to play with different sizes until you find the one that works assuming its a programming error in the firmware of one of your car's modules.



One Caveat.. On mine, changing the tire settings in the BCM did set a PCM P160 Calibration Error trouble code that wouldn't clear, however it never set a check engine light and i noticed no ill effects driving it, But at least the speedometer would actually agree with the GPS.

Wow, all this ^^^^^^^ ?!?
This is probably a good lesson to those who are looking a different wheel sizes. There are calculators online that can help with sizes without have to reprogram anything. E.g. bigger wheel > lower profile tire.





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I know it's an old thread but I want to add my 0.02$...

Speedometer are de-calibrated on purpose from factory (speeding ticket issues) while the odometer is required by law to be PRECISE.

This totally by design!


EDIT:

This is a quote from Australian Design Rules... also apply worldwide by others countries

Prior to July 2006 the ADR allowed the speedo read ±10% of true speed. This means that cars sold new prior to 1 July 2006 could comply with the ADR even if the speedo under-read by 10%. Despite this being theoretically possible, due to the testing procedures and the reasons stated below it was unlikely to occur in practice.

The reason the ADR are relevent to the debate is that some people argue that if the ADR allows cars to have speedos that under-read by up to 10%, then surely our road laws should tolerate people relying on their speedos and possibly driving up to 10% over the speed limit. Therefore, the argument goes, we should not be fined if we travel at 110kmh in a 100kmh zone because we are travelling within the tolerances allowed by the ADR. Such a situation would be quiet generous to motorists and would make it impossible for anyone to allege that they were mislead by their inaccurate speedo.

EDIT2 (to further back my fact [grinking])

“Speedometers are designed to never show speeds lower than actual speed.” Thomas Tetzlaff, Volkswagen Canada’s media relations manager, wrote in an email. “In order to do this... they will necessarily always show speeds slightly in excess of actual speeds.”

 

I know it's an old thread but I want to add my 0.02$...

Speedometer are de-calibrated on purpose from factory (speeding ticket issues) while the odometer is required by law to be PRECISE.

This totally by design!


EDIT:

This is a quote from Australian Design Rules... also apply worldwide by others countries



EDIT2 (to further back my fact [grinking])

I was thinking about this while reading the thread (don't know why it got revived after so long??) because I've known this to be true for years. This is why I can set cruise to 132kph in a 120kph zone and never get pulled over or flashed.


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Interesting fact: Once those 245's wear out, you'll notice your speedometer get closer to correct.

IMO: Either change back to a factory size, use Focccus to change the tire dimention calculation or suck it up buttercup.

 

GPS Verified my 2015 Focus speedometer today. It's right on the money! not one MPH less or more.

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On my first set of tires the odo ran slow so it under reported actual mileage driven to the tune of about 0.7% on average, but my current and second set of tires is just the opposite -- the odo over reports mileage by about 0.8% on average. The percentage varies over the life of the tires so as the tread wears down the tendency is to move towards over reporting mileage. I suspect that over time the tire carcass expands a bit and this partially offsets the reduction in circumference due to tread wear.

My speedo has always appeared to report about 0.8mph less than actual. I've measured using GPS as well as time and distance on interstates that have precisely measured miles.


Brian

 

So in 100 miles your odo was reporting 99.3 on old and 100.8 on new, how the heck do you get that precise of measurement with a GPS? or time and distance?

 

Just for fun, yesterday, I used my phone's GPS to check the speed. I set the cruise at 100km/h. The GPS was reading 101.9km/h. I tested at 60km/h and the GPS was reading 62.1km/h.

I tested with another phone and actual GPS - same result. I have stock wheels (mag + tire)... my tires are at 4½/32.

I will be switching to winter tire in less than a month. I'll test again. Same size and everything but they are actually 0.5%/1% smaller.

 

Are we really building a thread on a +/- 2 mph error?

You guys have so much free time in your hands [grinking]

 

For those of us without garages it's starting to get too cold out to be wrenchin' on our cars, we gotta have somethin' to do...

 

My speedo is off by 5 mph but I don't know how to correct it or even if I need to