How to verify speed of vehicle

[lincolnshibuya]

Drive next to a car with a digital speedo, like Honda Civic, and compare.

my 2007 camry hybrid is configured out of factory to always show +5, majority of toyota's seems to be configured this way. so when I drive my lincolns I get speeding tickets because I thought the speedo will always show more than the actual.

 

[TechGuru]

my 2007 camry hybrid is configured out of factory to always show +5, majority of toyota's seems to be configured this way. so when I drive my lincolns I get speeding tickets because I thought the speedo will always show more than the actual.

Sounds like wrong size tires installed. Maybe a dealer option was selected to "upgrade" the wheel type/size and they forgot to reprogram the computer for the new size.

 

[lincolnshibuya]

Sounds like wrong size tires installed. Maybe a dealer option was selected to "upgrade" the wheel type/size and they forgot to reprogram the computer for the new size.

they're designed that way out of the factory, verified by forum members in toyota.

 

[Machine090767]

It seems like Ford has their speedometers calibrated between 2-4 mph more than what the vehicle is actually doing. (speedometer reads 65, Actually only doing 62)

 

[drdoom]

I should have mentioned that when I recalibrated I used the laptop and was able to match it to the GPS. Instrument panel reading is not really that precise it seems.

 

[CDW6212R]

Use a good GPS to check speed, those are the best way next to a shop that can calibrate a speedometer.

The early Explorers all have a speedometer which reads high, those 15" tire trucks. Those are about 29" tires. The 16" tires that came optional later were 30" tall, and that diameter gives the closest to accurate speed reading. I don't know about the 3rd gen's and later, only that my 98's and 99 are accurate with 30" tires.

BTW, most highway mile markers are inaccurate, enough that checking a speedometer doesn't work well. I've got stretches of highway here with markers showing every .2 miles, I don't know why they'd do that.

 

[drdoom]

That's right don you have to use the markers that say "measured mile". Or as posted above the aircraft enforcement marks.

 

[TechGuru]

BTW, most highway mile markers are inaccurate, enough that checking a speedometer doesn't work well. I've got stretches of highway here with markers showing every .2 miles, I don't know why they'd do that.

The primary reason for markers is for reporting the location of accidents, must be a lot of accidents in that area, lol.

 

[TechGuru]

It seems like Ford has their speedometers calibrated between 2-4 mph more than what the vehicle is actually doing. (speedometer reads 65, Actually only doing 62)

I guess manufactures are doing this to avoid lawsuits for people getting tickets going the speed limit, but what if someone think's they're going the minimum speed limit and is really going under it because of this???

 

[CDW6212R]

The primary reason for markers is for reporting the location of accidents, must be a lot of accidents in that area, lol.

That's a likely reason, where I mention having the markers every two tenths is a parkway with few exits, and center barriers without cross over points. It's also the fastest highway close in town, 65mph now and down from 70mph. People drive faster than that of course.

 

[TechGuru]

That's a likely reason, where I mention having the markers every two tenths is a parkway with few exits, and center barriers without cross over points. It's also the fastest highway close in town, 65mph now and down from 70mph. People drive faster than that of course.

lol, we have 75 and 80 mph highways here along with a 85 mph toll road.

 

[IIGood]

I finally got around to checking this. I ended up downloading Waze and using the speedometer on it's GPS. I usually use Google Maps on my phone for navigation but unless I'm completely missing it, I think it's a little weird that it doesn't have a speedometer.

Anyway...my findings weren't as extreme as initially thought. When I got the Explorer up to what I thought to be 70, Waze's speedo said 69. At lower speeds it was a slightly larger gap...when my speedometer was showing 40, Waze said 38. So, supposedly not as bad as that road sign said but still off a little tiny bit apparently.

 

[Black Dynomite]

Here in NZ, those highway speed indicators are very accurate and generally find most Fords read a few kph over on the speedo.

IMO, the most accurate way to get your speed is a properly calibrated ODBII reading. By properly calibrated, I mean setting the actual tire size by 'chalk and roll'.

 

[Number Twelve]

I've got stretches of highway here with markers showing every .2 miles

If your local mile markers are 0.2 miles apart, they aren't mile markers.
If you think your local condition invalidates all mile markers, I'd like to know why.

 

[CDW6212R]

If your local mile markers are 0.2 miles apart, they aren't mile markers.
If you think your local condition invalidates all mile markers, I'd like to know why.

This thread is about accuracy of a speedometer, not what random guess or error you can include in testing the accuracy of a speedometer. I did not say all mile markers should be invalidated etc.

I made a general statement that testing speedometer accuracy shouldn't rely on mile markers. Doing that requires a long distance, not one mile, but many miles, and a constant speed over the entire distance without varying. The whole point is accuracy, if you cannot drive a dead constant speed for miles, and the mile markers may be inaccurate too, the test is not really viable.

Many people have already mentioned actual accurate methods to test a speedometer. Rely on those. I'd trust the police radar displays when they are available, rather than mile markers and a right foot or cruise control.

 

[Iwejun]

This is funny... go over to the BMW forum and they are discussing same findings. All cars coming out of factory are set up to read you going a couple mph/kph faster than you are going. Better safe than sorry you wouldn't want to be going around a tight curve thinking you are going the posted speed when if fact you are going faster. Some said it was per regulations, I don't know. Remember, general buying public just use it to get from A to B with no thought of inaccuracies, hell, most don't keep correct tire pressures unless Quick Lube kid does it for them.