speedometer error

Ok time to stir the speedo pot again - first real road trip and never paid attention until now... 08 sport - stock tires, reads 3-6mph faster than GPS... thought it was the GPS until I went thru 2 different speed minders up in Minnesota.... They were dead nuts on with the GPS... tried one 2 different times and still tracked mint with the GPS... I'm going to toyota and make em fix it.

 

Not gonna happen. They'll say it's "within acceptable tolerances". Mine was exactly 3mph off. After upgrading to 265/75/16's (approx 1" larger diameter), it is now dead on.

 

I think that most modern GPS devices are pretty accurate. As others have indicated, my Taco speedo reads, at 70mph, 4-5mph faster than the GPS shows. In my Prius there is no difference between the two up to about 65mph, then the GPS reads one mph slower as far up the scale as I care to go, so clearly the Prius speedo is much more accurately calibrated than the Taco. Oh well, my kitchen oven reads 25 degrees too low (at 350 it's really 375), so until I stuck a thermomenter in there to figure out WTF I kept burning stuff. The speedo issue is no big thang.....but one does wonder why when we're paying between $18-32K for a new truck they can't put in an accurately calibrated speedometer!

 

My 2008 reads 4mph faster than my gps at highway speeds, my son's F-150 is 3mph off. I checked the odo with freeway mile markers and it's right on. No biggy, just have to get used to it.

Lawnrevenge is correct, gps' are right on. Surveyors use them and they have to be within 1/10th of a foot.

 

The county I work in requires accurate measurements of no more than 2/100th of a foot (less than a 1/4") off This can be over distances of thousands of feet. GPS can get that accurate when using the right gear and techniques. GPS vertical scale is less accurate, but with technique, precision of operation, and the right gear accuracy in the 100ths of a foot is achieveable.

Government speedo tollerance is around 5%=/- IIRC. That's why Toyota can have sloppy speedo settings. Odometers are required to be more accurate. I think companies do it on purpose, to make us think we are slight over speed when in fact we are under the limit.