The mph reading on my Prius is +4mph. Is it possible to re-calibrate to give a more accurate

PA W

reading.? Speed comparison was with my Sat-Nav.

lilmissdisorganised

My mechanic told me that all vehicles are set a 3mph over.

SVOMAN

try a larger size tire, that always worked on older cars.. or look for a place that specializes in speedometer repair..































does that make you wonder, if it's off, then does that mean the odo is wrong to? check it either with the gps trip, or use mile post markers on the highway, go 10 miles for the best check. if it's got a 8% correction that will lower your MPG that much too : (































Aren't those GPS's great, I found my old BMW is reading 1-2 mph high

infoman6617

4 mph off and how did you come up with this... without calibrating it.... no car is right on the money every one will be a bit different... so im guessing you got a ticket for speeding if so pay the fine and live with it.... and drive 4 mph slower

mrvadeboncoeur

In Europe, by law, the speedometer can never show slower than actual speed. EEC directive 75/443 (1975) and the follow-up EC directive 97/34, which you can find here: http://europa.eu.int/comm/enterprise...5_443_cee.html















from paragraph 4.4: "The speed indicated must never be less than the true speed."































Although it is not in the English version, I am told that the German version of the document has further formulas in it. The translation I was given is:















"At the speeds specified for the test in 4.3.5 above and between these speeds, there shall be the following relationship between the speed indicated on the dial of the speedometer (V1) :















O * V1 - V2 * V2/10 + 4 km/h"















So therefore, the speedometer in an EC compliant vehicle will show at least 10% over the true vehicle speed.















http://autos.groups.yahoo.com/group/Priu...































Also, as others have mentioned, if you change tyres on your vehicle, or worn vs. new tyres, will have a different diameter or revolutions per mile figure, and that can also cause your speedometer to be off a few %.































Your GPS will usually be more accurate.































autos.groups.yahoo.com