I have a 1994 Honda Odyssey AWD, Recently, i noticed that the speed indicated in my Google Maps was 76km/h, but my speedometer was only showing probably 34-36km/h, is there somethin need to be checked? Can the speedometer be calibrated? Or somethin else.
( I have owned the vehicle for under a year, the previous owner changed the stock 15" mags into a 16" from a honda civic, the tires are "205/55/16", while the original size indicated in the usermanual is "205/65/15" )
The over sized tires have effectively changed your final drive ratio, and hence, your speedometer readout. Only way to fix it is to put the factory size tires back on.
For using the plus 1 rule the correct upgrade from a 205/65 15 you should be using a 215/55 16. Even if you don't plus size correctly your speedometer should only be a max of 5 mph off. You say you're showing half the speed. If that is true I would question if the speedometer has an issue.
You can check the reading from the speed sensors. If they are fine, odds are that the dash speedometer is faulty.
That tire size change is not enough to be causing the issue. While not the ideal match for size, you are within the recommended range of a less than 3% circumference delta.
