sjaskow - FSO wrote on 06/07/12 at 09:57:14:I have a 140/90-15 D404 on the back of my 06. The speedometer now seems to be accurate but my odometer is now 1/10 of a mile short per mile. This means for every actual mile I drive, I only record 9/10 of one.
As Serowbot pointed out, the speedo itself is current induced; called a d'arsonval movement. It's very similar to that used in volt and amp meters before the digital age. However, the odometer is usually gear or worm screw driven. Since it's mechanically coupled, it's probably more accurate than the speedo (to rear wheel RPM, not true speed). In any case, you need an external accurate distance measurement (or GPS) to see how truly accurate one or both readings actually is (like mile markers on some interstates). For instance, if you could find a 10 mile stretch of straight interstate and run steady at 60 mph, it should take 10 minutes (1 mile/minute). The amount of difference can be used to calculate true speed and speedo error.
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