My FJ Cruiser is running on the original size tires of 265/70/R17, and I've noticed that the spedometer is off by about 2-3 miles per hour. I'm curious to know - what size are you running, and how accurate is your spedo?
Yeah, mine's been off by 2.5 MPH since I bought it in '08 (stock tires). I believe the car was originally designed/spec'd with the larger tires and at the last minute they needed to get another MPG or two for bureaucratic reasons. Tire change last minute: No Problem. Speedo change and/or recalibrate last minute: Not gonna happen. Good encouragement to get 33's someday.
I had the same issue with my 2012. When I went to 285 70 R17 Nitto Ridge Grapplers (BMC, but no lift), it is now consistent with the speed indicated on the GPS.
I bought mine with 32s (i believe 31.8') and i recently noticed the speedometer is off. Mine is more off than yours though. If my gps says 75 my FJ days 71 or 72. It seems to be a ratio, the faster i drive the bigger the difference. I plan to put 33s on this fall. We'll see if it evens out