The speedo will read differently with different size tires, but does it have to be recalibrated?
1996 - 99 legacys
i used to think that the TCU was programmed to convert wheel revolution speed into mph for the speedo and wheel revolutions into miles for the odo, but this is wrong. the speedo is designed to read the info directly from the speed sensor. i don't yet know if there is any TCU invlovement in converting wheel revolutions into odo miles, i think there is, but i've been wrong before and unless there is a really good other reason to send the info through the TCU i doubt it does.
i just put a 96 leg L speedo in a 97 leg GT and there is a substantial error (about 1 mph error for every 6 mph of actual speed). the final drives are different and i assume therefore that the speedo drive gears are different, even though the tire diameter difference is about 1/2 of 1%.
has anyone measured the speedo error in a 2.2L car that has a 2.5L trans (in other words when you swapped the trans you got the wrong one and swapped the rear diff as well.)??
as stated above, tire size will mess with your speedo and there is no way yet discovered to 'recalibrate' the speedo.
Edited by johnceggleston, 30 April 2009 - 06:43 PM.