Spedometer inaccuracy?

[IllusionX]

Originally Posted by PK198105

yes but if downgraded after to 17's without resetting the ecu the speedo would be wrong

No. It doesn't change a thing. A sales guy at Brossard Toyota (he doesn't work there anymore) did the test with 2 echos. a hatchback with factory 14" (175/65R14) and a sedan with factory 15" (185/60R15). They did many tests driving side by side... both at 100kmh, the 15" would over take the 14". The sedan would have to drive at 96kmh to stay equal with the hatch, and the hatch has to drive at 104kmh to keep up with the sedan.
The test was done to prove that toyota did not adjust the ECU to reflect the different overall diameter size of the wheel/tire.
In fact, to match the 175/65R14, you would need 185/55R15.