<div class='quotetop'>QUOTE(Fishboy55)</div><div class='quotemain'>Somebody is gonna have to show me that having an under or overinflated tire causes it to roll further or less as far enough to throw the odometer off. I was in agreement with the tire size causing the problem in accuracy of the speedometer. But tire pressure?? Tell us more Mr. Science.</div>
when you over inflate the tires, the center of the tire moves outward from the center of the wheel. or in a better way to see, the center cups outward. when the tire is like that, mostly the center of the tire is touchign the ground. thats why the tires wear out more in the center when u have over inflated tires.
http://www.goodyeartires.com/img/over.gif
but back on topic. since the center cups outward and the tire touches the ground most with that, the actual circumference of the tire can change. ov course you can't see it in a short period of time but in the long run you can. but with this case this wouldn't be the problem since it would make the odometer say u travelled less than u really did.
in your case it could be under inflated tires. i actually experienced this first hand a few months ago. when your tires are under inflated, the center tends to cup inward. this making the tire contact with the ground more around the side walls. this again changes the radius of the wheel and can affect ur speedo.
http://www.goodyeartires.com/img/under.gif
<div class='quotetop'>QUOTE(TitaniumZ)</div><div class='quotemain'>Car is new (1 month old) on original rims and tires. Â*My only thought is that the wheel/tire combo on the GTZ is slightly smaller diameter than the ES/LS, and they use the same speedo package.
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on the i4 the tires original were P195/65 R15 89T
but im assuming u have a v6 since u said GTZ and the tires for those were P205/55 R16 89H
the DE ES and LS i4's had 15x6 inch rims while the ES LS V6 GTZ had 16x6 inch rims
<div class='quotetop'>QUOTE(BlueESV6)</div><div class='quotemain'>As far as the odo, try using the mile markers on the highway over a 10 mile distance... you can also clock your car going 60mph on the mile markers. Should be 1 mile=60 seconds @ 60 mph... this will give you an idea of how far off your speedo is. Let the dealer fix it if it's real far off as it sounds like it's under warranty. Good Luck!</div>
tirerack has a page on how to do so. uhm they have a page about it. they even show yu how long it takes u to do a mile @ different speeds. but i really do recommend doing this with a friend in the car. you or the friend can drive while the other one monitors the distance and the time take
here's another idea. i haven't really tested this nor do know the answer but it could be a possibility. i haven't had a chance to drive my car for a while in reverse but maybe sum1 might know if the odometer works when u are in reverse. meaning the odometer moves forward when u are driving in reverse. i don't drive in reverse for long periods of time so i wouldn't know it. but yea maybe it could just be factoriing u driving in reverse.
but if ur really paraniod take it to the dealer just to see what they say.