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Old 09-17-2010, 09:28 AM   #1 (permalink)
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Speedo calibration for tire size change

My 2007 Kia Spectra came from factory with 195/60/15 tires. To save a little cash, I went with 195/65/15 tires. Does anyone know if there is an inexpensive way to reprogram for tire size change. I know how to calculate for the change, but would like for the speedo an odo to be correct.

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Old 09-17-2010, 04:48 PM   #2 (permalink)
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...don't believe it's possible to "re-calibrate" the factory ECU.

...only under 'secondary' calibration--such as via SGII, etc.--can this be accomplished, but those results are not reflected on the instrument panel odometer or speedometer.
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Old 11-01-2010, 04:01 AM   #3 (permalink)
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when you change tires to 195/65/15
overal tire diameter increase %3.17

than, when you drive car 200km speed (124.2 mile)
you see on the your speedometer 194km (120.5 mile)

your choice
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Old 11-01-2010, 01:50 PM   #4 (permalink)
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Quote:
Originally Posted by KCF3712 View Post
Does anyone know if there is an inexpensive way to reprogram for tire size change.
Since this post is a couple of months old, this info may be too late for you. Could be helpful to others, though.

On most (all?) OBDII cars the dealer can flash the computer with the adjusted info to correct the odometer and speedometer for tire size and gearing changes. Call the dealer and ask their price, it should be reasonable (I've seen anywhere from $15 to $100).

If you would like to do it yourself, you can use products from Hypertech(not an endorsement, as I haven't used it personally) or other programmer companies, but you'll pay a bit of a premium (online price is ~$170).

Either way, if you want to have an accurate reading, it is easily done and somewhat reasonably priced.
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Old 11-01-2010, 11:31 PM   #5 (permalink)
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...uh, which dealership(s) can do that?

...I ask because both of our Toyota-made, defunct-GM Pontiac, Vibes' ('04 & '09), show a consistent "+2 mph" high reading on the speedometer, but NOT when read through the OBD-II connection via ScanGauge-II from the ECU.

...hence, at least for our Toyota/GM hybrids, it appears the "+2 mph" offset is being "added" at the dashboard display and NOT within the ECU...which would seem to rule out subsequent dealership reprogramming capability...but who knows?

...but, I'm curious to learn otherwise.
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Old 11-02-2010, 05:57 AM   #6 (permalink)
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The +2 MPH thing could be in either the ECU or the instrument panel, as there's no reason the ECU couldn't just give a different speed value to the instrument panel, and then store the correct one for the odo. I doubt it can be corrected by a dealer either way, as the ECU does actually know how fast it is going.
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Old 11-02-2010, 04:00 PM   #7 (permalink)
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Quote:
Originally Posted by tumnasgt View Post
The +2 MPH thing could be in either the ECU or the instrument panel...
...that's what the evidence, so far, seems to indicate. The Pontiac serviceman said it was a "cushion" against speeding (ie: an intentional 'error').
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Old 11-02-2010, 04:05 PM   #8 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
...I ask because both of our Toyota-made, defunct-GM Pontiac, Vibes' ('04 & '09), show a consistent "+2 mph" high reading on the speedometer, but NOT when read through the OBD-II connection via ScanGauge-II from the ECU.
Same here.

Dash reads 2-3 kph fast, but ScanGauge value matches GPS-speed

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