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Re: Question about rear end gear change and speedometer (SpyRacing)
Rear gear changes will have no effect at all -- I speak from experience. The feed is off the ring gear which is the same size on all C5. I have changed my rear gears and checked before and after using a GPS against the speedometer -- reads exactly the same. The only change you will see is the rpm levels different at the same speed before and after.
Since you have a six speed no re-programming is necessary at all -- just enjoy the improved SOTP performance. :D:D
A4s need reprogramming mainly due to shift points -- but not to correct the speedometer.
Tire size changes (larger or smaller diameter) will affect the speedometer.