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Ryan,
Doesn't the speedo based its measurement off the wheels/tires so the size of tires will affect it. But with a different diff ratio your rpm's would just be higher for the same speed and therefore should not affect the speedo reading. Typical error between speedo reading and actual could be 3% easily according to BMW.
-Roberto
 

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use a gps unit and see how much you off ...
 

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The gearing will increase the rpms of your engine by about 500. I don't believe it will affect the speedometer. So when in 6th and cruising at 80 mph my tac would normally read 2500 rpms. Now with the 3.45:1 diff, I am reading 3000 rpms. Hope this helps.

Mike
 

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The gearing will increase the rpms of your engine by about 500. I don't believe it will affect the speedometer. So when in 6th and cruising at 80 mph my tac would normally read 2500 rpms. Now with the 3.45:1 diff, I am reading 3000 rpms. Hope this helps.

Mike
+1.
Regards,
Jerry
 
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