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Your speedometer and tachometer will read exactly the same in relation to each other, no matter what size tire you have on the car. The speedometer is based on the rotation of some part upstream of the wheels so it is a calculated value based on a presumed tire circumference of OEM sizes.

The speedometer on my electric drive is 6% too fast, so using a tire that is 6% larger in diameter will result in the speedometer being accurate. But that can only be determined by some device that measures or calculates your physical velocity, like a GPS.

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with the needle on 45 or 50 or 60 what are your rpms?
I'm running 195/55/15s in all 4 corners. To answer your question: I don't care. I don't have a tach or scanguage. I listen to the engine and transmission. If it's purring along and hitting the shift points on the mark then I'm happy.

BTW, my 2009 Passion hates going 35 MPH - even with the Area451 cruise set to 35. The car goes into "Do I? / Don't I?" mode the entire time. Irritates the crap out of me.
 

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I thought about this when I was driving to work, but it is tough to write down a number when you are driving, and I suffer from CRS.. (can't remember ****)
 

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OK, here is what I came up with , 2008 Passion with 195/55 tires, ScangaugeII :

MPH ......RPM
30.........1977 (4th gear)
40..........1835
55..........2458
60...........3175
70...........3421

Kind of a rough estimate but should be close.
 
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