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I have the stock 185/65/15's on my car... just orderd some 215/40/17's

I used the tire calc and it states that the speedometer reading on the new tire size is 2.89% fast...

would that affect my gearing ratio in a negative or positive way???

One thing, I know if your rotational mass is larger than stock, you go slower, because there's more mass to turn... what if it's smaller?? would the car, in essence, go faster???

with that said, 185/30/15's * i know there isn't a tire with that size but for arguments sake* would make me go faster because of less rotational mass??

thanks for any help guys!!!!!!

 
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Acceleration wise, smaller tires will give you shorter final gearing (they don't effect the gears inside the tranny) and faster acceleration.
Top end... Larger than stock diameters will give you higher top speeds, but slower acceleration.
In theory, within a rim size there is such a small difference in inertia (since the mass is basically the same distance from the hub) that it can be neglected. Now if you're comparing 14's to 18's, yes... you will probably notice a difference in starts. Once the wheels are rolling at a good clip... it won't make too much difference.