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Get the tire you want, but dont be too concerned about gearing. The ONE inch height difference equates to 3.7% in gearing. In other words, if you had a 3.23 27" tire car to start with, installing a 28" tire would have the same effect as switching to a 3.35 gear ratio (if such a ratio existed).
Or yet another way of looking at it, 3000rpm with a 27" would have to become 3111 rpm for the same MPH.




Your math is correct, but your application is backwards. A taller tire (28") would give you a ratio closer to 3.11 NOT 3.35 when compared to a 27" tire 3.23 ratio. Installing a taller tire is effectively like going with a numerically lower gear ratio.