Throw tire size into the equation. To tall of a tire or to short of a tire will effect rear end ratio. You will need actual height of the tires. If your running a taller than original tire,
formula is orig tire height devided by new tire height times rear end ratio. That gives you your effective ratio.
Although with the higher RPM you describe i am inclined to think your tires are not tall enough. Not sure if you considered this, hope it will help you out.
Stranger

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