you don;t lose power (espescially if the after market rims are lighter then the ones you have) but it may feel like you chaged the gear ration a bit....putting bigger are or small rims has a non direct effect on your drive train, not your HP or TQ.
I think you might stay the same...If there heavier than your stock then I would say you might "lose" power because they are larger, and heavier so it would take more force to complete one revolution.
Roz
