I might not be understanding you right but what do you front tires have to do with gear ratio.
A 24" rear tire has a one to one ratio so tq at axle and road is the same any tire larger, tq at the road will be lesser depending ratio from 24", eg.. 24/30= 0.8 .8x 3.23 = 2.58 , 24/26=0.92 .92 x 3.23 = 2.97, so 2.58 and 2.97 would be the effective gear ratio .
Front tires have nothing to do with gear ratio on a rear wheel drive car. Just comparing the impact on effective gear ratio going from 26 to 30 inch tires. You could compare 24 inch to 32 inch, 26 to 25, 14 to 72 etc. etc.