mileage problem

[Ldub]

i did a serarch, and couldnt find an answer. sorry if i missed it. i was geting around 19 mpg everyday driving, 21 on road trips. i just changed wheels and tyres and i knew it would afect my mpg, but not this much. (32" cooper descovery stt) i just calculated my new gas mileage. 10.59 mpg. 50% decrease! is this all due to the new tyres and the sligte lift that was required to fit acomodate them. or is there something else wrong?

Have you compensated the mileage shown on the odo, to reflect the new tire diameter?...

Input your stock size & new size here, calculate the difference in %, then take your odo reading x that % value, add that many miles to your orig odo reading, THEN divide by gallons used.