@Paul H where did you get that 2182 from? did you measure it yourself or is it garmins auto calc?
the way garmin auto calc works is that it counts the revs for the first x miles (not sure what x is, may just be first ride) and uses the gps distance vs revs to calculate the wheel size (circumference)
if you really care about accuracy you need to go with a tape measure (you could get real anal and use more precise measurement devices, but thats up to you) and roll out the wheel for a full revolution, more accurate if you are sitting on the bike during the roll out . . . . . ?