Originally Posted by Moose
Even if on your 8 mile commute you rode 22mph for 4 miles and were slowed to a crawl of 5mph for the entire remainder of 4 miles your average should still be just over 16mph.
Your math, I think, is wrong. You're averaging 22 and 5 to get 16, which is not how an average is calculated. An average is just time/distance.
So, to use your representative example: 4 miles at 22mph is 11 minutes. 4 miles at 5 mph is 48 minutes. Total is 59 minutes, just about an hour. So my average would be, in fact, 8 mph.