“How Could I Improve this Graph?”

I'd like to improve the performance graph a little bit, but I need a suggestion for a statistical formula (or perhaps a process) which I absolutely can not remember, and I haven't been able to figure it out.

The problem with the current version of the graph is that it includes two numbers which paint a very incomplete picture of my actual cycling performance.

The first number, shown in the yellow line, is my year-to-date average speed. It's actually rather meaningless, it would be more useful if it showed the average speed of the last 5 rides, or something like that... essentially, it would be a smoother version of the other line on the graph.

The second number, shown with the white line, is the average speed of each ride. This is useful for determining my performance on a given day, and shows the "trend" of my performance by looking at the entire graph, but it's incomplete because it doesn't tell you how many miles I rode in that day. If I were only to ride for 10 miles, I could probably achieve an average speed of 21 mph, but if I ride for 45 miles I've (so far) only managed 17.5 mph.

So, the best graph would be some combination number which is something like a "grading system" based on the number of miles ridden that day, and the average miles per hour.

I've had a few ideas. Perhaps something like this would do the trick?

(today's avg speed X today's miles) / (total avg speed X total avg miles)

That would give me a general score for September 14 of 1.30, versus a general score for May 7 (my first ride of the year) of .82.

Is that a totally bogus way of doing this? I honestly don't know. Can anybody suggest something better?