Improving average speed can be discouraging. I have a real tank -- a 36 pound Ross road bike which I ride on a 15 mile set route. I my best average speed is 13 mph for the 15 miles. I recently acquired a 22 pound aluminum Trek 1400. My best average over the same route was 14 mph. The course is hilly, and I was looking for a greater improvement. My theory is once you're at speed, it's hard to improve your average speed unless you go to heroic efforts. My tank is slow on the uphills, but goes like a bandit down hill.
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"I am a true laborer. I earn that I eat, get that I wear, owe no man hate, envy no man's happiness, glad of other men's good, content with my harm." As You Like It, Act 3, Scene 2. Shakespeare.
"Deep down, I'm pretty superficial." Ava Gardner.