When I was new to cycling 4 years ago, I was like you, trying to build up my speed and go as fast as possible. I hit the same 15mph / 24kph you are at that first year. And slowly worked it up the next couple of years.

This year, I learned about heart rates and zones. I realized in the past, I was riding in zone 4 and burning sugar, that is why you feel so tired after a ride.

This year I'm going for distance, 3,500 to 4,000 miles is my goal this year and I'm riding in Zone 2 and Zone 3, which burns fat. I've lost 25 lbs this year so far riding over 1,500 miles.

Daily I can go on rides of 30 to 40 miles and not feel wasted after, but rather be ready to go the next day. Sure, my average speed in only 15mph, but that is ok, I'm not out there racing against anyone. I'm building my stamina to go on century rides and maybe even tour.

I'm right there with you, being 39 and 240 (was 265), 6'1". And you know what? I went on a group ride with an average speed of 16-18mph for 30 miles the other day, and I was able to hang with them. Yeah, I was last up the hill, but caught up easily on the down side.

Listen to the others - I have a cadence of 90 revs per minute on most rides.

Do different kind of rides - fast paced, long distance, low gears and spin, high gears, etc. Change it up to increase all areas of cycling ability - don't just focus on SPEED.

Mark
'03 Litespeed Blue Ridge - go long days
'98 Lemond Alpe D'Huez - go fast days
'01 GF Tassajara - up and down days