Update: I had the wrong number of teeth for sprocket nr4, it should be 19T in fact, so the correct graph looks like this:
Turns out it's not exactly easy to find a 46T chainring for SRAM Rival on sale anywhere. The closest I found was a complete 46/38T cyclocross chainset.
I did my second 100k (well 108.2km to be exact) bike ride for the season on Sunday, now with newly bought Tubus Fly rack and a pair of Ortlieb panniers. Much better weather and fitness compared to last time meant that I finished in just over 5 hours.
Ride details: 108.2 km, 5 hours 2 min, avg-speed 21.5km/h, avg-cadence 76, avgHR 118, calories: 1669 kcal.
Riding with panniers full of stuff (heavy stuff!) really changes the feel of ridig quite a lot. Without any bags uphills can be attacked in the big chainring by standing up and pedaling hard. With bags the bike feels much heavier and even small uphills need to be dealt with by shifting down into the small chainring and spinning at 80-90 cadence while sitting down.
My bike came with a 50T/34T compact SRAM Rival chainset and a 12T-27T 10-speed cassette. I wonder if changing the big ring to a more "cylcocross-like" 46T ring would make for better gearing? This graph I made shows the bike-speed at 80-cadence in the different gears. I used 2099 mm as the distance the bike travels when the wheel turns one revolution, taken from the auto-calibration data of my Garmin Edge 800. Changing to a 46T would give four gears in the 25-31 km/h bracket, instead of three currently. It's not like I need the 42 km/h top-speed that the 50T ring gives anyway.
Have updated to WordPress 3.2. The look of the admin-panel has changed slightly, otherwise hope everything is OK (the comment-settings usually get messed up when updating...)