Depends on what you want to put the stress on i suppose. A higher gear with a lower cadence will be rougher on your muscles but not as hard on your heart and lungs. A lower gear and higher cadence will bring your heart rate up a bit, but will be easier on your legs. I go with lower gear higher cadence, as do (im pretty sure but correct me if im wrong) most triathletes. Just keep getting that saddle time in and it wont be a choice, youll just feel like you need another gear. :)

-alan

I love Kylie's comment, about runners being mashers - I'm one. Recovering masher. I've been working to increase my cadence. Currently I'm not able to maintain the speed I could previously by pushing the bigger gears, but with practice it's getting easier. And, the great thing is that when I do get off the bike, my legs still feel quite good for the running.

Thanks all! Good stuff, I definintely mash (I'll stop). My next question is, how do you measure your RPM's?

You can get really cheap cyclo-computers that have cadence sensors, or you might even be able to upgrade your current computer for a few bucks with a cadence kit. That's what I did with my sigma BC1600.

Some people say that you should run a lower gear at a higher cadence. In pro cycling, most riders used to ride around 60 or 70 RPM, but Lance came along with "super high cadence" (~90) even up hills, and now everybody swears by it. I say that it depends on who you are, but I also think that for triathletes specifically, you should try to get your cadence up around 90 otherwise your legs will be shot for the run. I've read a few books, and heard interviews with pros, and it seems like many triathletes agree that your cycling and running cadence should both be up around 90 rpm.