how fast do you bike when you train?

Welcome!

A few comments.  First, it is impossible to say how fast you 'should' be going.  There are far too many variables.  I'[ve done training rides where I average less than 15mph (big climbing in the mountains) and training rides where I average well over 20mph, and everything in between.

Second, because of all fo the variables that affect speed, going by 'zones' is a good idea, if you can properly determine your zones, which will take some time.  Are you judging them by RPE (rating of perceived exertion), heartrate, or something else?

Best of luck with your training and your race!

I can't/won't advise "you" how to train but I can tell you how I've had success training on the bike. I have standard routes that I ride and I keep detailed records of how fast I ride them. When I first start riding, I push the same exact effort for the first 15-20 minutes or so. I use RPE and the effort is about 6/10 or slightly uncomfortable. I time my rides very accurately and I always have a point where I take my first split. I base my effort for the next segment upon that split (taking wind direction into consideration). If it's fast, I'll push a bit harder to the next split (7/10 or so). If it's slow, I'll do the rest of the ride at a comfortable effort (5/10 or so). Every time I get to the next split I'll do the same thing, increase my effort a bit or turn the rest of the ride into a fun comfortable ride.

If things go well, I'll be pushing very hard for the last segment trying to PR the course. I look at bike routes like a climber looks at "projects". I am constantly trying to ride longer routes with more climbing at speeds similar to what I can do on shorter/flatter routes.

This method ensures that I'm pushing harder/longer when my body is fresh and strong which is what I personally believe is best for me. Otherwise, I've ridden partly above comfortable and the rest at comfortable. Again, this is just my personal method that I've been very succesful with in the past so YMMV.

ETA:
When I lived in a flat area, if I made it to the point of a hard effort and was just dying in a pile, I'd switch to 2min on/ 2min off intervals where my "on" periods were pretty much all out and "off" periods were as easy as I wanted. I could sustain a "very hard" effort faster and longer by doing so. I don't do it here because my terrain is very challenging. The terrain often dictates my effort. My normal ~60 miler has ~5000 feet of climbing (in just 3-4 climbs) and all my rides end with a 400 foot climb at a 10% grade to 9800' of altitude.

Edited by breckview 2009-08-01 9:13 AM

Thanks for all the info!
I've just got a new bike and computer, so I'm trying to keep my cadence up around 90.  I live in a pretty flat area, and my race will be pretty flat too.  I like the idea of doing 2min/2 min.  That would have been good this morning in very high humidity, along with a tired body from yesterday's workout.
Thanks!