From what I've read/learned on Slowtwitch, the 2x20' trainer workout is the thing to do to get fast on the bike. I don't have a power meter - is there an effective way to simulate the workout based on how tired I am? I'm keeping everything as constant as possible (tire pressure, trainer resistance, and tension against the rear wheel), but without a power meter I really don't know if I'm going hard enough or too hard. I did it last night (10 min warmup, 20 minutes hard, 5 minutes easy, 20 minutes hard, 5 minute cooldown), but I definitely didn't feel like I left it all out there. How am I supposed to feel after this workout?

I am a fan of the flamme rouge method, I have been getting great results with it and have increased my FTP dramatically. It starts with a 20 minute all-out test to estimate FTP (FTP ~ 95% of your 20 minute power). Once you know this, the key workout is 2x20 @ 85% of FTP done twice weekly. After 3 weeks, rest for a few days and then repeat the cycle starting with the 20 minute all-out test to get a new FTP estimate. Repeat, repeat, repeat...

As to how to do this without a power meter, you have to go with what you have which will be speed (1st) and heart rate (2nd). I'm not sure how to relate power to these, especially HR which seems to vary a lot. You can certainly look at speed during the 20 minute all-out test and then use some fraction (not sure what) of that to estimate the 85%

The one thing I can tell you is that 85% of FTP is not all-out. It is not comfortable either, especially during the 2nd 20 minute interval. At least for me, the average heart rate during the 85% FTP intervals works out to almost exactly 85% of my 20 minute all-out test average heart rate.

The 85% FTP 20 minute intervals are difficult but not so difficult that you can't do well at your other training. If you go much above this you will need longer to recover and you may end up training less volume. I hear a lot of people talking about 2x20 @ 100% of FTP but I would not be able to run and swim effectively if I did those very often. With the flamme rouge method you are knocking out 1:20 per week at 85% of FTP and then 20 minutes every 3 weeks in a race-type simulation at ~105% of FTP to take your new baseline. Add a bunch of 75% riding in there as well and you are going to raise that FTP, no doubt about it. Plus you will still have enough in the tank to run and swim.

If possible, you might also try borrowing someone's power setup for the first 20 minute test and a 2x20 85% session to get a feel of what speed and HR those work out to. Good luck...