Originally Posted by Drew Eckhardt

Ride less with groups and more by yourself. Group ride fitness and terrain interaction with the pack speed and your weight are unlikely to produce optimum stimulus or rest.

Ride more threshold intervals (95-100% of lactate heart rate which is about what you'll average over the last 20 minutes of an all-out 30 minute effort, or 90-100% of the power you could sustain for an hour). 10-20 minutes is good. You don't need much rest between. With some training you might ride 2x20 with 5 minutes between. You get faster by stressing systems needing improvement and being fresh enough to go hard for that efforts. 1 minute intervals for 10 minutes are not optimal for forcing adaptations relevant (more plentiful and powerful mitochondria) to hour long rides.

Increasing your threshold power also increases how fast you can go at lesser efforts and how long you can sustain them.

Also note heart rate based zones need to be calibrated against your physiology - there's too much variation between individuals for the %of age formulas to be valid. Chris Carmichael has a system built on a pair of 8 minute all-out efforts which are psychologically and logistically easier to accommodate than Friel's half hour time trial.

Ramping up total stress helps too where this can be intensity (you go from 1 to 2 days a week riding threshold interval) and/or time based.

You also need to have less stressful (intensity^2 integrated over time) weeks and months.

Reading some books on cycling training would be wise. Popular selections are Friel's Cyclist's Training BIble and Carmichael's The Time Crunched Cyclist.