Thanks all for the feedback.

OK, here's the plan, tell me what you think...

My normal commute is 12 miles but I normaly do 20 miles on the way home. I cycle commute 5 days per week.

All morning rides, and Monday, Wednesday, and Friday nights are at fat burning (low HR) range, may increase the distance to 30 miles in the evenings.

Monday night commute is a 20 mile hammerfest, pushing the lactic threshold.

I'll increase the distance on Tuesday & Thursday nights to 40 miles in the cardio range.

Saturdays will be long training rides, starting at 60 miles, then adding 20 miles each week upto 140 miles i.e. 60 this week, 80 next week, 100 the week after, etc. which will leave me 4 or 5 Saturdays at 140 miles each, to get the times down.

Sunday is rest day.

Please critique this training plan, is it too ambitious?