Hi (and extra-Hi to all those who remeber me, sorry not been around for a while)
I did a 40 mile round trip 2-3 days a week for a year or so, starting in the suburbs, running right through London and out to the west of town. For me it was not about distance or time...it was all about terrain.
I share my route with many riders on this site (Bentmikey, Ianrauk etc) and take the A21 from Kent. I find riding through town is simple and very fast, despite the traffic and the lights I feel i could ride much, much further than I do (once I am in town) however, on my return leg, after around 15 miles I reach the "burbs" again and the traffic becomes much faster (making me feel much slower) I face an eternal headwind (every day without fail) and a slow monotonous uphill ride for 5 miles that really saps my remaining strength and leaves me feeling drained when I get home.
It’s a terrible end to the day for me (I know others do not feel the same).
When I get to work I feel invigorated and healthy, when I get home I feel knackered and …old.
So, check out the bikehike website and take a good look at the terrain. A hill in the middle is probably perfect as you will have a good 10 miles to recover each way and get back to rhythm.
Having said all that, I personally would prefer a 15 mile commute (30 mile round trip) that I could do every day as I have never managed more that 4 days in a week and averaged 3 (so plenty of 2 day weeks)
Incidentally, I did this on a 15 year old mountain bike that is still my hack bike today, so don’t be concerned about equipment just yet.
Good luck
Jonny
PS...I'm just getting into the same ride again this year and am working up to a 3 day week...not there yet, but I should be matchfit by July