Thought I'd wade in here....I don't have the technical data/knowhow, Watts, Joules, Faradays or whatever, but over the years have ridden many 12's with varying degrees of pain, sorry, success.
Firstly, some form of aero bar (I love chocolate
) is a terrific aid in a 12. When you start, you can get in the "tuck" up and down the dual carriageway and sail along. Then later, when you're feeling tired, can lean on them for a short doze
after all the guy who invented them based them on a comfortable ride in the RAAM.
I have always used my road bike with clip ons as I know it is comfortable enough to sit there for 12 hours whereas my TT position is just about OK for a 100. Am working on that for this year
I don't think many, if anyone, uses a skinsuit in a 12 as the aero advantage is minimal and the lack of pockets to stuff lardy cake, paste sandwiches and a pizza slice (plus some money for the McDonalds Drive Thru) are invaluable.
240 in your first one is some challenge, but then you have ridden 12 & 24 MTB's before. I'm still trying to make it - after my best last year of 238. I paced myself on heart rate, based on 80% of my max, which I am reliably informed is not the best way , but it meant that the first 4 hours seemed so slow that I felt like I'd just been down to the shops, but the last 4 hours at the same pace were incredibly tough.