I am trying to get my head around which is most important, physical or mental endurance.
as this is the question, FWIW here is my answer... I think mental endurance is the most important - there are thousands of riders who could easily do audax distances but don't because they don't want to, and hundreds who were only just able, and who have done it: clearly if you don't want to finish, you'll not start, or start and climb off somewhere and get a lift/hotel/train.
Physical endurance reduces, to some extent, the amount of mental endurance required for two reasons 1. getting the physical endurance requires hours in the saddle (or getting fit some other way) which requires / develops mental endurance. and 2 - although there will pretty much always be pain (and indigestion, and sleep depravation) involved in the early days, especially for distances over 200km, the fitter and stronger you are, the less it's going to hurt.
However, the idea that it's all about wanting it /mental endurance IMO is overplayed in sport in general, and in audaxing too - ultimately you've got to have the strength in your quads to get you round. The hillier the ride, the more important the power (and lack of excess weight) is. If your legs don't have it, they'll turn to mush, and even maintaining audax speed will be too hard. That said, you don't have to have
that much in your legs to get round flattish rides* at minimum speed, but you have to have a bit more fitness and a lower BMI than the average UK citizen.
I think that a advice to 'go for it' often underplays the need for a level of background fitness (and/or youth) to recover from big rides, and how much suffering will be involved if you don't have it. That's not to say it's bad advice, it's just that I don't think it prepares people for the suffering they're letting themselves in for, or helps them understand that the reason the riders around them aren't suffering anything like as much is that they've got 00's more long distance miles in their legs.
...in terms of PBP I decided to do it in 2015 around this time of year in 2010. I'm sure (with hindsight) it would have been possible, but given my state of fitness then (an average club cyclist who'd done a few 200 audax events) - i didn't think doing a first SR and PBP the following summer sounded like enough fun, or that it was achievable enough. I'd much rather have done what i've did and built up season by season: 2,3, and then 400 in 2011, (Wessex) SR in 2012, LEL 2013, Mille Cymru 2014... with a plan to do PBP next year. Obviously there's risks to that strategy because you never know what's going to happen in life, but there is a risk that overdoing it leads people to get back from Paris and put their bike in the shed until the following spring
, or worse decide that long distance isn't for them, when in fact with a slower build up, and being less close to their absolute limit for less time, they'd probably have enjoyed it much more, and might regularly be riding long distances now.
Andrew
* the consensus seems to be that PBP falls into the general category of 'flattish'