One of the best kept secrets in cycling is that long distance riding is more about experience and will power than any special types of fitness.
If you have not ridden a 400km ride before you should at least consider taking part in a 200km event. This distance will test your overall fitness and ensure that your bike is set up comfortably. In particular, you will want to know that your contact points (feet, seat and hands) are ready for a few hours on the road.
Audax UK, the governing body for long distance riding, gives advice on its website and dedicated forums are full of encouraging advice. Riders looking for events in the Chilterns should check out this page from the Westerley CC.
Watch out for events organised by
- Audax Club Hackney – they host a classic 300K ride from Oxford in early April
- Audax UK – provide listings of all audax rides in the UK
Take a look at the Audax page on this site for links to some useful blogs.
There is also a Strava group called LWL if you want o compare your efforts before (and afte) the big day.