From their Facebook page:

It's summer so it must be Chinnor! What more do you need?
Well, this year is our 20th anniversary so it's going to be bigger and better than ever. And still only £15.
The same great mix of bikes, bands and beer. Good friends and good times. There's the ride out, trade stalls, silly games and free camping. Our superb real ale bar will keep you refreshed between the two stages featuring excellent performances, the bike show and great food on offer.
If you've been before you'll know why you should put this in your diary. If you haven't, ask someone who has.
Only Chinnor has that unique Chinnor atmosphere.