Hello rohd6, and welcome to the ...Madhouse <insert manic laughter> you'll never be able to leave. Well done on signing up to do the L2B.
As others have said initially get down to your LBS Local Bike Shop, or, if you haven't got one the
Hellfrauds er, sorry
Halfords, and get sorted with some semi slick tyres to fit your wheels, which I'm guessing will be 26".
Pick the bike which has the least amount of 'suspension' as JC points out, suspension, especially on a budget bike, say under £500 is just a waste of time, you expend way too much energy kangerooing up and down.
once you have the bike sorted, checked over mechanically n.b. Don't go to Hellfrauds for this, do it your self or use the LBS, then pick a fairly traffic free route you are familiar with maybe a loop so you can set off and do your ride without covering the same roads, start with rides of say 5 miles which isn't too arduous, see how you feel, then just extend your route as you feel able to until you are doing 20 or more miles, do that twice a week, and before you know it you'll be doing 40 miles at a time, with no problem.
Keep hydrated and take something to eat, muesli bar or similar.
Be warned though...This cycling lark is seriously addictive, and before you know it you'll be lusting after carbon fibre bikes, hanging out in Know how and the cafe, and completely bonkers like the rest of us.
The L2B isn't a race, its an event, lots of people on bikes that should be in a skip will be out on the day, it's only 54 miles and most of it is down hill
