Because the idea is that, with an Oyster, you'll never be in the
position of being PFed, because if you travel out of zones you will
simply have the appropriate add-on fare deducted from your pre-pay
balance.

People will wise up to this and try it on, the only feasible
way to do it is to debit the maximum amount and re-credit it as
described.

Do you think so? I reckon most people with less than all zones have their
regular journey covered by it and only occasionally go out of zone (my Z1/2
is all I need most of the time). It also relies on manual gates being open,
the money being lost this way is probably low and I doubt your seasoned
dodger would chance this

The only other way is a more radical restructuring of the fares system
based on a much simpler capped flat fare system for Oyster replacing
all ticket types, be they Travelcards, seasons or whatever. It is a
shame that this has not been done.

Once they've gathered travel times and patterns from the large amount of
data being collected hopefully they will re-evaluate current tickets. I've
often thought annuals are unfair as although you pay for 10 months and get
12, there are a lot of weekends when you probably won't, holidays, sickness
and any other times you're not at work. When I worked shift I bought one
even though it may have been £100 a year more expensive than buying
individuals or weeklies purely because it was go anywhere for a whole year
with no queueing involved. I think there's another thread on this saying
pre-pay is already cheaper than an annual. It'd be good if you could load a
lot of pre-pay on the ticket for a reduced price (i.e. you could put £800 of
pre-pay on the ticket and get £1000 of travel). After all the system runs
whether you're on it or not.

Dave