This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
Picking the broadest curve through a corner may be obvious by the time
the preceding skills are mastered, but that may not be the best line,
either for safety or because the road surface is poor. Sometimes
hitting a bump or a "Bott's dot" is better than altering the line,
especially at high speed. Tires should be large enough to absorb the
entire height of a lane marker without pinching the tube. This means
that a minimum of a 25mm actual cross section tire is advisable. At
times, the crown of the road is sufficient to make broadening the
curve, by taking the curve wide, counterproductive because the crown
on the far side gives a restricted lean angle.