Originally Posted by
prathmann
And I think our instincts are correct in that. The figures are based on static weight distribution on level ground and no acceleration. Now consider the circumstance where I'm on a fast descent of a steep hill and see a rough patch of pavement ahead or a bunch of rocks that have been washed onto the road. My weight has already been shifted toward the front wheel by the grade and now is shifted even more when I hit the brakes - in fact if I hit the brakes hard almost the entire weight of bike+rider will be on the front wheel. This is also a circumstance where I really don't want to have loss of control from a fast pinch flat of the front wheel - but there's a big risk of that if I inflated the front tire based on the assumption that only 40% of my weight will be on that tire.
This was Jobst Brandt's objection to the figures when they started making the online rounds ~15 years ago -- that when climbing or descending a steep enough hill, nearly all of the weight is on one of the wheels. That's not only a good argument for keeping the tire pressures over a certain amount to prevent pinch flats, but to bump up the tire size if you find yourself needing to use high pressures to avoid them.