with most forks, the fatter diameter lower part slides over the skinnier upper stanchions.
with an inverted fork the fat part's up top and the skinnier lower legs slide up into it.
tricky to do with rim brakes because the brake bosses gotta move with the lower part. Halson Inversion did it by cutting slots in the uppers.
easy to do with disc brakes.
but why you say? Larger diameter tubes are more rigid than smaller diameter ones, so it makes good sense to put the fat parts up by the fork crown where their fatness and rigidity will do the most good.
probalby other reasons but I ride rigid, what do i know?
I got a whole box of Halson elastomers out in the garage, all colors, probably 50 or more.
Dual crown inverted forks work very well, to get more travel they make great sense because the space in between the dual crowns is used for the sliding of the stanchions. This means that compared to a standard dual crown fork, they have more bushing overlap, which is critical when we are talking about long travel.
Single crown inverted forks do not work very well. They do not have the benefit of increased bushing overlap, they in fact have the exact same amount of bushing overlap as a standard single crown fork. Another big problem is that they have no "brake arch" (it would go through the wheel obviously). This means that it is extremely difficult to make the single crown inverted fork stiff in the torsion (twisting) direction. The inverted fork is stiffer for-aft because the uppers are "bigger" than the stanchions, but you could make a standard fork stiffer for-to-aft by simply using bigger stanchions. There is also a myth of unsprung weight making the fork "plusher", but this is easily negated by fairly small variences in front wheels. In other words you might save half a pound of unsprung weight by having an inverted fork, but if you choose to run a tire/wheel that is 200 grams heavier, you have just negated that benefit. In other words if you were running a standard fork, you could get the same effect by dropping 200 grams off your wheel, which isn't very hard.
There is no good reason for a single crown inverted fork. The main advantage of the dual crown inverted fork is the increaesd bushing overlap, this helps a lot with the stiffness, and the 2nd (dual crown) feature also adds a lot of stiffness, this is why the dual crown version works.
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