Upside-Down vs Conventional Forks
Which is up, which is down?
The upside-down (USD) fork was the domain of race bikes before it was adapted for sportbikes. It is now seen on dirt bikes, small-capacity road bikes and even bicycles.
USD forks are technically telescopic hydraulic forks too. However, they are inverted with the larger portion slider part on top and the skinnier fork tubes at the bottom. Conversely, conventional forks hold the skinnier tubes up top (and attached to the triple clamps) while the fatter sliders at the bottom.
Why are my forks upside-down?
The answer is stiffness. With the larger portion clamped to the headstock, the forks do not flex as much.
Take note that the headstock is where all the forces are channelled into at the front. Braking, bump shock, rider weight, motorcycle weight, suspension rebound and cornering forces are borne by it. Consequently, the forks will flex if they are not stiff enough.
So, having stiffer fork sliders results in better feedback and responsiveness.
Do they benefit me?
Truth is, street riding does not result in the same forces encountered at the racetrack. (You are riding too fast for the streets, if you do.) This is the reason why the benefits of USD forks are heavily contended among bikers, although there are those who swear on better feedback (that has more to do with suspension tuning, in this writer’s opinion).
On the other hand, you know you have a track-ready or competition-ready motorcycle at your disposal. Besides that, USD forks allow for proper radial brake callipers mounting.
What are the drawbacks of USD forks?
The biggest issue is when they leak. Unlike conventional forks, the force of gravity draws out the oil faster. Additionally, that oil leaks very close to the front brake calliper. So, have the oil seal changed immediately when you notice your USD forks are leaking.
Another disadvantage is the lack of a drain plug at the bottom of the fork. This means servicing is trickier and best left to professionals, if you are unsure.