What are the advantages of upside-down (USD) forks vs traditional forks?
I have read they are 'better', 'stronger', etc., mostly in the context of motorcycles.
Some high end downhill bikes use them as well as some cross country bikes I've seen (that are equipped with RockShox inverted suspension), like this:
According to Wikipedia:
Conventionally, the fork stanchions are at the top, clamped to a triple tree (also called a triple clamp or a yoke), and the sliders are at the bottom, attached to the front wheel spindle. On some modern sport bikes and most off-road bikes, this system is inverted, with "sliders" (complete with the spring/damper unit) at the top, clamped to the yoke, while the stanchions are at the bottom. This is done (i) to reduce unsprung weight by having the heavier components suspended, and (ii) to improve the strength and rigidity of the assembly by having the strong large-diameter "sliders" clamped in the yokes. The inverted system is referred to as an upside-down fork, or "USD" for short. A disadvantage of this USD design is that the entire reservoir of damping oil is above the slider seal so that, if the slider seal were to leak, the oil could drain out, rendering any damping ineffective.
The article mentions reducing "unsprung weight" as an advantage, what does this mean and why is it advantageous?
Quote from yamaha-motor.com.au:
On inverted forks, the large outer tube of the fork is clamped in the bike’s triple clamps and the sliding inner tube holds the axle and front wheel. By locating the large diameter tubes in the triple clamp, the inverted or upside down fork have their largest and strongest parts combatting the highest stress.
This arrangement gives the forks high rigidity, which improves their response by reducing the side loading of the internal bushings (sliding surfaces). This kind of response is particularly important in high performance applications. Most inverted forks use cartridge-type damping systems.
Also, since the damping mechanisms are now held by the triple clamps, unsprung weight is minimised. Reducing unsprung weight is one of the biggest contributors to quality suspension performance, particularly for featherweight motorcycles like the YZ series or R1 and R6.
They also mention reduction of unsprung weight as one of the biggest advantages, as well as reduction in side-loading as another advantage.
The only disadvantages I've read about are the aforementioned oil leakage issue and a possibility of greater change of nicks on the stanchion from road debris. Are these valid concerns on a bicycle?
Are there any other pros/cons to an USD suspension setup on a bicycle?