Can Someone Explain How 25/30 Mm After Market Fork Internals Are Better Than Oem?

From what K-tech told me the bigger cartridge allows more oil, which in turn doesn't heat up and fade as quickly. Essential for flat out TT action, overkill for a Sunday blast or most track day riders.
The difference in Ohlins/K-tech internals however is a noticeable improvement in how well the bike tracks the road and how the adjusters actually work when you move them.
Not sure about very modern stuff but a few years back road suspension was usually made so no matter what you did with the adjusters it was still ok. Get race suspension wrong and a bike can be unridable.

 

What makes it more complicated is that similar looking forks can have quite different internals. From what I've read, including an article in one of the magazines last year, the Showa internals can vary a lot from one Ducati to another, even if the outside looks similar (for instance, I believe that my 900SSie has an inferior design to the similar looking 916 forks of the same era). Therefore, whereas some of the forks can be improved significantly by cartridge upgrades, for others it can be very costly to do all the work necessary. For an example of the potential complexity, this discusses Monster fork enhancement: Showa Blues, part 1&2.

In the case of the 900SS I found, eventually, that there appears to be truth in the argument that the design is so poor that the compression damping adjuster does little, and the rebound adjuster actually influences the compression quite a lot! I've concluded that it would take more than a change of cartridges to bring these up to standard, but if I did anything more than oil change, which I've been putting off, I'd go to one of the specialists mentioned above.

 

Also bear in mind that when manufacturers use a quality suspension component on their bikes it can be found quite often that these are not the same versions that you can buy. They tend to have cut down versions of the parts that are made to a specific price.

 

Can't expain the technicalities but the previous owner of my 749R had K-Tech cartridges installed in the Ohlins forks. The net result is that the front suspension is absolutely fantastic. It feels "soft" (and compliant) but behaves beautifully on track - no wobbles/shakes, follows all bumps and never bottoms out under heavy braking.
Lovely!