Want to upgrade forks to cartridge with full adjustability. SP forks are rare here in North America, and seem pricey from Japan. So how about CBR600 F2 (late) or F3 forks? They are 41 mm with cartridge design and adjustability, common and inexpensive. Anyone tried fitting these?

BTW club rules prevent use of upside down forks.

VFR400 forks (NC 32?) forks would be an option but do they have rebound adjustment?

http://reactivesuspension.com/product-section.php?subcategory_id=6
The people are listing racetech cartridges as compatible with all nsr250. It would be interesting to see if anyone has tried them
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Why do things simply when you can complicate them

I bought NC30 cartridge style uppers. They're a simple mate to the stock bottoms and a set of Tyga adjustable fork caps. From there, my suspension shop (Superbike Suspension in Naperville, IL) added new springs and a custom Ohlins stack of valving and shims. (I powdercoated the original bottoms in Ohlins silver while I was at it.)

Very nice, thanks for the info. Am I correct that those forks have compression damping adjustment but not rebound (or is it the other way around)?

Full tw0-way damping adjustment would be nice.