Can a SORA Brifter be used for a 9 speed system?
 

Heres the catch, I have upgraded my Spinergy to 10 speed Ultegras,..I have an Ultegra 9 speed cluster and a Sora Brake/Shifter (leftover from another training roady i sold) as well as other multiple bike parts (leftover upgrades from my BH, almost only the frame is left original, even that is not secure ha ha ha) now can I build a 9 speed running gear using the Sora Brifters? I plan to build a training bike for rainy and trashy weather. I know that Sora Brifters are only up to 8 speed but my mate said it doesn't matter and it can still do it. Whats the real deal? Thanks for your replies in advance.

It does matter.

The indexing is contained internally to the brifter, and there are only 8 detents, if you will. Meaning that while you could theoretically use them, you can only utilize 8 of the gears. So...pick low end or high end, I suppose.

Another issue may be spacing, though someone else can chime in here. I don't know if the brifters are so specific that the cable pull may be subtly different for derailleur travel, but here is the potential issue. Spacing between cogs on an 8 speed cassette is 3mm, while cog spacing on a nine speed cassette is 2.56mm. Tiny, but if the Sora brifter is calibrated towards 3mm spacing, it will travel the entire lateral distance of your cassette with only 8 indices. Not optimal.

No you can't. I would just get a cheap 8 speed cassette for an all weather bike. The 8 speed chain is a bit beefier, anyway.