888 RC3 EVO V2 TITANIUM / 2012 - spring rate
I bought a 888 RC3 EVO V2 TITANIUM / 2012.
The spring is the standard one (5.5 N/mm)
My weight with full apparel is 86kg (189lb).
Will the ti spring be ok for me or do i need to change it (i would rather not cause it is expensive...)? (i ride light downhill)
What adjustments (mainly in the preload) do you recommend in order to set it right for my weight?
Unfortunately I believe you are outside of the weight range for the stock Ti spring. Compensating for an incorrect spring rate with preload is not the way to go, as it will negate the benefit of running coil suspension in the first place by increasing the force required to get the fork moving from the zero travel point.
I weigh a less than you (180) and found the stock spring too soft, but you can try turning up the compression damping significantly and perhaps adding a bit of preload to get you by.
You'll find a lot more discussion on the topic here, reading back from the last page you'll find a few people that have asked the same question as you and relevant answers:
2010 Marzocchi 888 Evo tuning thread - Page 55