call bruce at pioneer motorsports in new york. www.pioneer motorsports.net
they are running a 2.3 kg spring for the fx nytros (shorty's and long tracks). they did this due to the mtx's only using a 1.7 kg spring, and the riders complaining it is too soft. and the shorty's are running a 2.5 kg set up and those riders complaining it is too harsh.
i have about half a day of riding on them, still trying to find the sweet spot. ski