First, where are you? I'd guess for your weight that 0.90 kg springs are about right, others may want to chime in. In the USA, RaceTech are very good for springs. In the UK K-Tech have a good range, or Maxton will sort you out.

Do not get progressive springs! None of the top suspension guys use them as it is impossible to set the damping rates for the varying spring rate. It is essential to get the correct spring rate and length.

 

I have ST4S forks on my '06 monoposto. I took the weight of my bike, added my weight (210 lbs. geared up), then looked at what the ST4 weighed. Between my lighter bike and heavier than average Italian rider (me), it looked like a wash. Subsequent riding confirmed no spring change was needed. Remember, the ST4 is a heavier bike. Another forum member, greggers, did the same swap and came to the same satisfactory conclusion. YMMV

 

That's incorrect. You need to properly measure unloaded and rider sag to determine the correct spring stiffness and preload.

 

old engineering joke - when you assume you make an ass of u and me. assume it to be true

as a very general rule, ducati springs in non sbk models are stupidly light (around 0.60kg/mm to begin with) and crappy dual rate. not really progressive. all ss and monsters pretty much.

as a contrast, st series (and ms4) have a linear spring that is 0.83kg/mm, so it's not bad. but st need a shit load more preload. usually you use 15mm with an appropriate spring, i usually go a 0.95 spring and 22 - 25mm base preload on an st, as they are very front heavy.

sc will not need the extra preload, as they don't have the nose weight. the spring at 0.83 is not too bad, a bit on the light side. from memory wilbers make progressive springs for the sc range that start out around 0.9, which gets around the issue with most progressive springs - they start out way too light so you lose a heap of travel in sag. just like the oem sc springs in the crap marzocchi or whatever make forks they are.

oil height makes a real difference too. lots of ducati use an oil height that leads to a rapidly climbing air spring effect toward full compression. call it progressive if you like. if you want to learn more about that, i did a heap of testing and writing. i enjoyed it.

Brad The Bike Boy: Marzocchi 43mm fork design and impact of oil level on spring rate
Brad The Bike Boy: Marzocchi 40mm fork design and impact of oil level on spring rate, Part 3: The crap ones
Brad The Bike Boy: Showa 43mm adjustable fork design and impact of oil level on spring rate, Part 2: 748 / 916 / 996 / etc
Brad The Bike Boy: Showa 43mm adjustable fork design and impact of oil level on spring rate, Part 1: M900ie
Brad The Bike Boy: Marzocchi 43mm fork design and impact of oil level on spring rate, Part 2

so, back to the original point, duckyboy's claim of success is entirely coincidental in this case, as the st series std spring rate is much closer to right than the original. if he'd chosen 900ss or monster forks, for instance, they'd be just as bad as the originals, just adjustable.

 

so, back to the original point, duckyboy's claim of success is entirely coincidental in this case, as the st series std spring rate is much closer to right than the original. if he'd chosen 900ss or monster forks, for instance, they'd be just as bad as the originals, just adjustable.

I like to think not "entirely coincidental", Brad, as I knew how much an unladen ST4 weighed and how much an SC weighed and that the ST4 was intended to tour with full luggage so I hoped (reasonable assumption) mother Ducati, in her limited wisdom, used an appropriate, heavier spring. Thanks for your experienced input.