Question to those with SBK forks

[caperix]

With winter the winter break in the riding season nearing I am getting ready for the next stage of my suspension mods on my monster.  I will be tearing the 998 forks apart soon to install proper springs for my weight.  I plan on changing the fork oil when I am in there, my question is about what weight to use.  From what I can find 10w is what is called for, with the lighter monster is it better to put a lighter oil in?  Gold valves are not in my budget at this time, but I have heard that these forks can be a little rough on a monster even with the correct spring rates.

[junior varsity]

by rough, most people mean firm/stiff rather than harsh, i believe.

in the past, it has been said that fatties need heavier oil, and vice-versa.


an ohlins upgrade to the valves probably isn't as expensive as you think - contact your local dealer / ohlins rep or one of the numerous shops that is ohlins certified on the web, and see what it turns out to be. (should be at or under 400)

[Mr Earl]

When I last changed fork oil, I typically over-thought it, and one of the results was finding this info:

http://www.pvdwiki.com/index.php?title=Suspension_Fluid

which discusses the observation that suspension fluid's primary property is viscosity, not weight, and the two are not necessarily related, especially between brands.  I wound up blending two "weights" of synthetic Silkolene to a specific viscosity that was slightly lower than the stock fluid.  Fun exercise, not sure it did me or the bike any good.

[junior varsity]

i just take the fork caps off and turn the bike upside down to get the old stuff out.

in true italian style, i'm running olive oil.

[Duc796canada]

I would go with a lighter weight oil, a 5wt. I would go a little more ccs of oil since it is lighter for bottoming resistance. The lighter oil oil will flow quicker through the valve stack, yo should be able to work with the standard stack by maybe removing a few shims(do some research) for a softer ride.

[Speeddog]

How much do you weigh?

[suzyj]

I just used 10wt oil in my 998 forks.  The rebound adjustment is only a couple of clicks off the stock spot, and I haven't needed to muck with the compression adjustment.  A can't see the point of changing to a different weight oil unless you're having issues getting the rebound and compression damping dialled in.

[fasterblkduc]

Do yourself a huge favor and buy this book. 

http://www.amazon.com/Sportbike-Suspension-Tuning-Andrew-Trevitt/dp/1893618455/ref=sr_1_1?ie=UTF8&s=books&qid=1287491932&sr=1-1-spell

Reading this book will make you far more knowledgeable than the people you are asking advice from. People here will be trying to get you to spend mega $$ on valving that you don't need with your setup and riding needs. You have SBK forks and are riding street. You already have what you need to get a well set up front end. Springs rated for your weight and riding style (street), are what you need. The expensive valving simply gives you a larger range of adjustability. Your forks already have plenty of adjustability for street riding and if you find yourself not able to get into the right setting, you can gain more by changing fork oil.
suzyj is spot on with her assesment. I've worked in the fluid power industry in many capacities for over 16 years, and have plenty of racing and street riding experience. The weight of the oil does play a part in the damping but until you get a baseline of your suspension, and actually run into a wall with where you need to adjust, you will not know for sure if you need to change the weight of the oil.  I may not give the most popular advice because I tend to get straight to the point of what you really need instead of what you can brag about spending on unneeded bling. Most of the people that put tons of $$ into their suspension still don't have it set up right...I've seen it many times trust me. Your front end setup is more than adequate for the street.

The best thing that you can do for yourself is buy that book and read it. 

[fasterblkduc]

When I last changed fork oil, I typically over-thought it, and one of the results was finding this info:

http://www.pvdwiki.com/index.php?title=Suspension_Fluid

which discusses the observation that suspension fluid's primary property is viscosity, not weight, and the two are not necessarily related, especially between brands.  I wound up blending two "weights" of synthetic Silkolene to a specific viscosity that was slightly lower than the stock fluid.  Fun exercise, not sure it did me or the bike any good.

Good info, great post. The viscosity will affect the speed of damping. The viscosity changes with the temperature. As your chart shows, the viscocity is not always consistent either. If you change it from 10w, it probably won't hurt to go lighter but until the OP gets a baseline, rides it, makes adjustments, rides it, runs out of adjustments, there is not an answer that is correct.

[caperix]

Thanks for the replies, I guess I am overthinking the job a little bit.  I just didn't want to disassemble the forks only to put them in and find they need to come apart again. 
I will have to check out that book, I have been using Max McAllisters tuning guide.  It has good info but could go a little more in depth.
I weigh about 170 with gear.

[silversled]

I didn't use "Ducati SBK" forks but installed K6 GSXR1000 units.  I'm 150lbs without gear and after a couple of tries, settled on .85kg/mm springs with 5wt oil.  The front end is spot on for me and my riding style now.

The best advice is to settle on a reasonable combination and baseline it with lots of riding. Springs and oil are to be considered tuning items just like the damping and preloaded adjusters.

Good luck.

[Duc796canada]

Tuning suspension is like cooking, it is all experimenting until you get a a recipe that tastes good. Riding dirtbikes, one finds out that as you get faster you have to adjust or customize your suspension. There were people that still believed in not adjusting their suspension and just riding the bike the way it was. Just sharing a story.