[superfly999]

I took my stock 999 Showa forks in for a service and wanted to change to a lighter spring. Say a .90. I'm 165 naked. My service race tech master said to leave the 1.0 spring and he would lower the oil level and then showed me a graph to explain it all.

Is this a good plan??

 

[jules_1972]

If sag is good with your weight then spring is fine, less oil will reduce harshness from the hydraulic dampening.

 

[Shazaam]

Not a good plan.

Lowering the oil level will increase the volume of air in the fork tubes. Air is compressible (hydraulic fluid is not), so at the upper end of the compression stroke, it acts like another spring has been added to gradually increase the spring force to help to prevent bottoming out the fork travel. You can reduce the stiffness of this air spring by decreasing the volume of hydraulic fluid that in turn increases the volume of air in the fork tube. (see figure) The fork manufacturer specifies the hydraulic fluid volume that they feels gives the desired air spring behavior.

That said, the stock springs should be OK for your weight. What are your sag numbers?

The need to change spring stiffness only arises when the weight of a lighter than the Ducati standard 160 lb. rider fails to compress the spring enough, or the weight of a heavier rider compresses the spring too much. The goal is to have the suspension sag enough under the rider’s weight so as to place the suspension in the middle of its travel. This avoids frequently bottoming-out the suspension by a heavy rider or topping-out the suspension by a light rider. Sag also controls the ride height so the correct spring will preclude too low a ride height for a heavy rider or too high a ride height for a lighter rider.

Once you determine the correct spring stiffness you are then free to modify the air spring to, for example, reduce bottoming the forks under braking or when encountering extreme pavement irregularities. Or you can make the suspension somewhat less harsh, starting at mid-stroke and continuing to maximum fork stroke.

As you can see, this has nothing to do with damping. Damper settings will also affect ride quality. Too much damping will give a harsh ride, too little will result in a bouncy effect that takes too long to settle down.

 

[jules_1972]

You can reduce the stiffness of this air spring by decreasing the volume of hydraulic fluid that in turn increases the volume of air in the fork tube. (see figure) The fork manufacturer specifies the hydraulic fluid volume that they feels gives the desired air spring behavior.
.

Bizarre......

 

[superfly999]

I think the sag numbers are in line with what everyone is saying so I actually thought that 1.0 springs would be fine. But after two years of track riding I'm still having a harder time turning this bike than I would like...After riding a friends race R6 I was shocked at how easy it was to turn...so I thought I'd try a softer spring to keep the bike lower in the front and help the turning...

But maybe reducing the oil will help the fork get closer to max stroke as right now its a good 1.5 inches left of travel and thats at max braking so during cornering its higher than that...So I'll let my mechanic reduce the oil level and if that doesnt help than I'll have to try something else...

Hey maybe this 999 will never turn well LOL

Also I'm finally going to try a stiffer rear spring than the biposto one I have now...He said thats going to help so thats the plan. Going to use a stock 1098 spring which is 8.7 I believe

 

[Chuckracer]

It's never going to turn like an R6, that's for sure!

Have you lowered the front and raised the rear as far as possible?

 

[Shazaam]

I thought I'd try a softer spring to keep the bike lower in the front and help the turning.

Also I'm finally going to try a stiffer rear spring than the biposto one

If your goal is to improve turning by changing the front and/or rear ride height, changing the spring stiffness front and/or rear is simply not the way to do it.

Front ride height can be lowered by moving the forks up in the triple tree support. That is, you can increase the distance the top of the fork legs protrude through the top fork yoke.

Rear ride height can be raised using the rear ride height adjuster rod.

Keep in mind that lowering the front ride height, or raising the rear ride height, are not equivalent adjustments. Lowering the front serves to lower the bike's center of gravity. With a higher front, raising the rear, raises the C.G.

Ducati Corse, in a 1996 memorandum that was posted on the old Ducati.com web site, recommended raising the front 10 mm to increase "flickability" in turns. Yes, I said raise, not lower. Raising the front end raises C.G., and a higher C.G. makes the bike go to the tire edge quicker according to the memo. I was told that the same advice is given in the factory race bike setup manual.

Familiar with the Mille SP? It has the capability to raise the engine in the frame to increase C.G. to improve flickability. Same effect. Even the Mille R has the engine mounted higher in the frame to do the same thing.

From a chassis design point-of-view you generally you want the C.G. to be a distance equal to half the wheelbase above the line connecting the axles. Raising the C.G. above this point biases the weight more to the inside of the corner so it makes the bike easier to turn.

As a reminder, first measure your initial settings and record all changes so you can return to the stock settings if necessary. Also, flickability in a chicane isn't necessarily the ultimate setup goal for most tracks. You generally want it to turn easily on the brakes, hold a tight line, and drive off smoothly on the gas. It's best to just give it a try and see what you think. Have fun playing!

Your mechanic may be knowledgeable (not sure about that) but you need to spend some time learning about the effects of various suspension adjustments. That way you can communicate your objectives to him clearly. By the way, pro racers probably spend more time working with their mechanics over suspension adjustments than anything else.

 

[superfly999]

Thanks for all the replies!!! Good stuff to think about...

Right now there are 3.5 lines showing above the triple clamp (not including the cap) and I'll bring it to 4 lines showing when I re-install the forks. Zero preload in the front and at least 40mm of sag.

The rear has been raised to 5 threads showing per end of the ride height adjuster...this is more than the 285mm that I think is recommended. Rear sag is 30mm or less and the bike almost tops out when free...thats why the stiffer rear spring is going in soon. All in all I think I'm getting to the point where there isnt alot left to do thats why the springs in the forks came to mind...but I'll give the oil level a try and then I guess springs...there are all kinds of conflicting info so I'll have to go at it myself and see what happens...

Also I feel that the damping settings are spot on to be honest. I've tried all around the range and I've got a great feel on all the tracks I ride on. Only need a click or two one way or the other from the base line settings. I can hit track bumps and pavement transitions at full lean and the bike just soaks it up...I'm not at all worried about the ride its fantastic...just want the bike to hold a line better...entry isnt too bad but then it all goes to pot and its a struggle to get the corner finished...

I do feel that the rear spring will help more than the forks...its just that the forks were the first thing I brought in to the shop

 

[ilampa]

Shazaams words are gold dust...totally true and spot-on. I bow to thee, oh suspension Guru!

There are currently at least two other suspension threads where posters would save their time by asking someone in the know, like the guru mentioned above.

Nuff said really.

 

[superfly999]

Shazaams words are gold dust...totally true and spot-on. I bow to thee, oh suspension Guru!

There are currently at least two other suspension threads where posters would save their time by asking someone in the know, like the guru mentioned above.

Nuff said really.

LOL thanks for that reply. FWIW I've read every post on here and searched and couldnt find anything on fork oil level. Thats why I asked in the first place. My guy (who runs a race team) and is the ohlins certified suspension rebuild shop as well, said to change fork oil level and I guess that its not a common run of the mill change cause I couldn't find much info on it...everyone talks springs and thats why I went to the shop in the first place...springs!!!

I'll have to wait till next year's first track day but I'll tell you this...I'll know after 15mins if this is all nonsense...

Just looking at that graph again I can see what my guy's talking about...as you drop the oil level the very bottom of the stoke becomes less progressive and more linear...Its set from the factory for the street and if you hit a pot hole in the road you get deep into the stoke without bottoming out the fork since it gets very hard near the end as the oil air resists compressing...
But on the track there are no holes to worry about hence the ability to reduce this progressive nature...
At least thats what it looks like to me?

 

[oleary]

My 848 race bike had the same "running wide" problem. We have the 25 mm Ohlin kit, Kyle link/shock/ride height adjuster setup and a 90 front/95 (I think) rear spring. I'm 185 lbs with full track gear.

The solution was to go an Attack (adjustable) 30 mm offset triples (stock is 36 mm). Dunno if this would work on the 999. Also, as stated earlier, playing around with front/rear ride changes the handling a lot.

I totally agree with everything Shazzam says here, by the way.