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Discussion Starter · #1 ·
G’day all,

I know this has been asked 1000 times, but can anyone confirm a good baseline for a stock 08’ 848 suspension. I weigh 98kgs with gear on. I don’t want to upgrade suspension, just set it up.

Looking at the manual I see that it states 18mm for front preload and 20mm for the rear. I measured my bike and using the racetech method of checking sag, I had 38mm front and 23mm rear. I checked the rebound and compression, they’re at factory settings. Full clockwise is zero and front has ? 3/4 turn out R: 12 clicks. Rear has C:2 turns R: 2 turns.

I have read numerous articles and it appears that 25mm sag for track and 30mm for road is about right so I am shooting for 30mm front and rear, can anyone confirm this is a good baseline using stock rebound and compression settings from the manual? Is equal front and rear sag correct for this bike with the fork tubes in original position?

I started the adjustment today, increased the preload raised the sag for the front from 38 to 34 and rode the bike. It has made a noticeable change and I’m happy with where it is going, the steering is much quicker at slower speed and the bike feels more stable. I ordered a wrench for the rear shock, waiting for that to get the rear done.

Cheers.

Rob.
 

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20mm of sag is ok. Set damping to factory spec. Ride the bike and see how it feels. Then adjust as needed. I always go two more on the front rebound to make dive a little slower. Never be tempted to go to stiff on the front because it’s compressing under brakes. Look at a motoogp bikes under brakes and see how much they dive.
 

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20mm of sag is ok. Set damping to factory spec. Ride the bike and see how it feels. Then adjust as needed. I always go two more on the front rebound to make dive a little slower. Never be tempted to go to stiff on the front because it’s compressing under brakes. Look at a motoogp bikes under brakes and see how much they dive.
Keep in mind that you can reduce dive under braking and also leave compression damping unaffected by raising the oil level in the forks.
 

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20mm of sag on the street seems a bit extreme. 30-35mm is more the norm.

I use ~35 F / 30 R on the street, and ~30 F / 25 R on my track bike.

If you can't get to the desired without maxing preload in either direction, you likely need to change springs.

It's not a bad idea to look into static and rider sag. Dave Moss's FB page and videos can be helpful.
 

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Keep in mind that you can reduce dive under braking and also leave compression damping unaffected by raising the oil level in the forks.
It might just be me, but that reads like a very misleading way to explain oil level/air gap. I always worry about articulating these sorts of things, because it can get confusing really quickly. I'll mention oil level first, and then a note about damper settings.

Raising oil level/reducing air gap will in fact adjust how far you can go in the stroke- but it will not affect the rate at which you go thru the stroke.

Increased oil level is meant to stop from slamming the internal bump stop and possibly damaging the cone.

So, correct oil level keeps the fork in the working part of the stroke- mostly under braking- so that there is still some damping control while at the limit of fork travel.

Now, reducing 'dive'- how quickly the fork goes thru the stroke under braking- is a function of compression damping and spring rates. Want to slow down fork dive? Increase compression damping.

The other thing of note for the OP is in regards to 'factory settings' for comp and rebound damping. Your bike is maybe 10 years old, and without knowing when the last time the fork and shock were serviced is really important.
As the fork oil ages, so does it viscosity. Since damping is basically forcing fluid thru the shim stack and piston, as the oil gets thinner, it flows easier.

So, if a fresh fork feels good at say, 'C8' - 'R5', that same fork with 10k miles on it might feel good at 'C14' - 'R10'.

Now oil level/air gap is not affected by fluid age- only the damping characteristics- since the air gap is basically a hydraulic bump stop.

Point being that while front and rear ride height, effective swingarm length, and other geometry points can be copied from anywhere, the comp and rebound settings are going to be very individual to your bike- unless you have a known fresh build.

I hope I didnt just make this more complicated.
 

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Raising oil level/reducing air gap will in fact adjust how far you can go in the stroke- but it will not affect the rate at which you go thru the stroke.

Increased oil level is meant to stop from slamming the internal bump stop and possibly damaging the cone.

So, correct oil level keeps the fork in the working part of the stroke- mostly under braking- so that there is still some damping control while at the limit of fork travel.

Now, reducing 'dive'- how quickly the fork goes thru the stroke under braking- is a function of compression damping and spring rates. Want to slow down fork dive? Increase compression damping.
Agreed.

My point is that you can reduce the amount of fork travel (dive) under deceleration. When you create a nose-down orientation you change the suspension geometry and cause undesirable effects to its handling characteristics. There's no real concern about the time it takes to complete its dive fork travel distance.

You shouldn't be using damping to address dive issues.

Heavy Damping. When the suspension has too much damping, the bike feels stiff and unyielding because it takes a long time before the suspension recovers from hitting a bump. If you hit a second bump before recovering from a first, the suspension “packs-up” and transmits higher impact forces to the bike and rider, and the wheel has more difficulty tracking pavement irregularities.

Light Damping. Alternatively, when the suspension doesn’t have enough damping, the bike feels unsettled because it takes a number of bounces (oscillations) before the suspension settles back down (reaches equilibrium) after hitting a bump.

Critical Damping. This is what you want to achieve. A critically-damped suspension system approaches equilibrium as fast as possible without any oscillation, and in the shortest time, after hitting a bump. This is best because it give a rapid recovery without producing either a harsh or bouncy ride, and will gives the best wheel tracking of uneven road surfaces so as to maximize the time in contact with the road. This maximizes tire grip in corners.

Using increased damping to reduce dive rate will obviously mess with this.
 

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I try to keep my setup answers as simple as possible for people. To much info leads to to much confusion. The OP,s weight falls into the design demographic of the suspension so I find the basic stock setting would work for him (and most riders for that matter) and this is how I set up for most people. Any further action that needs to be taken is then assessed on what the rider feels or THINK THEY FEEL. That last three words are very important because nine times out of ten most peoples shortcomings are in their lack of ability, not setup. So I then work on the riders head, which is most of the time far more productive:)
 

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That last three words are very important because nine times out of ten most peoples shortcomings are in their lack of ability, not setup. So I then work on the riders head, which is most of the time far more productive:)

Which means increasing the damping on the riders brain :wink2:
It also works best if his brain is given some time to stop oscillating straight after a test ride.
 

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Discussion Starter · #11 ·
Great tips guys. What do I do with a preload measurement from the manual? I thought that was another term for rider sag.
 

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Preload in the manual begins at the softest setting then add mm. Example: turn the preload adjuster to its softer positions the turn towards the firm position. 1mm, 5mm, 12,18......etc. I never fixat on sag, usually just eyeball it. It isn’t as critical to be perfect in the measurements here as people make it out to be. But it is a good way of checking if your springs are to stiff or soft. At your weight I feel the springs will be fine.:)
 

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The function of the preload settings in the Manual is to first establish the correct ride height of the bike. Raising or lowering the ride height raises and lowers the center of gravity which in turn increases and decreases the bikes ability to lean and turn in corners. When carrying a half tank of fuel, it also will place a standard rider weighing 165lb. (including gear) in the middle of the suspension travel when using the stock springs.

If you carry a passenger you need to increase preload in the rear spring to retain the proper rear ride height.

Sag is the amount of suspension travel that is used when you put the rider on the bike. Typically you would want about 30 mm sag on both front and rear springs as a starting point with the rider on the machine in the normal riding attitude.

The amount of rider sag is controlled by the spring stiffness and the rider weight. A rider significantly heavier than the standard 165 lb. rider will cause the bike in its suspension to move down more, so a stiffer spring (lb./in) may be needed to achieve 30 mm of rider sag.

Rider sag is affected by spring stiffness and unaffected by spring preload.

30 mm of rider sag is only a target. It represents a value of one-third of suspension travel for a superbike.

As a comparison, the Ducati Multistrada is designed with 170 mm of front and rear suspension travel while the Panigale and the ST4S has 130 mm. Using the standard rule-of-thumb of sag being set to about 30% of suspension travel, the Multistrada should aim for a loaded sag of 50 mm. The Panigale superbike and ST4S loaded sag should be set to 40 mm.

So, if you are a heavier rider and you are getting more than 30 mm of rider sag on a superbike you can use spring preload to raise the rider back to the correct ride height but there becomes a point for heavier riders where you should use stiffer springs instead.
 

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Rider sag is affected by spring stiffness and unaffected by spring preload.


Really?
 

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This one got me at first also. You have to notice carefully that he said “rider” sag.

Preload will change the initial static sag and ride height but regardless of how much preload is used the amount the bike sags after the rider gets aboard will remain the same.


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Not true. Preload is a means of making a spring carry more weight. Think this, when you compress a spring with your hands you get to a point where you can’t compress it anymore. This is the point where you have applied as much preload as you physically can. The spring can be preloaded more, you just don’t have the strength. Now think. Pretend the force you are exerting is the bike weigh. The bike is now at its max preload. Ease of the pressure, load is less, bike sits lower.
Of course with an overly soft or overly strong spring RATE you fall out of the range you need to preload. A (relatively) soft 7-7.5 works not bad with a single rider yet can be preload to carry a passenger without the arse of the bike dropping to much. Spring rate and preload ARE not the same. One is how much force is required move the spring, the other is making the spring carry more weight. (Spring rate does actually change slightly due to coil geometry but not enough to worry about)
Hope this makes sense.
 

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:) You’re still missing the difference the preload makes between total sag and rider sag.

Think about this. You measure the ride height of your bike only, no rider at 26.0 inches. Now you get on your bike ready to ride and you measure the ride height at 25.0 inches. So now you add enough preload to raise the ride height up to 25.25 inches total with you on the bike.

Now get off the bike and measure the ride height of the bike only again. It will be 26.25 inches. (Assuming you had enough free sag that the suspension didn’t top out).

The amount of rider sag has not changed. This is why measuring the difference between free, bike , and rider sag can tell you if you need a different rate spring.



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