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SAG the unasked question!

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So we all know, sag must be set to 90-120mm and 20-40mm or somewhere thereabouts.

Generally MX is 30/90 anyway. So, if I had a spring that gave me these perfect settings, and I then set my suspension to 40/110, would this still be correct? Or would I want to change to a stiffer spring that gives me 30/110?

 

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Keep in mind that "rider sag" is not really spring preload but is actually ride height.  By cranking down on the preload collar you are actually raising the back end, which moves weight off the shock, which allows the back end to sit higher.

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20 hours ago, moto_psycho said:

So we all know, sag must be set to 90-120mm and 20-40mm or somewhere thereabouts.

Generally MX is 30/90 anyway. So, if I had a spring that gave me these perfect settings, and I then set my suspension to 40/110, would this still be correct? Or would I want to change to a stiffer spring that gives me 30/110?

 

Depends on bike. 30/90 is way to low for most modern bikes. 35 with minimum 100, and maybe optimal 35-40 with 102-107mm depending on bike and preference.

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Static sag is more important than rider sag. It's better to have your static sag within it's specs than it is to get the rider sag within it's specs. Why???? When you push up and down on a unloaded bike you want it have floating room between full extended stroke and bike weight supporting spring engagement.  If you cranked up the preload until all the floating room was consumed just to achieve rider sag then your suspension will be pushing the rear of the bike into the shocks top out limit or beyond which in turn will make the rear of the bike like a constantly expanding spring and send you forward over the bars. That is why static sag determines appropriate spring rates for different wright of riders. The opposite is true as well. Too much static sag and you are losing stroke or unbalancing the chassis and can't steer.....etc....which causes other handling issues.

Edited by rjg
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Depends on bike. 30/90 is way to low for most modern bikes. 35 with minimum 100, and maybe optimal 35-40 with 102-107mm depending on bike and preference.
Very bike specific right?
For example.
When I asked questions on my rear shock setup I was told the yz250 should have 25/100

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Static sag is more important than rider sag. It's better to have your static sag within it's specs than it is to get the rider sag within it's specs. Why???? When you push up and down on a unloaded bike you want it have floating room between full extended stroke and bike weight supporting spring engagement.  If you cranked up the preload until all the floating room was consumed just to achieve rider sag then your suspension will be pushing the rear of the bike into the shocks top out limit or beyond which in turn will make the rear of the bike like a constantly expanding spring and send you forward over the bars. That is why static sag determines appropriate spring rates for different wright of riders. The opposite is true as well. Too much static sag and you are losing stroke or unbalancing the chassis and can't steer.....etc....which causes other handling issues.
So it is better to run excessive race sag than to have too little static sag? Not sure I agree with that. My recommendation would be to get the correct spring.

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1 hour ago, mikedabike said:
On 9/29/2019 at 12:20 PM, rjg said:
Static sag is more important than rider sag. It's better to have your static sag within it's specs than it is to get the rider sag within it's specs. Why???? When you push up and down on a unloaded bike you want it have floating room between full extended stroke and bike weight supporting spring engagement.  If you cranked up the preload until all the floating room was consumed just to achieve rider sag then your suspension will be pushing the rear of the bike into the shocks top out limit or beyond which in turn will make the rear of the bike like a constantly expanding spring and send you forward over the bars. That is why static sag determines appropriate spring rates for different wright of riders. The opposite is true as well. Too much static sag and you are losing stroke or unbalancing the chassis and can't steer.....etc....which causes other handling issues.

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So it is better to run excessive race sag than to have too little static sag? Not sure I agree with that. My recommendation would be to get the correct spring.

Of course a new spring is the best solution. I am only discussing the importance of static sag vs rider/bike weight

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My learning is also that static sag is to use ones you find a race sag and static that works. If I add 10kg weight it rarely change how the bike behave, as long as static is the same despite race sag maybe being 106-108.

 

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Static sag is priority then rider sag. If you are over weight for a spring and crank/tighten down the preload to achieve Rider sag (simultaneously reducing static sag) you will constantly be endo-ing off jumps. Because your spring wants to expand beyond the shocks available stroke range. It's not that hard to imagine.

 

As far as 30/90 vs 40/100 - those are reasonable for a given bike and rider weight. It's is riders preference to the handling of the bike as to where they choose to set it up within that range. Some want more turn in so 30/90. Some want more stability so 40/100

Edited by rjg
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The rider vs static sag is just an easy way to see if you have the right spring for your weight after you have set rider sag. I prefer to just measure how much preload I have in the spring when the rider sag is set to where the bike handles the way I want. Less sag gives quicker turn initiation but less high speed stability. More sag obviously the opposite. Baseline rider sag to start with should be in your manual. Usually 1/3 total rear travel. I prefer lighter spring with less sag for single track. Quicker steering and more rear squat for hill climbs. Heavier spring with more sag for mx. Stable high speed better bottoming resistance.

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Coming into a corner with weight transferred to the front will cause the rear of a bike with less static sag to rise higher. That will shorten the trail causing the steering to quicken. Could cause over steer or the front to tuck in that situation I guess.

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For me the 1" 4" sag relationship just proves you have a spring in the ballpark, from there you can tune and maybe end up with more or less wind on the spring as desired. 

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Also as mentioned a few posts up, a spring that is to light for your weight and preloaded to much in order to get the rider sag correct will cause the rear to kick up on takeoff. To much potential energy stored in the spring at the end of the stroke can overwhelm the low speed rebound damping.

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On 10/1/2019 at 2:01 PM, The Creature said:

does less static cause oversteer?

No, not if it's because the spring is too soft.

I don't agree with the static being more important, for that reason. If you have too much rider sag as well as too soft of a spring your bike will turn like a barge full of bowling balls and tend to run wide all the time. I've run heaps of preload with too softer spring when I haven't had the budget for the right one, with no issues except maybe a small loss of grip - no issues jumping. It can't over extend going into corners, if you know how to brake it's pretty much topped out anyway, the internal stop prevents it going further, and as soon as you release the brake it's going to drop to the race sag area, not static, unless you've already fallen off.

Edited by DEATH_INC.
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rider sag is much more important than anything else. It is defining the whole behaviour of the bike, static sag should be right of course but is less important than rider sag.

Edited by Gustl
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On 9/30/2019 at 12:31 AM, MxGringo said:

Very bike specific right?
For example.
When I asked questions on my rear shock setup I was told the yz250 should have 25/100

That is exactly what is recommended in the owners man for my 01 CR250. Does being an MX bike have a bearing as opposed to cross country bikes?

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I suggest you watch Dave Moss tuning in YouTube if you wish to get a better understanding of sag. He breaks it down into simple ideas. 

Let's break it down.

I weigh 220#

I buy bike that is stock setup intended for 175# rider. It has a spring preload of 7mm and a free sag of 675mm. Factory intended 30/90 as initial operating parameters.

I sit on it and sack it out with the factory presets. 

I crank up the preload to 'try' and get me 30/90.  Now I am at 20mm preload on the spring and have achieved 15/90 because given my weight and spring installed it's not possible to achieve the factory recommend settings. This now makes the back of the bike unloaded sit at 660mm. The spring is significantly closer to being stacked (made solid) even before I have go out on a ride. The only thing I have achieved is getting my rider sag to the recommended setting and now everything else is f'd up. Now when I am riding it the rear end of the bike is always rotating forward because I have preloaded the shit out of it in desperation to achieve rider sag. I have also managed to crank up my rebound damping to attempt to control and overly preloaded spring. I have also made it so I am that much closer to going solid spring when bottoming because i exceeded the recommended spring preload parameters will still easily blow through the stroke because the spring rate is too low. Sounds very unsafe to me.

You are not going to get into the proper operation of as the manufacturer intended by putting rider sag as the priority.

Conversely, if I make static sag the priority during the setup I and up at 30/105 I feel like I am wheelying all around and can't steer because I am chopperws out, but what I do know is that I have to get more weight on the front end. We already tried the other direction in this example and it doesn't work out very well but at least it steers the bike. I put less preload on it 0mm and it is rattling around on the shock.  The bike at reset now has 645mm free sag but a ride sag of 15mm greater than 90mm

It is obviously all a compromise but static sag is going to tell you that the bike is in the ball park that the manufacturer intended for proper operation.

Only thing left is to change out the spring.

Static sag is what tells you that you are either overloading/underloadung a spring for a given rider weight when the bike is at rest. Which is what the manufacturer intended for when you face an obstacle (corner or bump) Static carries the bike, rider carries bike and rider.

If money is a problem it's better to have too stiff of spring rates rather than than too soft.

 

Edited by rjg
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