suspension Sag - Wrist Twisters
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post #1 of 7 Old 02-27-2019, 08:06 AM Thread Starter
Tirone
 
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suspension Sag

Installed the .95 race tech springs and the new ohlins H0201.
Measured sag using the racetech method.

front is 27mm rear is 37 currently with the front set to stock mid range.

Haven't done anything with the ohlins as shipped yet.

Any recommendations on what range i should be shooting for on the front and rear?
intermediate rider, no track days, etc. I weigh 205 on a good day.

Thanks.

2002 Bandit 1250s
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post #2 of 7 Old 02-27-2019, 11:10 AM
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I've always used the 25% - 30% range as my rule of thumb for static sag, which is a proportion of the overall travel available in the suspension, and makes the rule of thumb extend to both short and long travel suspension. (LDH will be along shortly to bark out why that's totally wrong)

If you google it, try using % numbers rather than mm numbers, as they can be misleading and don't give any idea of the overall travel of the forks/shock. Youtube has some stuff, too.

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post #3 of 7 Old 02-27-2019, 06:32 PM
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I'll start with the following re 919 front end sag measurements.
It's some old notes on my laptop from old posts I did on the matter.

McRomo44 (SS) @ Dec 2009
My biggest beef with the 919 front end (mine is fully Race Tech valved/sprung/oiled) is the Stiction. I get as much as 15 mm of Stiction when doing classic Rider Sag checks. (With big Stiction numbers like 15 I don't not believe in using the +/-averaging method)I think the fork seals are too good and grab to some degree. The tubes are absolutely dry to the touch, unlike the tubes on our 600 and 750 that leave a barely detectable film you can more see than feel. I ended up creating a dynamic type Rider Sag check in order to get Rider Sag numbers I could trust. ( Hence my made up term “Dynamic Rider Sag”) Here is the method : 1 do a ballpark 35 mm Rider Sag or whatever number you are after. 2 get the front end off the ground, tire not touching and front end unloaded and full extended. 3 Add 5 mm to your target Rider Sag value. 4 take a piece of electrical tape and wrap it around the fork tube with the bottom of the tape at your Rider Sag + 5 mm value. 5 gently lower bike and get ready for a short slow ride close to home that has at least a 100 yard straight run. 6 putz along at 10-15 mph. 7 give it a touch of gas to unload the front end a bit and then declutch and stay off the front brake and just coast. 8 the coasting along will give enough input that the front end will find its true Rider Sag equilibrium point. 9 gently use the rear brake and come to a slow stop. See where the tape is in relation to the top of the fork seal, and now you know what your Rider Sag really is. Then go about changing your spring spacer length in pre 04 models or use your external ride height adjusters on your 04 and later models.

I think that much of the Stiction is due to the extremely effective fork seals (as is further compounded if there is no grease between the seals), and made even worse by the overly sticky dust seals.
You are also right about getting it where you like it, and if one doesn't know exactly where that is, as long as it’s good for you and your road riding it is OK. It really only becomes important if you are doing track time and playing with front and rear ride heights.
When you start playing with settings to that degree, you really want numbers front and back that you can be confident of. You need that for diagnostics as well as set up changes. And if you set up a 919 front end by the Classic Method, you do not know where it really is in terms of numbers you can talk to yourself or a chassis guy about.

I'll come back later with some suggested specifics.

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post #4 of 7 Old 02-27-2019, 06:59 PM
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Quote:
Originally Posted by CenCO 919 View Post
Installed the .95 race tech springs and the new ohlins H0201.
Measured sag using the racetech method.

front is 27mm rear is 37 currently with the front set to stock mid range.

Haven't done anything with the ohlins as shipped yet.

Any recommendations on what range i should be shooting for on the front and rear?
intermediate rider, no track days, etc. I weigh 205 on a good day.

Thanks.
I'm coming at this a bit differently that you were looking for.

Re the Rear.
I'm assuming you got the HO201 from Dan Kyle Racing = LDH, so if it's not already preset for you, there should be some setting notes to use.
I'd be using that.

Re the Front.
For your described particulars, the 0.95 kg/mm are on the stiff side. The harshness (stiction) of 919 forks equates to some number of spring rate points on initial bump, i.e when the motionless assembly has to break the static friction hold when the fork leg starts to move in relation to the fork tube. Also keep in mind that most common web site spring rate determinators call out for too stiff a front and too soft a rear.

But you have the 0.95s, so let's try to make them work the best possible.

I'd urge just 10 mm of internal preload. (that determination being done with your ride height adjusters fully backed out so all the indicator rings are showing)
What did you build to, mm's of internal preload that is?

I'd suggest no less than 140 mm of oil level, to soften the fork towards full compression.
Correct oil assumed.

I'd suggest starting with three rings of ride height adjuster showing.
I'd suggest then playing with the Rebound and get it where you want it.

Then try adding in two more rings of ride height (thus lifting the front end).

Then try backing the ride height adjusters all the way out, so all the rings are showing (thus lowering the front end).
Pick what you like best and stay with that.
If you find it harsher than you want, I'd suggest dropping down to 0.90.
It's not lost on me as to how many DKR LDH Ohlins front springs go out to the door for 919s at the equivalent of roughly a 0.88.

Hopefully this helps you.

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post #5 of 7 Old 02-27-2019, 09:20 PM
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And lets say we were talking about advanced group trackday settings? What would you do with the fork oil then, knowing the 919's desire to dive on the brakes. You would lower the air-gap so it doesn't squash the forks all the way, right? I'm shooting for a 35mm front and 30mm rear sag for the next track day, or maybe even 30/25 if I'm still grinding the pegs into the ground more than i'd like.

BTW, when you say adding rings and what not it completely loses me. Like i know what the rings represent but they dont really mean anything to me because i have no idea how many MM are between each line. Also, the preload adjusters sink into the fork tubes so that's like negative lines.

Also, what is internal preload? Is that like, how large the spacer is and how much it's already preloading the spring before the preload adjusters are wound in?

BTW, from what i've read, 27MM is far too low for the front, especially for street riding. Who knows how accurate this article is but it seemed alright to me.

http://odm.lt/wp-content/uploads/201...setup_tips.pdf

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post #6 of 7 Old 02-28-2019, 10:01 AM
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Sag is a mathematical equation of overall stroke. Forks have 120mm of travel so the middle 1/3 of that range is 38-40mm This gives equal amount of travel and oil on on both sides of the pistons etc.



Same with the rear shock except you only have about 90mm of wheel travel so the middle 1/3 is 30mm.


There are exceptions to that, but it is outside the scope of most riders and in some cases very bike specific. When we set up Pro Racers that are at or near the lap record they have a very narrowly focused window of operation with their suspension in extremely controlled conditions where we know every mm of travel they are going to use on every corner. Under those conditions we use different sag numbers and in many cases those numbers are dictated by the riders personal requirements. We custom tune the valve, spring, preload and fork oil to control the way the front end sets and returns to aid the geometry of the bike into and out of turn. Street riders don't get the luxury of such consistent conditions so they don't get the same type of tuning.



Dive is controlled by the valving NOT the springs. Fork oil height only really comes into play at the very end of the stroke unless there is simply too damn much oil in the forks which limits travel altogether.



What most riders never grasp is how little brake is actually used at or near lap records. In many cases pro riders are braking less than common trackday Novice group attendees. The pros carry more cornerspeed and trailbrake just enough to set the front end geometry to their requirements without scrubbing valuable momentum that most trackday riders give up freely.
mcromo44 and thegutterpoet like this.

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post #7 of 7 Old 03-01-2019, 06:40 PM Thread Starter
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Thanks ALL

good info

2002 Bandit 1250s
2003 SV650
1995 ZX1100e
2006 919
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