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Discussion Starter #1
this question has been raised in other threads by several members,

so simply because nobody else has taken upon themselves to do it I have decided to start a "how to do it" thread here.

I will try to be as clear and concise as I can but this is a very wordy thread.

setting your suspension sag is by no means all that needs doing to "set-up" your suspension but it is the first step,

i.e. a correctly set low-end shock will ride/handle much better than a badly set high-end shock, don't assume because you've paid £700/$1000 for a ohlins it is perfectly set-up for you.

it is also important to set front AND rear sag correctly to ensure that both forks and shocks are working in harmony,
this is what racers mean when they say a bike is "well balanced". and I cannot stress enough how much nicer this makes the bike to ride both for comfort and the ability to go FAST.

what is sag?

sag is the amount of suspension travel used under the weight of the bike and rider,
static sag is where the bike sits on its suspension and is adjusted by altering the pre-load setting,
rider sag where the bike sits under the weight of the rider and is used to determine the correct spring rate for the rider.

why do we need sag?

sag allows the wheels to follow the contours of the road i.e. if there is a 30mm/1" dip/pothole in the road the suspension will allow the wheel to move into this dip/pothole without the bike/rider being affected.
there are many other reasons for the benefits of sag but to try and keep this clear and simple I will not go into them at this point.

is everybody still awake? lol!

ok! so here is my version of how to

you will need the assistance of a couple of other people to carry out the measurements etc, (I prefer two scantily clad glamour models but this is not a requirement)

DO NOT HOLD THE BRAKES ON WHEN TAKING MEASUREMENTS BECAUSE THIS CAN STOP THE SUSPENSION FROM SETTLING INTO THE CORRECT POSITION

IF YOU HAVE DAMPING ADJUSTERS ON YOUR SUSPENSION TURN THEM ALL TO MINIMUM BECAUSE THEY CAN CAUSE DRAG ON THE SPRING SO AFFECTING THE RESULTS (NOTING HOW MANY CLICKS SO THAT YOU CAN RETURN THEM TO THEIR ORIGINAL SETTING IF YOU WISH)

MEASURING REAR SAG

step one

first lift the rear of the bike so that the rear wheel is clear of the ground and the rear suspension is fully extended, now measure the distance between two repeatable points, one on the swing-arm and one point on the frame/bodywork directly above the chosen point on the swing-arm, we will call this measurement 'A' (you can mark these points with either paint/marker pen or temporarily with tape)

step two - measuring static sag

lower the rear of the bike to the ground, now while holding the bike upright on its wheels being careful not to either push down or lift/support any of the bikes weight, your assistant can measure between the two marked points on the swing-arm and frame, we will call this measurement 'B'.
the difference between 'A' and 'B' is your static sag and should be in the region of 5mm-10mm for race/track use, and 10mm-20mm for road/fast road use.
you adjust this setting using the preload adjuster.

step three - measuring rider sag
while an assistant holds the bike upright on the wheels without pressing down or supporting the weight of the bike you sit on the bike in your riding gear and assume your normal riding position (hands on handlebars and feet on footrests)
now another assistant takes a measurement at the two points on the swing-arm and frame, we will call this measurement 'C'

this is rider sag and is dictated by the spring rate and indicates if you have the correct spring for your weight,

rider sag should be 10mm-25mm less than the static sag, if the difference between 'B' and 'C' is less than 10mm your spring is to hard if the difference is greater than 25mm your spring is to soft.

so for example:-
fully extended measurement 'A' is 140mm
static sag measurement 'B' is 125mm = -15mm
rider sag measurement 'C' is 105mm = -20mm
total sag is 35mm

the accepted target for total sag should be 1/3 of total suspension travel.
so because triumph twins are listed as having 105mm of travel that would mean 35mm of total sag

MEASURING FRONT SAG

step one

raise the front of the bike so that the front wheel is off the ground and the forks are at full extension, now measure the amount of chrome stanchion showing between the bottom yoke and the dust seal of the slider, we will call this measurement 'A'

step two - measuring static sag

lower the front back to the ground, now while holding the bike upright on its wheels being careful not to push down or lift/support any of the bikes weight measure the chrome stanchion again. we will call this measurement 'B'
the difference between 'A' and 'B' is your static sag and should be in the region of 15mm-25mm
to alter this on bonnie/scram forks you change the length of the pre-load spacer inside the fork

step three - measuring rider sag

again while your assistant holds the bike upright on its wheels without pressing down or lifting/supporting the weight of the bike you sit on the bike in your riding gear and assume your normal riding position (hands on handlebar feet on footrests) now another assistant takes a measurement on the chrome stanchion between the bottom yoke and the dust seal on the slider, we will call this measurement 'C'

this is rider sag and is dictated by spring rate and indicates if you have the correct spring for your weight.

front rider sag should be 15mm-25mm less than the static sag, if the difference between 'B' and 'C' is less than 15mm then your spring is to hard, if the difference is greater than 25mm your spring is to soft.

so for example:-
fully extended measurement 'A' is 140mm
static sag measurement 'B' is 120mm = -20mm
rider sag measurement 'C' is 100mm = -20mm
total sag is 40mm

the accepted target for total sag should be 1/3 of total suspension travel
so because triumph twins are listed as having 120mm of travel that would mean 40mm of total sag.

DO NOT THINK THAT ALTERING THE PRE-LOAD WILL CHANGE THE RIDER SAG. ONLY DIFFERENT SPRING RATES WILL CHANGE THAT.

different rider preferences will alter some of those parameters but I hope this will give you a "base setting" as racers call it,
sag is the foundation of a good suspension set-up, without your sag being set the rest is just guess work.


the end.........
 

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DO NOT THINK THAT ALTERING THE PRE-LOAD WILL CHANGE THE RIDER SAG.
But it does.

I'm not trying to shoot down your whole treatise here, but pre-load changes most certainly DO change the rider-mounted ride height... or "sag." At least it does up until we get to the point of reductio ad absurdum by taking pre-load to the upper or lower extremes of travel. That is, increasing pre-load on a topped-out shock, or decreasing pre-load on a bottomed-out one would, of course, do nothing to ride-height.

Changing pre-load is not necessarily the best way to change ride height, but it works in a pinch... and works well! That's why most standard shocks have the multi-cammed collar. Passengers sit on the back, and inceasing the pre-load raises the rear ride height so that...

1) the shock start its bump control nearer the top of its stroke, giving you more suspension travel than you'd have leaving the preload on the (for instance) lowest setting.

2) in the face of extra passenger weight (or fat single-rider like me), increasing rear shock pre-load returns some bit of normalcy to the front-geometry by raising the rear ride height.

The cammed collar doesn't change the spring rate of a single-rate spring, but it does change the spring rate of a progressively wound one.

And remember, on a progressive or multi-weight spring, close-cropped coils go AWAY from the point of impact. I see lots of bikes on the I-net with upside-down shock springs.

StMcK

PS: I was not going to say this because of the possibility of "the p*ssing wars" that I detest so much. But, I'm a former Ohlins and WP tech.
 

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I'm a former Ohlins and WP tech.
I'm always glad to meet someone with real experience so that some of my doubts are dispelled. One of them is something I've argued before in other forums and even wrote to a couple of shock absorber makers to no avail.

It's this:

On a shock absorber fitted with progressive springs, where should the closer-wound coils go? should they be at the top to minimise unsprung weight? or does it not make any difference.

Most bikes have them at the top but there are some that don't. Thanks in advance for any opinion.
 

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On a shock absorber fitted with progressive springs, where should the closer-wound coils go? should they be at the top to minimise unsprung weight? or does it not make any difference.
NOTE:
If any of this gets too boring, you can see all this stuff at work with a toy called a "Slinky." (at least that's what it's called in the USA) While holding onto the first few coils, stretch the Slinky across a table and then "pop" its bottom with your other palm. A wave will shoot to the opposite end, then return. The thin Slinky wire doesn't hold much energy but, watching it work, you can imagine why you'd want to avoid renegade waves in any spring whose job it is to control an event. In short, these harmonics scr*w up the spring's ability to react in an as-designed orderly fashion.


Close-cropped coils go AWAY from point of impact. Meaning, at the top of our shock and/or fork springs. Here's the reason...

If the close-cropped coils were at the BOTTOM of your rear shocks, assuming a pretty good bump, the intial hit will coil-bind this cluster of weaker, close coils, at which point they become, not COILS, but a BIG SLUG OF SOLID METAL. A big slug of metal with lots of kinetic energy.

This big slug of kinetic energy runs into the rest of the spring and sets up a big, nasty harmonic (a second hit as seen by the spring). Shown on a high-speed camera, you'd see odd twisting and pulsing movements happening to the spring and a secondary "compression event" would scamper up the coils ahead of the original bump-compression event. Then this secondary wave would "slam" against the shock's stationary spring retainer, bounce off, and then reverse to run head-on into the initial compression event... setting of yet anther compression event. The spring still moves up and down, but is no longer is in control of its movements.

I know how the poor spring feels. As I get older, I note that I, also, am gradually losing control of my movements. But I digress (therefore, I am)

On our street bikes, we might never know, and just assume "my new shocks are a bit disappointing, but I guess that's just the way they work." However, when you add nasty harmonics into a valve-spring situation, the springs overheat, overstress and lose their ability to control the valve.

Taglioni (hats off, heads bowed) used DesmoDromic valve gear to ward off the evil curse of valve spring failure at Ducati. Pneumatic "springs" are getting more "common," and race classes that require wire springs are seeing those springs changed every, 1)week, or 2)day, or 3) practice run.

Placed correctly, the initial hit compresses the weaker coils first. These are, of course, now located properly, at the top of the spring and away from the point of impact. These weak, close-cropped coils now compress in orderly fashion, and no secondary harmonics are started. No large renegade slug of coils is available to do the evil work.

I'll stop typing now while you all get a nice nap.

StMcK
 

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Fantastic explanation, many thanks. I'll save that for my next argument with someone...:)

I asked the same thing to Koni and this is the rather unsatisfactory explanation:

reply from Koni

It does not matter. A spring will act in the same manner either way.
Thanks,
Bob Noack
 

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Interesting, many years ago when I installed Progressive(brand) progressive springs into my SV forks, the instructions stated that it didn't matter how the spring was installed, ie, close wound to the top or bottom. They stated that the springs may make some noise depending upon orientation, but wouldn't alter their function. Hmm.
 

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Discussion Starter #8
But it does.

I'm not trying to shoot down your whole treatise here, but pre-load changes most certainly DO change the rider-mounted ride height... or "sag." At least it does up until we get to the point of reductio ad absurdum by taking pre-load to the upper or lower extremes of travel. That is, increasing pre-load on a topped-out shock, or decreasing pre-load on a bottomed-out one would, of course, do nothing to ride-height.

Changing pre-load is not necessarily the best way to change ride height, but it works in a pinch... and works well! That's why most standard shocks have the multi-cammed collar. Passengers sit on the back, and inceasing the pre-load raises the rear ride height so that...

1) the shock start its bump control nearer the top of its stroke, giving you more suspension travel than you'd have leaving the preload on the (for instance) lowest setting.

2) in the face of extra passenger weight (or fat single-rider like me), increasing rear shock pre-load returns some bit of normalcy to the front-geometry by raising the rear ride height.

The cammed collar doesn't change the spring rate of a single-rate spring, but it does change the spring rate of a progressively wound one.

And remember, on a progressive or multi-weight spring, close-cropped coils go AWAY from the point of impact. I see lots of bikes on the I-net with upside-down shock springs.

StMcK

PS: I was not going to say this because of the possibility of "the p*ssing wars" that I detest so much. But, I'm a former Ohlins and WP tech.
hi steve
like you i'm not a fan of pissing wars, but I urge you to re-read my post again more carefully. I think you are confusing rider sag with static sag

changing the pre-load setting does not change the rider sag setting, as I said in my first post only spring rate alters rider sag.
what the pre-load does is change the STATIC SAG setting which will have an effect on ride height, but using this way to alter ride height creates many other problems.
 

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Discussion Starter #9
Fantastic explanation, many thanks. I'll save that for my next argument with someone...:)

I asked the same thing to Koni and this is the rather unsatisfactory explanation:

reply from Koni

It does not matter. A spring will act in the same manner either way.
Thanks,
Bob Noack
Ernesto listen to the ikon tech, the weaker coils of a spring will react before the stronger coils to any input, they don't care which way up they are.
 

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Mike, on the question of rear shock travel is it acceptable to bottom out now and again? I have a piece of string indicating the extremes of movement and it is usually using most of it and sometimes jammed right against the bumper. Thoughts?
 

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Nice one Mike, I need to get around to doing this on both my bikes this year, probably need to shorten my fork spacers due to the Intiminators.
 

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I like the theory about the progressive wound springs, but I'm sure mine came with instructions tight end wound down.

I can see a reason for this. On smaller bumps where you want the softer compliance , only the bottom (soft wound) end of the spring moves. If you install it the other way around all the spring has to move on even small bumps.

That's enough thinking for today as I have to go to work.
 

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Great information guys, Thanks for posting
 

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I seem to remember reading somewhere to put the tightly wound coils at the top of forks so that there will be room for more oil.
 

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t

MEASURING REAR SAG

step one
, now measure the distance between two repeatable points, one on the swing-arm and one point on the frame/bodywork directly above the chosen point on the swing-arm, we will call this measurement 'A'

....
wont this dimension be affected by whereabouts you measure on the frame and swing arm? eg if measured towards the rear of the frame and swing arm it will give greater length measurement for the three steps than if you had markers further up towards the tank

wouldnt the correct way be to measure the mounting points on the shock where it connects onto the swingarm and frame?
 

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It doesn't matter where your reference points are as long you as you measure exactly the same way for all three measurements. If you let the tape angle change, you will get an erroneous measurement. It's best to pick a point above that is metal such as a subframe member and not any plastic part that can move. I usually go from an axle nut facet to a point on the subframe marked with masking tape.
 

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Yes, but if you're comparing the total sag to 1/3 of the rear shock compression these aren't the same measurements. If the shock compresses 105mm along its length that doesn't equate to 105mm of vertical compression. Granted, the rear shocks are fairly vertical, so we're not talking about a big difference. But if you were trying to get exact it would seem to matter.

It doesn't matter where your reference points are as long you as you measure exactly the same way for all three measurements. If you let the tape angle change, you will get an erroneous measurement. It's best to pick a point above that is metal such as a subframe member and not any plastic part that can move. I usually go from an axle nut facet to a point on the subframe marked with masking tape.
 
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