Setting your Suspension Spring Rate. Sag Settings

[Bibio]

Foreword:
taking sizes is very very difficult without the proper stands and help of an additional person, in fact its near imposable. if you dont have someone to help then dont bother trying.

with an additional person it is possible not to need the proper stands. as you can lift/rock each end using the side stand.

get a notepad, pen/pencil and a measuring tape.

the bike sag (static) measurements are the most important sizes you need to take so DO NOT SKIP THAT PART.

dont bounce the bike at any point while taking measurements.

to find your datum's, the front is easy as we use the dust cap where it joins the fork leg and the bottom of the yoke for RWU and the top of the knuckle where the stanchion joins for USD. the rear is a little more difficult, you need to find a datum directly above the rear axle nut on the bodywork that is easy to replicate, when taking the rear measurements use either the underside of the swingarm just rear of the axle or the centre of the axle. if your bodywork is rounded then get a piece of masking tape and affix at the correct position then draw a horizontal line and this is your datum. its better to find straight edges rather than use masking tape.

Taking Measurements:

Free Sag,
first get both wheels off the ground and take measurements. this is crucial as it gives you the free sag sizes (total length of the suspension 'topped out'). if you dont have a front headstock stand or an ABBA type stand then you will need to rock the bike on the side stand to lift the front and rear to take measurements. you cant use paddock type stands for this part as it will not allow the suspension to fully unload.

1.with the bike suspension unloaded take your measurements of each end and jot them down on the notepad. congratulations you now have the free sag sizes.

Bike Sag,
2.now put the bike back on the ground and stand it upright, get your assistant to hold the bike upright while you push down on the seat about an inch or so then slowly lift your hands and let the bike come to a rest. with the bike still upright and without disturbing the bike take measurements using the datum's like you did earlier and jot them down on the notepad.

3.now you and your assistant go to each end of the bike and lift the front and rear around and inch or two then slowly let it fall back down and come to a rest, again with the bikes still upright and without disturbing the bike take your front and rear measurements and note them down.

Sag Measurements,
once you have the measurements you can now figure out the bike front and rear sag setting.

lets say we have a rear free sag setting (1.) of 600mm and the measurement of (2.) is 580mm and the measurement of (3.) is 590mm we would subtract (2.) from (3.) which would in this case would be 10mm we now divide this 10mm by two which gives us 5mm. now add the 5mm to (2.) which now gives us 585mm. now subtract this from (1.) which will give us 15mm. the 15mm is your bike sag measurement. do exactly the same for the front.

now we know where the bike is actually sitting on its original settings we can adjust the preload till we have the correct bike sag settings. so go ahead and turn the your preload adjusters till you have the bike within the below measurements using your datum's. again the bike must be standing upright and not disturbed.

Rear = 10-15mm
Front = 20-25mm

congratulations all your hard work and effort has now put the bike in the proper range of bike sag.

Rider Sag,
rider sag measurements are the biggest talked about measurements in bike suspension but most get the concept completely wrong.

rider sag and bike sag are directly connected so you cant change one without changing the other. if you change the rider sag you also change the bike sag. no really you do.

rider sag measurements are for dictating if the spring rates are correct and to a point they are NOT for setting up the suspension ride height. this is why the bike sag settings are so important as without them you are going to either top the suspension out or bottom the suspension out in use depending on spring rate and rider weight.

let me try and explain this a little more before we move on. lets say we have a rider that weighs 16st but the bike has a spring rate for a 10st rider, the 16st rider not knowing any different will wind the preload up to match his/her weight while sitting on the bike, all well and dandy till they step off the bike at which point the bike suspension tops out, whats wrong with that? well the answer is simple, the bike suspension will also top out going over crests as there is no negative rate which in turn gives loss of control, same applies to braking, under heavy braking the front will dive and the rear will lift as it will top out due to not having that negative 'leeway' this in turn can cause loss of control as the bike looses traction at the rear so the rear ends up skidding add to that the front spring rate is too soft so the front suspension will compress to a point that there is no travel left and bottoms out. hit a bump in this situation and your off the bike and into a hedge if your lucky. are you now seeing why the bike sag is important? if not then stop reading put your tools away tell your assistant to go home and look on google for an answer that you prefer.

still reading.. want to know more.. good.. lets move on..
Rider Sag Settings,
get the rider to completely kit up in their gear including helmet, gloves and so on as if they were going out on the bike and sit them in their normal riding position with feet on the pegs and hands on the bars.

this is where a chock stand comes in handy but if you dont have one you could at a push use a rear paddock stand as we need to take measurements with the bike upright on the ground and the rider sitting on the bike while the other person takes the measurements. a third person is ideal as they can hold the bike upright.

with the fully kitted rider on board and sitting in their normal riding position take measurements like steps (2.) and (3.) above and jot them down. again like steps (2.) and (3.) above remembering about the bikes free sag work out your sag measurements. but this time the reference measurements are..

Rear = 30-35mm
Front = 30-40mm

if the rider sag measurements dont fall within that range then YOU NEED NEW SPRINGS AT THE PROPER RATE FOR YOUR WEIGHT. you might be tempted to adjust the preload at this point to get it within the range but remember what i said before about ''the rider and bike sag being directly connected and changing one will change the other''.

now after all that the measurements quoted are not gospel and you might find moving them around once you have new springs beneficial for stability and individual preference for terrain.

please dont ask me if '''my settings are right''' i have given you the information to work it out for yourself.

after taking the measurements you dont like what you have found out then you can either sit in a river in Egypt or splash the cash and sort it, its entirely up to you.

spring rates and sag settings are just the first step in getting your suspension sorted after which you can start to think about the internals ''dampening'' of your suspension.

disclaimer:
the information given above is given freely and the author holds no responsibility for anything or people using it wrong or as actual facts which may result in injury or damage. the information given is the authors own concept of the subject and may or may not be correct. if you dont like what the author has wrote then go read someone else's take on the subject.

p.s. properly set up suspension is not going to suddenly turn you into the worlds greatest motorcycle rider so please take care and ride within your capability.


Thank You.

[theenglishman]

Succinctly put, for the Arabian river dwellers amongst us

I've tried doing it myself and it really is impossible. Now I just pay someone who knows what they're doing to sort it while I go swimming about the cost

[aesmith]

Question, are the figures for the front measured along the length of the fork, by which I mean the the 30mm figure would be compressing the forks by 30mm, not a 30mm vertical movement?

[Bibio]

sag = the measurement of compression from the ''free sag'' size. you cant take measurements without know the free sag size. to measure the sag on RWU forks you measure from the dust seal where it joins the fork tube to the underside of the bottom yoke. like measuring a bit of timber for cutting.

you cant take measurements with the bike on its side stand. the bike must be sitting upright.

[Bibio]

NOTES:

once you have the correct spring rates fitted you only need to set the ''bike sag'' and where the ''rider sag'' settles should be in the correct range. the most important setting is the ''bike sag'' do not alter the back more than a few mm.

taking pillions and luggage:
you need to set the ''rider sag'' with everything on the bike including the rider, luggage and pillion. if you ride with luggage and a pillion all the time then you need to get the proper spring rates for this.

once you have your bike set up then put a cable tie around one of the fork legs and slide it down to the dust cap, after a few rides check where the cable tie is sitting. with the front you want to use as much travel as possible with about 10-15mm in reserve for those ''emergency'' situations. adjust the front preload accordingly till you hit the sweet spot.

[yorkie_chris]

Originally Posted by Bibio

please dont ask me if '''my settings are right''' i have given you the information to work it out for yourself.

There is no right and wrong here. There is sag and then there is the dynamics of what is actually going on with the bike at any particular state.

Example...
Rear suspension rider sag, is controlled by AND also controls the anti squat function of the rear suspension. This is also heavily influenced by the comp damping of the rear shock.



And... for fooks sake... do NOT obsess about a couple of mm either way on sag, just get it in the ball park.

[Bibio]

completely agree YC. dont fret over a few mm.

dampening though is a whoooole other subject.

[aesmith]

Just fitted my new springs, K-Tech linear, so this thread came at just the right time. Although the springs are a little shorter than stock I get the correct sag with the preload adjusters right in the middle.

It's made a worthwhile improvement, I can't think why I didn't do this years ago. What's pleasing is that the stiffer springs don't seem to result in any more harshness.

[Bibio]

Originally Posted by aesmith

What's pleasing is that the stiffer springs don't seem to result in any more harshness.

they wont unless its very oversprung. harshness is due to dampening being wrong.

[Davemurphy007]

Thank you for taking the time to write this thread and share your experience.

I'm very happy with the general workings of cars and planes - but motorbikes I'm struggling to get my head around the adjustments and knock-on effects of those adjustments by trying to reason things in my own mind. Threads like this, giving guidance and putting things into lay and terms, really help a lot.

Cheers