Static Sag and Rider Sag.

[tommyardin]

After recently doing some suspension modding on my FZS600, I have been reading a lot about bike/suspension set up and there is one thing that is confusing me.
Nearly all stuff I have both read (On-Line) and watched (YouTube) say that it is important to set the static (Just weight of motorcycle) sag before doing anything else.
This procedure is:

Raise the front of the bike off the ground, to allow front forks to be fully extended. (Centre stand with a prop under the engine) measure from the top of  the fork leg oil seal to the underside of the bottom yoke. Mine is exactly 150mm fully extended (Now there a coincidence)

Set the bike back on its wheels (Off the stand) and bounce the bike up and down a few times without using the front brake and allow the bike to settle under its own weight and remeasure the distance from the top of the fork leg oil seal to the underside of the bottom yoke again. Deduct this figure from you fully extended measurement and you have static sag. Mine is 126mm giving me 24mm of Static Sag on the front end.

The procedure for the rear of the bike is much the same by getting the weight off the back wheel (Just centre stand will do that ) but you will need to stick a parcel or paper label on the rear seat fairing vertically above the rear wheel axle, measure the fully extended measurement up from the underside of the axle (Sprocket side is easier as no exhaust can in the way) and put a pen mark on the label as a datum point (I used 450 mm)

Set the bike back on its wheels, bounce up and down on the back of the bike a few times just to settle the suspension and allow the bike to come to rest under its own             weight, then measure the distance from the underside of the axle to your datum mark you put on the paper label earlier. Mine is 432mm from the original 450mm measurement giving me 16mm of static sag.

The next procedure is to set the Rider Sag, again this is taken from the full extended suspension measurements. My front forks full extended 150mm as above, my back shocker fully extended (Using datum mark 450mm), now the rider with all his riding gear on, leathers, boots, gloves and bucket sits on the bike bounces a few times, without touching the brakes and the measurements are taken again, this measurement is then deducted from the fully extended measurement and the remainder is your rider sag.

Ideal rider sag, now there seems to be a plethora of opinions on this and I think it could be to do riding style, or whether the bike is used for commuting or for track day events, or maybe just personal preferences. The figures I am going to aim for and that seems to be the most commonly occurring figures for a road bike (spirited riding style) is 40mm front rider sag and 30mm rear rider sag.

Now here is the rub, that which causes me confusion, why do we have to go through the static sag  process at all? Because if the rider sag is not within the measurements we are looking for, we adjust our pre-load to get to those measurements, we have now undone all the static sag setup we went through. All the measurement for Static and Rider Sag are taken from the fully extended measurements.

A couple of mates are very useful when setting up these sag measurements to hold the bike upright without either applying up or down force when the measurements are taken, plus you will be sitting on the bike for rider sag measurements.     

[robbo]

Hi Tommy,
I thought you need to achieve a static sag front and back in the region of 20-25mm as a ball park figure for any sportily ridden bike.If the preload was almost maxed out to achieve this figure it would prove that stronger springs/spring were needed.Then as you've said you'd go ahead setting your rider sag to achieve the figure you've been advised to get.As you've just rebuilt the forks it would be nice to know how they're performing using cable ties,ideally with one marking the bottomed out position so you'd know how much fork you're using under heavy braking etc.It is a bit of a minefield at times,I must admit.

[robbo]

Just spent an hour or so reading UK and US suspension set up sites.The static sag figures seem to vary from site to site, anywhere from 20 to 30mm. Obviously your rider sag figure is the one that is imperative to achieve. As far as I can see the main point of static sag is to determine whether the spring rates are going to be up to the job, so if anything approaching half of the preload adjustment has been used up achieving static sag, then there's not much point in carrying on as the springs are too soft/knackered and it's time to spend more money . Once you've attained the rider sag you're after, most sites I looked at suggested, with someone to hold the bike upright when it's on its wheels, to push down firmly to the rear of the filler cap(about the centre of the bike) and observe hopefully both ends of the bike returning to its static sag height at the same time, proving that the rebound damping speed is the same front and rear.
Well that's whiled away the afternoon.

[tommyardin]

Yeah some of the sites I visited recommended no sag at all, and it's all about full extension, but then realised I was on the wrong sort of sites.


I have been looking around the web as well with regard to sag both static and rider, and as you say it's a minefield.
A suspension modder from an Ohlins workshop recommended 10mm to 15mm static sag rear and 25mm to 30mm rider sag rear this is for Raceday and Trackday riding.


Front was recommended at 15mm to 20mm static sag and aim for 30mm rider sag, again Raceday and Trackday.


He suggested adding 10mm to each of the Rider sags for spirited road riding and 15mm for comfortable everyday riding.


Which of course is great if you are a sleek 10 stone racing snake like Sharpie, but for us girls with the fuller figure we are not going to find it easy to keep within all these boundaries. So it seems then for us the rider sag is the important figure.


I am going to aim for Front Rider Sag 40mm and Rear Rider Sag 30mm. None of this is set in stone, but is a starting point to fine tune for personal preferences that include ride comfort and handling qualities.


I'm guessing it's no good having a bike that handles like Guy Martin's Honda yet shakes the shit out of you every time it runs over a twig or an acorn.


Thus far I have only ridden on the static sag settings of 16mm rear and 24mm on the front. This weekend a couple of trustworthy mates are going to set up the rider sag with me.


I'm a bit anal when it come to setup and want it to be right, I know a few guys who would be happy to help out setting the rider sag up, but with some of them near enough is good enough and of course it is not.
I seems to me if you have an exact starting point you can then fine tune from that point.
I sure we all know people that say things like 'yep that's about 30mm' when in fact it's 26 or 27mm, not helpful.


Someone on here pointed out that I am becoming a grumpy old foccer, but that's not true I have always been like it but I think maybe I am getting worse in my old age.

[robbo]

You want it right, not about right. I totally agree. You're going to feel much more confident knowing it's cock on to your own requirement rather than within half a brick of spot on. Confidence in the bikes abilities as well as your own are, as you know, key factors. Good luck for the weekend, hope the weather stays fine for all the testing you're going to be doing.

[tommyardin]

Cheers Robo

[tommyardin]

With 2 b's

[tommyardin]

I'm told the best way to check front fork travel is to set it down hard from a wheelie with a cable tie around the forks. 
Think I will go with hard front braking.

[robbo]

Love it .......On the other hand, when you were rebuilding the forks, when you've got a leg fully collapsed like when you're checking the air gap, place a zip tie around the stanchion tight against the fork seal. When the forks are back on the bike that zip tie will be quite a distance from the seal. Then place a second zip tie nearer the seal, then under heavy braking, the lower zip tie will be moved up the stanchion. The length of the "unused" section of fork will be the distance between the lower edges of the two zip ties. As long as that is at least 10mm, then you know you've got sufficient "reserve" in case you hit a pothole etc before the fork bottoms out. What a pallava.