SV650SK6 - K-Tech Springs and YSS Valves Fitted

[aesmith]

So I finally got my finger out to do the front end upgrades I've been planning. K-Tech 8.5 linear springs, and YSS "emulators". I wasn't sure about suitable weight/viscosity oil so as a starting point I've used hydraulic 32 since that's what I have available by the gallon. Hopefully since that's a known starting point I can go straight for the correct grade of proper fork oil once I know whether to go thicker, thinner or the same.

Same really with the emulators, I've started at 2.5 turns of preload.

So far so good, although it's a slightly negative assessment because what it really feels like it's doing is making the rough and bumpy parts of my route feel smoother. If I didn't know what it felt like with the original forks I'd think nothing of it. Huge reduction in "clonks". Dive on the brakes is funny, on a static test it feels like it dives just as far and fast as before, and rebounds pretty quick as well. When moving it doesn't feel like that at all, although the front is pressed down you can feel it pressing back and it's much steadier.

So a couple of questions, what test would I carry out to determine (1) whether the preload on the valves should be increased or decreased and (2) what tests to decide whether to go thicker or thinner with the oil.

To be honest it feels perfectly fine as it is, but if I can fine tune then so much the better.

Thanks in advance, Tony S

[aesmith]

PS - yes the springs are called and marked 8.5 rather than 0.85, presume they're marked in N/mm rather than kgF/mm.

[DomP]

Did the exact same here mate then measured and adjusted all the sag settings from Bibios tutorial. Feels much more sporty and reassuring as much as anything.

Out of interest how much do you weigh? Im 10 1/4 to 1/2 stone

[DomP]

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.

[DomP]

The above i shamefully stole from Bibio, couldnt work out how to quote it.

[Bibio]

you dont say if you welded the rebound holes up and opened the bottom holes on the damper rods.

there is no point using 'hydraulic 32' as a starting point due to not being able to blend it with other oil. suspension oil is pretty specific stuff and when blending keep to the same brand, my suggestion is silkolene maintain pro as it comes in loads of viscosity's.

you set the popper on bumps. you set the dampening via oil.

its always a compromise but the more important thing to get right is rebound and this can be tested via a simple 'bounce test' to get in the ball park. it takes practise to be able to do it properly but once you learn its easy. cold will be different to hot so after doing a cold bounce test always go for a 30 mile ride and do a hot test. same goes for your tyre pressures.

[DomP]

I welded and bored out Bibio + maintain pro 7.5

[Bibio]

7.5 is a good starting point but with experience i would say a bit light depending on how good the check valves are on the forks. its the rebound you wont to control most.

like everything though its rider dependant, most like a firm and bumpy ride i personally prefer on the slightly softer side which gives quicker dampening at the expense of outright 'brain out' riding as i tend to ride on bumpy single track roads. no matter the compression dampening the rebound is always the same for any bike rider.

watch towards the end of the vid to see how a rebound test is done https://www.youtube.com/watch?v=_QcNKfFxUi4

[DomP]

Thanks Bibio, your a star. Ive watch quite a few OTT videos on youtube

[DomP]

You're for the perfectionists out there!