996 forks springs

[MonsterHPD]

I spoke again to one of ktechs main technicians , and he says that it does seem that my forks are not working properly and that the spec that i asked for was probably not delivered ,(issues with the ex staff member who prepared my forks)

I may be able to modify the shim stack myself if needed but he also said a much softer spring was required ,and we are trying to source an .8 also lithter oil  ,it seems that 10w oil might have been used  , there is no way i can get these forks back to Uk for at least 5 months as they have to be carried in my luggage ,in and out of thailand if i ever want to see them again  and I am off to work next week anyway ,

oh well its an on going project

I am about 62 kg without gear,and I use 8.0 N/mm springs in both my Öhlins forks and my modified Showa (Part No  4745-80); preload is about halfway in (a bit more for track days, a bit less for road use). I've tried 8.5 N/mm springs but they were definitely too hard and are now in the forks of a friends 900 SSie; I suppose he'd be about 70 kg. I think 8.0 springs would be on the soft side for you.

You must have had bad luck with the person doing your shim stacks, my K-tech stacks have all worked very well. I agree with the opinion that your forks seem far to "stiffly" valved.  

Assuming you have Showa SBK forks, Öhlins R&T springs will fit as far as diameters go, but you would/ might have to manufacture spacers to compensate for the short Öhlins springs. They are available from 7 or so to 11 or so N/mm in 0.5 N/mm steps. Very handy.      

[FrankenDuc]

I'm glad you're getting some support from K-Tech, let's hope they carry through for you.

Given the long lead on getting the forks back to UK, don't be afraid to dig into the forks yourself, especially if you're getting the support you need from them - if it was me, given 5mo of harsh ride, or a week of the bike down while I get around to doing the work, or not ride at all ( ), I'd dig in...  Just make sure your workspace is clean, pristine sort of clean - unimaginably small little hairs of thingys in between the shims in the stack make them behave a bit different... Outside of a very clean workspace, I "pressure" wash all of my shims off with brake-cleaner right before putting them in the stack on the rod, just in case.

IMO, suspension in and of itself is an ongoing project - personally, no matter how hard I try, I just can't stop mucking with mine...  In my experience, once you dig in there, you just can't stop 

Best!!!

[jerryz]

HPD and frankenduc

thanks for the support

I agree that suspension is an ongoing thing ,
my going to work today has been delayed until monday so i took the opportunity to go back to ohlins agent in bangkok  as he had found some .85 springs from some spare 916 forks
we swapped them over but checked them on his test rig they were actually .86nm  we kept the same oil which  7.5w as its clean  and the 130mm airgap  and also we wanted to do one step at a time , he did notice that the forks seem a little reluctant to move stiction but all is perfect  mechanicly , bushes ,stanchions seals all perfect alignment so he thinks perhaps the ktech shim stack might need adjustment for a lighter action  but we will leave that for now , he is interested in stocking the ktech products in future , we need some research and advice from ktech before we go there though .

he also thought that a slightly stronger rated  rear spring in my Ohlins PRCS46 shock might be in order in the future as he noticed i have it set with max preload , although the rear end is nicely set up for me solo it could be a good idea especially when touring with sabblebags or a passenger .

he is helpful to me as I have done him a favour or two in the past on his 999 racebike vis a vis
fuelling maps and valve gear setup  and he is a genuine bike nut .

any way we did a test ride and after dropping the compression damping to only 2 in and rebound to 7 in from minimum  the bike felt much nicer over bumps/ imperfections  and more stable too ? , still Zero preload which is weird   but riding the 70 miles home was better ...not perfect ......perhaps lighter oil might help the shim stack respond better  5w? 2.5w???

spoke tonight with ktech  technical in Uk , the guy was concerned about the Zero preload and the fact that i am only getting 22mm sag he said it should be 25-30mm,
he also said that Ktech actually reccomend 5w oil, so he is suprised that it is 7,5w ?
tommorow i will recheck the sag yet again  , he think that the issue is not the shimstack at all  but there is something very wrong in my forks  if they are on Zero preload !!!

anyway still may look for .8nm spring as well but next step will be to get some Motul 5w oil

cheers jerry

[FrankenDuc]

Rad, you got a helping hand out there    Glad to hear!

Be careful with oil weight, it's not really the oil weight that matters, it's the viscosity.  Viscosity varies between brands (same weight label), and also with temperature, so your tech may have chosen a 7.5w of some brand to get the right viscosity, maybe because of the warmer climate, maybe just how viscosity works out for that brand, so on.

I don't know the K-tech's, or your stack setup, so can't say how they'll respond to oil viscosity changes. Assuming  the valve throats and stack setups are not too restrictive, changing oil viscosity would impact the low speed response, braking and acceleration primarily, some to bump response but not as much.  However, more restrictive valve throats and/or shim setups would see more of a change in damping over the full suspension velocity range from a viscosity change.  Worth playing with, oil's relatively inexpensive, just bear in mind it's hard without knowledge of the valving to know what it'll do.

for stiction/binding concerns, with the front end off the ground and supported, you can loosen both fork caps, and slide the whole wheel assembly up and down in the fork tubes, it should move smoothly and freely with minimal resistance throughout the range of travel.  

Also, you could check sag and stiction again with all of the clickers wide open - I have maybe as much as 3mm with clickers wide open on my Monster, but clickers at my current ride settings it looks much larger,  maybe 15~20mm, I've never measured but it looks big!  I have a lot of low speed damping on both compression and rebound, which limits slow suspension movements like those during a stiction and sag checks.

for sag/preload, this is 22mm difference between fully unloaded (front wheel off the ground) and loaded with you in standard riding tuck?
If so, it sounds like the spacers are too long for the fork springs.  That's an easy one to fix, take any extra spacer shims out (don't remove the steel washer than goes betweeen the spring and spacer/shims), and if more sag is needed just cut what you need off of the spacers.  It's more difficult to fix too much sag, unless it's a small amount and can be safely shimmed up, so err on the side of cutting less.

IMO, for road, 25-30mm sag even seems quite low to me.
Assuming you have some sag at all, preload sets the useful ranges of compression movement verses rebound movement.  Assuming you're not bottoming out on the front side of bumps or topping out on the back side of bumps, it shouldn't affect ride over the bumps.  It is a trade-off
- smooth track where you want as much useful compression range to handle the heaviest braking loads, lower sag works, towards 25mm for the smoothest tracks.  During braking as much as the whole weight of the you, the bike, plus the deceleration force all act to compress the forks, so more compression range means higher deceleration force can be achieved before bottom out.  
- rough roads, having rebound range available to allow the forks to extend to keep the tire on the road on the backside of bumps, dropoffs, potholes, etc., seems a useful thing.
I've seen/read/heard a lot of different recommendations, as high as 45mm for streetbike road use. My target is, with ~110mm useful travel, 35mm sag for everyday road riding, or about 30% of useful travel.  So I set my front 35-40mm preload full out, and I can turn it in for smoother surfaces.  

For neutral chassis balance, set rear sag to match front, so seems like you could turn the rear out some. Still doesn't mean the spring rate is right, so very much worth looking into (think Ohlins is kind enough to have this printed on their springs, so maybe if you look   )

[MonsterHPD]

There is one further hint the sag numbers can give you; if you check the difference in empty sag and rider sag, it will give you a hint if the spring has the right rate for you or not.

For trackdays I run empty sag 20 to 30 mm front and 5 to 10 mm rear, and rider sag 35 to 45 mm front and 20 to 40 mm rear.
In other words, 15mm difference front and 15 to 20 mm difference rear is about right. Less than these number indicate too stiff springs, more indicates too soft springs.

For road use, you'd go for maybe 10 o 15 mm more sag front, and maybe 10 mm more sag rear, but with the right springs, the difference will still be the same, i,e, around 15 to 20 mm. Remember also, the difference is not affected by preload.

Seems these numbers are about the same as those stated by Frankenduc.....so probably 


Oil viscosity is measured in centistoke (cSt), which is a unit for which I have no feel at all. The 5W and so on numbers are also viscosity numbers, but more alluding to the known engine oil viscosity grades. I do not think there is a standard defining what a "5W" oil really is and as a result different brands can vary.
The Öhlins oil specified for their R&T forks has 19cSt @ 40°C; for the BelRay oils I've been using this is a little thicker than their 5W, but considerably thinner than their 7W but I don't remember the exact numbers. Usually, you can find these numbers somewhere in the manufacturers documentation, or you can ask them for it.

I do not think most of us would notice the difference between 5W and 7W oil, but I use the thinner oil since it will change less with temperature, or so I believe, at least   
       

[jerryz]

I carefully rechecked front sag today and i have 32mm from forks fully extended on stand to rider sitting on bike so seems about right , still with Zero preload ,,,,Ktech recommend Motul 5w Factory line fork oil for all the forks they set up or manufacture , and remember they service most of the MotoGP teams so they know a bit about oil .I cant get motul factory line in thailand  only motul regular fork oil but will get some in UK.

oh my front pirelli diablo corsa is nearly all used up so a new tyre may also help matters
will go for Dunlops next time either Q2 or Roadsmarts , probably put a new rear on as well to match but a set of decent tyres here is $600 unless one wants shinko then its only $200 a set but are they any good ///?

looks like i am going offsghore tuesday for 2 months then to UK so this will all have to wait

cheers jerry

[MonsterHPD]

I carefully rechecked front sag today and i have 32mm from forks fully extended on stand to rider sitting on bike so seems about right , still with Zero preload ,,,,

Sounds about right, even if it's a bit strange you're not having any proload (not knowing what the installed preload might be).

It would still be interesting to see what the difference between sag under bike load and sag with rider is, to hava hint if the spring rate is about right.

[jerryz]

sag with no rider is 22mm with rider 32mm, there is no installed preload spacers all preload is done on adjusters and they are fully wound out

[MonsterHPD]

sag with no rider is 22mm with rider 32mm, there is no installed preload spacers all preload is done on adjusters and they are fully wound out

OK, seems to support the opinion you already have that the springs are too stiff.

[jerryz]

OK, seems to support the opinion you already have that the springs are too stiff.

my thought exactly but still cant find any one who has .8nm springs in stock
tried Ohlins ,Ktech , hyperpro ,hagon ,ducati and Maxton all only supply 8.5 or progressive springs and racetech who list .8 spring never answer emails from USA or UK ??

will keep looking , springs are cheap so i dont mind trying some

[MonsterHPD]

Well, as discussed earlier, I finally resorted to using Öhlins R&T-springs for exactly that reason: Could not find 8.0 N/mm springs thyat would drop right in anywhere.
Making the new preload tube was not much trouble as I have access to a lathe, but I suppose it would not be that costly to have them made either. 

[jerryz]

i will speak to my ohlins agent ,

[MonsterHPD]

Fine.

This pic has been on the forum before, but this is what it looks like:

[FrankenDuc]

sprung weight on the front end (bike + rider) and spring rate determines ride frequency, or ride firmness vs. response.  More firm is the trade-off you give for faster suspension response (i.e. more time of the tire on the ground, and thus more traction).

There's a couple of things here that matter here WRT sag, that is installed preload and total sag (bike + rider + gear and all). You're tuning sag to get the desired range of available travel in both the compression and rebound direction,
1) more sag, more rebound travel to soak up potholes
2) less sag, more compression travel to soak up bumps and braking forces
So, take this as... the harder you are on the brakes, the more compression range you need...

And installed preload to get a baseline compression range.
1) the harder the  spring, the more braking force the suspension can tolerate (before doing something bad like hitting the oil lock, where the forces on the tire just make it give up...)
2) the softer the spring, the slower and the softer the suspension response, and less time the tire spends on the ground creating this thing we love called "traction"... but then, the less the bike tries to buck you off of it...

I've currently got my forks, for road use, tuned for the bike+rider load only,. i.e I take the load the bike and I, rear wheel totally off the ground, 245Kg's load
- this force should just push the forks to the oil lock limit.  that is, for my Monster, ~245Kg's, if held constant (i.e. damping aside) should compress the forks from fully topout to ~the oil bottom-out lock level. (discounting air spring and assuming sustained load)... At this level, braking forces push it over the edge, so I can only brake so hard on the street...

For track use, you're going to be (hopefully you let yourself) much harder on the brakes, [and of course the road surface is much smoother], so one or both of two things need to happen:
1) sag set much higher in the full stroke - that is, you give more travel to the compression side to handle the braking forces, and you assume you need less rebound travel due to the smoother road surface
2) spring set much firmer - the higher ride frequency of the stiffer spring helps you keep the tire on the ground more of the time, ie. more traction.  Additionally, the stiffer spring reduces your travel on load, further increasing the braking forces you can apply before bottom out.

Anyway, I've taken a very roundabout and [trying to be diplomatic] way of saying this - bike static vs rider load is going to vary with the rider's weight, regardless of the sag setting's aggressiveness...
At your 0.86Kg/mm current spring rate, and your 22mm bike only, 32mm you+bike, that makes you an added 17Kg to the front of your bike (surely you weigh a bit more than 17Kg... but that's all you're loading the front with...)

You bike is, I'm going to guess, ~85Kg on the front and ~180Kg total.
If you strive for 15mm static vs. rider sag, you'll wind up with 0.56Kg/mm springs... which will in fact lower your ride frequency into the range of that of a Lincoln Town Car - very nice and plush... But will also not give you much margin at all to brake hard...  

I get away with ~15mm static vs. me sag because I'm borderline obese for my size, and it works, I can just bottom out my suspension with the oil level nice and low... But at my weight I'm also a substantially larger portion of the front end and total weight of the bike.. ~25KG out of 96Kg for the front, and ~96Kg out of 245Kg (don't forget to leave the 40lbs unsprung weight of front wheel, brakes, etc. out of the equation...).

I don't know the exact weight of the front end of a watercooled S4, but I think you can get down to 0.8Kg/mm safely, and enjoy it very much for regular spirited country rides, but I wouldn't go much lower than that.

[jerryz]

Frankenduc , wow you must love posting a lot of hard work there ...thanks , actually when braking my bike dives in a very contolled  manor , and not much either ,

still at home so will go for a run tommorow , may even go down to Cambodian border  thats a round trip of 600 miles ,cant do much to the bike until I can source  some parts , in UK