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Discussion in 'Japanese polycylindered adventure bikes' started by FlyNavy, Dec 18, 2007.
Anyone notice a difference in performance by changing the fork oil in your Wee or V?
Yeah on the Wee, I put 30 wt and the front end feels more planted, like having a fork brace. Reduced brake dive. Preload is set to full soft. Not to good in the washboard stuff but plows right through sand.
If you want a cheap experiment try full synthetic ATF. It has the consistency of about 11wt. I weight about 12 stones.
So an old timer sez
"An old trick we used to use on dirt bikes was to put and extra 50ml
of oil in the fork to stiffen it up".
Does this work? Is it safe?
Yes, it can make a huge difference, but I think you have to figure out what it is you are trying to improve and then figure out what change is needed to accomplish that, not just do what everybody else does.
There is a quite a bit of info in the VSRI forum, you can read through that and see how it worked out for different people. Also, the suspension is very different on the V and Wee. Which one do you have? Make sure you look for the advice/experience that is relevant for your bike.
Yes it works and it's safe. Adding more oil reduces the air volume in the fork, and that determines (increases in this case) resistance to bottoming. The suspension will be firmer in the last part of the stroke (resisting bottoming, which probably is important on dirt bikes), but not will not change the suspension's behavior over smaller bumps. If you run out of travel often, probably a good thing to do.
To be honest a spring change is not all that costly and you may benefit much better. Sonic Springs are roughly $100 for a quality spring and Rich Desmond of SS is a V-Strom rider!
+1 and +1 on the two previous posts. You really need to understand what is it that you try to accomplish, never follow "cookie cutter" advise from anyone else.
Using heavier fork oil is a terrible way of reducing front-end dive under braking. You are basically turning a wrong "knob".
Spring rate is the correct knob for that problem.
Agreed, heavier fork oil will reduce the ability of the oil to flow in either direction, so you are both reducing the compression and rebound dampening at the same time. Not so good for most applications.
To be precise it doesn't reduce dampening it increases dampening which on a poorly dampened system is usually an improvement. If you did it to WP forks it would be a problem but with cheap forks it is probably better if only by accident.
Ah, finally someone who uses their brain!
Here's my take. First, stiff and harsh are two different things, the former is controlled by damping, the later the springs.
Having just broken in my new DL650, the slow speed damping is ok but the spring rate is too low. This is fine on a smooth to mildly bumpy road. The problem shows up when the bumps get steeper. Because the springs are too soft, the damping system is called on to control compression, it becomes over-taxed and the result is "too stiff." What you end up with is a very stiff feel in the high speed compression action. Using heavier oil will only make things worse.
What the 650 needs is a higher rate spring, that will relieve the stiffness in the high speed compression action. After that, maybe better valving is next with the right selection of oil. Not sure what to do about the rear shock at this point. It suffers from the same problem. Might try a higher rate spring there, too.
Before trying heavier oil, try higher rate springs. .90 if you're 180-200lbs without gear, .95 if you're 205 or more. Valves are a last resort as far as I'm concerned. The best test is washboard. If it's adequate I'll be happy.
I'm 200lbs and am going to give .90s a shot before any other change. Then I may try a slightly heavier oil. Not sure what weight the stock oil is (5 or 10wt??) Regardless, if it's 10 stock, 15wt might do the trick with the spring change.
I also have a DL1000 and it suffers from the same general problem. However, the stock compression damping (high and low) is not as stiff as the 650 is. The 1000 is too soft everywhere, which makes washboard a real pain... Higher rate springs and heavier oil may be all it needs.
Has anybody tried the Wirth springs (available from touratech)? Seems like a progressively wound spring is a good idea, and they are about $140 ( I think).
Why not stiffen the rate of the springs you have?? You can do this by actually pulling spring out, and cutting about 2-3" of spring off, heat the last coil and bend it flat(regular propane torch will work for this) , grind/file it smooth and then make a spacer out of pvc pipe to take up the space from the section of spring you removed.
Many people have doubts about this process working. But it does work, it is safe, and it dosent cost a thing if you have some 1" pvc laying around. It only takes about an hour to do. Save that $100 for something else.
And if youre wondering about durability, I did this mod to the forks on my xr650r last year, no problems at all. The suspension on that one sees a little more "punishment" than the V-Strom ever could.
I'll go into more detail on how to do this when Im not at work.
I think you have it backward. Higher rate springs make the bike stiff (or firm, depending on your starting point), more damping would make it harsh if you have too much high speed compression damping.
That's why heavier oil with weak springs isn't really a good fix, it controls movement by preventing the springs from doing their part, which creates a harsh ride.
I have just installed Hyperpro progressive springs to my KLV front end with 10W fork oil ... Wooowww thats really work ... much better then with stock springs... Oil level acording to Hyperpro leaflet 180 mm. I recomend Hyperpro springs supplyed with Hyperpro oil 10W...
I agree with this. Most folks who stiffen their suspension (either by stiffer springs or by stiffening up the damping) say their bike works better, but unless you do a proper setup and know what you're doing, you're probably making things worse.
If you're just using stock springs (either because they are the right ones or you haven't resprung), then you probably want to keep pretty close to Suzuki's stock fork oil viscosity. Even with heavier springs, I wouldn't make a drastic change in viscosity - if the spring are 20% stiffer, I'd tend to put in 20% thicker fork oil if I made any change at atll. And if I decided to make a fork oil change from stock, I'd first start with fork oil height (air volume) before I'd change fork oil viscosity. Fork oil viscosity would be my last fine-tuning thing.
What viscosity is the stock DL650 fork oil? That's an interesting question as the fork oil mfg's are notorious for not using consistent viscosity measurements and/or naming their fork oils with misleading names, partly to satisfy buyers who think a bigger number is better.
The DL650's service manual calls for "Suzuki SS-08" fork oil which is also specified for various other Suzuki bikes (including many Gixxers). The Gixxer folks report that it is exactly the same oil as Kayaba 01 fork oil. This is a fairly low-viscosity fork oil; mfgs these days generally specify very low-viscosity fork oils and the forks are designed for this - stick a thick oil in there and the fork is probably going to work poorly.
The reference below shows a viscosity of Kayaba 01 of about 15.6 cSt@40C. (This viscosity measurement is generally considered the best cross-reference measurement to use.) You can find a bunch of fork oils which are about the same as this and they are generally not "10wt". Personally I'd use a mix of Silkolene Pro RSF in 2.5wt and 5wt to match the stock viscosity, but I'll admit that's probably a little anal. But Silkolene is fine fork oil and they specifically say you can mix it to build a custom viscosity. But any fork oil around the right viscosity should work fine.
If you just throw in something that says 10wt, you're probably going way too high compared to stock. For example, a Silkolene Pro RSF 10wt has a viscosity of 47.7 cSt which is triple the viscosity of the stock fork oil! I would think this would give very poor results although I'm sure some would try it, give it the parking lot test with the front brake held, feel the heavy damping, and declare they've made an drastic improvement.
I'm on an '06 DLK so don't know it this will apply to you. I didn't like the front on my DLK straight away on the first ride. Too softly sprung, lotsa fork dive and very harsh over sharp little bumps with my 240 pound body on it. ( just coming off lotsa miles on BMW GSs spoiled me ;-) First thing I did was order progressives and 8 weight ( I think, it's been over a year ago now). Put the forks back together and back on the bike. adjusted sag to about 2" if I remember right. Ditto for rear sag. Really made a difference in the bike and running the same way today at 16000+ miles later.
Well, I might it have it backwards. I'm dyslexic, sorry.
It's my understanding that in the suspension world, these terms are used thus: harsh is spring-related, stiff is damping-related. Most riders can't tell the difference between harsh and stiff in their terms.
Either way, we're on the same page. Not going to pick fly shit out of the pepper. Bottom line, as is true for most bikes, these bikes are under sprung. Or better said, are delivered for 160lb riders, a compromise as always. A too-stiff bike won't be appealing on a test ride and hence won't sell since most people never touch the suspension. Too soft feels better and is easy to fix for those of us who care.