Harsh front suspension – here’s a thought. (a bit lengthy)

I’ve been irritated by the harsh suspension on my current GRiSO (2010 Tenni) since I bought it a couple of months ago. It becomes even more of an issue when I recall my old 08 8v model which had the standard suspension rebuilt by one of the local suspension gurus.
Tried all sorts of combinations of damping and spring preload which did diddly-squat to improve the situation.
As I don’t currently have the finances or the opportunity to rebuild the suspension on this bike, I was looking for cost effective alternatives to improve the situation.
It occurred to me that if the damping is so harsh then one of the contributing components, may be the viscosity of the oil.
In very simple terms the higher the viscosity the slower it will flow through the damping orifices, which will contribute to the harshness of the damping, that’s my theory anyway.

As I can’t at this time change the fork internals I thought I would try the fork oil.
I don’t know what the standard GRiSO fork oil is but I had seen somewhere that it was 7.5 weight but I’m happy to be corrected on that.
Working on that basis, I thought that 5 weight oil should flow more freely and hopefully reduce the harshness of the damping. Allied to this I believe the original oil has never been renewed and at 40,000km it is probably past it’s best, the common manufacturers recommendation is to replace it every 20,000km?

I changed the oil this morning using Fuchs – Silkolene 5w fork oil - not recommending this it was just the brand I was able to buy locally. Other 5w oils may or may not work as well, there is conjecture as to how consistent the viscosity ratings are between the manufacturers, so other brands may work differently.

This afternoon I took the bike for a ride to test it out before I head off tomorrow on a 500km Sunday run with a couple of mates.

Well you may ask, what happened?

In this instance it has made a dramatic difference, reducing the front suspension harshness significantly, so much so that I enjoyed my 40km run in the rain more than any of my previous rides on this bike.

To give some context I had the suspension preload and damping settings exactly as they had been before I changed the oil and I rode a bit of road I use most weekends of the year. This is one of the local racer roads and the surface ranges from smooth to choppy with some large woops in between where the road surface has deteriorated.
I stopped halfway to reduce the compression damping slightly which further improved what was already a much more supple front fork.
As it was raining I didn’t ride as quickly as I normally do through this section, so it was a less severe test than it could have been but the ride was still quite brisk and in my opinion a valid comparison.
The improvement may not be totally down to the lighter? fork oil, as the old shitty original oil may have contributed to the previously crap ride quality of the fork.

Let me make it clear this has not changed the suspension to a magic carpet ride and when I get some cash I will look at having the forks rebuilt but in the mean time the suspension has gone from unpleasant to something I am happy to live with and has made further changes less of a priority.
For those reticent to change the oil themselves let me assure you it is not a difficult task if you take your time and are reasonably competent and it will only cost you a litre of good quality fork oil.

For any novices interested, I found a link to a video which will explain the process in simple terms. They say a picture is worth a 1,000 words but let me assure you a video is worth 10,000.
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There is a small cost to access the video but it is a small amount to pay for the potential improvement to your bike and some new knowledge.

You will need some tools and a means to secure the bike and lift the front of the ground.
The service manual should help in working out how to remove the fork tubes.
Tips:
Take note where everything is before you start i.e. the position of the fork tube in the triple clamps and the damper screw settings.
Loosen but do not remove the fork cap (Red cap/nut at the top) before you remove the fork from the bike.
Info:
I drained around 450 mls from each fork but this will vary depending on how much time you allow the oil to drain and remember to pump the fork a few times and then drain again.
Only replace the same amount of oil you extracted from each tube.
You will need something to measure the amount of oil that came out and it should be able to hold more than 500 mls, a plastic measuring jug will do the trick.

I will report back after my ride tomorrow which should be at a reasonably brisk pace over all sorts of road surfaces and of sufficient length to be definitive about my impressions.

Mark heres a thread from another member on here, regarding rebuilding front suspension.

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OK, did 560 kms (340 mls) today on a ride with a few mates.
Is there a quantifiable improvement in the front suspension performance - Yes
Is it a significant improvement - No - but it is a bit better.
The most noticeable effect is over small sharp bumps but more severe ripples and potholes of which there were many today (New South Wales rural roads) it was only marginally better.
It still felt like you were holding a jackhammer at times but it just wasn't as big a jackhammer.

Is the improvement due to a different oil viscosity (don't know what the original was) or is it just that the new oil is better than the old shitty oil - stuffed if I know.

Was it worth doing? yes and it is a normal service requirement, but it has not resolved (and I didn't expect it to) the core issue which is damping that is excessively harsh and needs to be modified to get the best out of the suspension.

At least I got to see 250 km of roads I had never ridden before.

First, I am in no way a suspension expert, but in have a tiny bit of knowledge about it.  

You didn't mention your weight or give your settings, but based on what you wrote, I'm going to guess that you are relatively light (< 180 pounds) and that you're using factory preload settings.  Since you noticed improvement from your viscosity and compression settings change, I'm going to take a wild guess and say the springs are too stiff for your weight.  If you haven't already set the sag properly, you might try reducing the preload to zero (leave compression where it is for now) and see if that helps?  At some point, you will also have to back off the rebound to compensate for the reduced preload.

Talking,
Thanks for the feedback, as you said my weight is pretty low (just under 180 in my riding gear) and yes the springs are a exessively stiff for my weight. Having run with both zero spring preload and zero compresion and damping and having tried multiple variations of both with appropriate rebound settings I can confirm that the suspension is still excessively harsh for Oz rural roads, it is ok on smooth stuff.
It actually works best with some spring preload 3 turns in and a small amount of compression damping dialed in i.e. almost fully would out.
Apart from the need to renew the old fluid in the forks, trying 5w oil was an experiment to see if it had any affect on what is clearly an issue with the damping components in the forks.
Whether my percived slight improvement from crap to slightly less crap is a result of a different viscosity oil or just new oil I can't say as I haven't been able to confirm whether there is a difference between the 2.
Either way it has confirmed that I need to get the fork damping modified to suit my weight and riding as it is unpleasant on many of the roads I use and nowhere near as good as my previous GRiSO which had the suspension modified.
I should say that it goes around corners ok even with the harsh damping, it is just not as enjoyable to ride in our conditions as it should be.

Had the same issues with my Bellagio, although the rear was more of the problem. As you already have the experience of professionally modified suspenders, you know now what to expect.

With each successive bike I have gone a step further, now with Bella I have gone way too far. Meaning I can't really afford a new bike because I know how much it is going to cost in mods to get it to a point where I am satisfied.

Bella did put a very big smile on my face yesterday, I am now at peace with the world.

So... Is 5W fork oil OK to use? My local shop(not guzzi, just motorcycle shop) has that no problem and I was going to have them do it

B3177h : you won't have any issues with the 5w fork oil, and it will soften things up a bit. 
As an experiment I changed mine out with 2.5 w motul. 2.5 is too thin for the track , had to wind in the rebound and compression screws til they touched then out about an 1/8 of a turn, and Spring preload all the way in too.    
The amount of oil you put in can play a big part of how stiff or soft the front end feels. I put the book capacity of 530 ml ( please check ) of 5w in the Rosso's forks and it felt like a tank. So a large syringe with a piece of plastic tubing was inserted down the top and sucked out 50 ml, result - better feel, but still a little harsh. 
 Uzidzit did a very good write up on here regarding the revalving of our standard forks. Link to how to -
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Thansk Ron! I dont use it for the track so maybe being a little soft won't hurt

I don't know how you guys operate over there, but our girls have a saying.......
"Go hard or go home "

I use 5W in mine.

5W Penrite in mine - pretty good stuff