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.[You must be registered and logged in to see this link.]
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.
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.
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.