Not sure if this is just me, but when I try and ride quicker than usual on my bike it can feel really twitchy at the rear, especially on high speed left hand bends or roundabouts where I am leaning left. It also happens on acceleration after the roundabout if I am still slightly leaning to the left. Obviously its pretty unnerving when it does this. It's usually near the start of the ride, but I do allow quite a lot of time for tyres, engine, breaks etc to warm up properly before I start to give it some. I do have a leaking left front fork which I am replacing soon fingers crossed, could that be it? My tyres are Dunlop Sportmax front and rear if that has anything to do with it? I'll be getting BT023'S next time I think. Also, I have stock suspension by the looks of it and weigh just over 13 stone in gear. Any help or similar experiences would be great thanks.
04-03-13, 10:48 PM
(This post was last modified: 04-03-13, 10:52 PM by darrsi.)
Fork oil levels can chuck the bike right out of sync, get that sorted, use 15w heavier fork oil and you may find a massive improvement?
More people are born because of alcohol than will ever die from it.
Yeah I thought it was likely the forks, which brings me back to the dilemma I put up in a whole new thread ages ago :\ Yeah I'll try out the heavier fork oil when the leaking fork has been repaired / replaced. Cheers 
04-03-13, 11:35 PM
(This post was last modified: 05-03-13, 12:19 AM by darrsi.)
I tried the 15w oil recently, very happy with the outcome, it feels much more stable up front.
More people are born because of alcohol than will ever die from it.
Are you running the bike loaded (topbox etc), or normal? What tyre pressures are you running, and your pre-load setting? How old / what mileage are your tyres (ie, could they still need scrubbing in?)?
.........+1
One, is never going to be enough.....
05-03-13, 10:01 AM
(This post was last modified: 05-03-13, 10:13 AM by packie.)
(04-03-13, 11:13 PM)Yamazer-92 link Wrote: Yeah I thought it was likely the forks, which brings me back to the dilemma I put up in a whole new thread ages ago :\ Yeah I'll try out the heavier fork oil when the leaking fork has been repaired / replaced. Cheers
Before you go taking off your fork and replacing the seal, here's a little tip that might save you some time and money.
Stick about a 0.1 feeler gauge down past the dust seal and right into the fork seal and work the gauge (by pulling) all around the whole fork leg. If you haven't a feeler gauge, try to use a stiff business card. A lot of the time there is just only just a build up of dirt/dust after getting past the dust seal and has also worked its way inside the fork seal too. All you are doing it clearing this trapped dust/dirt so the seal can seat back onto the fork leg again.
I know what you are thinking!!....Just like me, I thought it was a mad cap idea at first. I was on the verge of replacing both seals of my forks a while ago. Both had what I would call substantial enough leaks.
I tried this trick for the laugh thinking that it was a mad cap idea and that a stiff business card couldn't possibly get past the seals anyway. The business card did get past both seals, so I treated this idea with a bit more respect and used a feeler gauge for a proper job.
I noticed a lot of dirt after been dislodged during this procedure and was amazed. I then wiped down the fork leg when I was finished and drove the bike for a day or two while monitoring the situation. The leak instantly got less after the first ride, up to a point where there was only a tiny film of oil was on the fork leg. A big improvement and I would have settled for that. But after the second day, this thin film was completly gone and the the forks and the sealing were like as if I installed brand new seals.
The fork sealed must have settled back down onto the forks by the second day and both seals haven't leaked since.... and that was over 2 months ago now. Although I would have done the job myself, I saved the price of the seals, the oil, and a few hours of labor while I could have been out enjoying riding the bike.
Because you have a leaking seal you are losing dampening in the fork leg, no wonder it feels twitchy...
Im not sure 15w oil is going to be any good for your weight unless you ride very hard as it will increase the compression and make the front end "feel" alot harder..
What are you doing with the throttle as you corner?
+1 for what packie said, i used to do this when i raced motorcross at the first sign of a leaky seal..
One thing to keep in mind tho is how is the dirt getting in? Or is it the slide bushings losing there bronze coating and breaking down, putting debri in the oil from the inside causing the leak?
If it's the rear of the bike that feels peculiar then perhaps that's where the problem is!
Have you checked things like worn swingarm bearings giving lateral play, or excess slop in the vertical direction caused by knackered bearings in the shock linkage? (Note there will be 2 or 3mm vertical play at the rear wheel even with new bearings in the shock linkage, more than that indicates a problem.)
The OE shock was never brilliant to start with and if there's a fair mileage on the bike, particularly if it's spent a good proportion of that heavily laden, then it may be worth trying a replacement.
(05-03-13, 12:08 PM)Fazerider link Wrote: If it's the rear of the bike that feels peculiar then perhaps that's where the problem is!
Have you checked things like worn swingarm bearings giving lateral play, or excess slop in the vertical direction caused by knackered bearings in the shock linkage? (Note there will be 2 or 3mm vertical play at the rear wheel even with new bearings in the shock linkage, more than that indicates a problem.)
The OE shock was never brilliant to start with and if there's a fair mileage on the bike, particularly if it's spent a good proportion of that heavily laden, then it may be worth trying a replacement.
If the front suspension was working properly i would agree but as he said the fork is leaking oil, so that makes thing a bit more complex..
If he's losing oil, the forks are losing dampening, meaning they are returning too quickly, which will upset the bike while cornering, even worse if only one leg is leaking as it will twist the front end..
If it were me i would get the forks serviced, and as Fazerider says check the rear shock (best to do with the shock off and the spring out) or you can do it car style by pushing on the back end and letting it go watching for a smooth and positive stop at the top of the stroke, check linkage and arm bearings.
Set sag and go for a ride, if its still not right, start contemplating a suspension upgrade..
Wow, a lot of interesting replies on this. The bike is usually unloaded with just myself on board when I attempt to ride a bit harder on it, tyre pressures I did yesterday at 33 front 36 rear. The tyres have done about 3-4k miles I think and have still got a fair few mil of tread left, havent measured exact amounts. They are definitely scubbed in though, I havent edged them but the chicken strip is very thin all the way around. Preload I am not actually sure, how would I check this?
Packie, thats a good tip and I did try that before but I think there is a more substantial issue with my left fork as it still leaked after the feeler gauge trick, so I replaced the seals and it still leaked. I think I need a new stanchion but can't afford it until next month and am not sure whether to get a new stanchion, OEM dust seals and fork seals and bushes and do it myself or just buy 2nd hand forks, probably end up at roughly the same amount but my forks are good other than the leaking left one.
Wezdavo, most of my riding is commuting but I do take it out for proper rides and like to corner a bit harder without going too nuts and ending up in a bush. Would you suggest the 15w to be too much for that? I never do track days etc. During corners I dont go nuts with the throttle, just hold it steady and then lightly accelerate out I guess. I haven't had any problems thus far on other bikes but then again this is the most powerful I've owned so far.
I dont think the rear has any issues, the shock isn't leaking or anything and there is no play in the swing arm. The bike has done about 21000 miles so its not really worn. I have stood the bike upright and compressed the rear suspension and it is all smooth and stops positively as you say. Where would you suggest would be good to get the forks serviced and how much roughly do you think that would cost? Even if they aren't the only reason for the problem they still need repairing and are top of my list. Cheers again guys
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