FF: Forks Modified Steering Stem

[Martyn Goodwin]

That's excellent feedback Martyn, I hadn't even thought of the loose stuff. Most all I know so far have indicated that they feel the steering damper is near redundant, as the steering now feels so much more stable. I know on the racer I set the hydraulic damper to it's middle position and never changed it, There was one corner about 2 thirds the way down the main straight at Lakeside called "The Kink" which you could take very fast and on full throttle if you had enough "Bottle" I don't know if I ever actually held it on full chat going through there, as immediately coming out the other side was quite rough I'm guessing because of ridges caused by cars. I am guessing that a stock front end Vincent would have almost certainly shook it's head Violently going through there, But I remember very well the racer getting shaken quite a bit going through, but never did it shake it's head. This was probably the track that I either raced at or held practice days the most, so I got to know the track very well. Lakeside is a very historic track here in Australia, and quite a dangerous track too, several people killed there over the years particularly on bikes. I didn't want that to happen to me, though I did get knocked off on my second ever racer there.............

Greg,

I agree with you IN PRINCIPLE about the steering damper BUT having had an off as a result of violent head shake with a 'D' friction damper fitted and suffered the consequential broken bones etc. I consider a hydraulic steering damper prudent insurance - would not ride without one fitted. On my Comet I ride with my (Kawasaki) damper on its second softest setting and it seems to have no detrimental effect on the way the bike feels or steers, even at walking pace.

As we all should know, at any speed of head stem movement, like you get in a tank slapper, the standard friction damper does NOT provide any dampening no matter how tight it is - friction dampers ONLY work to supress slow speed movements. With hydraulic dampers, the faster the headstem/handle bar movement the greater dampening they provide.

Martyn

 

[BigEd]

Greg,


As we all should know, at any speed of head stem movement, like you get in a tank slapper, the standard friction damper does NOT provide any dampening no matter how tight it is - friction dampers ONLY work to suppress slow speed movements.
Martyn

Dear Martyn,
Not to say you are wrong but on what evidence do you base your statement. Just thinking that brakes work on friction but continue to work when rubbing speeds become faster albeit maybe less efficiently.
The hydraulic damper is good insurance, fairly simple to do, relatively inexpensive and a modification everyone should consider using.

 

[greg brillus]

I'm not suggesting any of us run without a steering damper, just that the changes in the geometry have overcome the inherent design fault that gave the Girdraulics a bad name that resulted in so many tank slappers in the past. That was the fundamental reason for this whole exercise. The efforts at trying to soften the front end to give a smoother ride is a secondary issue, and one that is wholly restricted by the total available movement, which is not very much by modern standards. No less than the rear end, when I compare the length of the rear swing arm on a Vincent to a modern bike, some moderns are nearly half as long again. No wonder they are so much more comfortable. We are only trying to make the best with what we have. As far as the singles go, we sorted that out back before Christmas, springs, shocker, steering damper, best handling Comet I've ever ridden.............Just ducked outside, my package of springs from Norman has just arrived. Good as gold, cheers.........Greg.

 

[Martyn Goodwin]

Dear Martyn,
Not to say you are wrong but on what evidence do you base your statement. Just thinking that brakes work on friction but continue to work when rubbing speeds become faster albeit maybe less efficiently.
The hydraulic damper is good insurance, fairly simple to do, relatively inexpensive and a modification everyone should consider using.

Problem is as speed increases friction become less effective. Drive your car at 5 mph and slam on the brakes, bet the wheels lock up instantly. Try it again at 40 mph , bet it takes some time before they lock up, now try it at 80+MPH and at first there will be little retardation, but increasing retardation as all gets slower. And thats the problem with a friction damper - when we need it to work at its best is with a tank slapper but thats when all the bits are moving fastest.

The test for hydraulic effectivness is simple. Pull a flat stick through water at slow speed and there is not much resistance, increase the speed and the resistance rises very quickly.

 

[timetraveller]

Greg (573 above) is right. Six months ago I thought that we had all the parameter well defined and then Chris decided to fit some needle roller bearings (Greg uses ball races) to the rear of the lower link. None of us involved expected, or even understand, why this should have made such a difference but it does. We first of all had to go to stronger springs, which because of the geometry/prelod have to be shorter to give the correct angle to the lower link. Then we found that what had been apparently perfect damping when the Oilite bushes were used had to be increased. If Vibrac intends to use Oilite bushes then I think that I can say with confidence that we know what is required. (30 or 33 lbs/inch springs and an AVO damper on its lightest setting. The range in the spring strengths is a function of total weight so depends upon the bike + rider weight and is not critical.) If ball races are to be used then I think that we are there but feedback from more than just Chris is needed to take into account a variety of road and rider variations. I should be able to start to send out kits with dampers once the first batch of four standard AVO dampers arrive in the next few days for those continuing to use the Oilite bushes. We think that we are also there with defining what is required when ball races are used but it will still require some feedback to ensure that I can send out the optimised combination of part to all users.

 

[timetraveller]

Although this concerns the rear end rather than the front end I thought that it might be worthwhile passing it on to those who fit coil over rear dampers. Chris came up with this idea to measure exactly how much movement he was getting on the rear end. To some extent the front suspension is affected by the rear but it was proving difficult to distinguish between springing that was too hard, damping that was too stiff or hitting the bump stop on the rear AVO damper. Chris invented the gadget shown on the attached photograph which relies on a cable tie fastened around the moving shaft to show exactly how much movement had taken place. If you decide to build your own just ensure that there is enough travel to ensure that the limit is the damper and not the measuring device.

 

[timetraveller]

OOOPPPPSSS Picture too large.

 

[Martyn Goodwin]

Although this concerns the rear end rather than the front end I thought that it might be worthwhile passing it on to those who fit coil over rear dampers. Chris came up with this idea to measure exactly how much movement he was getting on the rear end. To some extent the front suspension is affected by the rear but it was proving difficult to distinguish between springing that was too hard, damping that was too stiff or hitting the bump stop on the rear AVO damper. Chris invented the gadget shown on the attached photograph which relies on a cable tie fastened around the moving shaft to show exactly how much movement had taken place. If you decide to build your own just ensure that there is enough travel to ensure that the limit is the damper and not the measuring device.

When setting up my rear coil over preload - a Thornton - on my comet all I did was fit a cable tie to the shaft of the shocker. Push it up against the shocker body then go ride. At the end of the ride, the position of the cable tie shows how much travel was used. You then adjust as you see fit. I did the same at the front.

Simple.

Martyn

 

[Chris Launders]

That would work to a large extent Martyn but it wouldn't tell you if you were hitting the bump stop or by how much, the rubber stop would push the cable tie back.
Chris.

 

[greg brillus]

I think it's pretty safe to say you will definitely "feel" when it bottoms out. If this occurs only over the heaviest of bumps then its probably not too bad, but on a regular basis would not be good for rider or machine. I have felt the rear of mine Bottom out, but only two up, and also over a bump that would cause the best of any suspension to bottom as well.