FF: Forks Modified Steering Stem

[Oldhaven]

I am just amazed that all this is still being sorted 68 years after the design first appeared. I had a minor (meaning I stayed on) tank slapper in the 80's on my '52 Rapide, and my brother's Shadow shattered his ankle while tossing him off during a wobble and put him off motorcycles for life with one in the 90's. I know some riders have many, many thousands of miles without incident on Girdraulics, so it is not a simple problem. This is important work being done here.

 

[Martyn Goodwin]

Getting back to out of round tyres, Most rims I have seen have some out of roundness, Where the weld is.
I have just picked up a pair of old wheels from the 50 s/60/s, For my next project, And one hub was not dead centre, I had a wheel built some years ago with the same fault, The out of round rim must make the tyre out of round also ?.
So there are two things to start the ball rolling, Of the forks shaking !!. Cheers Bill.

only slightly off topic - about 15 years back I purchased a brend new Yamaha YP250 motor scooter. The rear tyre only lasted about 1,500 miles till it was toast. The replacement tyre/wheel was dynamically balanced and off I went a short time later one of my riding chums commented about the back wheel of my scooter jumping about like a kangaroo! I was unaware of it I assume because of the high unsprung weight and very compliant rear suspension. On subsequent checking I found the cast aluminium rear wheel (not the tyre) seemed to be out of round; what was actually wrong was that the axle hole in the wheel had been machined off centre. It was replaced under warranty - THREE TIMES. Why 3? well it took that number of replacement wheels till the dealer came up with a wheel (less the tyre) that was a) actually round and b) had the axle hole in the centre.

Even with 'modern' bikes from reputable makers it still pays to check the wheels with care.

Martyn

 

[litnman]

Bill,
The V8 bike crashed when it started to wobble and the front wheel disintegrated. That was the end of the girdraulics. I'll post some videos on youtube when I get a chance.

 

[Black Flash]

When riding my Hinckley Triumph I noticed that I hardly use the rear brake as opposed to riding my brothers Comet.
The rear brakes on his Comet are a delight and I have to use them when braking hard as the front brakes perform period 50's style.
I wonder if many of the problems occur with riders using a lot of modern bikes and mainly using the front brake only.
By applying the rear brake first the front of the bike will dive a little and if I understood the thread till now rightly this will stop the fork from locking up.
I know this sounds like treating the symptoms rather than the source of the problem but it could be an explanation why some riders using their Vincent for decades never experienced the wobble and others have.
Just my thoughts. I am looking forward to changing my stem in the future never the less.
Bernd.

 

[Bill Thomas]

Hello Bernd, I find with a Twin, As you shut off the twist grip, The weight of the engine moves the forks to the "David's safe" position, I did this even when Racing, I was not that fast !!. Cheers Bill.

 

[hadronuk]

Anybody noticed this in the MCN review of the new Brough? I quote:

"That unusual suspension system contributes to a very flat, firm riding experience. Weirdly the front end rises when you accelerate but barely dives at all when you brake hard. This flat non-diving front end thanks to the suspension does make worse perhaps the only major flaw on the bike which are the fiercely un-progressive front brakes. They are a little scary at first and it takes an unbelievably gentle touch to avoid over-braking. Overnight the Brough engineers changed the master cylinder and piston to soften the braking force and on a brief test ride it proved to be a lot better."

The system uses long double wishbones which look to be unequal length. The modern bit is that the front hub pivots on the ends of the wishbones like a car suspension turned through 90 degrees. System invented by Claude Fior. In essence, it is still a girder fork.
http://www.broughsuperiormotorcycles.com/news/details/what-is-our-front-fork-technology.html
Weird steering linkage, doesn't look as if it could work.

 

[BigEd]

Anybody noticed this in the MCN review of the new Brough? I quote:

"That unusual suspension system contributes to a very flat, firm riding experience. Weirdly the front end rises when you accelerate but barely dives at all when you brake hard. This flat non-diving front end thanks to the suspension does make worse perhaps the only major flaw on the bike which are the fiercely un-progressive front brakes. They are a little scary at first and it takes an unbelievably gentle touch to avoid over-braking. Overnight the Brough engineers changed the master cylinder and piston to soften the braking force and on a brief test ride it proved to be a lot better."

The system uses long double wishbones which look to be unequal length. The modern bit is that the front hub pivots on the ends of the wishbones like a car suspension turned through 90 degrees. System invented by Claude Fior. In essence, it is still a girder fork.
http://www.broughsuperiormotorcycles.com/news/details/what-is-our-front-fork-technology.html
Weird steering linkage, doesn't look as if it could work.

Dear Rob,
I thought I would post the picture of the Brough linkage I showed you last time I visited. Also some pictures of the discs. The disc brakes appear to be by Beringer and each disc is two close mounted disc with a central pad so that each side of the wheel in effect has two brakes. Link: http://thekneeslider.com/beringer-4-disc-brakes/
My friend Tony and I had quite a good look at the Brough Superior stand when we visited the Motorcycle Show at the NEC last week. We wondered what market the bike was aimed at. We managed to nail the two men on the stand and asked some questions. We asked what the engine was from and they said it was their own. (I think more likely they told “a company” what sort of thing they wanted and got a few built, who knows?) They said they were only going to produce 2 or 300. They said the price was £55,000 each! How many had they sold? One said 5 and his mate corrected with 3 definite and 2 more ... maybe.
At that sort of price I would think that they might sell a few to people with money who want something a bit exclusive or maybe a collector or two. If you are spending that kind of money most collectors would be looking at buying a genuine classic rather than something that just has a great name on the tank. Not wanting to sound too cynical as it may well be interesting to ride but can’t think that their projected sales figures are realistic.

 

[davidd]

When riding my Hinckley Triumph I noticed that I hardly use the rear brake as opposed to riding my brothers Comet.
The rear brakes on his Comet are a delight and I have to use them when braking hard as the front brakes perform period 50's style.
I wonder if many of the problems occur with riders using a lot of modern bikes and mainly using the front brake only.
By applying the rear brake first the front of the bike will dive a little and if I understood the thread till now rightly this will stop the fork from locking up.
I know this sounds like treating the symptoms rather than the source of the problem but it could be an explanation why some riders using their Vincent for decades never experienced the wobble and others have.
Just my thoughts. I am looking forward to changing my stem in the future never the less.
Bernd.

Yes, as Bernd says, using the rear brake allows the the wheelbase to change, which in turn allows the Girdraulic to move up and down. This was mentioned as a mitigating factor in the original article I wrote for MPH. Although a possible solution, I thought curing the problem was a better one. Sometimes using the rear brake is not possible or advised and it is difficult to hit the rear brake just enough to allow the front end to move without affecting the grip of the rear tire.

My crash on the track happened after I lost the adjustment in the rear brake. I did not think twice about not using the rear brake for the last lap, but I would have if I had known the bike would crash.

David

 

[vibrac]

looking at that "Brough" it looks like another rehash of the Hossak (said he with a GS1100)

 

[greg brillus]

If you look at the black wishbones in the picture vibrac posted above and pointed those down at the front.......This is very similar to the action of the Girdraulic's.