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Rapide front brakes

macvette

Well Known and Active Website User
VOC Member
Hi again
Surprised to hear that there is some dive on people's Vincent forks - mine have never dipped appreciably on braking and I was always led to believe after 60+ years of ownership, that this was their greatest merit.
Perhaps it is because my brakes have never worked properly and the bike has only been used as a tourer for the last 100,000 miles or so!!
Matty
My open D was the same until I installed the steering stem mod which stops the front suspension locking under braking. I can now bounce the front of the bike with the front brake applied. This was not possible before and significantly improved braking particularly downhill.
 

davidd

Well Known and Active Website User
VOC Member
Surprised to hear that there is some dive on people's Vincent forks - mine have never dipped appreciably on braking and I was always led to believe after 60+ years of ownership, that this was their greatest merit.
Matty,

It turns out that it is more likely that your Girdraulics do not dip during braking because the fork seizes as you squeeze the brake lever. The new JE steering stem will allow the fork to dip because the new axle path does not cause the fork to seize. This is the same problem that occurs during the brake test video that causes the tire to squeal. As the brake is applied the fork seizes and eventually causes the tire to slip, which causes the squeal. Squealing tires generally indicate a reduction in tire grip or poor traction, not superior traction.

Many modern riders prefer the dip as they learned to ride with telescopic forks.

I suppose the tire in the video is underinflated to give a large contact patch. The manufacturer determines the pressure at which the tire is called "flat." The manufactures of large truck tires tend to choose 10% as the number. A tire with a recommended pressure of 100 lbs. is considered flat at 90 lbs. and will not be warrantied.

I still think it is a good thing to know what brake lining material you are using. Because Safetek is one of the largest sellers of ScanPac linings, I would guess you are using GGW (assuming the linings are green). I also think that these would work on steel or cast because the linings use aluminum oxide, which works well on both materials.

David
 

timetraveller

Well Known and Active Website User
VOC Member
Without setting up a test rig on which one can measure trail versus fork movement/spring compression it is quite difficult to appreciate what is happening at the front end under braking. Many years ago I used to try racing and even braking heavily at the end of the long straight at Silverstone I had never realised what was happening. What really brought it home to me was borrowing Dick Sherwin's Knight just after it had had a disc brakes fitted to the front wheel. I went for a five mile ride around the roads where Dick lives and the brakes were dramatically stronger than my own 7" drum brakes, with which I am normally satisfied. Applying the front brake caused the whole of the 'dashboard' to rise up in the air and 'look at me'. My guess is that it came up about 3". That meant that the front wheel was dropping about that amount under braking. If you can't borrow an enclosed 'D' with a disc brake try and find a friend with such a bike who will take you for a pillion ride and keep a good look out over their shoulder.
 

Glenliman

Well Known and Active Website User
VOC Member
Matty,

It turns out that it is more likely that your Girdraulics do not dip during braking because the fork seizes as you squeeze the brake lever. The new JE steering stem will allow the fork to dip because the new axle path does not cause the fork to seize. This is the same problem that occurs during the brake test video that causes the tire to squeal. As the brake is applied the fork seizes and eventually causes the tire to slip, which causes the squeal. Squealing tires generally indicate a reduction in tire grip or poor traction, not superior traction.

Many modern riders prefer the dip as they learned to ride with telescopic forks.

I suppose the tire in the video is underinflated to give a large contact patch. The manufacturer determines the pressure at which the tire is called "flat." The manufactures of large truck tires tend to choose 10% as the number. A tire with a recommended pressure of 100 lbs. is considered flat at 90 lbs. and will not be warrantied.

I still think it is a good thing to know what brake lining material you are using. Because Safetek is one of the largest sellers of ScanPac linings, I would guess you are using GGW (assuming the linings are green). I also think that these would work on steel or cast because the linings use aluminum oxide, which works well on both materials.

David

The tire squeal in the video is from the rear tire. I've learned to not pull quite so hard on the front brake as to lock the front tire.
It would also be best not to lock the back wheel , but I find that difficult to do in hard braking. As the weight comes off it tends to lock, so the rear just slides along for the last bit.
My wife and I were on this bike on a 70 mph highway some years ago when a pickup truck pulled out from a hidden driveway. We came around a corner and there was the truck rolling across our line of travel. As she pulled onto the road, the driver saw us and did the worst possible thing. She panicked and stopped, completely blocking our lane.
There was oncoming traffic so the only thing to do was apply the brakes hard. We went from 70mph to zero in a very short amount of space. We came to a full stop just a few feet from the door of the pickup truck.
The braking forces were enough that I ended up sitting on top of the fuel tank.
You can ride for years and never really need much braking and then one day events come together such that you need everything working.
On the dive/no dive topic, it's interesting that the latest greatest front forks, the Showa big piston used on Thruxton R, late model GSXR and other bikes with names that end in R, has an anti dive feature built in. It seems to make cornering at speed a lot easier than with the previous generation sportbike front end, that is anything built before 2014. Maybe I should say anything built between 1955 and 2014 :)


Glen
 
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oexing

Well Known and Active Website User
VOC Member
They tried antidive on teles from the 80ies but reportedly these were not overly effective. So big question, do the new types really work as advertised ??

Vic
 

timetraveller

Well Known and Active Website User
VOC Member
I'm not sure that the girdraulics can be described as 'anti dive'. My understanding is that the idea was that for a lot of riding the movement of the front wheel was essentially vertical and thus the wheel base stayed constant. I am not sure why this was thought to be a good idea. The problem arises when one looks at the whole of the front wheel travel path. When the wheel is at its lowest position it moves backwards to give about five inches of trail. It then moves forwards and upwards until it gets to that part of its track where the movement is essentially vertical. Further than that, when the wheel is at its highest point it is then moving forwards again. Look at the angle of the lower link on most bikes and it is very low at the front when compared with the rear i.e. the eccentrics. What this means is that when a bump is hit and the wheel tries to move upwards there is a lot of force in the lower link trying to force the link backwards through the eccentric. The combination of a horizontal lower link and bearings of some sort to replace the Oilite bushes in the eccentrics seems to be what frees up the front end dramatically and allows it to respond rapidly to small bumps in the road surface.
 
Last edited:

Vincent Brake

Well Known and Active Website User
VOC Member
Its indeed a luxury ride Norman.

Maybe a bit to much.
In the repositioning of the rear bottom link.

But I and the ladies like it a lot.

Staying on topic, dear mr moderator;
If i hit the barkes really hard, Despite tthe diving it still folows the tarmac.

And thats not in the hard way.....

Cheers
 

macvette

Well Known and Active Website User
VOC Member
My open D was the same until I installed the steering stem mod which stops the front suspension locking under braking. I can now bounce the front of the bike with the front brake applied. This was not possible before and significantly improved braking particularly downhill.
Forgot to say that before I did the mod my bikes front end was compliant but stiffened noticeably under braking
 

davidd

Well Known and Active Website User
VOC Member
The tire squeal in the video is from the rear tire. I've learned to not pull quite so hard on the front brake as to lock the front tire.
That would certainly explain things. The rear is lifting slightly with the weight transfer forward. That is my mistake. However, owners have often claimed that they can make the front wheel squeal, which I maintain is not a good thing. The squealing means you are losing traction. it is not usual to hear GP racers squealing their tires through corners even when they are near the limits of traction.

Once, while talking with Kevin Cameron, about the Girdraulic, he mentioned the "anti-dive" braking interest in the 1970s. I asked him why it all disappeared. He said, manufacturers found that they could simply lower the center of gravity on the racers and the problems were solved.

MacVette's comments all seem to be exactly what I would expect with his mods; suspension movement while braking and improved braking.

David
 

vibrac

Well Known and Active Website User
VOC Member
On the dive/no dive topic, it's interesting that the latest greatest front forks, the Showa big piston used on Thruxton R, late model GSXR and other bikes with names that end in R, has an anti dive feature built in. It seems to make cornering at speed a lot easier than with the previous generation sportbike front end, that is anything built before 2014. Maybe I should say anything built between 1955 and 2014 :)
Glen
I rode the Yamaha GTS 1000 hub center steerer in the 1990,s "Aint no front end dip" on that magic machine
a bike well ahead of its time and like rear end springing in HRD /Vincents time the motorcycle public was (and is) far too conservative. I wish I could have afforded one.
I am sure its time will come.
 

Robert Watson

Well Known and Active Website User
VOC Member
I had the use of a GTS 1000 Yamaha and here is my take on it. (Yes Bruce, it was Tony's demo one)

The non adjustable windscreen directed the air flow directly at the bottom of my helmet and made the noise intolerable.

My 1953 John Deere tractor with straight cut gears shifted smoother than that thing. After all those years why could they not make a gearbox that even shifted and nicely as a stock Vincent twin?

I never did get far on it as the two above mentioned issues distracted me so much the handling became a moot point.
 

vibrac

Well Known and Active Website User
VOC Member
Mine was a standard bike demonstrator from flitwick motors in Bedfordshire and they went on to race one at the TT Steve Linsdell said he had never ridden a TT and finished so fresh he and Ollie also had it at Silverstone one track day and it was fast!
 

Tony Cording

Well Known and Active Website User
VOC Member
Ah yes, the Yamaha GTS. Let me first of all tell you the things i liked best about the GTS. First it was a free demo bike for a year. Second, the insurance was paid for, third the gas came free and service was included. Oh yes, if i met with a dealer and we had lunch - it was covered by expenses. What's not to like. However, beyond the personal benefits what did i think of the machine. For those of us who remember there was much magazine chat about how engines were the only focus and suspension was being left behind. The GTS was Yamaha's gambit into new directions, as they had done many times in the past. I am an average rider so could never put the GTS through its paces the way a Robert W. would do, but I could certainly give an evaluation of how I found the bike. My biggest negative was engine heat which was trapped by the fairing sides and baked your legs. Notchy gearbox, yes, windshield did not blow in my face, but my riding posture is different to Robert's. As for the front new wave front suspension the great thing about it was you didn't notice what it was doing so well, there was no discernible feeling of "soaking' up the highway bumps and lumps it was so smooth. I rode from the north of Vancouver Island on the old island highway, notorious for its poor surface and on stopping for breakfast in Nanaimo it was only then it occurred to me that the ride was so plush. So there you have it, the suspension worked, but it was before its time, and given the average rider's [propensity from steering away from out of the ordinary (PCV knew all about this) it is no wonder the GTS was phased out, a significant but minor blip of the motorcycle highway. Take care and stay safe.
 

Matty

Well Known and Active Website User
VOC Member
For those who want to know about and setting up Vincent brakes, in addition to the above there is more and useful information in an excellent article on page 23 of the July 2020 issue of MPH.
Though whatever method is used it becomes obvious once the mechanics are understood
 

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