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Racer Suspension

greg brillus

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Tim, you need to jack the rear of the bike up quite a lot, this will help the bike to "Turn in" on corners which is a great asset. On my twin racer the rear chain looked like it would fall off, but with the rider on it is fine.

(Vibrac asked for a new thread to be started. The first three posts here have been moved from the "Most Original Lightning" thread. BigEd.)
 
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Bill Thomas

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VOC Member
Did you ever work out the trail on your racer Greg ?.
Can't work out which way it would go with Standard forks, If we jacked it up too much,
I have used the long Petteford ? springs , But some people think it makes the Bike Twitchy ?,
Cheers Bill.
 

greg brillus

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Hi there Bill, Yes I probably did, but can't remember, I get a bit slack at writing things down.........I know the rear and front coilover shocks were 270 mm long and the attachment bracket that mounted it to the RFM was an extension as well. It would have added 40 to 50 mm to that again........I know after we fitted 18" rims front and rear I jacked the back up some more. I wanted to do the same at the front but this was too difficult. Anyway Phil who owns it now recons he can out-corner other riders on bikes with Featherbed frames, and this does not surprise me at all. It is still the best Vincent I have ever ridden, power, brakes, handling and even comfort........ I want to basically copy it, but even better for my next twin project........ This will be a road bike, not a racer.... Cheers.......... Greg.
 

vibrac

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VOC Member
I have an AVO shock on the rear and a new steering stem on the front. Clearance under the crankcase without catch tank is 7" on 18" wheels.
I remember the guy who raced in Japan 25 years ago (Reg Bolton. Big Ed) put extensions on his RFM to raise the rear but I would like to see how she steers before effectively steepening the forks.
Now Bob Newby has got a stronger 30mm belt I hope that the primary (we have to look standard) won't grow out for clearance of belt. More on that soon.
 
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vibrac

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VOC Member
As for chain being slack with jacked up suspension I see the belt drive nessitates a smaller rear sprocket range with a mid point around 45 so I am taking the opportunity to go 520 and use a range of Honda sprockets on a carrier ( cheap as chips)'not sure if that would make the slack effect worse
 

Chris Launders

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VOC Member
Be careful jacking the back end up too much on a road bike. I got my twin from a friend partly because he'd had a tank slapper and woken up in hospital, he'd repaired the bike and fitted a hydraulic steering damper.

When I got it and put it on the road it immediately felt strange and the first bump on a roundabout nearly pitched me off, I'd done just over a mile total !!!

I thought it had felt strange when I got on it and it had always looked "hump backed", on checking against a few others I found sidecar springs with the mountings at full stretch lifting the RFM pivot 1.5"and sagging springs in the front dropping that. My friend had never had a Vincent before so was not familiar with how it should have felt.

The previous owner to him had been Chris Williams, renowned sidecar racer and I wonder if he'd set it up for track use. Once I'd fitted "pettiford" springs at the correct length and new fork springs it was back to normal, still not happy with it I fitted one of the first JE steering stems, springs and AVO damper on the front and AVO coil over on the back, bliss.
 

Bill Thomas

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VOC Member
I think it was more the sagging front springs, The early Know thy beast said how bad the trail is when the forks come up too high, And to always use inner springs to stop them coming up too high.
I use D.D./ T.T. front springs, But I have had to pack them out a bit.
The Hydraulic damper is for me a MUST.
 

Chris Launders

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VOC Member
I've just recalled, I had noticed the sagging front springs after the previous owners crash and HE had fitted new "D" springs before I got it so my experience wasn't due to them.
 

vibrac

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VOC Member
Yes we have the JE with steering damper the springs are 30lb (without looking at notes) but when loaded with rider look about right
sfe.jpg
 

BigEd

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VOC Forum Moderator
Yes we have the JE with steering damper the springs are 30lb (without looking at notes) but when loaded with rider look about right
View attachment 32242
Timetraveller's instructions say:

"Then the rider should sit on the bike, or get someone of a similar weight to do that and then check that the front of the lower link is now slightly above the rear of the link."
 

vibrac

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VOC Member
Timetraveller's instructions say:

"Then the rider should sit on the bike, or get someone of a similar weight to do that and then check that the front of the lower link is now slightly above the rear of the link."
And I think thats where it is in photo (you can just see Bens hand he is siting on bike) In use if it settles lower we may need to up the springs ( if not perhaps a broom handle may be called for :D)
 

timetraveller

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VOC Member
Just to clarify this; what I discovered after quite a lot of testing, and I put the graphs on here, is that if the front lower spindle is half an inch below the rear spindle, that is the one through the concentrics, then the wheel will move forwards when the suspension is compressed. That is what JE and DD were trying to avoid. If there is about quarter of an inch, 6 mm, difference in height, then there is an almost vertical movement of the front wheel before is starts to move both upwards and backwards. Provided that the height difference is less than this then the suspension will behave as wished, this is all with the rider seated. Because it is difficult to get this just right on ones own then I always emphasise that the lower spindle should be about horizontal and if there has to be an error then it should be along the lines of the front being very slightly higher than the rear. The higher that it stars off the less potential movement there is but for racing that will not be important. For comfort on the road then the most movement possible will make for a better ride.
The springs provided for Vibrac are the weakest that I have had made as they are hoping to build a light weight bike. If it turns out that the springs are too weak in use then they can either move up from 30 lbs/inch to 33 lbs/inch or alternatively pack the spring slightly. For racing, where one wishes to get the very best from the system some amount of experimenting will be required but with an adjustable AVO damper and the various rates of springs I have available then it should be possible to get the best out of the system that is possible.
 

BigEd

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VOC Forum Moderator
And I think thats where it is in photo (you can just see Bens hand he is siting on bike) In use if it settles lower we may need to up the springs ( if not perhaps a broom handle may be called for :D)
In your photograph, it looks (to me) like the front of the link is below the rear concentric end of the link. If Ben has his weight on the bike wouldn't that suggest the springs are too long or too heavy? (Or Ben is too light. ;) )
 

davidd

Well Known and Active Website User
VOC Member
Jacking up the rear end has always been a trick to get much better cornering out of a Vincent. This was used in the 1960's by Coburn Benson on the Flash. He made spring box bolts that were 3" long and put them on both ends of the rear spring boxes. Later, Reg Bolton did the same thing with his mod:
552 at 39 Bolton Mod.JPG
I suggested this mod to Carleton Palmer. He tried it and never took it off. He got three national championships with it on the bike. I should also mention that we bolted these mods up tight and did not use the small divot for the seat tube, just two triangular plates fully tightened, but otherwise followed Reg's drawing.

I think the 1-1/4" is a very good choice on a racer. I think that is about a 4 degree decrease in the rake, bringing it down to 26 or 27 degrees.

The Horners also used this concept on the Goodwood racer to get better handling. It is relatively easy to do with a coil-over on the rear. Much like the extended rear spring bolts it allows you to reduce the rake. Patrick Godet uses a longer F106/1, as I do also.

Generally, mods on the rear will not create a wobble problem. The primary cause of a wobble is due to a lightening of the front end (of some type). With the stock Girdraulic it is the fork seizing that causes the tire to bounce ever so slightly. This loss of front wheel traction is just enough to disturb the grip and allow a wobble to develop. This does not mean that a crazy set-up on the rear can't contribute or exacerbate a problem.

As for where the spindles reside, I think folks with the JE stem should follow Norman's advice. As for my own stem, which is slightly different, I tell users that the spindle position is not important in terms of the handling. (I think Norm is saying it is important in terms of adjusting the ride.) Both designs get rid of the fork seizing under braking, which doesn't cure the wobble problem, but it does a good job of minimizing it.

I certainly wish that more folks could try the handling of these race bikes. The results are unbelievable as Greg writes. Cam Donald also wrote about the unexpected fantastic handling of the Grey Flash, considering what he had heard about Vincent handling. Both Cam and Dave Roper won their first races on these bikes with close to no practice time. Beau Beaton (Horners' rider) rode Greg's racer and was really impressed with its ability.

David
 

Shane998

Well Known and Active Website User
VOC Member
Jacking up the rear end has always been a trick to get much better cornering out of a Vincent. This was used in the 1960's by Coburn Benson on the Flash. He made spring box bolts that were 3" long and put them on both ends of the rear spring boxes. Later, Reg Bolton did the same thing with his mod:
View attachment 32243
I suggested this mod to Carleton Palmer. He tried it and never took it off. He got three national championships with it on the bike. I should also mention that we bolted these mods up tight and did not use the small divot for the seat tube, just two triangular plates fully tightened, but otherwise followed Reg's drawing.

I think the 1-1/4" is a very good choice on a racer. I think that is about a 4 degree decrease in the rake, bringing it down to 26 or 27 degrees.

The Horners also used this concept on the Goodwood racer to get better handling. It is relatively easy to do with a coil-over on the rear. Much like the extended rear spring bolts it allows you to reduce the rake. Patrick Godet uses a longer F106/1, as I do also.

Generally, mods on the rear will not create a wobble problem. The primary cause of a wobble is due to a lightening of the front end (of some type). With the stock Girdraulic it is the fork seizing that causes the tire to bounce ever so slightly. This loss of front wheel traction is just enough to disturb the grip and allow a wobble to develop. This does not mean that a crazy set-up on the rear can't contribute or exacerbate a problem.

As for where the spindles reside, I think folks with the JE stem should follow Norman's advice. As for my own stem, which is slightly different, I tell users that the spindle position is not important in terms of the handling. (I think Norm is saying it is important in terms of adjusting the ride.) Both designs get rid of the fork seizing under braking, which doesn't cure the wobble problem, but it does a good job of minimizing it.

I certainly wish that more folks could try the handling of these race bikes. The results are unbelievable as Greg writes. Cam Donald also wrote about the unexpected fantastic handling of the Grey Flash, considering what he had heard about Vincent handling. Both Cam and Dave Roper won their first races on these bikes with close to no practice time. Beau Beaton (Horners' rider) rode Greg's racer and was really impressed with its ability.

David
got these with a set of old spring boxes they are about 3 inches long Someone must have also used this mod in Australia
785DDEE4-52A7-42A9-A370-F2446F8F97B0.jpeg
 

vibrac

Well Known and Active Website User
VOC Member
I could not think of Reg Boltons name the other day when I wrote but came across his mod in 25 years on research the only caveat I have is this was not with a JE stem
Anyway we have fitted a JE stem and a coil over and gone from a single to a twin and thats enough variables for now cant change too much at once. Eddie that photo is not so good the front bottom pivot is actually slightly higher than the concentric center and dont forget the whole shebang has not hit a bump or a road yet yet since being built. If its not its a coil cut or a lighter spring
 

Bill Thomas

Well Known and Active Website User
VOC Member
Don't forget the weight of all your riding gear, My leathers were very heavy, Never did bother to weigh them.
And a tank of petrol.
 

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