FF: Forks New Coilover for Girdraulics

hadronuk

Well Known and Active Forum User
VOC Member
I have been talking to a suspension specialist (not AVO) about the possibility of their making a coilover unit that will fit Girdraulics in place of the original damper.
They think they can do it and have asked for more detailed information about available space etc.
But before we go any further, I would greatly appreciate some feedback so I can see if there is some demand.
Two main questions:
  • Would you be interested in buying such a unit?
  • What benefits, specifically, do you think a coilover would give?
I would particularly appreciate comments by racers who have experience of using Girdraulics with a coilover.
Am I right in thinking the Thornton/Works Performance rear coilover fitted the front if a shorter spring was used?

Also, if there is already a supplier, I really need to know!
 

ray vinmad

VOC Drawings Manager
VOC Member
I have been talking to a suspension specialist (not AVO) about the possibility of their making a coilover unit that will fit Girdraulics in place of the original damper.
They think they can do it and have asked for more detailed information about available space etc.
But before we go any further, I would greatly appreciate some feedback so I can see if there is some demand.
Two main questions:
  • Would you be interested in buying such a unit?
  • What benefits, specifically, do you think a coilover would give?
I would particularly appreciate comments by racers who have experience of using Girdraulics with a coilover.
Am I right in thinking the Thornton/Works Performance rear coilover fitted the front if a shorter spring was used?

Also, if there is already a supplier, I really need to know!

Was the lug on the front of the Head Clip designed with the thought of continuously supporting the weight of the machine after 60 years use?
 

vibrac

Well Known and Active Forum User
VOC Member
the one on my Brampton Alphabet twin copes but at the top it retains the tapered hole fixing and at the bottom the spring anchor is reinforced with plates from the head lamp lug
Of course the handling on Bramptons was good before I fitted which is why I took the Girdralics off a long time ago (so long that I paid £100 for the girders:cool:) Now with this unit the front has even better handling.
1542124679463.png
 

hadronuk

Well Known and Active Forum User
VOC Member
Was the lug on the front of the Head Clip designed with the thought of continuously supporting the weight of the machine after 60 years use?
Good point. But it should have been designed bearing in mind that it could be subject to some substantial shock loads when the damper bottoms out. And the original damper bottomed out much harder than a modern damper with a rubber bump stop.
 

highbury731

Well Known and Active Forum User
VOC Member
In principle, I like the idea of a front coil-over, to go with a rear one.... Gets rid of wearing parts and eliminates a source of stiction.
Where to AVO stand wrt front coil-over? Is a different supplier needed?
Paul
 

hadronuk

Well Known and Active Forum User
VOC Member
Because of tight clearance where the damper passes through the top link, the coilover has to be "upside down" to put the spring at the bottom. This cannot be done with the type of damper the AVO Vincent range is based on.
 

davidd

Well Known and Active Forum User
VOC Member
  • Would you be interested in buying such a unit?
  • What benefits, specifically, do you think a coilover would give?
Rob,

I think the front coil over is an excellent way to go. I would not be in the market as I purchased Works Performance units for any future needs.

For racers, there is an obvious improvement in weight reduction and simplicity. You get rid of a lot of parts.

The front coil overs seem to deliver a better ride. Carlteton Palmer has done a comparison and he far prefers the coil over to the twin springs. I suspect this is due to the different motion ratio of the "A" arm type suspension that the bottom link provides as opposed to the spring box attachments, but I do not have any number comparisons.

I have determined that the FF1 is strong enough for racing. I don't know about street use. I had someone competent do the math and he was OK with it. He asked if it had been done before and I replied it had. John Renwick used this mod on several of his racers successfully. I always buy a new FF1 because the racer bits I start with are always short on parts. I feel it is good insurance. The FF1 could be made out of 7075 or even steel.

The Works Performance damper works well for the front coil over because it is upside down.
500 03.GIF

Patrick uses them front and rear and I have not talked to him about his set up, but it looks similar to mine. The fork is at full extension and it clears the top link.
DSCN2421.jpg

Our own Peter Barker was kind enough to thread this for me when he was last visiting. This was 6"to the top of the thread from the lower perch, if I remember correctly. I prefer using a short spring, but I was unable to get exactly what I wanted, so I settled for the 6.8" spring, 120 lbs., inside diameter 1.75", 0.262 wire diameter, 8.3 coils, 4.63" total deflection. I had to compress it to 6" to install the spring. I would consider an additional inch of thread, or threading to the top, which is more convenient.
DSCN2454.jpg

The photos shows the fork at full droop and there is plenty of clearance. If I were making springs I would make 6" long springs for this use mostly because a longer than 6" spring does not yield any benefit. The top spring perch on this is a short one. The short perches need a lock ring. Works shifted to the long top perch, which does not need a lock. It is also much easier to install a longer spring with the longer perch, because you can start the long perch on the body thread before it hits the spring.
DSCN2424.jpg

I have not tested the 120 lbs. springs so I can't give any information on them. Carleton runs 150 lbs. on his open D Shadow, but he says it at 150 it is a solo bike and cannot handle 2 up well. Works made a 100 lbs. spring that was 5.8" long.

David
 

hadronuk

Well Known and Active Forum User
VOC Member
For racers, there is an obvious improvement in weight reduction and simplicity. You get rid of a lot of parts.
The front coil overs seem to deliver a better ride. Carlteton Palmer has done a comparison and he far prefers the coil over to the twin springs. I suspect this is due to the different motion ratio of the "A" arm type suspension that the bottom link provides as opposed to the spring box attachments, but I do not have any number comparisons. David
David, thanks very much for your very useful and detailed reply. From studying Girdraulics, I thought the coilover might give less friction and more linear springing that made better use of the available travel.
But feedback from those that have actually tried it beats all theory!
Rob
 

timetraveller

Well Known and Active Forum User
VOC Member
Just be careful with trying to use all the travel. It will depend upon what that means but as recently as yesterday the solution to a problem with travel on the JE steering heads has become clear. One of our members is just fitting his kit and is having trouble with the mudguard hitting the front exhaust pipe nut. This was a problem that John Emmanuel warned me about early on as he had that problem. What became clear yesterday is that if one tries to use more that about three inches of total movement then either the bottom link is too far down at the front and/or too far up on full compression with the collision between exhaust nut and the top link very near to the handlebars. I, only now, understand why John was having problems while almost no one else has had the same problem. John had a special front damper and my guess is that it allowed more travel than the AVO. The member with the problem is using a damper with lots of travel and no bump stop and my guess is that changing that will solve his problem.
 
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