SP: Spring Boxes (Rear) AVO coil overs..

[greg brillus]

If the rear of your racer was soft, as in bottoming, the fault is too weak a spring........ On my twin racer, I went from a 250 Lb spring to a 300 and that fixed the problem..........When looking at these issues, if the suspension can easily bottom or is too rigid, the spring rate is the first port of call, the damper just controls the spring oscillation in either direction. When going from a standard rear set up to a fully sprung seat the spring rate will need to be increased on account of the extra load imposed on these springs........You are moving your weight forward of the center attachment point on the rear frame.

 

[timetraveller]

You can't really leave the rear of the seat on the original friction damper supports. That system moves the rear of the seat up and down as the suspension moves. The more the movement of the suspension, the more the up and down movement of the rear of the seat. Not a problem for the person on the front, very uncomfortable for the pillion passenger.

 

[Chris Launders]

I fitted an AVO coil over to mine as while I was doing some of the front spring/damper testing for Norman as I got so far but the roughness from the rear end was affecting what I thought the front was doing (Koni damper, Pettiford springs on the rear).
However unless you change to a fully sprung seat this introduces another problem. The back wheel and therefore the back of the seat are a lot more active due to the improved damper and springing, the change to a fully sprung seat is of enormous benefit here.
As I had made my own longer seat with much stronger frame all I had to do was make two struts, if you have a standard seat I recommend fitting an additional strengthener between the front and back mountings somewhere.

 

[Bazlerker]

I always ride solo, so no worries about passenger comfort…I also have petteford springs in the rear.

 

[timetraveller]

In that case you might get away with just a rear AVO damper. Just remember that the springing will not be adjustable.

 

[Martyn Goodwin]

By coincidence I was discussing this yesterday at the John Lumley Pie and Pint meeting of the North Kent section. From my understanding the Spares Company has thought about providing supports but this has not happened yet. It is not a series 'D' style support. As Comet rider above says most people make their own but I do have a design. I don't have ACAD on this PC but I could draw something up tomorrow. I will try to describe what I see as a solution. One can do just as CR describes but the problem then is that a lot of strain is placed on the two supports at the front of the standard seat and occasionally one will see them starting to give way as the seat tries to move backwards. One solution is to weld another piece of tube from the front of the main support forwards where it can be supported either in the sidecar tube or the front of the seat support stud. Vibrac has a very neat version of this on his Comet wherein he has a rose joint at the front of each of the extra forward facing struts, which are only in tension.

What I was trying to describe yesterday is an alternative to this forward tensioning tubes. If one looks at the standard pillion footrest plates there are several holes at the rear end of these. The upper ones are there to support the pillion footrest and the lower ones seem not to be used. Perhaps not all bikes have the lower holes but if they do, or you are prepared to make the holes then there is a ready solution. Imagine a flat piece of steel bar which will bolt to the vertically separated two rear holes. Now weld or braze the support tube which goes up to the rear of the seat to the top of that steel bar. If that steel bar and the weld/braze are strong enough then the support tube for the rear of the seat cannot pivot backwards. Instead any turning force is passed to the pillion footrest plate.
If you do not still have the original pillion footrest plates but instead have a Dave Hills centre stand then the plates are different but the bike we were looking at yesterday had two vertically seperated holes about an inch forwards of the rear or the plates. Those holes could be used but the design of the plate/support tube combination would have to be slightly different.

The attachment shows exactly what happens to the seat when you fit a 'simple' fully suspended seat - IT FAILS!

I also describe how to avoid that problem.

Martyn

 

[stu spalding]

It has been said before but here goes anyway, the rear springs should be removed and the suspension travel checked before deciding on the length of seat stays when going fully sprung. It is surprising how far up the rear wheel travels. Cheers, Stu.

 

[Bill Thomas]

In that case you might get away with just a rear AVO damper. Just remember that the springing will not be adjustable.

Not sure what you mean T.T. ? . The AVO you can just screw the ring up and down for spring pressure,
And you can add Bits of Broom Handle for the front ?, Or cut bits off the front springs ?.
Cheers Bill.

 

[timetraveller]

AVO make, or did make, a rear damper without the spring. These was avaialable before the coil overs and were intended to replace any of the original Vincent, Armstrong or Koni dampers previously used.. It uses a lower tube offset to below the damper body to allow more movement for those using Pettiford spings. This means that if you want to alter the rear springing then the only adjustment is to screw the top and bottom eyebolts in the spring boxes inwards or outwards.

 

[vibrac]

If the rear of your racer was soft, as in bottoming, the fault is too weak a spring........ On my twin racer, I went from a 250 Lb spring to a 300 and that fixed the problem..........When looking at these issues, if the suspension can easily bottom or is too rigid, the spring rate is the first port of call, the damper just controls the spring oscillation in either direction. When going from a standard rear set up to a fully sprung seat the spring rate will need to be increased on account of the extra load imposed on these springs........You are moving your weight forward of the center attachment point on the rear frame.

Yes I forgot we upped the spring as well following AVO recomendation
I walked in and had not got to the desk and the guy looked and said "Vincent"