FF: Forks Modified Steering Stem

[timetraveller]

Remember that I have 30 lbs/inch springs made and in stock. The 36s, 33s,
and 30s are all supplied to be fitted with 3" of pre-load and this can be reduced by reducing the length of the spring as Greg has done. The 3" of pre-load was a figure arrived at to give the correct lower link angle with typical weights of bikes and riders. If weaker springs are required then there is no problem getting them made but there has to be a compromise between weak springs and the correct ride height. Feedback is required from several people to arrive at an acceptable compromise. The springs only cost £30 a pair so it is not too expensive to experiment. The stiffer AVO dampers were required with a heavy rider on a twin with the Greg mod. If they are not required on a single with a normal weight or light rider then, if you have bought one of the stiffer ones, AVO will modify it and if not then perhaps the standard AVO will suit you. Most recent feedback from the Tilleys suggest for touring on their twin, two up, the stiffer AVO damper together with Greg's mod and 36 lbs/inch springs is working well.

 

[vibrac]

Greg that description of your fork action sounds uncanilly like mine did.Was the resultant steering a little heavy too?
I took the AVO damper to founders Day and the consensus was at the lowest setting it was stiff but probably the same as the original koni
I have shelved the whole thing untill the autumn when I have time to rebuild both front end and the engine which has contributed to my lack of testing
i did try some sort of static test with a spring balance earlier and got 28 & 14 lbs respectively for a steady movement I also put the AVO and a old rear koni coupled in line and a pull or push resulted in both compressing or extending together indicating to me neither were much different at those speeds

 

[greg brillus]

Well I took the bike for a good blast today, and the front end felt no better if not worse. So I removed the Icon shocker, pushed up and down on the bars again with no shock absorber and the forks feel great. So I have reinstalled the AVO and just leave it at that, as I think taking more off the springs is definitely not necessary. With the lighter weight of the bike verses a twin, it seems as though it is more sensitive to the restriction of heavy damping............I have an original Armstrong which is much lighter in its action on the rebound, so I might even try that as an experiment. This bike has enough power that the Conway's Honda clutch can barely hold the torque even after I shimmed up the springs...........Does anyone know if stronger ones are available.........?

 

[Bill Thomas]

If you want a light shocker, You could always use the old type standard one !, Not sure they do much, But I put one on my Comet. Cheers Bill.

 

[timetraveller]

I've just had an email from Chris and Tracy Tilley with a photograph of their bike as it was loaded up for their trip to the French Rally. The interest for this thread on the forum is that before their trip Chris had found the front end too stiff. He has the Greg mod to the lower link, a stiffer than standard AVO damper and I had provided 45 lbs/inch springs. Chris changed the 45 lbs/inch springs to 36 lbs/inch spring before the trip and found the change absolutely perfect for the whole of their trip. I also provided one of my new hydraulic steering dampers, designed to fit the new steering heads. They were impressed by the performance of the front end so it seems as though we are homing in on the best combination of springs, dampers etc. to be used by most twin riders. The photo is below.

The photo was provided by Chris and Tracy Tilley. They covered 1992 miles and found that the hydraulic steering damper worked well on its softest setting.

 

[Chris Launders]

Hi Norman
Did they try it before loading up, if not one possible reason for the softer springs being better is there is a lot of weight BEHIND the back axle, this is acting as a counter balance taking weight off the front, I would think if they could weigh the front with and without the load it would surprise you.
Chris.

 

[timetraveller]

That is a very good point Chris. Only the Tilleys can tell whether they tried it out one up beforehand. I do know that before they left they had found the 45 lbs/inch springs too hard but I do not know whether that was two up with no luggage or Chris on his own.
If it turns out that to get the best out of this system one needs to have adjustable springs at the front then anyone who has the fitting instructions will find the design for an adjusting system for the front towards the end of the instruction. It would not be too difficult or expensive to make up this system but so far no one has expressed interest.

 

[greg brillus]

The Comet I have here, I have been able to try several different spring and shock absorber combinations. This is with the bearing mod to the lower link........With a pair of 33 lb springs, with one inch cut off so it is not topped out and the new AVO damper supplied by the owner, I found the front end very stiff and only move up and down over heavy bumps, I swapped back to the Icon it had before and this was really no better. I then put one of the original Armstrong's that was on my Rapide, and the front was much more alive, but on a downhill run and hit the front brakes quite hard I could get the front end to bottom out quite easily. This is without chopping the spring cases, I have not done that to any bikes yet, but this one might need it. I then removed the left spring and replaced with a 45 Lb spring again with one inch removed. This was much better, but I could still get it to bottom on heavy braking..........Yesterday I removed the Armstrong and replaced with a new Thornton shock and this is probably the best so far, but again I can still get it to bottom out if I try. This to me means that it really needs the heavier springs both sides............To me it appears that a stiff shock absorber is "Masking" the springs.......I would say you need heavier springs with less preload, and a shock absorber with far less damping. the easiest way I proved this, was you remove the front shock absorber all together and push up and down on the bars to see how weak/stiff the front end is resting on the springs only. This not hard to do and it proves how freely the front moves up and down without being inhibited by the damping of the shock absorber. Remember it is not the job of the shock absorber to arrest the weight of the bike, that is the job of the springs, the shocker just removes the oscillation's of the forks. I feel the AVO is way too stiff, this makes the front end feel like the springs are stronger than they actually are. With this bike I will probably end up with a pair of 45 Lb springs and try to work out which shocker will suit without either being too stiff, or too soft. But a softer shock gives a much softer ride and allows the forks to work far more freely. Most of the conversions I have done have been on the heavier twins, and this is probably the first time since the very first Comet I did that I have been able to experiment so much. That first Comet probably had springs around the low 40 lb range, with an original Koni shocker on its weakest setting. The owner feels the shocker could be a bit softer...............This almost confirms my findings.............. This should raise a few eye brows..................

 

[timetraveller]

Greg writes that he has not shortened any spring boxes. I urge anyone who has this conversion to shorten their spring boxes, one inch off the bottom of the outer and one inch off the top of the inner. While helping with a racing twin with this conversion, and in conversation with others, I found that you need to do this if you want the full three inches of movement. All this feedback might be confusing at the moment but in the end it will help us all to get the best out of the system.

 

[vibrac]

As I said earlier I think gregs experience with a comet matched my limited testing I did cut that inch off the boxes and finished at 30 lbs and a strong feeling of over damping I shall now await further developments before dragging the comet out of the naughty corner in the autumn
My back up attempt is my twin with a coil over Brampton and a coil over rear let's hope I can get it started for the rally