Just to be clear - My Crash Test Rider is Dave (aka Harry) Hulstone. The intrim springs I played with came from David Dunfey.
Martyn
FF: Forks Modified Steering Stem
- Thread starter greg brillus
- Start date
Martyn
David's theory of using shorter stiffer springs is near relevant to what we are doing here, though in David's case, he was deliberately lowering the front end to avoid the link/danger zone. Whereas in this case, we have overcome the geometry issue, and we have regained any lost travel. So as a benefit to this, we are trying to soften the front as much as is practicable, but not to the point of bottoming easily. I feel too much pre-load in this set up leads to the fork assembly "topping out" but on the other hand if we were to use short springs and pack them up as required to get the ride height correct, then the spring rate is getting unnecessarily high. It is this fine tuning if you like, that will give the correct ride height and keep the spring rate as low as we can, though I agree with David's thoughts that at least with short springs you can pack them up if needed. Because it is not so practical for each user to cut springs down, it is best to arrive at say 3 different spring rates with equal overall lengths that can be interchanged where needed, and I know this is what Norman has been trying to achieve. Of course now also is the issue of who upgrades to the bearing in link mod, verses who leaves their link standard ........This appears to alter things as well. Anyway it appears that Martyn's Comet is on the home straight, and it has given the result I was expecting. I know he will be chomping at the bit to ride again, and I look forward to his feedback given the amount of riding he does. Look at it this way Martyn.........You currently have "The best handling Vincent in Victoria" and that is saying something............
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Martyn has set up his springs the same way I set up mine. I believed that several springs were necessary to accommodate riders of different weights and loads. I also wanted to use as little preload as possible to allow for the adjustment of ride height, adjusted the way Martyn has done by setting the sag at 25%.
The springs are color coded so that they can be used in different combinations:
Red 75 lbs/in
Blue 110 lbs/in
White 130 lbs/in
In combination they can be used to achieve the following spring rates:
Color Springs Front End Rate
Two Reds 75 and 75 lbs/in 150 lbs/in
One Red and One Blue 75 and 110lbs/in 185 lbs/in
One Red and One White 75 and 130 lbs/in 205 lbs/in
Two Blues 110 and 110 lbs/in 220 lbs/in
One Blue and One White 110 and 130 lbs/in 240 lbs/in
Two Whites 130 and 130 lbs/in 260 lbs/in
If the load you are trying to balance is 210 Lbs./in. then the red and white spring would be best at approximately 205 lbs./in (as Martyn chose). Then the preload can be adjusted, which is really a question of how quickly you want the springs to get to the 210 Lbs./in. If you use a lot of preload, and compress the spring box a long way to get the bolt on, you will get to the 210 Lbs./in. immediately and there will be little or no sag. If you use no preload and just slip the bolt in by hand, you will have no preload and the bike will sag quite a bit. But, if it sags too much, you can slip some spacers in the spring boxes until you hit the mark you want (suggested 25%-30%).
Just a note on preload, it can be changed slightly by your choice of parts. If you run eccentrics, the solo position has the least preload and the sidecar position has the most. The concentric position puts it right in the middle. Again, it doesn't change the rate of the spring, but how quickly you get to the higher poundage.
I was interested to hear Martyn and Dave's experience on full compression. When I originally selected the rates for the springs I used the original Vincent numbers for full compression. I was hoping that maybe these numbers were too high and it could be lowered, but the few reports we have seem to confirm that they need to be high.
I also designed the red springs just for my racer and the Comet. They worked perfectly on the racer, but they do not provide that high full bump number. On the track it was not an issue. As mentioned, I had plenty of surface problems but,they did not cause bottoming out (probably due to the lightness of the bike). In the original Comet Suspension thread it was reported that the reds were too soft for use as a pair on the Comet. I revised the instructions that were written for the springs, accordingly. The red is probably best used as Martyn did in this situation, too soften a heavier spring when paired.
The more testing that is done the bigger the data base will be.
David
The springs are color coded so that they can be used in different combinations:
Red 75 lbs/in
Blue 110 lbs/in
White 130 lbs/in
In combination they can be used to achieve the following spring rates:
Color Springs Front End Rate
Two Reds 75 and 75 lbs/in 150 lbs/in
One Red and One Blue 75 and 110lbs/in 185 lbs/in
One Red and One White 75 and 130 lbs/in 205 lbs/in
Two Blues 110 and 110 lbs/in 220 lbs/in
One Blue and One White 110 and 130 lbs/in 240 lbs/in
Two Whites 130 and 130 lbs/in 260 lbs/in
If the load you are trying to balance is 210 Lbs./in. then the red and white spring would be best at approximately 205 lbs./in (as Martyn chose). Then the preload can be adjusted, which is really a question of how quickly you want the springs to get to the 210 Lbs./in. If you use a lot of preload, and compress the spring box a long way to get the bolt on, you will get to the 210 Lbs./in. immediately and there will be little or no sag. If you use no preload and just slip the bolt in by hand, you will have no preload and the bike will sag quite a bit. But, if it sags too much, you can slip some spacers in the spring boxes until you hit the mark you want (suggested 25%-30%).
Just a note on preload, it can be changed slightly by your choice of parts. If you run eccentrics, the solo position has the least preload and the sidecar position has the most. The concentric position puts it right in the middle. Again, it doesn't change the rate of the spring, but how quickly you get to the higher poundage.
I was interested to hear Martyn and Dave's experience on full compression. When I originally selected the rates for the springs I used the original Vincent numbers for full compression. I was hoping that maybe these numbers were too high and it could be lowered, but the few reports we have seem to confirm that they need to be high.
I also designed the red springs just for my racer and the Comet. They worked perfectly on the racer, but they do not provide that high full bump number. On the track it was not an issue. As mentioned, I had plenty of surface problems but,they did not cause bottoming out (probably due to the lightness of the bike). In the original Comet Suspension thread it was reported that the reds were too soft for use as a pair on the Comet. I revised the instructions that were written for the springs, accordingly. The red is probably best used as Martyn did in this situation, too soften a heavier spring when paired.
The more testing that is done the bigger the data base will be.
David
Having had time to consider and re-examine the installation of the modified head stem on my bike I have a few post installation recommendations.
The main effect of the mod is to change the path that the front axle moves through as the suspension compresses or extends, thus reducing the likely hood of a tank slapper. Unmodified, as the suspension moves upwards the wheel moves outwards - away from the motor, the modification reverses this in that as the wheel/axle move upwards it now also moves backwards, towards the motor. The modification also changes the relative position of the axle and the front links so in any given state (of loading) they are higher than with the standard setup.
With this in mind there appears to be some caveats that need to be carefully checked before you can call the modification complete - it’s a tad more involved than simply replacing the head stem.
With the spring boxes removed AND the front wheel off the ground you need to make sure that there is at least a 3/4 inch clearance between the rear of the mudguard/mudguard stay and the front of the motor. At this stage also move the forks from full left lock to full right lock checking to ensure that NO cables ir wires are catching anywhere or are being stretched or are at risk of being squashed.
Now slowly lower the bike onto its front wheel (again without the spring boxes in place) and check again for a minimum ¾ inch clearance between the front guard and the motor throughout the full travel of the suspension. Again, do the cable check.
If you have less than ¾” inch clearance at any point of the front suspension travel between the mudguard/mudguard stays and the motor, you will need to reduce the radius of your front mudguard, shorten the mudguard stays to suit and also make up replacement mudguard hangers (FF68) to match the reduced radius mudguard.
While the bike is sitting on its front wheel without the spring boxes and with the front shock absorber fully compressed, measure the distance between the spring box mounting points - that’s the bolt in the centre of the concentric bush in the lower link and the bolt hole at the foot of the fork blade. Now take a pair of the spring boxes without any springs in them and push them together and measure the distance between the mounting points on the spring boxes themselves. This second measurement needs to be at least a 1/2" shorter that the distance between the mounting points on the bike. If this is NOT the case then there is a risk that the spring boxes themselves may 'bottom out' when riding SO you will need to shorten both your inner and outer spring boxes, by as much as need to give the minimum 1/2" clearance.
If you attend to these matters, the implementation of the improved head stem should proceed without any suprises.
Martyn
The main effect of the mod is to change the path that the front axle moves through as the suspension compresses or extends, thus reducing the likely hood of a tank slapper. Unmodified, as the suspension moves upwards the wheel moves outwards - away from the motor, the modification reverses this in that as the wheel/axle move upwards it now also moves backwards, towards the motor. The modification also changes the relative position of the axle and the front links so in any given state (of loading) they are higher than with the standard setup.
With this in mind there appears to be some caveats that need to be carefully checked before you can call the modification complete - it’s a tad more involved than simply replacing the head stem.
With the spring boxes removed AND the front wheel off the ground you need to make sure that there is at least a 3/4 inch clearance between the rear of the mudguard/mudguard stay and the front of the motor. At this stage also move the forks from full left lock to full right lock checking to ensure that NO cables ir wires are catching anywhere or are being stretched or are at risk of being squashed.
Now slowly lower the bike onto its front wheel (again without the spring boxes in place) and check again for a minimum ¾ inch clearance between the front guard and the motor throughout the full travel of the suspension. Again, do the cable check.
If you have less than ¾” inch clearance at any point of the front suspension travel between the mudguard/mudguard stays and the motor, you will need to reduce the radius of your front mudguard, shorten the mudguard stays to suit and also make up replacement mudguard hangers (FF68) to match the reduced radius mudguard.
While the bike is sitting on its front wheel without the spring boxes and with the front shock absorber fully compressed, measure the distance between the spring box mounting points - that’s the bolt in the centre of the concentric bush in the lower link and the bolt hole at the foot of the fork blade. Now take a pair of the spring boxes without any springs in them and push them together and measure the distance between the mounting points on the spring boxes themselves. This second measurement needs to be at least a 1/2" shorter that the distance between the mounting points on the bike. If this is NOT the case then there is a risk that the spring boxes themselves may 'bottom out' when riding SO you will need to shorten both your inner and outer spring boxes, by as much as need to give the minimum 1/2" clearance.
If you attend to these matters, the implementation of the improved head stem should proceed without any suprises.
Martyn
Finally a new post in this thread.
I'm eager to hear new testing results. I guess you have also been stopped by solid ice on the road.
Finally after weeks below 0C it started thawning and soon it will be warm enough to go back to the garage and play.
Good luck with testing
Bernd
I'm eager to hear new testing results. I guess you have also been stopped by solid ice on the road.
Finally after weeks below 0C it started thawning and soon it will be warm enough to go back to the garage and play.
Good luck with testing
Bernd
Thank you to MartynG for his comment on precautions to be taken while fitting the new steering heads. All his points are covered in the 'Fitting Instructions' which are supplied with each new steering head. The point about shortening the spring boxes is on page 2 and the point about checking clearances is in red at the bottom of page 4 and repeated at the bottom of page 5. A pdf version of these instructions was attached to an earlier posting. If anyone wants a copy in either WORD or pdf format email me at enw07@btinternet.com.
I should also point out here that Greg has offered to make a batch of plates to fix to the base of the new steering heads to allow the interfacing of a hydraulic steering damper. These are based upon my design, but suitably tweaked by Greg, based upon his experience fitting this mod to various of his customers bikes. They are available to allow the damper to be positioned on either the left of right hand side of the bike and I am prepared to order a batch from Greg to be supplied with the steering heads over here in Europe if you wish. I do not know the price yet but I do not imagine that it will be a 'rip off'. Contact me on the above email if interested and I can work out a price depending upon how many are ordered, shipping costs and whether import duty is charged etc.
Feedback on the use of both the 33 lbs/inch springs and 36 lbs/inch springs on Comets is still pending.
Thank you
I should also point out here that Greg has offered to make a batch of plates to fix to the base of the new steering heads to allow the interfacing of a hydraulic steering damper. These are based upon my design, but suitably tweaked by Greg, based upon his experience fitting this mod to various of his customers bikes. They are available to allow the damper to be positioned on either the left of right hand side of the bike and I am prepared to order a batch from Greg to be supplied with the steering heads over here in Europe if you wish. I do not know the price yet but I do not imagine that it will be a 'rip off'. Contact me on the above email if interested and I can work out a price depending upon how many are ordered, shipping costs and whether import duty is charged etc.
Feedback on the use of both the 33 lbs/inch springs and 36 lbs/inch springs on Comets is still pending.
Thank you
I have 2 Shadows very nearly back on the road both with the new stem kits, both using the Kawasaki steering dampers, one has an original Koni up front and the other has an original Vincent shocker, but it is one of the new ones not a refirbed original, both had the bearing mod to the lower link. This gives me a total of 6 bikes with this mod carried out. My good friend with the Comet is still away, so I can't do any experimenting with springs till he returns, though Martyn will be out and about on his Comet very soon, and I know we will get some good feedback from him in due course. I feel that the current springs in my Rapide are probably fine for a light rider and riding solo all the time, as riding two up, I could feel it bottom on a particular sharp dip, that is going across a causeway and then sharply up on the exit, which is expecting a lot from any suspension. It is this kind of testing that will dictate a more accurate outcome, and I am very close to a final result. To answer Normans question about the alloy damper brackets, they work out to be about $60 dollars Australian, which is about 25 pounds give or take, and they can be made to suit left or right mounted dampers, they bolt straight on with no further mods. The cylinder head bracket is something I make up from a piece of 50 x 50 x 3 mm thick angle iron, cut and shaped to nicely fit the two left cylinder head bracket studs. It all works very well, and with a couple of extra details, it can be installed to clear a crash bar if one is in use. Hope this is what you were asking Bruce. Cheers...............Greg.
Hi Bruce, yes, the base of all the steering heads are supplied with three M6 threaded holes and I provide two outline designs for plates to allow the fitting of Kawasaki type dampers. The simplest of these designs can be made with hand tools. The larger and more complicated one requires the use of a milling machine.. Greg has been getting the more complicated one made and has kindly offered to get a batch made. He has had them made in both left hand and right hand models. if you wish I can send you the instructions which contain designs for both types of plate.