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T: Fuel Tank New Project

erik

Well Known and Active Website User
VOC Member
I think on a girder fork it is better the connecting links are horizontally or pointing upward.Facing down makes the good effect of the mod. steering stem gone.Regards Erik
 

timetraveller

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VOC Member
It is the combined length of the eyebolts and damper which control the total movement and the range of movement. It is important than when you sit on the bike with your feet off the ground and the bike on its wheels that the lower link is either horizontal or a few mm low at the front. It does not matter if the front is low with the bike only but ideally it should move down at the front when you sit on the bike by about 12 mm. If it does not do that then probably the springs are too strong but it always pays to use the bike a little to make sure everything is working properly before you change anything. If you want the full range of movement then you also should cut about 25 mm off the top of the inner spring box and the bottom of the outer spring box.
The modification does two things. The geometry change, which is entirely due to the work of John Emmanuel, will alter what happens when you brake and gives a safer ride. The other modifications are due to me, with testing feedback from Chris Launders, and are intended to give a more comfortable ride with more movement. The development work of Hadronuk with AVO gave the damping that is now available. The rider can tune the system to give them the most satisfaction. For example, Robin Stafford came up with a further useful dodge. He needed the 33 lbs/inch springs for the combination of his weight and the weight of his twin. However, over the most sever potholes he found that the front end could bottom out. He tried putting the original Vincent inner springs inside the new springs but cut down in length so that they did not come into play until there had been about one and a half inches (37 mm) of movement. This now gives him the advantage of a very compliant movement over small bumps in the road but prevents the bottoming out over severe holes and/or heavy braking.
 

erik

Well Known and Active Website User
VOC Member
I understand.I have the mod. steer. stem on my twin and there I cutted the spring boxes 30mm ,so i will do this again.Regards Erik
 

greg brillus

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VOC Member
just for everyone's benefit, and quite contrary to what most of you think you have found........I have been studying up on suspension mostly for my racer but this also proved my thoughts on the front suspension........It would appear that you are generally much better off to have stiffer springs with less pre-load than softer springs with more pre load. That is not to say that the springs for the modified stem are heavy/stiff at all, but that you should not use a stiff shock absorber to "mask" soft springs........Something for you to ponder about.
 

Chris Launders

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VOC Member
That's what I've ended up with Greg, I weighed 130kg and ended up with 47lb/in springs and 11mm packers but the damper set at it's first click. At this the link is level when I'm sat on it but just into the bump stop when hitting a speed hump or emergency braking, in normal use the front is active all the time.
For those who haven't seen how this changes the behavior of the forks there is a video of mine on "Modified Steering Stem" thread, post #584.
 

timetraveller

Well Known and Active Website User
VOC Member
To avoid confusion here; we have found that to get the best our of the front end one has to pay attention to the weight of the rider and the bike. That is whether it is a twin or single. Both bike sizes have the same un-sprung weight in the front suspension and a pillion passenger and/or luggage at the rear seems to make very little difference to what i required at the front. Therefore it seems to be the mass, and hence inertia, of the centre of the bike which is important. Chris is one of the heavier riders and did most of the test riding when the system was new. Before he changed the rear bearings in the lower link he had 36 lbs/inch springs and the standard AVO damper. Once he changed over from Oilite bushes to the Greg mod at the rear (he used needle rollers rather than ball races) there was so much yoyoing at the front that his first impression was that the damper had failed. This was overcome by changing to 45 lbs/inch springs with two inches of preload from 36 lbs/inch springs with three inches of preload and getting AVO to build a stiffer damper. Eventually Chris had to pack the springs and the lowest setting on the stiffer damper might not be very different from the stiffest setting on the original AVO damper. Greg has long maintained that stiffer springs and a softer damper are the best combination and yet here in the UK people who have started off with the stronger springs and a variety of dampers, all weaker than the AVOs, have all found that the front is not as comfortable as they would like. In Europe, Canada and the USA people seem to be happy with the longer travel of the weaker springs and cut down spring boxes rather than Greg's recipe but Greg has fitted more of these than any other person, he has had about fifty kits, and he has raced very successfully with his combination. This has left me with a problem. Is there a single best option or can both options be made to work? That is; stiffer springs and a soft damper or weaker springs and a stiffer damper. Note that the AVO dampers are adjustable and feedback from various parts of the northern hemisphere suggest that most people are using the AVO at about, or less than, half the maximum stiffness. Even with the AVO damper turned down to the minimum stiffness all the mid weight riders to whom I first supplied the 45 lbs/inch springs have asked for them to be changed to the 36 lbs/inch ones, or even 33s, or even 30s on the stripped down singles. Greg does not cut down the length of the spring boxes and my understanding is that his method of checking the front suspension is to run the bike down a slope without the engine on and with no damper and then once up to, say, 30 mph to slam on the front brake and to determine how much movement there is. Remember that Greg is a competent racer and so I value his views but that is not what I was trying to achieve with the combination which I normally supply. I wanted a system in which the damper modifies the spring pressure/movement; a little on the compression and more on the extension. This seems to be acceptable to most of the people who have provided me with feedback. I would have absolutely no problem with supplying people with stiffer springs but where a weaker damper could be found I don't know. The AVO turned down to a minimum is certainly not what I would call stiff but then I do not pretend to be a suspension expert. My impression from reading around this subject is that for comfortable road use the combination of softer springs and stiffer dampers are preferred. Do we have a suspension expert who reads this who could give us professional level information?
 

greg brillus

Well Known and Active Website User
VOC Member
Sorry guy's we didn't want to change this thread to a suspension one..........I think there is some belief that on the twins you are going to get a nice soft ride up front.........This is simply not the case, on the singles yes the ride is much softer. On both bikes the forks are much more 'Livelier than stock" without a doubt, and for a long time Vincent rider this does take some getting use to. The end result is that we still have a pretty small amount of travel compared to a modern bike, and this is where the compromise is, especially if you ride solo and two up without making any changes, this is mostly too difficult on these bikes. The actual comfort level on a Vincent is mostly in the rear end anyway, and that is why I came up with some fully adjustable seat stay suspension struts to fix this for my dear wife.......... ;) .......... Cheers........ Greg.
 

MartynG

Well Known and Active Website User
VOC Member
Sorry guy's we didn't want to change this thread to a suspension one..........I think there is some belief that on the twins you are going to get a nice soft ride up front.........This is simply not the case, on the singles yes the ride is much softer. On both bikes the forks are much more 'Livelier than stock" without a doubt, and for a long time Vincent rider this does take some getting use to. The end result is that we still have a pretty small amount of travel compared to a modern bike, and this is where the compromise is, especially if you ride solo and two up without making any changes, this is mostly too difficult on these bikes. The actual comfort level on a Vincent is mostly in the rear end anyway, and that is why I came up with some fully adjustable seat stay suspension struts to fix this for my dear wife.......... ;) .......... Cheers........ Greg.
Take care Greg, mention of a "rear end" may have an anonymous Censor delete your post, could be thought of as "sexist"
 

erik

Well Known and Active Website User
VOC Member
On my brake the aktuating lever will have the same length as the original on the rfm.On your it looks as the arm is longer,same length as the pedal? Regards erik
 

erik

Well Known and Active Website User
VOC Member
The brake pedal shaft I made from the brake camshaft of the rear brake,cutting off the brake cam.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Yes Erik, Mine looks a bit too long, Yours will be better, When I start Welding, I am out of Control :D .
With my Big Feet and Long Legs, I find the pad of the pedal has to be very low !.
But I wanted the stainless rod horizontal and the pad where it is , So that's how it finished.
I had to fit a stop bolt on the return, And the brake maybe too powerful, We will see.
Good Luck, Bill.
 

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