Didn't John Surtees mount alternate dampers on his Lightning at a farther forward position?
Rear Springs
- Thread starter Albervin
- Start date
Didn't John Surtees mount alternate dampers on his Lightning at a farther forward position?
I think i remember seeing that he used spring/damper units in place of the standard spring boxes up front?
Vince, as you said earlier, the only way to change the spring rate is to change the spring .... or wear it out, or do clever things with lots of heat and buckets of water and oil.
What you can change by altering the mounting/pivot points is the effective spring rate. It doesn't matter what the spring does, it's what the wheel does that matters so if you want the wheel to move 1" for every 100 lbs worth of bump you can mount a 100lb/inch spring over the wheel spindle. But, if you mount the spring half way between the wheel spindle and the swing arm pivot you'll need 200 lbs and the spring will only move half an inch, so the spring rate would have to be 400 lbs/inch but the effect at the wheel would still be 100 lbs/inch. So if you keep the springs the same, and vary the levers and pivots, you won't change the spring rate, but you will change the effective spring rate at the wheel.
We travel miles with those twisty bits of metal working overtime, and never think about how they work. Thanks for starting this Alyn.
H
H,
Thanks for the explanation.
I had the pictures in my head, just couldn´t put them into words.
I´m not very good with "Theoretical/Effective" & Co. Prefer much more the "Actuall + Physical side of it because you don´t need a calculator (just a bit of imagination and buckets of oil/water heat & metal
)
I am not sure I am a lot wiser after all of this? I will certainly need to digest it all. At one stage I was picturing the mode Velocette used to change spring rate & wondering what the
effect of changing the angle of the spring/damper had on the damping rate?! Since, for all intents & purposes we are locked into a fixed angle on our Vincents, we are left to play with
"rates". Our standard springs are linear in that they are a consistent wire gauge & windings/inch. Modern bikes often have linear springs but they also have links between the swing arm
and the spring/damper that impart a non linear movement. What we want, ideally, is a nice compliant (i.e. soft) ride that will stiffen up gradually as you reach the limit of travel. This, if I
understand correctly, is what the Thornton system does.
The alternative is for someone to work out a system using cranks & levers which seems a bit too erudite (or just plain too complex) for a 60 year old motorcycle.
Thanks anyway to all those who have contributed & sorry that some were a little bruised in the process.
effect of changing the angle of the spring/damper had on the damping rate?! Since, for all intents & purposes we are locked into a fixed angle on our Vincents, we are left to play with
"rates". Our standard springs are linear in that they are a consistent wire gauge & windings/inch. Modern bikes often have linear springs but they also have links between the swing arm
and the spring/damper that impart a non linear movement. What we want, ideally, is a nice compliant (i.e. soft) ride that will stiffen up gradually as you reach the limit of travel. This, if I
understand correctly, is what the Thornton system does.
The alternative is for someone to work out a system using cranks & levers which seems a bit too erudite (or just plain too complex) for a 60 year old motorcycle.
Thanks anyway to all those who have contributed & sorry that some were a little bruised in the process.
H,
Thanks for the explanation.
I had the pictures in my head, just couldn´t put them into words.
I´m not very good with "Theoretical/Effective" & Co. Prefer much more the "Actuall + Physical side of it because you don´t need a calculator (just a bit of imagination and buckets of oil/water heat & metal
I usually save theory and calculators for work, and save the oily hands stuff for the bike myself, but I think that needed a long winded effort.
I know about that, because I moved the spring attachment points on the swing arm of my Egli to get more movement, and a bit more comfort. It worked well and Girling had a huge range of spring rates and lengths to fine tune it.
The problem was, I used the original shock absorbers so it lifted the back of the bike, which meant that the travel was 2.5" below tightest chain point and 1.5" above so the chain tension was always a poor compromise. I needed to move the top mounting or find a shock absorber about 3/8" shorter, so I've gone back to standard mounting and I stay on smooth roads.
H
Velocette? Very clever idea by a very clever man. Simply changes the lever ratios to change the preload and spring rate (at the wheel spindle not the spring/damper unit).
H
The John Surtees bike referred to above has different springing both front and rear. At the rear longer spring/damper units go from the top of the rear frame triangle to the stud in the top of the rear cylinder head bracket. This gives a much longer spring and the ability to pre-load, as many other swinging arm type systems do/did. Hard to fit this to a touring bike though!
At the front each spring for the girdraulics is replaced by a long damper/spring unit and there is no additional damper between the fork blade. Once again, these were special units available John Surtees through his trade contacts and they would have to be made specially now. Also interesting to note the position of both John Surtees and John Emmanuel's eccentrics.
At the front each spring for the girdraulics is replaced by a long damper/spring unit and there is no additional damper between the fork blade. Once again, these were special units available John Surtees through his trade contacts and they would have to be made specially now. Also interesting to note the position of both John Surtees and John Emmanuel's eccentrics.
Just to chuck a spanner in the works, a machine of a similar age, if a sidecar can be called a machine, the Steib S501 had an initial spring rate of 70lbs per inch, but which was wound so as to become progressively harder as it compressed. I seem to remember that the spring coils were closer together at the bottom of the travel. Perhaps this is what the Vincent needed, but due to the spring length, I think that this would be difficult to achieve. Also, The LE rear wheel suspension was so good, that I used the same principal on my Diplomat, and it worked! Hey Ho, ET43
That is correct Nulli. Both bikes have their 'eccentrics' in what would normally be considered the middle position, that is half way between solo and sidecar trail. Presumably this gives less trail and more rapid response when rapidly going from leaning over on one side to leaning over on the other. I would also guess that there would be more chance of a tank slapper but both chaps know what they are doing.
Regarding multi rate springs; from talking to spring manufacturers there should be no problem making a short multi rate spring, the problem is the barrel shaped rear springs. A set up like the Thornton one should make it easy to use multi rate springs and I do not understand why Thornton used the rather crude system that he does of sticking a short length of spring inside the longer outer spring. I did some design work a few years ago for a chap who builds racing grass track sidecar outfits and all his models used multi rate springs both front and rear. Multi rate would be very easy on our front springs.
Regarding multi rate springs; from talking to spring manufacturers there should be no problem making a short multi rate spring, the problem is the barrel shaped rear springs. A set up like the Thornton one should make it easy to use multi rate springs and I do not understand why Thornton used the rather crude system that he does of sticking a short length of spring inside the longer outer spring. I did some design work a few years ago for a chap who builds racing grass track sidecar outfits and all his models used multi rate springs both front and rear. Multi rate would be very easy on our front springs.