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Re: Yes it's another Genmar question....

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  • rick
    ... Mark, The GenMars are their own problem, separate from your fork settings. They are just a mechanical issue of having sufficient brake hose lengths, etc.
    Message 1 of 9 , Apr 3, 2011
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      --- In TriumphTrophy@yahoogroups.com, "Mark" <highwayknight@...> wrote:
      >
      > Ok, don't ya'll jump up on your soapboxes and start telling me about the FAQ section...I've been there and not found all the answers I'm looking for.

      Mark,

      The GenMars are their own problem, separate from your fork settings. They are just a mechanical issue of having sufficient brake hose lengths, etc.

      Setting up the suspension always seems to be a mystery, when it needn't be. As Adiuex alluded to, spring rate and ride height are two totally separate things. Changing the pre-load on the springs with spacers simply changes the height at which the front (or rear) will settle. More spacer length means the front will ride higher. Spring rate on the other hand, is the force/distance or strength of the spring. You can set a stiff or weaker spring to ride at any height you want with spacers (static sag).

      Separate from all of this is the steering geometry of the bike. Once the springs are set up the way you want, you adjust the attitude of the front by clamping the fork tubes higher or lower in the trees, so the bike will produce the steering responsiveness you want.

      So basically, you have three independent variables to work with.

      The Trophy forks have 150 mm of total travel. Ohlins and most manufacturers recommend setting the static sag at 25-30% of the total travel, thus giving your forks room to absorb bumps. For some reason, RaceTech simply states a sag of 25 mm (not %)which makes no sense to me, as fork travels vary.

      From the factory, the Trophy has right around 50 mm of sag. The tops of the fork tubes are set even with the top surface of the tree. I have experimented a lot, and I think these numbers produce and almost perfect tradeoff between quickness of steering and stability. So when all is said and done, you want the bike to settle to a static sag of about 50 mm, with you sitting on the bike with your full weight.

      You can accomplish this in two different ways. 1 - increase the fork spacer length (pre-load) which it appears the earlier owner did. 2- Use new stiffer springs, typically with a spring rate of about 0.95 - 1.0 kg/mm for the Trophy. You would then cut new spacers ( a lot of trial and work error) such that their pre-load will allow the bike to sag to about 38-50 mm (25-30% of full travel). In my experience, with a sag of only 30-40 mm, you will find the steering starts to become noticeably slower. To compensate, you would clamp the tubes up above the trees by some amount (say 20 mm if the sag were only 30 mm).

      So to help you with your current dilemma and keep things simple, find a small jack to fit under the oilpan of the bike, and with a thin piece of wood to protect the engine and the bike on the centerstand, raise the front of the bike back up so the wheel clears (and/or have someone heavy sit on the rear). You might want to confirm the oil levels by compressing the empty forks, using wood blocks to push the front wheel up to the end of its travel. Oil level should be about 125-130 mm typically. Use a tape and flashlight to measure from the oil to the top of the tubes. Note this method isn't highly accurate, as the forks should be removed and held vertical, but its close enough to make sure there is about the right oil in them.

      Remove the blocks under the front wheel (if you measured oil level) so the forks are fully extended, and insert the springs and spacers that came out. To screw in the top fork nuts without cross threading, I use a 7/8" deep well socket (or use the exact metric if you own one), with a long extension bar and ratchet. Cover the tank with a blanket, then stand up on the bike (carefully) and use your body weight to press down on the cap while keeping everything aligned, and you should be able to screw the caps back in without a problem, even though you won't have much feel as to whether they are cross-threaded. Using this approach though, you can get things pretty well-aligned visually, and should be ok.

      To check the sag, wrap a zip-tie or nylon thing above a fork seal, and measure the total distance from the bottom of the lower tree surface to top of your ziptie. Then, remove the jack and take it off the centerstand. Let the bike settle with you sitting on it (without a helper, you have to use a little weight on one foot to balance it). Subtract the new distance from the fully extended to obtain the static sag. You only have to measure the fully extended distance once (and put it in your logbook), but can do numerous trials of the weighted length (keep pushing the ziptie back down each time), until you feel you have it somewhat accurately. The factory stock setup should give you in the vicinity of 50 mm of sag, give or take your exact weight, etc.

      Then give it a test ride. If the bike seems to handle too sharply, either increase the spacer lengths even more to decrease the static sag, or lower the tubes in the trees below the top surface of the tree. If the steering is slow, do the opposite, until you get it the way you like it. More often than not, you will be raising the tubes above the tree. Note, work from the top surface of the triple tree, not the GenMar.

      Eventually, you might want to use stiffer spring rates of about 1 kg/mm, and then set the forks up as above for proper sag. The Trophy will become a taught, excellent handling little animal with better suspension. Of course, if you do this, the rear will be out of balance, so after that you will want to replace the rear shock with a top after market unit, set up in a similar way with stiffer springs.

      Before you go that route though, just screw the caps back on, check the sag (and again, record everything in a log book so you don't have to do it all again) and make small, rational adjustments until you get the bike handling the way you like.

      Of all the things you can do to the bike, suspension improvements will yield the best rewards, I think anyway. I put Ohlins springs on the front with RaceTech emulators, and an Ohlins rear shock (both no longer available) and the stability and handling of the bike are phenomenal. RaceTech springs are still available, along with a variety of top quality shocks. Start with what you have though, and then as you get comfortable, start to tweek things. None of this work is difficult, and you can easily do it once you see it once.

      Good luck,

      Rick Hartwick
      00 Trophy 900
    • garyviggars
      Wow got a headache are you a rocket scientist? I work in the bike trade and still got lost !!! Regards Gary ps not taking the piss that was very nice input (
      Message 2 of 9 , Apr 3, 2011
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        Wow got a headache are you a rocket scientist?
        I work in the bike trade and still got lost !!!
        Regards
        Gary
        ps not taking the piss that was very nice input

        ( been sitting in the background for a few months )
        2001 BBBB ( Very fast Blue )
        --- In TriumphTrophy@yahoogroups.com, Adeux <adeux60@...> wrote:
        >
        >
        > I know nothing of genmars although I am interested in you raising the bars So
        > would like to hear about what you achieve.
        >
        > What might be useful to you - albeit i will give you metric units any
        > consistent units will do.
        >
        > F=-kx
        >
        > The minus sign is an indication that force and displacement (compression of
        > the spring act in opposite directions.
        >
        > So as you drop the bike 250kg(excluding the weight of the wheels) (x10 for
        > force f) onto it's suspension and it drops say 50mm (x=0.05m) you can work
        > out the approximate spring constant (k)
        >
        > Thus sticking a spacer in of 50mm changes the deflection of the spring and
        > in all likely hood the bike doesn't sink the original 50 mm. The weight of
        > the bike and the spring constant remain the same. But the force acting
        > against the wheels increases. If the spring bottoms out due to it's internal
        > design it will do so at the predefined deflection and identical force. So
        > adding a spacer to a spring that bottoms out already is a pointless
        > exercise.
        >
        > Sorry to pontificate.
        >
        > Just raising the bike by 50mm seems pointless. Although if the bike already
        > stands at the top of it's travel and then a spacer is added then the ride
        > height is unchanged and the minimum force required to start deflecting the
        > spring is increased by the equivalent force to the deflection.
        >
        > I am starting to go off the additional spacer idea (I value my wrists) it
        > would seem to me that getting the spring constant right and responsive to
        > the road conditions would be paramount. Whilst if you had a super smooth
        > track you could afford to run rigid that is not the case on the road.
        >
        > Dual rate springs try to accommodate two frequencies of motion but generally
        > widens the frequency band and reduces the amplitude of what would have been
        > a single natural frequency. This is where the crux of the problem lies.
        >
        > To get back closer to what you asked (I hope...) I lowered the bike on the
        > front forks by 50 mm ( cutting holes in the plastic cover(with a soldering
        > iron). I did this as I felt the bike centre of gravity was high and thus
        > slow to respond to changes of direction (as hampered by the high weight too)
        > I was pleased with the result. I then went on to take about 25mm out of the
        > seat height again I was pleased with the result. but then I tend to put more
        > weight on the front when I want it to grip in a bend (ie I lean forward in a
        > bend)
        >
        > Are you the same as me? Probably not!
        >
        > I also had it mind that Reactiveness (ease of direction change and opposite
        > of inertia) is subject to the square of the centre of gravity (if the
        > inertia around the c of g is of concern- I think so) the square factor makes
        > it very beneficial to reduce the c of g)
        >
        > I didn't go for the rear change (the 180 trick) it horrified me that this
        > would cause the chain to rub more on the swinging arm. Having once lost a
        > chain all temptation evaporated.
        >
        > The other attack on this is to change the mass of the bike particulary the
        > wheels and everything that is far away from the c of g. So don't strap your
        > tool box to the front fender. Also as it applies to me if I could lose
        > weight then I would have less inertia too.
        >
        > Coming to the bars. Taking the weight of my body off the bars reduces the
        > inertia of the bike too as my weight is then closer to the c of g. And you
        > would get less of a smack through the wrists.
        >
        > So in search for the answer to your questions I have to ask where do you
        > think the bike is and in what direction do you want to go?
        >
        >
        > Sorry it must be alone on a Saturday night and the tv must be poor.
        >
        > Please do not hesitate to disagree with me I am just sounding out my
        > thoughts in case someone has just invented a perfect triple rate spring and
        > wants me to test it for free.
        >
        > Final opinion - go with the lightest possible damping oil as long as the
        > bike doesn't pogo. The faster the wheels react to the surface the better as
        > long as they don't create motion of their own.
        >
        > Did wonder if I could just clamp the handlebars to the raised forks without
        > spacers but the I saw I had to faff with extending all the controls so never
        > tried. Although I have two bits of brass ready to turn into spacers.
        >
        > A2
        >
        >
        > -----
        > A2
        > Trophy 900, fox eyes, mostly red, mostly upright in southern England
        > --
        > View this message in context: http://old.nabble.com/Yes-it%27s-another-Genmar-question....-tp31304280p31304867.html
        > Sent from the Triumph Trophy mailing list archive at Nabble.com.
        >
      • Adeux
        Sorry I deleted this as I thought I waffled on and it was a bit theoretical and not particularly proven nor rigourous nor applied to creating the result you
        Message 3 of 9 , Apr 4, 2011
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          Sorry I deleted this as I thought I waffled on and it was a bit theoretical
          and not particularly proven nor rigourous nor applied to creating the result
          you may be looking for.

          Perhaps I also don't believe that tuning forks is particularly productive
          without considering their response to the expected road. Although I
          obviously hear others make alterations and I can only relate the experience
          corresponding to my weight. Partly I wish for forks that cope with the
          unexpected pot hole but then would it be a sports bike any more?

          I think it would be interesting to know what Triumph expected as their
          average user weight and perhaps act accordingly. (if you want to match your
          riding experience to others of different weight)

          I should also point out that I have never attempted to alter my suspension.

          Partly I have listened to group members suggest riding position is paramount
          for comfort eg preventing wrist damage.

          Then I can take an extreme analogy with the likes of the rolls Royce where
          comfort (lack of deflection over the bumps) is entirely due to a high
          vehicle mass and a relatively very low wheel mass (I believe the term is
          unsprung weight)

          Considerations that occur to me are for instance upgrading the brakes could
          involve a higher unsprung mass - slowing down the response of the wheel to a
          bump. Or you could get faster suspension responsiveness by putting on
          lighter wheels and tyres.

          You could look at the suspension problem as a change in momentum (mv) and
          presumably what you gain in mass (m) you lose in velocity(v).

          I think tuning focus has to include the weight of the bike as you ride it
          and changes made to accommodate holiday weights etc taken into account. Or
          another interpretation is don't expect to scratch about when fully loaded.

          I was trying to get to this point. The wheels move a bit like a tuning fork.
          You strike it and it bounces back at a speed that corresponds to it's mass
          and spring stiffness. Ie it plays one note on the tuning fork.

          You can chose another tuning fork and play a different note and the wheel
          will return to position at a different speed. Will that suit you, your load
          and the expected road.

          This natural frequency if repeated (from the road bumps) on a bike tends to
          excite the motion and amplify the movements of the body of the bike(I
          generalise). This is why you require damping. You can also file off a little
          off one side of the tuning fork so it tries to play two notes. Ie you use a
          dual rate spring. Both have to be able to suspend the bike (similar working
          stiffnesses) but one will respond better to fast bumps and the other slow
          bumps. The overal effect is a blending of the two responses into a wider
          band of reduced amplitude. (is this proven to be better?)

          ultimately you start thinking about fitting super fast computers that
          attempt to read the road ahead and suck up the wheel over the bumps and
          blowing it out over the holes in the presumed hope of limiting the motion of
          the frame whilst maximising the movement of the wheels. (if hydraulics were
          fast and accurate enough)

          What I believe is the motion of the suspension should not be greatly
          decelerated by the damping oil as that corresponds to passing the damping
          loads to your wrists and this I believe I have confirmed when I have changed
          the usual found thick syrup to the lightest of oils. Similarly you could add
          oil in two mixed thicknesses as each will damp best at different
          frequencies.....what have I started?

          Anyway I appreciate the responses and have read them carefully as on this
          group you are bound to learn something useful.


          A2









          >
          >
          > I know nothing of genmars although I am interested in you raising the bars
          > So
          > would like to hear about what you achieve.
          >
          > What might be useful to you -  albeit i will give you metric units any
          > consistent units will do.
          >
          > F=-kx
          >
          > The minus sign is an indication that force and displacement (compression
          > of
          > the spring act in opposite directions.
          >
          > So as you drop the bike 250kg(excluding the weight of the wheels) (x10 for
          > force f) onto it's suspension and it drops say 50mm (x=0.05m) you can work
          > out the approximate spring constant (k)
          >
          > Thus sticking a spacer in of 50mm changes the deflection of the spring and
          > in all likely hood the bike doesn't sink the original 50 mm. The weight of
          > the bike and the spring constant remain the same. But the force acting
          > against the wheels increases. If the spring bottoms out due to it's
          > internal
          > design it will do so at the predefined deflection and identical force. So
          > adding a spacer to a spring that bottoms out already is a pointless
          > exercise.
          >
          > Sorry to pontificate.
          >
          > Just raising the bike by 50mm seems pointless. Although if the bike
          > already
          > stands at the top of it's travel and then a spacer is added then the ride
          > height is unchanged and the minimum force required to start deflecting the
          > spring is increased by the equivalent force to the deflection.
          >
          > I am starting to go off the additional spacer idea (I value my wrists) it
          > would seem to me that getting the spring constant right and responsive to
          > the road conditions would be paramount. Whilst if you had a super smooth
          > track you could afford to run rigid that is not the case on the road.
          >
          > Dual rate springs try to accommodate two frequencies of motion but
          > generally
          > widens the frequency band and reduces the amplitude of what would have
          > been
          > a single natural frequency. This is where the crux of the problem lies.
          >
          > To get back closer to what you asked (I hope...) I lowered the bike on the
          > front forks by 50 mm ( cutting holes in the plastic cover(with a soldering
          > iron). I did this as I felt the bike centre of gravity was high and thus
          > slow to respond to changes of direction (as hampered by the high weight
          > too)
          > I was pleased with the result. I then went on to take about 25mm out of
          > the
          > seat height again I was pleased with the result. but then I tend to put
          > more
          > weight on the front when I want it to grip in a bend (ie I lean forward in
          > a
          > bend)
          >
          > Are you the same as me? Probably not!
          >
          >  I also had it mind that Reactiveness (ease of direction change and
          > opposite
          > of inertia) is subject to the square of the centre of gravity (if the
          > inertia around the c of g is of concern- I think so) the square factor
          > makes
          > it very beneficial to reduce the c of g)
          >
          > I didn't go for the rear change (the 180 trick) it horrified me that this
          > would cause the chain to rub more on the swinging arm. Having once lost a
          > chain all temptation evaporated.
          >
          > The other attack on this is to change the mass of the bike particulary the
          > wheels and everything that is far away from the c of g. So don't strap
          > your
          > tool box to the front fender. Also as it applies to me if I could lose
          > weight then I would have less inertia too.
          >
          > Coming to the bars. Taking the weight of my body off the bars reduces the
          > inertia of the bike too as my weight is then closer to the c of g. And you
          > would get less of a smack through the wrists.
          >
          > So in search for the answer to your questions I have to ask where do you
          > think the bike is and in what direction do you want to go?
          >
          >
          >  Sorry it must be alone on a Saturday night and the tv must be poor.
          >
          > Please do not hesitate to disagree with me I am just sounding out my
          > thoughts in case someone has just invented a perfect triple rate spring
          > and
          > wants me to test it for free.
          >
          > Final opinion - go with the lightest possible damping oil as long as the
          > bike doesn't pogo. The faster the wheels react to the surface the better
          > as
          > long as they don't create motion of their own.
          >
          > Did wonder if I could just clamp the handlebars to the raised forks
          > without
          > spacers but the I saw I had to faff with extending all the controls so
          > never
          > tried. Although I have two bits of brass ready to turn into spacers.
          >
          > A2
          >
          >
          > -----
          > A2
          > Trophy 900, fox eyes, mostly red, mostly upright in southern England
          > --
          > View this message in context:
          > http://old.nabble.com/Yes-it%27s-another-Genmar-question....-tp31304280p31304867.html
          > Sent from the Triumph Trophy mailing list archive at Nabble.com.
          >


          -----
          A2
          Trophy 900, fox eyes, mostly red, mostly upright in southern England
          --
          View this message in context: http://old.nabble.com/Yes-it%27s-another-Genmar-question....-tp31304280p31319106.html
          Sent from the Triumph Trophy mailing list archive at Nabble.com.
        • Adeux
          Well I agree I didn t think it was clear so I initially deleted it. So thanks for your comment. If you want me to explain myself better on a point or two let
          Message 4 of 9 , Apr 4, 2011
          • 0 Attachment
            Well I agree I didn't think it was clear so I initially deleted it. So thanks
            for your comment. If you want me to explain myself better on a point or two
            let me know.

            What I don't think I explained well is inertia around the c of g very well
            and a parallel is the spinning skater who by pulling in the arms can
            massively accelerate. Well similarly something with the weights pulled in to
            the centre can change position faster (lean or rotate quicker)

            In extremis - you could try to extend the length of the bike put all the
            weight at either end and drive as fast as possible then the bike frame will
            tend to keep going straight forcing the suspension to do more work.
            similarly the width and height for leaning speeds.

            Inertia is a good measuring of the ease or not 'to change' and is only the:

            sum of all the masses x (each respective distance to the c of g) squared.

            I was trying to explain that the distance squared is the the most sensitive
            factor to how much inertia you have - that resists changes of direction.
            Although I wouldn't bet against an elephant on turning circle but you will
            note the slow rate at which they can change turning from one direction to
            the other.

            A2







            Gary-148 wrote:
            >
            >
            > Wow got a headache are you a rocket scientist?
            > I work in the bike trade and still got lost !!!
            > Regards
            > Gary
            > ps not taking the piss that was very nice input
            >
            > ( been sitting in the background for a few months )
            > 2001 BBBB ( Very fast Blue )
            > --- In TriumphTrophy@yahoogroups.com, Adeux <adeux60@...> wrote:
            >>
            >>
            >> I know nothing of genmars although I am interested in you raising the
            >> bars So
            >> would like to hear about what you achieve.
            >>
            >> What might be useful to you - albeit i will give you metric units any
            >> consistent units will do.
            >>
            >> F=-kx
            >>
            >> The minus sign is an indication that force and displacement (compression
            >> of
            >> the spring act in opposite directions.
            >>
            >> So as you drop the bike 250kg(excluding the weight of the wheels) (x10
            >> for
            >> force f) onto it's suspension and it drops say 50mm (x=0.05m) you can
            >> work
            >> out the approximate spring constant (k)
            >>
            >> Thus sticking a spacer in of 50mm changes the deflection of the spring
            >> and
            >> in all likely hood the bike doesn't sink the original 50 mm. The weight
            >> of
            >> the bike and the spring constant remain the same. But the force acting
            >> against the wheels increases. If the spring bottoms out due to it's
            >> internal
            >> design it will do so at the predefined deflection and identical force. So
            >> adding a spacer to a spring that bottoms out already is a pointless
            >> exercise.
            >>
            >> Sorry to pontificate.
            >>
            >> Just raising the bike by 50mm seems pointless. Although if the bike
            >> already
            >> stands at the top of it's travel and then a spacer is added then the ride
            >> height is unchanged and the minimum force required to start deflecting
            >> the
            >> spring is increased by the equivalent force to the deflection.
            >>
            >> I am starting to go off the additional spacer idea (I value my wrists) it
            >> would seem to me that getting the spring constant right and responsive to
            >> the road conditions would be paramount. Whilst if you had a super smooth
            >> track you could afford to run rigid that is not the case on the road.
            >>
            >> Dual rate springs try to accommodate two frequencies of motion but
            >> generally
            >> widens the frequency band and reduces the amplitude of what would have
            >> been
            >> a single natural frequency. This is where the crux of the problem lies.
            >>
            >> To get back closer to what you asked (I hope...) I lowered the bike on
            >> the
            >> front forks by 50 mm ( cutting holes in the plastic cover(with a
            >> soldering
            >> iron). I did this as I felt the bike centre of gravity was high and thus
            >> slow to respond to changes of direction (as hampered by the high weight
            >> too)
            >> I was pleased with the result. I then went on to take about 25mm out of
            >> the
            >> seat height again I was pleased with the result. but then I tend to put
            >> more
            >> weight on the front when I want it to grip in a bend (ie I lean forward
            >> in a
            >> bend)
            >>
            >> Are you the same as me? Probably not!
            >>
            >> I also had it mind that Reactiveness (ease of direction change and
            >> opposite
            >> of inertia) is subject to the square of the centre of gravity (if the
            >> inertia around the c of g is of concern- I think so) the square factor
            >> makes
            >> it very beneficial to reduce the c of g)
            >>
            >> I didn't go for the rear change (the 180 trick) it horrified me that this
            >> would cause the chain to rub more on the swinging arm. Having once lost a
            >> chain all temptation evaporated.
            >>
            >> The other attack on this is to change the mass of the bike particulary
            >> the
            >> wheels and everything that is far away from the c of g. So don't strap
            >> your
            >> tool box to the front fender. Also as it applies to me if I could lose
            >> weight then I would have less inertia too.
            >>
            >> Coming to the bars. Taking the weight of my body off the bars reduces the
            >> inertia of the bike too as my weight is then closer to the c of g. And
            >> you
            >> would get less of a smack through the wrists.
            >>
            >> So in search for the answer to your questions I have to ask where do you
            >> think the bike is and in what direction do you want to go?
            >>
            >>
            >> Sorry it must be alone on a Saturday night and the tv must be poor.
            >>
            >> Please do not hesitate to disagree with me I am just sounding out my
            >> thoughts in case someone has just invented a perfect triple rate spring
            >> and
            >> wants me to test it for free.
            >>
            >> Final opinion - go with the lightest possible damping oil as long as the
            >> bike doesn't pogo. The faster the wheels react to the surface the better
            >> as
            >> long as they don't create motion of their own.
            >>
            >> Did wonder if I could just clamp the handlebars to the raised forks
            >> without
            >> spacers but the I saw I had to faff with extending all the controls so
            >> never
            >> tried. Although I have two bits of brass ready to turn into spacers.
            >>
            >> A2
            >>
            >>
            >> -----
            >> A2
            >> Trophy 900, fox eyes, mostly red, mostly upright in southern England
            >> --
            >> View this message in context:
            >> http://old.nabble.com/Yes-it%27s-another-Genmar-question....-tp31304280p31304867.html
            >> Sent from the Triumph Trophy mailing list archive at Nabble.com.
            >>
            >
            >
            >
            >


            -----
            A2
            Trophy 900, fox eyes, mostly red, mostly upright in southern England
            --
            View this message in context: http://old.nabble.com/Yes-it%27s-another-Genmar-question....-tp31304280p31319273.html
            Sent from the Triumph Trophy mailing list archive at Nabble.com.
          • Adeux
            I find a combination of eBay colours cuts the most eccentric dash....I must find out how paint works..... ... A2 Trophy 900, fox eyes, mostly red, mostly
            Message 5 of 9 , Apr 4, 2011
            • 0 Attachment
              I find a combination of eBay colours cuts the most eccentric dash....I must
              find out how paint works.....


              Gary-148 wrote:
              >
              >
              > Wow got a headache are you a rocket scientist?
              > I work in the bike trade and still got lost !!!
              > Regards
              > Gary
              > ps not taking the piss that was very nice input
              >
              > ( been sitting in the background for a few months )
              > 2001 BBBB ( Very fast Blue )
              > --- In TriumphTrophy@yahoogroups.com, Adeux <adeux60@...> wrote:
              >>
              >>
              >> I know nothing of genmars although I am interested in you raising the
              >> bars So
              >> would like to hear about what you achieve.
              >>
              >> What might be useful to you - albeit i will give you metric units any
              >> consistent units will do.
              >>
              >> F=-kx
              >>
              >> The minus sign is an indication that force and displacement (compression
              >> of
              >> the spring act in opposite directions.
              >>
              >> So as you drop the bike 250kg(excluding the weight of the wheels) (x10
              >> for
              >> force f) onto it's suspension and it drops say 50mm (x=0.05m) you can
              >> work
              >> out the approximate spring constant (k)
              >>
              >> Thus sticking a spacer in of 50mm changes the deflection of the spring
              >> and
              >> in all likely hood the bike doesn't sink the original 50 mm. The weight
              >> of
              >> the bike and the spring constant remain the same. But the force acting
              >> against the wheels increases. If the spring bottoms out due to it's
              >> internal
              >> design it will do so at the predefined deflection and identical force. So
              >> adding a spacer to a spring that bottoms out already is a pointless
              >> exercise.
              >>
              >> Sorry to pontificate.
              >>
              >> Just raising the bike by 50mm seems pointless. Although if the bike
              >> already
              >> stands at the top of it's travel and then a spacer is added then the ride
              >> height is unchanged and the minimum force required to start deflecting
              >> the
              >> spring is increased by the equivalent force to the deflection.
              >>
              >> I am starting to go off the additional spacer idea (I value my wrists) it
              >> would seem to me that getting the spring constant right and responsive to
              >> the road conditions would be paramount. Whilst if you had a super smooth
              >> track you could afford to run rigid that is not the case on the road.
              >>
              >> Dual rate springs try to accommodate two frequencies of motion but
              >> generally
              >> widens the frequency band and reduces the amplitude of what would have
              >> been
              >> a single natural frequency. This is where the crux of the problem lies.
              >>
              >> To get back closer to what you asked (I hope...) I lowered the bike on
              >> the
              >> front forks by 50 mm ( cutting holes in the plastic cover(with a
              >> soldering
              >> iron). I did this as I felt the bike centre of gravity was high and thus
              >> slow to respond to changes of direction (as hampered by the high weight
              >> too)
              >> I was pleased with the result. I then went on to take about 25mm out of
              >> the
              >> seat height again I was pleased with the result. but then I tend to put
              >> more
              >> weight on the front when I want it to grip in a bend (ie I lean forward
              >> in a
              >> bend)
              >>
              >> Are you the same as me? Probably not!
              >>
              >> I also had it mind that Reactiveness (ease of direction change and
              >> opposite
              >> of inertia) is subject to the square of the centre of gravity (if the
              >> inertia around the c of g is of concern- I think so) the square factor
              >> makes
              >> it very beneficial to reduce the c of g)
              >>
              >> I didn't go for the rear change (the 180 trick) it horrified me that this
              >> would cause the chain to rub more on the swinging arm. Having once lost a
              >> chain all temptation evaporated.
              >>
              >> The other attack on this is to change the mass of the bike particulary
              >> the
              >> wheels and everything that is far away from the c of g. So don't strap
              >> your
              >> tool box to the front fender. Also as it applies to me if I could lose
              >> weight then I would have less inertia too.
              >>
              >> Coming to the bars. Taking the weight of my body off the bars reduces the
              >> inertia of the bike too as my weight is then closer to the c of g. And
              >> you
              >> would get less of a smack through the wrists.
              >>
              >> So in search for the answer to your questions I have to ask where do you
              >> think the bike is and in what direction do you want to go?
              >>
              >>
              >> Sorry it must be alone on a Saturday night and the tv must be poor.
              >>
              >> Please do not hesitate to disagree with me I am just sounding out my
              >> thoughts in case someone has just invented a perfect triple rate spring
              >> and
              >> wants me to test it for free.
              >>
              >> Final opinion - go with the lightest possible damping oil as long as the
              >> bike doesn't pogo. The faster the wheels react to the surface the better
              >> as
              >> long as they don't create motion of their own.
              >>
              >> Did wonder if I could just clamp the handlebars to the raised forks
              >> without
              >> spacers but the I saw I had to faff with extending all the controls so
              >> never
              >> tried. Although I have two bits of brass ready to turn into spacers.
              >>
              >> A2
              >>
              >>
              >> -----
              >> A2
              >> Trophy 900, fox eyes, mostly red, mostly upright in southern England
              >> --
              >> View this message in context:
              >> http://old.nabble.com/Yes-it%27s-another-Genmar-question....-tp31304280p31304867.html
              >> Sent from the Triumph Trophy mailing list archive at Nabble.com.
              >>
              >
              >
              >
              >


              -----
              A2
              Trophy 900, fox eyes, mostly red, mostly upright in southern England
              --
              View this message in context: http://old.nabble.com/Yes-it%27s-another-Genmar-question....-tp31304280p31319289.html
              Sent from the Triumph Trophy mailing list archive at Nabble.com.
            • Adeux
              I worked through your piece and understand now that static sag is required to push out the suspension into holes in the road before the frame decides to take
              Message 6 of 9 , Apr 4, 2011
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                I worked through your piece and understand now that static sag is required to
                push out the suspension into holes in the road before the frame decides to
                take this route.

                I am concerned about my rear standard unit as the oil can only be getting
                presumably more contaminated and thicker. In some ways i am stunned that the
                rear copes with the massive differences between lone riding and fully kitted
                out with a passenger. My feeling is that the compromise could well be better
                served by two completely different setups. Presumably the levers in the rear
                progressively increase the loadings to compensate for added weights probably
                explaining the worse bang coming from the rear over the potholes.

                I blew a front seal in a year and was stunned by the change in the oil in
                that time. Pity there isn't an additional small bleed screw at the bottom of
                the forks to allow quick oil changes. Where's my drill and self tappers?
                Kiddin!

                Well stated
                A2

                -----
                A2
                Trophy 900, fox eyes, mostly red, mostly upright in southern England
                --
                View this message in context: http://old.nabble.com/Yes-it%27s-another-Genmar-question....-tp31304280p31319488.html
                Sent from the Triumph Trophy mailing list archive at Nabble.com.
              • Mark
                Rick, thanks your your input. You cleared up a lot of my questions and provided well explained insight into front suspension tuning. I did manage to put it
                Message 7 of 9 , Apr 4, 2011
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                  Rick, thanks your your input. You cleared up a lot of my questions and provided well explained insight into front suspension tuning. I did manage to put it all back together this weekend even if I did end up doing it twice! (Practice makes perfect!)

                  --- In TriumphTrophy@yahoogroups.com, "rick" <rhartwick@...> wrote:
                  >
                  >
                  >
                  > --- In TriumphTrophy@yahoogroups.com, "Mark" <highwayknight@> wrote:
                  > >
                  > > Ok, don't ya'll jump up on your soapboxes and start telling me about the FAQ section...I've been there and not found all the answers I'm looking for.
                  >
                  > Mark,
                  >
                  > The GenMars are their own problem, separate from your fork settings. They are just a mechanical issue of having sufficient brake hose lengths, etc.
                  >
                  > Setting up the suspension always seems to be a mystery, when it needn't be. As Adiuex alluded to, spring rate and ride height are two totally separate things. Changing the pre-load on the springs with spacers simply changes the height at which the front (or rear) will settle. More spacer length means the front will ride higher. Spring rate on the other hand, is the force/distance or strength of the spring. You can set a stiff or weaker spring to ride at any height you want with spacers (static sag).
                  >
                  > Separate from all of this is the steering geometry of the bike. Once the springs are set up the way you want, you adjust the attitude of the front by clamping the fork tubes higher or lower in the trees, so the bike will produce the steering responsiveness you want.
                  >
                  > So basically, you have three independent variables to work with.
                  >
                  > The Trophy forks have 150 mm of total travel. Ohlins and most manufacturers recommend setting the static sag at 25-30% of the total travel, thus giving your forks room to absorb bumps. For some reason, RaceTech simply states a sag of 25 mm (not %)which makes no sense to me, as fork travels vary.
                  >
                  > From the factory, the Trophy has right around 50 mm of sag. The tops of the fork tubes are set even with the top surface of the tree. I have experimented a lot, and I think these numbers produce and almost perfect tradeoff between quickness of steering and stability. So when all is said and done, you want the bike to settle to a static sag of about 50 mm, with you sitting on the bike with your full weight.
                  >
                  > You can accomplish this in two different ways. 1 - increase the fork spacer length (pre-load) which it appears the earlier owner did. 2- Use new stiffer springs, typically with a spring rate of about 0.95 - 1.0 kg/mm for the Trophy. You would then cut new spacers ( a lot of trial and work error) such that their pre-load will allow the bike to sag to about 38-50 mm (25-30% of full travel). In my experience, with a sag of only 30-40 mm, you will find the steering starts to become noticeably slower. To compensate, you would clamp the tubes up above the trees by some amount (say 20 mm if the sag were only 30 mm).
                  >
                  > So to help you with your current dilemma and keep things simple, find a small jack to fit under the oilpan of the bike, and with a thin piece of wood to protect the engine and the bike on the centerstand, raise the front of the bike back up so the wheel clears (and/or have someone heavy sit on the rear). You might want to confirm the oil levels by compressing the empty forks, using wood blocks to push the front wheel up to the end of its travel. Oil level should be about 125-130 mm typically. Use a tape and flashlight to measure from the oil to the top of the tubes. Note this method isn't highly accurate, as the forks should be removed and held vertical, but its close enough to make sure there is about the right oil in them.
                  >
                  > Remove the blocks under the front wheel (if you measured oil level) so the forks are fully extended, and insert the springs and spacers that came out. To screw in the top fork nuts without cross threading, I use a 7/8" deep well socket (or use the exact metric if you own one), with a long extension bar and ratchet. Cover the tank with a blanket, then stand up on the bike (carefully) and use your body weight to press down on the cap while keeping everything aligned, and you should be able to screw the caps back in without a problem, even though you won't have much feel as to whether they are cross-threaded. Using this approach though, you can get things pretty well-aligned visually, and should be ok.
                  >
                  > To check the sag, wrap a zip-tie or nylon thing above a fork seal, and measure the total distance from the bottom of the lower tree surface to top of your ziptie. Then, remove the jack and take it off the centerstand. Let the bike settle with you sitting on it (without a helper, you have to use a little weight on one foot to balance it). Subtract the new distance from the fully extended to obtain the static sag. You only have to measure the fully extended distance once (and put it in your logbook), but can do numerous trials of the weighted length (keep pushing the ziptie back down each time), until you feel you have it somewhat accurately. The factory stock setup should give you in the vicinity of 50 mm of sag, give or take your exact weight, etc.
                  >
                  > Then give it a test ride. If the bike seems to handle too sharply, either increase the spacer lengths even more to decrease the static sag, or lower the tubes in the trees below the top surface of the tree. If the steering is slow, do the opposite, until you get it the way you like it. More often than not, you will be raising the tubes above the tree. Note, work from the top surface of the triple tree, not the GenMar.
                  >
                  > Eventually, you might want to use stiffer spring rates of about 1 kg/mm, and then set the forks up as above for proper sag. The Trophy will become a taught, excellent handling little animal with better suspension. Of course, if you do this, the rear will be out of balance, so after that you will want to replace the rear shock with a top after market unit, set up in a similar way with stiffer springs.
                  >
                  > Before you go that route though, just screw the caps back on, check the sag (and again, record everything in a log book so you don't have to do it all again) and make small, rational adjustments until you get the bike handling the way you like.
                  >
                  > Of all the things you can do to the bike, suspension improvements will yield the best rewards, I think anyway. I put Ohlins springs on the front with RaceTech emulators, and an Ohlins rear shock (both no longer available) and the stability and handling of the bike are phenomenal. RaceTech springs are still available, along with a variety of top quality shocks. Start with what you have though, and then as you get comfortable, start to tweek things. None of this work is difficult, and you can easily do it once you see it once.
                  >
                  > Good luck,
                  >
                  > Rick Hartwick
                  > 00 Trophy 900
                  >
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