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RE: [T TBS R] Re: Fork Oil Replacement Questions (long)

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  • Pete Twissell
    Beware of using thicker oil to achieve stiffer damping. It s not as straightforward as it may appear. More damping = more heat More heat = thinner oil Thinner
    Message 1 of 9 , Oct 6, 2005
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      Beware of using thicker oil to achieve stiffer damping. It's not as straightforward as it may appear.

      More damping = more heat
      More heat = thinner oil
      Thinner oil = less damping

      In other words, the whole system will reach an equilibrium. Damping will be stiffer, but not as much as you might expect and temperatures will be higher.

      The biggest downside is inconsistency. When you start off from cold, your forks will be stiff as a board. As the oil warms, damping forces will drop. A secondary effect will be rapid degradation of the oil and seals due to high running temperatures.

      Good luck,

      Pete.

      -----Original Message-----
      From: triumphthunderbirdsportriders@yahoogroups.com [mailto:triumphthunderbirdsportriders@yahoogroups.com] On Behalf Of petermholmes
      Sent: 06 October 2005 12:47
      To: triumphthunderbirdsportriders@yahoogroups.com
      Subject: [T TBS R] Re: Fork Oil Replacement Questions (long)

      > I ordered a quart of 5wt fork oil from Amsoil (per the manual), and
      > they sent me a quart of 10wt by accident.

      > What do you guys think? Will my bike act too wierd with the wrong
      > oil?

      You'll get a stiffer ride because the higher weight oil slows down the suspension, preventing it from traveling as far as it normally would on compression and rebound. How weird it's acting is more a matter of your taste than anything. If you've got smooth roads you may even find that you prefer it.

      > Will it break stuff?

      It shouldn't. I used to both change to and mix different weight fork oils just to experiment (and, in the case of my RD350s, to try to get them to actually go around corners).





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    • welderboy@juno.com
      I just replaced the fork oil and springs on my 03 TBS - went with .95 kg. Race Tech springs to hold up my fat a** and 10w oil as suggested by Race Tech s
      Message 2 of 9 , Oct 6, 2005
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        I just replaced the fork oil and springs on my '03 TBS - went with .95
        kg. Race Tech springs to hold up my fat a** and 10w oil as suggested by
        Race Tech's tech. guy. Immediately following the work I hooked up with
        that marylandtbird dude for a 1000 mile trip down the Blue Ridge Pky. I
        was thinking about selling the bike before, but not now! I'm not a fan of
        progressive springs like the stockers are.

        Shawn
        On Thu, 6 Oct 2005 13:08:59 +0100 "Pete Twissell"
        <PTwissell@...> writes:
        > Beware of using thicker oil to achieve stiffer damping. It's not as
        > straightforward as it may appear.
        >
        > More damping = more heat
        > More heat = thinner oil
        > Thinner oil = less damping
        >
        > In other words, the whole system will reach an equilibrium. Damping
        > will be stiffer, but not as much as you might expect and
        > temperatures will be higher.
        >
        > The biggest downside is inconsistency. When you start off from cold,
        > your forks will be stiff as a board. As the oil warms, damping
        > forces will drop. A secondary effect will be rapid degradation of
        > the oil and seals due to high running temperatures.
        >
        > Good luck,
        >
        > Pete.
        >
        > -----Original Message-----
        > From: triumphthunderbirdsportriders@yahoogroups.com
        > [mailto:triumphthunderbirdsportriders@yahoogroups.com] On Behalf Of
        > petermholmes
        > Sent: 06 October 2005 12:47
        > To: triumphthunderbirdsportriders@yahoogroups.com
        > Subject: [T TBS R] Re: Fork Oil Replacement Questions (long)
        >
        > > I ordered a quart of 5wt fork oil from Amsoil (per the manual),
        > and
        > > they sent me a quart of 10wt by accident.
        >
        > > What do you guys think? Will my bike act too wierd with the wrong
        >
        > > oil?
        >
        > You'll get a stiffer ride because the higher weight oil slows down
        > the suspension, preventing it from traveling as far as it normally
        > would on compression and rebound. How weird it's acting is more a
        > matter of your taste than anything. If you've got smooth roads you
        > may even find that you prefer it.
        >
        > > Will it break stuff?
        >
        > It shouldn't. I used to both change to and mix different weight
        > fork oils just to experiment (and, in the case of my RD350s, to try
        > to get them to actually go around corners).
        >
        >
        >
        >
        >
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      • petermholmes
        ... straightforward as it may appear. ... will be stiffer, but not as much as you might expect and temperatures will be higher. ... your forks will be stiff as
        Message 3 of 9 , Oct 6, 2005
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          > Beware of using thicker oil to achieve stiffer damping. It's not as
          straightforward as it may appear.
          >
          > More damping = more heat
          > More heat = thinner oil
          > Thinner oil = less damping
          >
          > In other words, the whole system will reach an equilibrium. Damping
          will be stiffer, but not as much as you might expect and temperatures
          will be higher.
          >
          > The biggest downside is inconsistency. When you start off from cold,
          your forks will be stiff as a board. As the oil warms, damping forces
          will drop. A secondary effect will be rapid degradation of the oil and
          seals due to high running temperatures.

          While I'm much more of an empirical guy than an engineer, I personally
          found the "oil tuning" process to be pretty straightforward. Also,
          for what it's worth, I never lost an oil seal in the process.

          Obviously, though, YMMV. And you should keep in mind that I was
          experimenting with '60s and '70s suspensions. Perhaps suspension
          tuning has gotten more complex over the years? I don't know. I
          haven't played with the suspension on my TBSes because I like them the
          way they are.
        • ncbtbs
          Thanks for the input. I think I ll use the 10wt as a flush and the 5wt as the actual fork oil. I liked my bike s suspension before, and don t have any reason
          Message 4 of 9 , Oct 6, 2005
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            Thanks for the input. I think I'll use the 10wt as a flush and the
            5wt as the actual fork oil. I liked my bike's suspension before, and
            don't have any reason to change it.

            NutCaseBob
          • Pete Twissell
            Your observations regarding older suspension are correct. 60 s forks often specified 30 or 40wt oil as standard. From that starting point, almost any change
            Message 5 of 9 , Oct 7, 2005
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              Your observations regarding older suspension are correct. 60's forks often specified 30 or 40wt oil as standard. From that starting point, almost any change would be an improvement! The use of thinner oil requires tighter manufacturing tolerances on the parts which control damping. At one extreme would be the BSA bantam, which had no proper damping but could be 'tuned' by using different densities of grease! At the other extreme, the dampers which I work with use the lightest oil available (2.5w), maintain damping from below zero to 180°C, and use components manufactured to tolerances of 2 microns (with a price tag to match!).

              Pete.

              P.S. excuse my ignorance of forum abbreviations, what is YMMV?

              -----Original Message-----
              From: triumphthunderbirdsportriders@yahoogroups.com [mailto:triumphthunderbirdsportriders@yahoogroups.com] On Behalf Of petermholmes
              Sent: 07 October 2005 06:03
              To: triumphthunderbirdsportriders@yahoogroups.com
              Subject: [T TBS R] Re: Fork Oil Replacement Questions (long)

              > Beware of using thicker oil to achieve stiffer damping. It's not as
              straightforward as it may appear.
              >
              > More damping = more heat
              > More heat = thinner oil
              > Thinner oil = less damping
              >
              > In other words, the whole system will reach an equilibrium. Damping
              will be stiffer, but not as much as you might expect and temperatures will be higher.
              >
              > The biggest downside is inconsistency. When you start off from cold,
              your forks will be stiff as a board. As the oil warms, damping forces will drop. A secondary effect will be rapid degradation of the oil and seals due to high running temperatures.

              While I'm much more of an empirical guy than an engineer, I personally found the "oil tuning" process to be pretty straightforward. Also, for what it's worth, I never lost an oil seal in the process.

              Obviously, though, YMMV. And you should keep in mind that I was experimenting with '60s and '70s suspensions. Perhaps suspension tuning has gotten more complex over the years? I don't know. I haven't played with the suspension on my TBSes because I like them the way they are.





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            • petermholmes
              ... 40wt??? Holy Cow!!! Who was specing that? My Bultacos all started with 15wt in them if I recall correctly. The RD350s, I think, had 10wt to start with
              Message 6 of 9 , Oct 7, 2005
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                > 60's forks often specified 30 or 40wt oil as standard.

                40wt??? Holy Cow!!! Who was specing that? My Bultacos all started
                with 15wt in them if I recall correctly. The RD350s, I think, had
                10wt to start with but it didn't matter because, as best I could tell,
                no amount of tinkering short of pouring in 90wt gearbox oil and
                ripping most of the bottom of the bike off would make one of those
                things go around a corner.

                > P.S. excuse my ignorance of forum abbreviations, what is YMMV?

                The EPA disclaimer - Your Mileage May Vary.
              • petermholmes
                ... maintain damping from below zero to 180°C, and use components manufactured to tolerances of 2 microns (with a price tag to match!). P.S. What the *heck*
                Message 7 of 9 , Oct 7, 2005
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                  > the dampers which I work with use the lightest oil available (2.5w),
                  maintain damping from below zero to 180°C, and use components
                  manufactured to tolerances of 2 microns (with a price tag to match!).

                  P.S. What the *heck* are you making that is manufactured to a
                  tolerance of 2 microns? NASA stuff? Air Force? I remember when the
                  steam turbine engineers were as happy as clams if you could give them
                  a CNC tape which would recreate the profile of their '50s cams (drawn
                  using French curves and made by hand) to within .015".
                • Pete Twissell
                  Triumph forks used the same oil as the engine. I wasn t aware of any RD350 s in the 60s. Most of those that I came across were in the form of a twisted crank,
                  Message 8 of 9 , Oct 7, 2005
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                    Triumph forks used the same oil as the engine. I wasn't aware of any RD350's in the 60s. Most of those that I came across were in the form of a twisted crank, clutched by soft pink thing which was asking me to rebuild and weld it!

                    -----Original Message-----
                    From: triumphthunderbirdsportriders@yahoogroups.com [mailto:triumphthunderbirdsportriders@yahoogroups.com] On Behalf Of petermholmes
                    Sent: 07 October 2005 14:08
                    To: triumphthunderbirdsportriders@yahoogroups.com
                    Subject: [T TBS R] Re: Fork Oil Replacement Questions (long)

                    > 60's forks often specified 30 or 40wt oil as standard.

                    40wt??? Holy Cow!!! Who was specing that? My Bultacos all started with 15wt in them if I recall correctly. The RD350s, I think, had 10wt to start with but it didn't matter because, as best I could tell, no amount of tinkering short of pouring in 90wt gearbox oil and ripping most of the bottom of the bike off would make one of those things go around a corner.

                    > P.S. excuse my ignorance of forum abbreviations, what is YMMV?

                    The EPA disclaimer - Your Mileage May Vary.





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                  • petermholmes
                    ... Wow! ... There weren t any. I had a 73 and a 75 before I finally gave up on them.
                    Message 9 of 9 , Oct 7, 2005
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                      > Triumph forks used the same oil as the engine.

                      Wow!

                      > I wasn't aware of any RD350's in the 60s.

                      There weren't any. I had a '73 and a '75 before I finally gave up on
                      them.
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