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Thread: DUC32 tuning

  1. #1
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    DUC32 tuning

    Any tuning suggestions for the DUC32?

    I have a ML7 with a DUC32 that I use for just about everything. I have the fork set to the recommended factory settings for a 165lb rider. The 6" of plush travel works great for trail riding, but is less than ideal for racing. I know it's not the perfect fork for XC and short track racing, but it's what I'm riding. For short track, I run the fork in the lockout mode for the whole race to minimize bobbing. For XC I tend to lock out the fork a lot and run the full travel when descending. Luckily the lockout lever is really convenient to get to.

    Are there any recommendations for settings to stiffen the fork up (less bob) when accelerating out of the saddle, while mimimizing suspension compromises on midsized hits? For a race course, bigger hits tend to be nonexistent. I'd like to optimize the suspension for racing during the core of the race season, then set it back to trail settings for the rest of the season.

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    If you don't mind losing small bump performance, you can experiment with the shim stack all the way up to 21,15,15,12 setup.

    Your starting point should be the Aggressive All Round setup which is 21,15, 12, with piston flat side down so the stack is preloaded.

    You should also start experimenting with oil viscosity. This is easier than it sounds and requires that you buy two viscosities that span your likely range of adjustment and then mix them in proportion. You will pretty soon get quick at replacing the oil.

    Buy oil on the basis of its cSt viscosity at 40 degC and get decent quality that has a high VI. Your thin oil should be around 16cSt which is typical of a lot of 5wt oils. Your thick oil can be something down around 30cSt (which is what I use at 210lbs).

    Buy a decent brand from a range that doesn't suffer from too much marketing. Silkolene RSF oils are a good example, as used in this mixing chart

  3. #3
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    Checking the Pro RSF viscosities, pure 5w may be close to what you need, so refill with 5wt Pro RSF and then see in which direction you need to head. If you need it slower still, then mix 5wt with 7.5 wt. If not, buy a bottle of 2.5wt and get mixing.

  4. #4
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    DUC tuning

    Be careful of over damping the fork thru it's shim stack. Going too firm on the shim stack will make the fork feel very harsh. You need a combination of shim stack, oil weight and over all pressure. At 165 lb rider looking for a firmer feel, I would do this:

    10wt oil, good quality as Petercam mentions, this will keep the rebound in check for a slighlty higher over all pressure that i will recommend.

    85-90psi in the damper cartridge, this will help with the last part of the travel by making it a more progressive feel.

    12-15cc of thick oil in the air cartridge, again this will make the fork fairly progressive.
    We recommend Sram Red Rum or Fox Float Fluid for this.

    The next step after trying these steps first, would be to try a heavier negative spring. This is normally reserved for people running higher than 115+ air pressure. But, by using the 6Nm spring you can run higher pressure in the main air side and have the fork supple off the top but ramp up quickly into just the first 1/3 of its travel.

    I might suggest using the "lite" shim stack, from piston up = 21mm,12mm,15mm.
    This will give the small and medium hits to remain supple.

    So the key to all of this is to use air pressure to control slow fork movement (bobbing), shims to control bigger hits, with out losing small bump compliance. Oil viscosity to control rebound, amongst every thing!

    Enjoy-

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    Ethan Franklin is a studly mechanic.

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    thanks

    Cool. These posts are just what I was looking for. I'll give it a try. I'll post feedback after I've ridden it a bit.

  7. #7
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    Quote Originally Posted by Count Zero
    Ethan Franklin is a studly mechanic.
    Quote Originally Posted by mikesee
    Better suited to non-aggressive 125# gals named Russell.
    I ride so slow, your Garmin will shut off.

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    Quote Originally Posted by Count Zero
    Ethan Franklin is a studly mechanic.
    ... and I try to be as stupid as him

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    wait a minute!

    I though all oils had o be at least 30; but that REDUM was closer to sixty! for this particular project. So then do them shims fillibrate properlly? Cheers, Carl


    Quote Originally Posted by Ethan F
    Be careful of over damping the fork thru it's shim stack. Going too firm on the shim stack will make the fork feel very harsh. You need a combination of shim stack, oil weight and over all pressure. At 165 lb rider looking for a firmer feel, I would do this:

    10wt oil, good quality as Petercam mentions, this will keep the rebound in check for a slighlty higher over all pressure that i will recommend.

    85-90psi in the damper cartridge, this will help with the last part of the travel by making it a more progressive feel.

    12-15cc of thick oil in the air cartridge, again this will make the fork fairly progressive.
    We recommend Sram Red Rum or Fox Float Fluid for this.

    The next step after trying these steps first, would be to try a heavier negative spring. This is normally reserved for people running higher than 115+ air pressure. But, by using the 6Nm spring you can run higher pressure in the main air side and have the fork supple off the top but ramp up quickly into just the first 1/3 of its travel.

    I might suggest using the "lite" shim stack, from piston up = 21mm,12mm,15mm.
    This will give the small and medium hits to remain supple.

    So the key to all of this is to use air pressure to control slow fork movement (bobbing), shims to control bigger hits, with out losing small bump compliance. Oil viscosity to control rebound, amongst every thing!

    Enjoy-

  10. #10
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    Quote Originally Posted by font9a
    I though all oils had o be at least 30; but that REDUM was closer to sixty! for this particular project. So then do them shims fillibrate properlly? Cheers, Carl
    What's are we talking about? The bottom of the damper tube of the air spring cartridge or the top of the spring air cartridge?
    In the Duc 32 manual, it is said "Add 5ml of 5-15wt oil into the Damper Tube before inserting the Piston, and 3ml between the Piston and Seal Head", we say 15wt max.
    Now, you can read in the DUC32 & SC32 Tuning chart "Oil Volume - bottom of cartridge, say 5ml (but no more precision about the viscosity) and Oil Volume top of air spring piston Same (Red Rum or 80wt oil)".

    And now you say "12-15cc of thick oil in the air cartridge, again this will make the fork fairly progressive. We recommend Sram Red Rum or Fox Float Fluid for this."
    I think you mean 12-15cc in the bottom of the damper tube. But, between 5-15wt and Red Rum (or Fox Fluid) there is a very big difference, no ?
    Ethan, it will be very very interesting to have a better view of the different adjustements and their effects on the behavour of the DUC32. The chart is clear but sometimes ... less. Imagine an exploded view for each leg with indicated pressure, oil level, wt, shims position >> with their effect on the answer.

    thanks for you help

  11. #11
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    The 12-15cc is definitely in the bottom of the air cartridge (damper tube).

    The principal job of the lower air spring lube is to vary the air space volume. If you use an oil like red rum, it may also cling to the side walls of the cartridge, lubricating the underside of the air spring o-ring. This effect is secondary compared to the modification of the air spring. You could use 15ml olive oil to vary the air spring characteristic. The refinement of using something like red rum has come from experience with the fork in real world use.

    There is a big confusion caused by SAE oil ratings. 80wt gear oil is on a different viscosity scale to 15wt suspension /engine oil. It turns out that their viscosity is pretty similar. The oil in the air spring doesn't go anywhere near a shim stack. The oil in the damper cartridge needs to be accurately chosen to an appropriate viscosity to work properly.

  12. #12
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    Quote Originally Posted by petercarm
    The 12-15cc is definitely in the bottom of the air cartridge (damper tube).

    The principal job of the lower air spring lube is to vary the air space volume. If you use an oil like red rum, it may also cling to the side walls of the cartridge, lubricating the underside of the air spring o-ring. This effect is secondary compared to the modification of the air spring. You could use 15ml olive oil to vary the air spring characteristic. The refinement of using something like red rum has come from experience with the fork in real world use.

    There is a big confusion caused by SAE oil ratings. 80wt gear oil is on a different viscosity scale to 15wt suspension /engine oil. It turns out that their viscosity is pretty similar. The oil in the air spring doesn't go anywhere near a shim stack. The oil in the damper cartridge needs to be accurately chosen to an appropriate viscosity to work properly.
    clear, thanks

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