Fork Oil Height

Discussion in 'Bonneville' started by DGBland, Oct 4, 2022.

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  1. DGBland

    DGBland Member

    I am aware this question has probably been asked before but I have a 2015 t100 and have drained the old fork oil out and am ready to replace it with new oil. However I now have progressive fork springs from TEC and I don't know if the fork oil height should change from the normal. The manual tells me how much oil and what the height should be with stock springs. Do I follow the advice in the manual.?

  2. Ducatitotriumph

    Ducatitotriumph Crème de la Crème

    Apr 25, 2019
    I could be totally wrong but I think it's the same amount?
    I THINK you can change the "weight" of it (viscosity) though.
  3. Dartplayer

    Dartplayer Crème de la Crème

    Aug 8, 2018
    New Zealand
    If height measure is down from the top of depressed fork, without springs, it remains unchanged.
    The importance is the air gap.
    • Agree Agree x 2
  4. ChessNibbler

    ChessNibbler Member

    May 29, 2022
    Orange County, NY
    @DGBland I just installed the TEC prgressive springs on my T120 with OUTSTANDING improvement. They are much better than the OEM springs. I measured the oil coming out of both forks at 12oz and put back that exact same amount of oil. I used 10 weight oil. I did not measure air gap because I'm lazy and didn't know what the correct amount was supposed to be. So sealed it up and the ride was very stiff, but marvelously more contrlled than the original shocks.

    After more than 200 miles of use, they have broken in and the improvement in control has made me a much better rider. I can now drive over extremely bumpy uneven pavement at high speed while in a turn and feel complete control. So 12oz works but might be a bit stiff at first. After 200 miles I think the feel is perfect. I have the adjusters backed all the way OUT. They are at their lowest pressure setting so I have tons of room for tightening as the miles tick away.
    Good Luck.
  5. tim scott

    tim scott Well-Known Member

    Aug 30, 2021
    Interesting thread, I’ve just done the same as Chessnibber. Bought myself some Tec springs earlier in the year and finally got round to fitting them last Friday. The initial ride was somewhat laboured not because the springs were wrong in any way but because the bars hadn’t gone back exactly right and my bar end mirrors were giving me a great view of the beautiful blue sky - but for rear visibility were about as much use as Anne Franks drum kit
    One small adjustment later and I’m thinking about the springs rather than my rear viz - which is where I should be

    what a transformation

    I dialled the adjusters all the way in then backed them out until the thread was just visible, the ride home was eye opening. All hints of nervousness and skittishness from the front were gone, the springs soaked up the minor imperfections and the ride was a revelation, but it was still a little hard

    However Saturday I wound the springs all the way out and then dialled them in 4 full turns and the results were significantly better. I’m a bit of a lump but this tweak made the front seem to float over the bumps ( my main roads are back lanes and KCC are a bit rubbish at road maintenance). I may tinker further but for now it’s superb

    Hagon rear springs to follow next year but in conjunction with the Avon Spirits I put on earlier in the year the ride is not only more refined but also hugely confidence inspiring, utterly recommended for a mere £139.

    Delboy (of Delboys Garage fame) confirms the fork oil is exactly the same, although it’s worth letting the springs drain into the fork leg for a couple of minutes when you take them out.
  6. havschk

    havschk New Member

    Apr 13, 2023
    United States
    When you change to progressive fork springs, you may need to adjust the oil level and viscosity to optimize the suspension performance. Typically, progressive springs have different characteristics than the stock springs, and they may require a different oil height to achieve the desired damping effect.

    In general, it is recommended that you follow the instructions provided by the manufacturer of the progressive springs. They may suggest a different oil level or viscosity to match the new springs. Alternatively, you can consult with a motorcycle suspension specialist or a mechanic who has experience with your specific bike model.

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