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  • Fork offset makes my brain hurt.
  • cupotea
    Full Member

    I’m in the process of ordering a fork for Sonder Signa Ti but I’m confused about offset. In the launch video for the frame with Singletrack Neil mentions that with the 42mm offset it felt that the front wheel was more underneath than the 51mm.  My understanding was it would be the other way around. Am I being particularly thick today?

    wwaswas
    Full Member

    This isn;t bad – it shows relationship between ofset and trail.

    https://www.mbr.co.uk/news/fork-offset-head-angle-trail-342679

    antares
    Free Member

    As above. The smaller the offset the bigger the trail figure as th3 wheel moves further “under” the bike

    cupotea
    Full Member

    Ah ok. Does the decreased trail not make the fork ‘flop’ more?

    andyrm
    Free Member

    Here you go!

    Really good article from Seb Stott, an experiment with Chris Porter:

    https://www.bikeradar.com/mtb/gear/article/pushing-the-limits-of-fork-offset-an-experiment-45343/

    And here’s the Pinkbike article where Transition credit the above for sowing the seed for their research that led to SBG:

    https://www.pinkbike.com/news/transitions-new-speed-balanced-geometry-2017.html

    dmorts
    Full Member

    curvature
    Free Member

    A headache yes but also remember that playing with fork offset and travel may well alter the wheelbase.

    Ibis state that I should use a 51mm offset fork on my Ripley. However as I was going for a 140mm travel fork I stuck with a 42mm offset fork as it would keep the wheelbase slightly shorter.

    I haven’t ridden a Ripley with a the 51mm fork offset but all I can say is I have owned my Ripley longer than any other bike and have no intention of changing it other than the new 11sp groupset ordered yesterday.

    cupotea
    Full Member

    Thanks @sweaman2 , that first one made the most sense to me.

    I think that with the Sonder being a not obscene 66 degree HA that I will stick with 51mm offset.

    the00
    Free Member

    Just had a quick play on CAD to come up with this:

    Based on wheel diameter of 770mm (wide 29er).

    So 10mm off your offset, results in a similar effect in trail to a 1deg slacker head angle.

    cupotea
    Full Member

    I’m confused again! I though that the increased trail meant a shorter wheelbase and therefore make it feel steeper.

    geex
    Free Member

    Stop overthinking it and just ride your bike (more)

    cupotea
    Full Member

    This is n+1 so not impacting on riding 😉

    That said, I have an order in so I just need to stop second guessing myself. Really looking forward to it being built up.

    Mbnut
    Free Member

    So I am looking at the Signal Ti too….

    If I want to run a 42mm offset fork is it a good idea to size up or maybe knock a degree off the HA, they do custom.

    geex
    Free Member

    no @cupotea. All I meant was it doesn’t matter. And the more (different) bikes you ride. the more it won’t matter. The human brain and body are great at automatically recalibrating the subtle differences between slightly different but very similar things.

    Except that one guy who chucks his beer down his shirt if it’s served in a slightly different glass? Don’t be that guy.

    Northwind
    Full Member

    Just pretend like you understand it. If it helps, do some press releases and produce a bike, that way other people will read it and ride it and pretend to understand it.

    I had a G2 Fox 34 and a Pike and I really just about convinced myself I could feel the difference from the magic fork offset of the Foxes for a while, til I discovered that the Pike had the exact same offset and just didn’t give it a special name. From this I concluded that stickers are powerful

    the00
    Free Member

    Head angle effects the ‘directness’ of the steering, whilst also changing the mechanical trail and front centre dimension.

    Fork offset effects mechanical trail and front centre only.

    But the changes shown above are pretty small, so I whilst we might find it interesting, I mostly agree with Northwind.

    philjunior
    Free Member

    Head angle effects the ‘directness’ of the steering, whilst also changing the mechanical trail and front centre dimension.

    Fork offset effects mechanical trail and front centre only.

    Not sure this is entirely true. But I’d welcome an explanation of why.

    FWIW I tend to ride a bike and if it feels OK just enjoy it, then needlessly judge potential new bikes for being dissimilar to it… Although undoubtedly what I’m running has changed.

    Geometry has been played with a lot and it’s not surprising that offset has now become a variable rather than a standard number.

    I remember somebody was doing some serious research into how steering geometry affected a bike’s rideability/stability – although a range of numbers for making a stable (no hands rideable) bike are known, the physics aren’t well understood… I’d be interested for someone to take it a bit further and study how things go when it gets lumpy (if you’re going over a bump, the trail will decrease and perhaps become negative at certain points as you pass it.).

    The research did manage to make a bike that had a head angle >90° that still self balanced – although there was some significant messing about with the centre of gravity (which is where stem length and TT length/BB position come into the cornering of a bike).

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