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Weirdly fitted crankset on a 2017 Synapse?

daniel_bdaniel_b Posts: 11,432
edited March 2021 in Workshop
Afternoon all,

tried to index the gears on my mates 2017 Synapse that has never been right, and no surprise it was bought from Evans.

Rears I got shifting perfectly, up and down the block, no issues at all - used the limit screws, and sweet as a nut.

Re-positioned the front derailleur, as it was too high and not perfectly parallell.

One gear I cannot get to work, but it is not rubbing the cage.
So 34T on the front, and 11 on the rear - the chain is catching on the 50T
How can that possibly happen, or is the crankset somehow fitted incorrectly, and too far inboard...?

On first glance, it looks ok positioning wise in relation to the BB area, and he was delighted to have 21 gears available to him which was a high percentage increase, but I've never seen that happen before.
Felt F70 05 (Turbo)
Marin Palisades Trail 91 and 06
Scott CR1 SL 12
Cannondale Synapse Adventure 15 & 16 Di2
Scott Foil 18

Posts

  • whyamiherewhyamihere Posts: 7,681
    edited March 2021
    Is it a Synapse disc? Disc bikes have a slightly wider hub, putting the 11t further from the centreline of the bike. Depending on the chainline of the cranks and the chainstay length, that can give an even worse chain angle than usual in that combination, which could cause the chain to touch the outer ring. Some cranks have had their chainline increased by a couple of mm to accommodate this.
  • david37david37 Posts: 1,313
    the current synapse isn't even a meaty 135 its a 142! can you fit a space on the drive side crank to move it out slightly?
  • daniel_bdaniel_b Posts: 11,432
    whyamihere said:

    Is it a Synapse disc? Disc bikes have a slightly wider hub, putting the 11t further from the centreline of the bike. Depending on the chainline of the cranks and the chainstay length, that can give an even worse chain angle than usual in that combination, which could cause the chain to touch the outer ring. Some cranks have had their chainline increased by a couple of mm to accommodate this.

    david37 said:

    the current synapse isn't even a meaty 135 its a 142! can you fit a space on the drive side crank to move it out slightly?

    It is a disc version!
    ah never come across that before.

    Hadn't considered a spacer, but will look into it.

    Pleased it's not me going nuts then.
    Felt F70 05 (Turbo)
    Marin Palisades Trail 91 and 06
    Scott CR1 SL 12
    Cannondale Synapse Adventure 15 & 16 Di2
    Scott Foil 18
  • whyamiherewhyamihere Posts: 7,681
    The cassette position is actually identical regardless of whether it's a 135mm QR or a 142mm through axle. On a bike with a through axle, the hub's end-caps are slightly recessed into the dropouts. That's why you can easily convert between 135mm QR and 142mm through axle on many hubs, the freehub body stays where it is, just the end-caps change.
  • itboffinitboffin Posts: 20,050
    Erm convert from 135mm QR to through axle doesn’t the frame need to be through axle already?
    Rule #5 // Harden The censored Up.
    Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
    Rule #12 // The correct number of bikes to own is n+1.
    Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.
  • whyamiherewhyamihere Posts: 7,681
    itboffin said:

    Erm convert from 135mm QR to through axle doesn’t the frame need to be through axle already?

    I was purely talking about the hubs, not converting a frame.
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