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thegreatdivide
thegreatdivide Posts: 5,807
in Road general
My mind has been fried from looking at too many work stats in the office this morning, so I need help answering this simple (and obvious) bike fit question.

If new bike A has a stack measurement 11mm higher than old bike B (both stack measurements are measured without headset caps) and old bike B has 15mm of spacers to get my fit spot on – I just need a 5mm spacer added to new bike A to match the stack of old bike B yeah?

NB - 1mm stack difference will make no difference to my fit and how bike feels (it really won’t) and they both have the same reach, will be running 90mm stems and matching bars/shifters.

Comments

  • me-109
    me-109 Posts: 1,915
    Yes, other size spacers are available so you can fine tune. Your headset config could alter the maths a little too, but not hugely.
  • thegreatdivide
    thegreatdivide Posts: 5,807
    Thanks me-109. Major case of overthinking this morning.
  • joeyhalloran
    joeyhalloran Posts: 1,080
    It will (very marginally) affect the reach values too.
  • singleton
    singleton Posts: 2,523
    edited March 2023
    I'm not intending to split hairs, but since you were talking about a 1mm change to stack, you also need to be aware that adding / reducing spacers will also impact reach.
    There are other calculators out there, but this is on example https://www.bikestem.fit
    Since the head-tube is angled towards you, as you add spacers, the bars come backwards and closer to you reducing the reach.
    How much will depend on the angles, but 10mm difference in spacers is likely to have a small (3mm?) impact on reach.
  • thegreatdivide
    thegreatdivide Posts: 5,807
    Both bikes have the same headtube angle, and when you get into sub 5mm differences it's the equivalent of bar tape thickness.
  • joeyhalloran
    joeyhalloran Posts: 1,080
    It's a 3mm affect on reach, not much but might be noticeable for some if on the edge in their current set up.
  • pippi_langsamer-2
    pippi_langsamer-2 Posts: 1,470
    https://www.bikegeocalc.com/ is also very good. You can input spacers, even stack of your headset cap. Also handy to put multiple bikes in and compare/ 'shadow'.

    As mentioned though, I think we're getting into the realms of quantum bike fitting here, and i think your spine probably compresses/ extends a lot more than some of these measurements we're talking about at any given time on any given day...
  • dannbodge
    dannbodge Posts: 1,152
    In answer to your question yes.

    You'd probably lose/gain more than 1mm just by wearing gloves

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