Effective Top Tube Length

keithc440
keithc440 Posts: 277
edited September 2010 in Workshop
When looking at a bike I currently own it has an effective top tube (EFT) of 57cm measured from the centre of the seat tube to the centre of the head tube. However I ride with spacers under the stem on this bike as it has quite a low head tube of 150 mm. If I want to compare this frame to another should i really be measuring the EFT from the centre of the steerer at the top of the stem to the centre of the seatpost. All measurements taken horizontally of course. If I were to use the second method of measuring the EFT, am I right in assuming I could actually ride a bike with a shorter top tube assuming the height of the head tube is not taller than my current head tube and spacers length combined. I know seat tube angle also has to be considered when comparing EFT but I am asking here about the use of spacers and the corresponding effect on EFT.
Apologies if this is a bit of a numpty question but I want to make sure my understanding of bike fit is correct.

Comments

  • synchronicity
    synchronicity Posts: 1,415
    :? Are you basically asking if a taller front end (longer head tube with no spacers) will affect the effective top tube length?

    I prefer to look at things in terms of saddle to bar drop, and top tube centre-centre measurements on the frame itself. Why?
    Because things can vary like saddle length, stem clamp height, spacers, saddle offset, etc...
    vertebr.ae | precision braking & shifting
  • PeterBL
    PeterBL Posts: 209
    Seat tube and head tube angles are almost identical on most bikes, so it shouldn't make any real difference, where you measure the effective top tube.
  • keithc440
    keithc440 Posts: 277
    Thanks for the replies. Peter I think you have made the correct point that it depends on the angles. Realised myself as I was thinking it out over lunch. Thanks for the confirmation.

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