Bike Fit/ Math Question

Triathlon Forum
1

For the experts:
Looking to remove 1 remaining spacer on E112, head tube angle 72.5 degrees, trigonometry question:

  1. By how many cm will my aerobar pads move forward for additional 1cm drop at 72.5 degree head tube angle?
  2. To preserve my hip angle, the saddle will have to slide forward a bit? Any eyeball rough figure?
  3. For every mm/ cm saddle forward, how many mm/ cm do I go up to preserve the saddle to BB distance/ saddle height?
    Just being lazy to start drawing it and calculating. Hoping that there are some ST fit gurus hanging around. Thanks.
2

  1. cos72.5

  2. not sure, maybe 5cm? Moving forward doesn’t increase hip angle as much as you think

  3. 15% maybe?

You should draw it on graph paper if you are actually interested in drawing it.

3

Thank you, will try here in a few minutes.

4

For the experts:
Looking to remove 1 remaining spacer on E112, head tube angle 72.5 degrees, trigonometry question:

  1. By how many cm will my aerobar pads move forward for additional 1cm drop at 72.5 degree head tube angle?
  2. To preserve my hip angle, the saddle will have to slide forward a bit? Any eyeball rough figure?
  3. For every mm/ cm saddle forward, how many mm/ cm do I go up to preserve the saddle to BB distance/ saddle height?
    Just being lazy to start drawing it and calculating. Hoping that there are some ST fit gurus hanging around. Thanks.

wish i had my autocad…

i guess i could figure it out using the ol’ Ti83…

lazy man am i

5

From a previous post of mine:

Tried it on the Saturday long ride, and sure enough, it ain’t right. Some quick math a minute ago yields that dividing the HTA by 36* gives me the vertical change of adding/removing spacers, and from there I can subtract the horizontal effect. Ergo, removing a 2.5mm spacer moves the bars down 2.02mm, and forward .48mm.
(At least with a 73 HTA and 2.5mm spacer change)

So, I think it’s safe to ASS U ME that by dropping 1cm in stem stack height, you’ll add ROUGHLY 1.92mm in pad reach.

You may not need to change anything vis a vis your pads or your saddle. Ride it first.

*Nobody corrected my math the first time around, so I’m sticking with it unless somebody smart says otherwise.