Daft question about bike fit measurement

mosa
mosa Posts: 754
edited December 2013 in Road general
I was bike fitted on a 54cm in the past. I now have a 56cm bike which feels fine but was considering returning to get fit to it. I have just found the detail sheet I got with last one. Can I use the same measurements & just calculate the difference between bikes. Ie if my saddle to handlebar reach was 53cm do I just match that up with reduction of stem Keeping my saddle gore-aft the same at 75mm

Couldn't get another 54 when got other bike but I've rode both and both seem fine. 54 was cervelo s2. 56 is madone
My bikes

2018 Trek Emonda SL6 Pro

Comments

  • MichaelW
    MichaelW Posts: 2,164
    Pretty much, yes, use fore-aft, up/down from the bottom bracket and you will replicate your position.
    Make sure you have the same crank length.
  • mosa
    mosa Posts: 754
    Cheers. The pain is the seat height (wish they would just measure from floor)
    My bikes

    2018 Trek Emonda SL6 Pro
  • bottom bracket or pedal length to your saddle will be the same on both bikes.
  • mosa wrote:
    Cheers. The pain is the seat height (wish they would just measure from floor)

    If diff bikes had diff heights from centre of crank axle to the floor and/or diff crank lengths - it would bu**er that measurement though .
  • mosa
    mosa Posts: 754
    edited December 2013
    Cheers. I suppose if I get the seat height & fore aft right then I won't need to do the plumb bob on my pedals do I ?
    My bikes

    2018 Trek Emonda SL6 Pro
  • buckles
    buckles Posts: 694
    Assuming same length cranks on both bikes, to measure saddle height simply measure distance to top of saddle from floor then subtract distance from BB centre to floor.
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  • One thing not mentioned far is that going from a 54cm to 56cm the wheelbase will normally be longer, so this could affect the handling of the bike, which you wouldn't realise if you just sat on the new bike in the shop and didn't test ride it. Also there's the question of steering angles, fork rake and stem length will affect the handling. It's not just a question of making the distance from bottom of pedal stroke to top of saddle the same.

    Personally I don't have any experience with Madone or Cervelo bikes so I can't comment on the particular models you are thinking of choosing.
  • Grill
    Grill Posts: 5,610
    The difference in wheelbase will have an inconsequential effect on handling, but that short ass stem will make the larger frame feel really nervous.
    English Cycles V3 | Cervelo P5 | Cervelo T4 | Trek Domane Koppenberg
  • giant_man
    giant_man Posts: 6,878
    mosa wrote:
    I was bike fitted on a 54cm in the past. I now have a 56cm bike which feels fine but was considering returning to get fit to it. I have just found the detail sheet I got with last one. Can I use the same measurements & just calculate the difference between bikes. Ie if my saddle to handlebar reach was 53cm do I just match that up with reduction of stem Keeping my saddle gore-aft the same at 75mm

    Couldn't get another 54 when got other bike but I've rode both and both seem fine. 54 was cervelo s2. 56 is madone
    This is possible as every frame has a different geometry, including two of the same size ie. 54cm
  • MichaelW
    MichaelW Posts: 2,164
    mosa wrote:
    Cheers. I suppose if I get the seat height & fore aft right then I won't need to do the plumb bob on my pedals do I ?

    It is useful to use a plumb bob from the top tube to the BB centre. Mark/measure the position with tape and use that as your index for up/down, fore/aft measurement. A bit of simple adding will give you the dimensions you need. It is easier to do with horizontal top tubes but you can make it work with sloping tubes.