Originally Posted by
spclark
I've been riding my '72 Motobecane with a seat-to-bb height @ 28". Seat tube on that measures 23" bb spindle to top of seat tube, 58.5cm.
Arrived at that same dimension after a year's worth of saddle time on my 56cm Tarmac.
Yesterday I put together the alloy '26 Diverge E-5 the UPS driver dropped off on Friday.
I'd ordered a 56cm model then had second thoughts a few days later, changed that to a 54cm. Wheelbase on the Diverge is significantly longer than the Tarmac, pretty close to the MB. Motivation for buying a gravel bike's the not-too-friendly gravel roads that abound here'bouts riding the Tarmac.
Specalized's website tells me I should be putting my seat @ just shy of 29", which seems absurd until
I look at how much is left of the seat tube! Top of the mauve tape's the Do Not Pass line.
Pretty obvious I can go higher, right? Should I just go with Specialized tells me & get used to it?
so... seat tube length is generally inconsequential (for where you set your saddle height) unless you fall outside the max insertion...
Your saddle height will generally vary very little, going from one bike to another if their frame dims, riding purpose are similar...
But your saddle height will be affected to some extent by your saddle setback, so a change in setback will prolly mean you'll also have a bit diff saddle extension.
54, 56, 58, not sure what that means for your position, you would know that - or take a stab at getting it to where you ride most effectively - for the riding you expect to do on the new bike.
No one can tell you your optimum saddle height/extension - you'll determine that as you ride. Sometimes we are not sure what that might be so 1. we experiment and then decide 2. we ask someone else to show us 3. we use 'numbers' we might get from something like a power meter to help determine what might be a good spot...
ANy one of those might not be 'optimum' - depending what we really want...
WHy not 'start' with the saddle position (Height & setback & tilt) being the same as what you have been using? It's not permanent You can then 'adjust' and see how an adjustment works.
The things I highlighted in your post are NOT the things which are important, I hilighted them because they have NO bearing on what might be your optimum saddle position.
Of course, since you've already had a similar setup in both your prior bikes - that might be a good place to start.
Ride On
Yuri