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Frame sizing gaps...

by Fibblesnork
Thu, May 31, 2018 22:06
2

As we all know, getting the best fit makes the world of difference when it comes to comfort however, the manufacturers seem to put their sizing breaks in different places so what should be priority?

Inside leg? or should it be reach and stack?

I am on the 56/58cm cusp of a lot of frame sizes going off of my 34" inside leg.  I'm a slightly stoopy 6'3" with long gibbony arms and I think, a short torso.. This could be why my 58cm road bike (which is for sale by the way.. ahem) has always felt a bit stretchy despite an inline seatpost and 90mm stem..

Anyway, long story short then, I'm likely be more comfortable with a 56 (for riders with a 34" inside leg) next time or have I missed something really important?

I am more than aware of how subjective this all is though sometimes, "sitting on to test fit" can't practically be done easy...

And a bespoke frame is a off the end of my budget though I would say, greatly desirable if not that attainable...

If you're new please join in and if you have questions pop them below and the forum regulars will answer as best we can.

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2 comments

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Mathemagician | 6 years ago
1 like

If you Google "bike comparator", you'll find a very handy spreadsheet, which can give you a schematic overlay of any two bikes provided you know the dimensions (nearly always available online). You can then compare the bike you're interested in to what you have, and can immediately see whether it's longer/lower/etc. But really, it sounds like you need a decent independent bike fit to make sure you get the right frame for you.

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kil0ran | 6 years ago
1 like

The way I approached this was to look at stack and reach on a known comfy bike and buy the frame that closely matched that. Once that was done I could look at fine tuning from my parts bin - I've got stems ranging from 90mm all the way up to 130, a couple of seatposts with different setbacks, and two crank lengths available. When you've got flippable stems and an uncut steerer there's a lot of variation possible with just small parts changes. Being older I do seem to be quite sensitive on the saddle to bars distance (less flexible) and I certainly notice even a 10mm reach change.

Whilst head tube and seat tube angles also matter (particularly seat tube as saddle setback relative to BB is important for efficiency and knee comfort) you should be able to dial those out with stems and seatposts to a certain extent. 

If you're looking for an off-the-shelf steel frame talk to Shand, Condor, Bowman, or Fairlight. Of those, Fairlight should be able to get a frame to fit you the best - their "tall" geo probably fits your proportions:

https://fairlightcycles.com/why-fairlight/fit-function-form/?v=79cba1185463

Stack/reach ratio is also somewhat important as it defines the starting position for your back angle. If you're saying you're stretched on a 58 it might be that it has a relatively low stack to reach ratio (1.4 or lower)

Good discussion of this here - https://forums.thepaceline.net/showthread.php?p=2207837

This is effectively what Fairlight's proportional geo is doing. For the Strael the 54R has a ratio of 1.42 whereas the 54T is 1.53. Same frame size but the T is more upright and suited to riders with relatively shorter torsos.

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