Bike Sizing: Stack And Reach

When it comes to bike size and fit, the industry has suddenly started talking a new language. And high time too. 

I am flying out to Oregon in a few weeks and for the first time intend to cycle while I'm there. Details are still to be confirmed but one option I've been looking into is hiring ('renting' for the Americans) a road bicycle from a bike shop. But my bitter experience has taught me that stock sizes provided by mainstream manufacturers simply do not fit me. Nonetheless, I have indulged in two short periods of daydreaming about renting a bicycle utterly different from my own, just for the sake of it. 

As it happens, the only two models of bicycle available for me to hire are

• the Raleigh Capri (year/model and precise build not known)

the 2015 Raleigh Capri Carbon 1 (not available in the UK)

• a 2013 Jamis Xenith Comp  

the 2015 Jamis Xenith Comp (as the 2013 archive data is virtually illegible)

The Raleigh is available for me to hire in a size 50cm, the Xenith in a 51cm (as the sizing and measurement methods vary by manufacturer). While size numbers usually relate to seat tube length, the crucial question for me is, how long is the reach? Typically for this size, the effective top tube will be 53-54cm, which is much too long for me even with the tallest headtube, an uncut steering tube and fitting the shortest high rise stem known to man. (Don't ask me how I know this. Okay, do ask -- but it'll all get covered in my Surly Cross Check review, when I get around to writing that!)

It was a matter of 15 seconds to determine that there was no possible way I could ride the Raleigh or the Jamis in any size. 

However, perusing their respective geometry charts revealed something very intriguing. Alongside data for seat tube angle, head tube angle, seat tube length, top tube length, chainstay length, standover, etc etc were two new 'dimensions':  

stack  and  reach

'Reach' of course I know quite a lot about, but I knew immediately from the figures (e.g. 370mm for the Jamis) that this could not be 'reach' as I know it, i.e. the measurement of the top tube, effective or otherwise, plus the length of the stem to the back of the handlebars. 

As for 'stack', I've been using that word myself for some time to refer to the height of the front end of my bikes, from bottom of the head tube to the top of the stem where it sits on top of all the spacers. But with figures like 523mm for the Jamis, again it was obvious that the manufacturers were using a totally different definition than I was. 

So I ran a Google search and found a few images illustrating what bike manufacturers mean by 'stack' and 'reach', such as this one: 

Stack is the vertical height of the frame, from the centre of the bottom bracket up to the top of the head tube. 

Reach is the horizontal distance between the centre of the bottom bracket to, again, the top of the head tube. 

The result:  a square -- or, to be more accurate in the world of bicycles -- a rectangle. 

I'll admit, with my obsession with fit and geometry, this came as something of a revelation -- and a very welcome one. Finally, we have measurements that are intrinsic to the frame without reference to angles, without danger of 'dilution' by how a bike is built up, i.e. by choices of seat post, stem, handlebars. 

I then found a bike fitter's website with an article on determining the right size of bicycle. After explanations of the aspects and variables, there is a subheading titled "So What Is Your size" with a table: 

Suddenly, in a tangible, visible sense, my problems with the industry's approach to sizing became obvious. I am 5' 4" (164cm) tall. My inseam (or pubic bone height if you insist on getting both personal and technical) is 32", which happens to be exactly half my height. Unusual? I don't know. But let's look at that table. According to that, my height means I should ride a size 50cm frame. My inseam however puts me on a 54cm frame.  

This was beyond interesting, it was becoming downright intriguing. I dug out the Bike CAD drawing of my custom Enigma Etape. Its seat post measures 510mm, which by industry standard makes it a size "51cm" or "XS" as Enigma would normally categorise a stock geometry frame (although that seems relative only to men, to be honest; you'd hope that "XS" in a women specific design would be considerably smaller than 51). 

The Enigma's reach is 365mm, which isn't too far out of the ballpark compared to standard-sized frames. But its stack? A whopping 593. In mainstream bike frame sizing, that's a size 58cm! Compare that with the (pitiful) 523mm stack on the Jamis Xenith in size 51cm. 

(Funny story here: I had never heard of the Xenith until the Oregon bike shop told me that's what they had. Later I went to have a look at the geometry and spec but even while on the phone during that first call, I found myself saying "yeah, that might work... if the steerer's uncut and you can put 60-70mm's worth of spacers on top"!) 

Before I go any further, here are the respective geometry charts for the Raleigh and the Jamis, and then the "frame blueprint" for my Enigma. (Geometry geeks, feel free to pause here and re-join the discussion in a few hours. Or days. No, seriously, I know how you feel!)

Raleigh Capri Carbon 1

Annoyingly, the chart does NOT specify (a) the effective top tube length,
which for the 50cm will be longer than 515mm), (b) the stack, or (c) the reach.
Not particularly helpful.
As you can see, Raleigh's whole approach to sizing is to ask
how tall you are and that's the end of it. 

 2015 Jamis Xenith

For the 51cm size, the effective top tube length pushes 53cm.
Of more relevance is the stack (517mm) and the reach (371mm). 

My custom Enigma Etape

(Oh the joys of custom!)
Seat tube length: 510mm all well and good.
Effective top tube length: 526mm -- only a smidgen shorter than the Jamis.
Reach:  an unexceptional 526mm (only slightly shorter than usual for a "51").
Stack:  a sky scraping 593mm.
(THIS is why my bicycle looks so "odd" to casual observers.)

So while I'd been thinking of the reach in terms of the length of my body plus arms (with an attempt to factor in variables such as flexibility, handlebar height, how much do I want to lean forward, etc.), it seems we have additional data to consider that may be more objective. Could this make comparisons of the sizes and potential fit criteria across lots of different brands and models easier, more meaningful and potentially much more helpful in making purchase decisions? (Or bike hire decisions, as the case may be.) Even if the answer is "yes", does adding stack and reach to the list of figures to compare between bikes add an additional layer of complexity to the process? Hmmmm. 

Then, reading the July 2015 issue of Cycling Active magazine, I noticed something new in their group test of "sportive" bikes: 

Firstly - an express interest in geometry (although the reviews themselves did not actually address it)

And then this info box, which essentially aims to boil down the huge unwieldy study of frame geometry into one simple matrix:  Stack-to-Reach-Ratio 

Bearing in mind the arbitrary classifications (>1.5 = comfortable; <1.4 = racy), no wonder the reviewers couldn't detect any real difference between the bikes in their group test in terms of comfort. The Merida Ride has an STR ratio of 1.61 (stack = 611mm; reach = 378mm). The Lapierre Sensium 200CP scored 1.51 (stack = 578mm; reach = 383mm). The Tifosi Scalare Ultegra (described as having a frame that is "pretty compact, even by today's standards") has a counter-intuitive STR ratio of 1.38 (stack = 540mm; reach = 395mm, the very antithesis of "compact"!)  In the final analysis, the Tifosi won the group test, quite surprising given the stated purpose was to find which one of the three was "most comfortable" over longer distances. The reviewer admitted to preferring the Tifosi's more stretched-out feel and frankly, lighter weight, better groupset and marginally better (of a bad lot) wheelset. Hardly a meaningful review with regard to geometry, except....

Cycling journalists are using a new data matrix,

christened the Stack-to-Reach ratio or "STR". 

So, getting back to my "real world bicycles" -- 

• the Jamis has a STR ratio of 1.396 (pretty racy)
• the Raleigh has an STR ratio of 1.41 (still pretty aggressive)
• my custom Enigma as my point of reference has an amazing STR ratio of 1.625 (which actually isn't all that surprising once you've digested all the facets of its geometry). 

As a side note, the Surly Cross Check that I ride most days has an STR of 1.357, the most aggressive of the lot! This demonstrates the vital role played by its uncut steering tube and approximately 80mm of spacers. (Gulp.)

If confirmation were needed that this new STR calculation isn't just one cycle journalist's conceit, an article specifically on the industry's non-standard approach to sizing appears later on in this issue of Cycling Active, with STR mentioned as a tool that cyclists themselves can use to compare different bicycle frames. 

So there you have it. It's all in the STR!


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Post Script 6th June 2015

Today I tried out Sigma Sport's new "Fit & Find" online sizing calculator. The only measurements requested are height and inseam (in millimeters). I put mine in: 1640 and 820 respectively. I got an "warning" message:

I clicked "Auto Calculate" to see what the recommendation would be:

The auto-correct changed my inseam to 8020.

I tried it again, this time clicking Find bikes" to proceed anyway with the correct inseam of 820. Here is the result:

I could not make this up if I wanted to.