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The top-tube length is no longer a good measurement for sizing a bike. Stack and reach are better for reasons I won't reiterate here.

The problem is, while there are many lookup tables and calculators to roughly guess a top-tube length for person's height, I cannot find the same for S&R.

The long and detailed articles on S&R (etc.) only talk about how to measure it on your bike, and not how it maps to the reader's body in a practical way where they can immediately apply it to shopping online.

Whenever someone asks my question, the responses (across the web) avoid a direct answer and offer instead that "its complicated", "get a proper bike fit", "go into a shop" or "you can only know by riding".

But these answers don't help at all. The reader is left with no answer and they just fall back to using the original flawed top-tube vs. height when choosing a bike from an online seller, hence every advert still quotes the TT length.

So, I know its complicated, but if the bike mags are right, then I'm better off shopping to a flawed S&R measurement than to an even worse top-tube length.

I assume that OEMs choose perhaps 5 different S&R sizes for their frames to target a set of approximate customer heights, so there must be a table somewhere.

What's the ballpark S&R for a 178cm man? (thanks!) ...inside leg, 85cm

  • Are you looking for a straight handlebar or drop bar bike? Do you like a long low position or more upright? There’s a reason there’s no simple answer. – Andrew Jul 2 at 18:41
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    I came across a bike fit calculator earlier this year, before I bought my first road bike (ever). Rode it on a trainer for a while and more recently have done a few hundred km on it, so far so good! competitivecyclist.com/Store/catalog/fitCalculatorBike.jsp With this calculator, you measure pretty much everything, so it seems to be using a bit more elaborate math, but in the end it gave me 54cm frame, which I was also getting with simpler sizing guides. – Gaston Jul 2 at 19:27
  • @gaston thanks but outside the US, it redirects to another site saying something about GDPR. It's interesting that it ended up giving you a 54cm frame, which the old TT measurement that's supposed to be defunct because of modern frame designs. It strikes me that I need to wait 10 years until people have updated calculators and sales brochures and eradicated the old TT measurement from their heads. I'll just place my chips on 54cm like everyone else and yawn disdainfully next time someone talks about stack and reach. – Luke Puplett Jul 6 at 20:37
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The lack of definitive answers you've noticed is due to the amount of (often unknown) variables at play here. Body height and inseam are indeed good starting points, but people around the internet won't be able to estimate just how flexible you happen to be. Arm length, discipline and your personal preference on how 'aggressive' of a riding position you want also play a major role.

In this light, the advice you've received is reasonably good. After riding a certain bicycle long enough to get a feel of it, you'll be able compare the S&R of that bike to another one and make a somewhat educated guess on how that other bike would feel for you. The perk of going to a bike shop is the opportunity to throw your leg over bikes of your choosing, which likewise will give you some sort of an idea of which size would fit you.

Of course, your question is valid in a sense that for most people, there exists a ballpark of S&R measurements where they should probably start looking at. However, bike manufacturers often got your back on this. Along with the geometry charts, most of them provide you with a model-specific rider height recommendation. While it's not technically a S&R recommendation for your specific dimensions, it's the starting point you should be looking at instead of any arbitrary stack and reach that you haven't tried yourself.

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It's not possible to specify an appropriate stack and reach for a person's height measurement. One reason is that people have different leg, torso and arm length proportions Two people of the same height may require different size frames. The other big reason is that frames deigned for different riding styles will have different stack and reach geometries.

The only reasonable way to approach basic frame sizing is for manufacturers to specify a nominal height range for each frame size for each style of bike e.g., casual hybrids get different height ranges for each size than aggressive race bikes. After that you have to experiment with the nominal size and one larger or smaller.

Experienced riders can figure out the stack an reach ranges they need or want for a particular style of frame and select frame sizes that way.

Bear in mind that on most modern bikes seat tube or top tube measurements are really just synonyms for small-medium-large type size labels. If say I ride a '54cm' road bike frame I really mean I ride a medium frame.

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