stack/reach

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Poulidor
Posts: 74
Joined: Sun Aug 23, 2015 3:50 am

by Poulidor

Please excuse my ignorance.

Now, I know all too well my contact points which I think is fundamental for a happy life on top of a bicycle. Saddle to bars drop, point of saddle to center of bars, bottom bracket to saddle... even point of saddle to bottom bracket distance and point of saddle to brake grips. I also understand that longer chain stays allow for a more comfortable ride, and rake has to do with turning, etc. I can go on a little further with angles and so on, but I'm a rider, not a frame builder.

In any case, pray tell what's with stack and reach...? I imagine that it would have something to do with finding the right point of balance of the body on top of the bicycle. The reality of it is that I don't get it and I would appreciate greatly to be illustrated. Thank you so much.

Raineman
Posts: 185
Joined: Mon Oct 06, 2014 2:03 pm
Location: Kent, UK

by Raineman

Image

It is purely 2 dimensions useful for looking at how 2 frames compare in terms of fit. The rest of the geometry table is useful regarding handling though.

Some manufacturers define stack and reach slightly differently but generally center of bottom bracket to the top of the headset (tri bikes is often to the arm rests though for example)

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RyanH
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Joined: Tue Jan 17, 2012 4:01 pm
Location: Los Angeles, CA
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by RyanH

It's an efficient and accurate way to compare frames since it takes into account variations in geometry like HT length, angle, BB drop etc...

In short, stack is the vertical distance from the center of the BB to the top center of the head tube. Assuming your saddle height stays the same (from BB to top of saddle) then it tells you how much drop the frame will provide.

Reach, is the distance from the top of the head tube to the vertical, perpendicular line intersecting the BB. As the name implies, it's your reach. You can modify the reach by using a longer or shorter stem, but when comparing frames, you'll find that some frames (Wiliers as an example) have a pretty long reach and you would have to run a silly short stem to get the same bar position. The thing is, top tube length can change, but that's a result of the HT angle, height and seat tube angle and c to c. So, if you have two frames, one with a really slack STA, and one with a 74* angle (everything else the same), the top tube may be 1-2cm different but the reach stays the same, since you're just affecting where the saddle goes.

When I was looking at the Colnago's, their reach didn't change between a 48s and a 54s, so I could theoretically ride any of the sizes as long as I can work with the stack and change stem length. Cervelo is one of the few that actually drops their reach by a consistent amount (9mm I believe) for each size.

Now, one other thing I learned was that you may have a mfg that's reach doesn't change from a M to an XS, but that's because the head tube is shrinking on each. If you run spacers, the reach decreases due to the stem being further back.

Valbrona
Posts: 1629
Joined: Fri Oct 28, 2011 3:25 am
Location: United Kingdom of Great Britain and Northern Ireland

by Valbrona

You'll get it with more riding experience.

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