Like it was explained in an earlier article about choosing a correct frame size, modern frame designs make it impossible to tell if a frame will fit a rider just by measuring the seat tube length. Quick and relatively simpler way for sizing, explained in the mentioned article, is measuring the effective top tube length. However, since saddle position is set up relative to the bottom bracket (see: setting up a comfortable riding position), the most precise method for measuring the effective bicycle frame size is measuring relative to the bottom bracket – which is achieved using “stack and reach” measurements. What are stack and reach and how to measure them? That is explained in this article.
- Introduction – why does this even matter?
- Explanation of the terms “stack and reach”
1.1. What is “stack”?
1.2. What is “reach”?
- Methods for measuring effective frame size
2.1. Stack measurement
2.2. Reach measurement
- Final notes – saddle and handlebar stack and reach
- Making this simpler – more practical
In order to get a frame that fits the rider, it helps a lot if the rider, or at least the salesman/mechanic know a given frame’s effective size.
For cyclists: before buying a new bicycle, it is best to try a few, find one that suits with size, then measure and write down that bicycle’s frame stack and reach (will be explained later), in order to know when shopping which effective frame size is suitable. Two riders of the same height, depending on their flexibility and riding style might look for frames with two different effective sizes.
For salesmen/mechanics: know which effective frame size is suitable for which rider height (and torso to leg length ratio). At least roughly. Write it down, have it on hand, at least for 5 cm height increments (…160, 165… 185, 190 cm…).
Frame sizes expressed in seat tube length (like 54 cm, or 21″ inches) are very unreliable. Sizes expressed by manufacturers (such as S, M, L, XL…) are also very roughly given, even if a suitable rider height charts are provided for the sizes. Stack and reach are the only really reliable frame size measurements. No matter what type of frame is considered (road, MTB, trekking…).
Reach is horizontal distance from the (middle of the) bottom bracket to (middle of) the top of the head tube. Picture 2 says it all.
Cycling literature usually shows these two measures together (picture 3), but that can look a bit confusing, pictures 1 and 2 show exactly what is meant by the terms.
When measuring stack and reach, it is important that the bicycle has both wheels and that it is put upright, on a flat surface. Best done in a corner of a room – leaned against a wall to stay upright, and rear wheel put against the other wall so there is a vertical surface from which measurements can be taken. This can be improvised, as the following pictures will show. Also, as long as the bike isn’t moved between measurements, the rear wheel doesn’t have to touch (and stain) the wall.
The measures are usually expressed in millimeters, less often in centimeters.
Measure the height of the top part of the head tube from the floor, then the height of the (middle of the) bottom bracket. Subtract the bottom bracket height from the top tube height and that give the frame’s stack. Pictures 4a and 4b show the procedure. It is important that the bicycle is vertical!
In the example from pictures above, stack is: 870 – 305 mm = 565 mm.
First measure distance of the head tube top middle from a wall behind (or in front) of the bicycle, then the bottom bracket distance from the same wall. Subtract larger from the smaller measurement and that gives the reach. Shown in pictures 5 and 6.
In the example from pictures above, reach is: 1285 – 835 mm = 450 mm.
Stack and reach, apart from the frame, can also be measured for other contact points of rider and bicycle: saddle, handlebars etc. They are always measured as vertical and horizontal distance from the bottom bracket. See picture 7.
Both saddle and handlebars have a relatively wide range of setup closer-farther and higher-lower. However, if effective frame size is too far from optimal (dependent on rider height and riding style), needed position alteration of handlebars and saddle may be too much to make the alteration possible.
That is why if a frame’s effective size is off by more than 20 mm, it should be checked which saddle and handlebars stack and reach fit the rider and whether that can be achieved on the frame.
Saddles can usually be moved up and down easily (stack), but for and aft position (reach) is limited to several cm. With handlebars, vast changes of height and “distance” can affect bicycle handling (using a stem that is too long, or too short for example). That is why it is preferable and easier to use a frame with a stack and reach that fit the rider.
Method of measuring effective top tube length, explained in the post about “correct frame sizing” is a (pretty good) approximation of the stack and reach method. Main advantage is that it also accounts for seat tube angle. That is also the main disadvantage 🙂 – it practically includes saddle reach into the head tube reach “dimension”. Stack and reach method, with included seat post stack and reach, takes more time to measure and compare, but gives a full, spot on view of a frame’s fit.
4. Making this simpler – more practical
Today, high-quality bicycles and frames are usually sold like the T-shirts, in sizes: S, M, L, XL… 🙂
Manufacturers provide a list of rider heights (in cm, or feet & inches) that fit a given frame size. For example, here’s the sizing chart for the Giant Fathom 29 1 – which is an XC MTB (but the same goes for any other type and model):
If you need it: on-line feet & inch to cm converter (give me the metric system, or give me death! ).
As you can see from the pic, a 5’7″ cyclist, with a 30″ inside leg, can choose either S, or M sized frame. The choice boils down to personal preference (some people prefer smaller frames). But such a rider should not choose an L sized frame – it will be too big, and won’t fit.
Some sellers only state the seat tube length – in inches, or centimetres. In the article on how to choose a correct bicycle frame size, I’ve explained why such numbers are useless without the manufacturer’s sizing charts. Here, I’ll just put a picture explaining the problem:
So, if someone tells you: “you should get an 18-inch frame,” know that the person may not know what they are talking about.
Such statements only make sense when they are referring to a particular frame (bicycle) model. For example:
“For the Giant XTC ADVANCED SL 29, you need a 17-inch seat tube length” (which is the M size frame for that particular model).
Related post – Setting up (a comfortable) bicycle riding position: