Stack & Reach: The new sizes in bike fitting

Anyone who bought a new bike not too long ago, or is at least dealing with it, will have noticed the terms stack and reach, which have been in use for a few years and have replaced the frame size as a selection criterion. For all those who are not yet familiar with these terms, we would like to explain what they are and why the classic frame size is not a useful tool in bike fitting.

definition

Reach is the horizontal distance from the center of the bottom bracket to the top of the head tube, i.e. the length of the bike.

Why the new method?

The rider of a bike has three points of contact with his bike. These are the pedals (hence the middle of the bottom bracket), the saddle and the handlebars. From a biomechanical point of view, every rider has an optimal seating position, which determines the saddle position in relation to the bottom bracket. For racing bikes, some people are probably familiar with the rule of thumb that when the pedals are in a horizontal position, a plumb line should go through the knee and through the pedal axle. With time trial or triathlon bikes, the rider is rotated forwards around the bottom bracket. Without this rotation, the hip angle becomes more acute (narrower), ie breathing is negatively affected, muscles are stretched and effectiveness is reduced. It also makes it difficult to switch to running due to the more stressed muscles. So the saddle/bottom bracket position is different than on a racing bike, but in both cases this position is fixed and should/can be transferred to a new bike.

This means that two of the three contact points between the rider and the wheel are not changed. The third contact point, i.e. the handlebars, now largely determines the rider’s position, and that’s exactly why it’s so important. Bikes with a lot of stack and little reach are therefore higher and shorter, and thus the rider's position is more upright, while low stack and much reach promise a very stretched and bent position.

Long & low or short & tall?

Dan Empfield, from Triathlon Forum Slowtwitch.com, for example, divides bikes into two categories: "Long&Low", for riders with a long torso or who want very extreme positions. "Short&Tall", on the other hand, is for riders with a short torso, relatively long legs, or especially for those whose muscles are not flexible enough to ride in more extreme positions. Thus, there should be significantly more “Short&Tall” candidates among age groupers than a glance at the transition area often suggests.

Of course, more and more bike manufacturers are trying to find a balance between "Long&Low" and "Short&Tall" in order to offer a geometry that suits many potential customers. Many bikes that belonged to the “Long&Low” category have been toned down a bit in recent years to make them accessible to riders with a moderate position, although very aggressive postures are still possible with the appropriate spacer or handlebar setup. Especially with triathlon bikes, the handlebars are an important component for fine tuning anyway, and if they offer the necessary adjustment options, they can offer a wide range of adjustments.

Statement criterion about position and driver type

Using the stack and reach measurements, you can quickly assess whether a bike will allow for a more moderate or more extreme position, or what type of rider the bike suits. Many websites and magazines now also publish graphics that clearly show or compare stack & reach data from bikes, so that you can get a quick and easy overview here.

What is the frame size?

While one measures the seat tube to the top edge, another may only measure to the interface with the top tube. This means that two frames can be absolutely the same size, although they are specified with completely different frame sizes. This becomes even clearer with sloping frames, i.e. frames with a sloping top tube. And if a manufacturer only specifies the size as S / M / L / XL anyway, then it's clear that the frame size is no longer of any importance. The only difference then is how far the seat post has to be inserted into the frame, and whether it is three centimeters more or less in the frame is completely irrelevant for a fitting.

Top tube length, seat angle & Co

If the difference in seat tube angle is not too great, it can be compensated for by moving the saddle.

Two bikes with the same top tube length can therefore be completely different if the seat angle is different. If you judge a bike by the length of the top tube, you should always take the other dimensions into account. Especially with small frame heights, it is often the case that the top tube lengths are shortened by steeper seat angles, but without changing the stack and reach. So often two small frames from one manufacturer are effectively the same size despite different frame sizes.

The head tube length can also be deceptive, since it is only a reliable measurement if the installation length of the fork does not differ. However, if the fork is somewhat shorter or longer due to its design, it also changes the head tube length without affecting the stack.

bike fitting

It should be clear to everyone by now that professional bike fitting is highly recommended. It not only improves the position, but also ensures that the driver can use his muscles more effectively and can therefore achieve more. However, you should consider whether you "first" go to the fitting with the bike you have already bought, or whether you do the fitting before you buy it (with a fitting bike which systems such as Retül, Guru, Shimano, Trek ... offer) to determine which bike model suits you at all (or whether the desired model you have in mind suits you). Because once the wrong bike has been bought, in the worst case you can only make makeshift adjustments (keyword: spacer towers). And once you've ridden a perfectly fitting bike, you won't be satisfied with anything less.

Thanks to Cervélo for allowing us to use the graphics from www.cervelo.com .