The manufacturing of bicycles has changed a lot in recent years. Brands no longer produce bikes just for road cycling and for mountain biking, and even other types such as gravel and e-bikes. Within each of these categories, there are different styles and types of use. And this has resulted in notable differences in frame geometry. That's why the frame tubes of two road bikes from the same brand and size can have different measurements, since they are designed for different uses. The amateur cyclist who rides every weekend has also increased their demands as the geometries of bike frames have evolved. When buying, they no longer just look for a bike that is reliable and aesthetically appealing, but other factors are also considered. This is also determined by the fact that even two bikes from different brands that share the same style, type of use, and even size—for example, two cross-country bikes in size M—actually have different frame dimensions. It's a phenomenon similar to what happens in fashion, where a size M t-shirt from one brand may be too small for you while from another brand it fits perfectly.
This is where stack and reach become important, two measurements that determine the real size of a bicycle and serve as a kind of standard measuring stick between different models and types of bikes. They are also two very reliable indicators for knowing your bike size.
👉 How to calculate the stack and reach
The reach—also known as reach—of a bicycle is the horizontal distance parallel to the ground between the vertical line from the bottom bracket axle to the superior part of the head tube. The stack—called frame height—is the vertical distance perpendicular to the ground from the horizontal of the bottom bracket axle to the superior part of the head tube. Both measurements are independent of the head tube angle, the height of the bottom bracket relative to the ground, and the seat tube angle. These are measurements that brands usually indicate in the technical specifications. And they are especially interesting when buying a bicycle because they tell us directly about the size that would best suit our height and leg length.
👉 How to choose the correct bike size
Types of bicycles according to stack and reach
Depending on how long or short the reach is, and how high or low the stack is , we will have a bicycle suitable for one specific type of use or another. The relationship between these two measurements determines whether the bike has a more or less relaxed frame geometry, more or less racing, and more or less aggressive. The stack and reach define the types of bikes, especially on the road. The main ones are:
Endurance or Gran Fondo
This type of bicycle has a high stack and a short reach. This allows the rider to adopt a more relaxed position while pedaling. In this way, we will ride with a more upright back and, therefore, be more comfortable.
Racing and Aero
Racing bikes are the classic race bikes. They usually have a lower stack and a greater reach. The head tube is farther from the saddle and in a lower position than in Gran Fondo bikes, so the rider will have to pedal more bent over the bike. This is neither positive nor negative, it is simply a characteristic of these bikes, which are designed to make the most of each pedal stroke and achieve greater speed and reactivity by sacrificing rider comfort. If you are used to riding bent over and feel comfortable, it is a good idea to let your biomechanic know so they can adapt the recommended stack and reach data to your preferences and needs. Watch out! Not everyone can handle four hours pedaling in a racing position. That’s why before buying a bike with this geometry, you should be very clear about what kind of routes you are going to do and how much time you are going to spend on it to know if you will adapt to it properly, without discomfort.
👉 See Aero bikes
Problems resulting from a poor choice of stack and reach
We’ve all fallen in love with a bike at some point and just couldn’t get it out of our minds. The process of buying a bike can be long and painful, especially when the bike of our dreams doesn’t seem to be suitable for us. If the chosen bike has a reach greater than what we need, we will most likely have problems with numb hands (at least the pinkies) and back pain. And if, on the other hand, it’s the stack where we’ve come up short or gone too long, we’ll have problems in the hamstrings, calves, back, etc. Of course, choosing the size of our new bike based on the stack and reach is a key point, although for this it is necessary to carry out a biomechanical study.
The importance of a biomechanical study
To calculate your bike size, you can use the Tuvalum Size Guide. But if, due to the combination of your height and leg length, you are between two sizes, it is most advisable to get a biomechanical study done. The biomechanical study will help us determine the parameters that set the most suitable bike geometry and size for us. But it will also give us other key data, such as the best position to place the cleats, saddle height, saddle height and tilt, etc. Nowadays, biomechanical studies are quite affordable. And they also last forever, since our physical measurements don't change.
What to do if you choose the wrong size
If you have chosen the wrong size when buying your bike, or if the stack and reach of the frame don't match your body's measurements well, there are small modifications you can make to vary the frame's geometry to achieve a position as compatible as possible with you. The main corrective measures you can take to compensate for inadequate stack and reach are:
- Move the saddle longitudinally (to compensate for the reach)
- Change the saddle height (to compensate for the stack)
- Tilt the stem (to compensate for the stack)
- Change the stem for one of a different length (to compensate for the reach)
- Use headset spacers (to compensate for the stack)
- Other measures include: changing the cranks for ones of a different length, installing a wider handlebar, modifying the position of the brake levers, etc.
Simply by changing the position of the saddle (both in height and relative to the seat tube), the stem, and the handlebar, you will notice a change in your posture on the bike.
More measurements! What are the trail and the offset?
The frame geometry and our comfort on the bike do not depend solely on stack and reach. There are more measurements that directly influence and that, in some cases, are worth considering. For example, in mountain biking, it is increasingly common to pay attention to the trail and the offset, which tell us whether the bike is more of a climber, a roller, or a descender. The trail is the distance from the front wheel axle to the projection onto the ground of the steering tube axle. This measurement contributes to the stability of the bike when riding in a straight line. In mountain biking, an enduro bike has a greater trail than an XC bike to ensure greater stability and maneuverability on technical terrain. The offset is the fork's offset relative to the front wheel axle. That's why this measurement is also known as rake. That's why some forks are not straight, but have a slight curve. The offset serves to increase or decrease the trail. The greater the offset, the smaller the trail. and vice versa. A third measurement to consider in frame geometries is the head angle, which is measured by the relationship between the head tube and the horizontal ground.