Detailed explanation of road bicycle frame geometry

Frame geometry has always been a problem that troubles many novices. Today I would like to talk about frame geometry. To put it simply, a frame consists of four tubes, seat tube, top tube, down tube and head tube, and four forks: There are chainstays, chainstays, and front forks, but there are actually quite a lot of details to pay attention to. These subtle parts will have a great impact on a road bike, its handling, and riding experience. , according to a road car, according to its use, it can basically be divided into two types, one is a competition road car, and the other is an endurance road car. The competition road car has a more radical geometry and better Aerodynamic gains, while endurance road bikes have a relatively friendly riding posture, are more stable and comfortable, and are suitable for long-distance riding. In addition, the size of the frame will also have a certain impact on the frame geometry.

Today we will explain from several aspects the characteristics and differences between first-class racing road bikes and endurance bikes, the impact of frame size on frame geometry, and detailed explanations of geometric parameters.

sava bike frame geometry


Racing Bike:

Radical geometry, aerodynamic stance

Geometry: agile handling and quick response

  • Larger, more agile steering angle
  • Long stem
  • Shorter and stiffer rear triangle
  • Pneumatic tube type

Riding position: lower and more forward, with a flatter back, curved hips, and a pronounced forward lean

  • Reduce the frontal windward area
  • Lowers the center of gravity and puts more weight on the front wheels to improve grip and handling
  • Stress on shoulders, arms, neck and wrists, making long-distance riding easy to fatigue

Racing road bike riding positions

Endurance Bike:

Long-distance riding, upright riding posture, stable control

  • Suitable for long-distance endurance riding
  • Pursue stable and predictable handling, agility is not the first priority
  • More upright riding position
  • Greater wind resistance and slower speed
  • Comfortable for long distance riding and not easy to fatigue

endurance bike

Effect of frame size on frame geometry

The larger the size, the longer the tube shape, and other minor changes resulting from the same wheel diameter.

Problems caused by small sizes and too short wheelbase: Toe overlap

Solution: Smaller sizes use a smaller head tube angle to increase wheelbase

Top tube length: Distance from head tube to top of seat tube
top seat tube

Horizontal top tube frame and inclined top tube frame (compression frame)
Giant designs the first top tube that slopes backward and downwards
Shorter chainstays and seatstays: smaller geometry, lighter weight
 Effective top tube
Too long leads to overreaching, causing discomfort; too short leads to crowding
  • Race: long top tube, short head tube
  • Endurance: short top tube, long head tube
  • Can be fine-tuned by adjusting the stem length

adjust stem

Seat tube length:The distance from the bottom bracket axis to the seat post
After compressing the frame, the selection of frame size becomes less meaningful.
Ride Impact: Compressed frame results in shorter seat tube length, longer seatpost length

  • Seat post is longer, curved and shock-absorbing
  • Use carbon seatpost and D-section seatpost to increase shock absorption function

seat tube length

Reach and Stack

Reach: the horizontal distance from the bottom bracket axis to the top of the head tube
Stack: The vertical distance from the bottom bracket axis to the top of the head tube

sava frame geometry

Impact on riding: plays a decisive role in frame selection
Long Reach+Short Stack= Race
Short Reach+Long Stack=Endurance

STR, which is Stack/Reach. Generally, this value is not provided on geometric diagrams, so you need to calculate it yourself. This value is divided into 1.45. <1.45 is a radical frame (that is, what is usually promoted as a climbing frame, a comprehensive frame, etc.), >1.45 is comfort, and is generally promoted as an endurance frame.

Wheelbase:The distance between the front and rear wheel hubs

Impact on riding: Affects bicycle control and stability

  • Long wheelbase: better stability, suitable for Endurance (usually greater than 1m)
  • Short Wheelbase: Responsive and suitable for Race (usually less than 1m)

Head Tube Length

head tube length

Impact on riding: affecting riding posture

  • Taller head tube length: More upright riding position, suitable for Endurance
  • Shorter head tube length: lower riding position, suitable for Race

Head tube angle

head tube angle
Impact on riding: Affects steering control

  • The larger the inclination angle, the farther the front wheel is from the driver, the steering is smoother and slower, and the stability is improved - Trail (drag distance)
  • The larger the Trail, the more stable the steering will be. If the Trail is too small, the phenomenon of virtual confusion will occur.
  • The smaller the head tube angle, the larger the drag distance.
  • The greater the front fork offset, the smaller the drag distance

Endurance and gravel bikes usually have smaller inclination angles


Seat Tube Angle

seat tube angle
Impact on riding: affecting riding posture and leg power

  • The steeper the inclination of the seat tube, the closer it is to the pedals, and the leg muscles can exert force more directly, improving pedaling efficiency.
  • The body leans further forward, lower, and the posture is aerodynamic

The common angle is 73-74 degrees, with steeper angles for TT and S-works Shiv Disc bike's seat tube angle is  77 degree 
Moving the seat forward can increase the effective angle to a certain extent

Chainstay Length

Chainstay Length
Impact on riding: affecting control sensitivity and stability

  • The longer the CL, the better the stability and shock-absorbing ability, but it will drag your feet.
  • The shorter the CL, the worse the stability, the faster the pedaling feedback, and the more agile the control.
  • Mainly affects Wheelbase

With the popularity of wide tires, there is a trend to become wider

BB drop/BB height
The vertical distance from the bottom bracket axis to the front wheel axis

BB drop/BB height
Impact on riding: Affects riding stability

  • The larger the BB drop, the closer the bottom bracket is to the ground and the center of gravity is low and stable.
  • However, it is easy to hit the bottom on sharp corners and gravel roads.(Crank length needs to be matched with the crank length to avoid this problem)

 Difference between BB drop and BB height

The BB Drop is an inherent attribute of a car's frame, but the parameter of BB height will change as you change wheel hubs with different diameters and tires with different tire widths.

Different models have different geometric parameter settings. SAVA Bicycles has made more accurate size recommendations in terms of bicycle size. How to choose the bicycle size and frame size? Below we will also explain the method for you.

What are the common size indications?

Number: riser length or equivalent upper tube length
S/M/L/XL... like SAVA R08 frame size (44cm,47cm,51cm,54cm,56cm)

Different frames require different considerations
Traditional bicycle frame horizontal top tube frame/diamond frame

Compact bicycle frames

Semi_compact bicycle frames 

What is PBH?

public Bone Height pubic height
How to measure PBH?
Public Bone Height and Inseam are about the same size

public Bone Height

How to determine the size based on PBH and Standover?


Standover size
Horizontal top tube frame: PBH>Standover 2-3cm
Compression frame: PBH>Standover 4-5cm

For example: My PBH is 84cm,how to choose my SAVA Hawkeye7.2 bike size?

Hawkeye bike frame geometry size

PBH-4cm=84cm-4cm=80cm,according to the size chart,The standover size 803mm is more closer,So the frame size 58cm is ok

A few notes:

Such a selection method is actually an empirical choice. It is more suitable for most people with this body length ratio. However, if your hands and feet are relatively long with such a body length ratio, then this method may be suitable for you to choose. One frame is a little rough, so you may need to consider in detail the reach and stack value of a bicycle, and whether it is suitable for your body length ratio. For example, if you are a person with particularly long hands, at hip height If you are satisfied, then you must choose a frame with a slightly larger reach value, if you have relatively long legs, but if you choose a size with a relatively large hip height, if you are the kind of person with long legs and short hands. In terms of body length ratio, your reach value may be too long. If you have a special body length ratio, you need to refer to some parameters in more detail, or use other fine-tuning methods, such as using a longer length. For the stem, use more washers to choose a more suitable size.

Why is it recommended to choose a larger size?

The size increases and the Reach value changes very little

But the Stack value can be increased a lot, about 2cm, which makes it more comfortable.

Whether it is correct or not depends on the individual,Some people pursue a more radical and aerodynamic posture, while some people actually prefer a more upright and comfortable riding posture. This depends on your personal riding habits.


I'm stuck between two brands, so how do I choose the right size?

If your size is awkward, you will be sandwiched between these two brands

But But the premise is PBH>Standover

If you are faced with the above choices, you can consider the following 3 points.

1.Riding style: aggressive or comfortable,The first is your personal riding style. Do you prefer an aggressive riding position or a comfortable riding position? If you like more aggressive riding, For a more aerodynamic posture, you can consider choosing a smaller size frame. If you are more accustomed to a more comfortable and upright riding posture, then you can choose a larger frame.

2. Body flexibility. : everyone must have a clearer understanding of their body flexibility. If you are a person with good flexibility, then you can choose a smaller size, because such a small size brings more radical You may be able to adapt to the riding posture.

3.Ape index=arm span-height,The third point is to consider the relationship between your arm span and height. This is actually related to an index, which is called Ape Index. Its value is equal to your arm span minus your arm span. Your height, if your wingspan is longer than your height, if your wingspan is longer than your height, then you can choose a larger size frame, because it is larger Frame sizes usually correspond to a slightly longer reach, and vice versa.