Steeper seat tube angles put the rider closer to the bottom bracket and give the legs a more advantageous position to press down the pedals.
The effect can be easily illustrated if you try to smash an aluminum can with your foot. It’s much easier to do so when the can is directly under your leg and hips. If you position the can further away from the body, you will lose power.
Since road bikes are all about generating power on paved roads, some people wonder why road frames don’t have maximally steep seat tube angles.
Most road bikes have a 73-74° seat tube angle which is considered a medium range. (It’s neither steep nor slack.)
The reasons why road bikes don’t have maximally steep seat tube angles are:
A steeper seat tube angle allows the rider to generate more torque, but the position places more stress on the knees and potentially the hips.
Road cycling isn’t just about generating power; it’s about maintaining a medium power output over a long period of time. That task cannot be accomplished when the rider isn’t in a fairly comfortable position.
A steeper seat tube angle puts the rider in a more upright position and thus generates more drag. And as we know, road bikes are all about maximizing aerodynamic efficiency.
- Balanced Performance
An extra steep seat tube angle helps with climbing by positioning the rider closer to the front wheel. The weight shift increases front wheel traction and reduces the weight on the front wheel. The result is easier pedaling.
However, an extra steep seat tube angle is not ideal for pedaling on flat roads and on descents. Therefore, it makes more sense to use a conservative seat tube angle that isn’t optimized for one terrain only.
FAQ: I want the angle of my road bike to be steeper. What can I do?
The actual seat tube angle cannot be changed once the frame is built. However, one can affect the effective seat tube angle.
If you slide the saddle forward towards the handlebars, you will steepen the effective seat tube angle.
The change is not massive even at the maximum level, but it can be sufficient in some cases.
FAQ: Why do road cyclists move towards the nose of the saddle from time to time?
Sometimes road cyclists move their hips onto the front end of the saddle to artificially steepen the effective seat tube angle in order to generate more power.
That practice is done for short sections of higher difficulty such as small hills. However, no one can pedal in that position for a long time as it aggravates the perineum, the knees, and potentially other joints.
FAQ: Why does the seat tube angle get progressively steeper on smaller frames?
A steeper seat tube angle shortens the effective top tube of the bike and thus makes the frame more compact for smaller riders.
The effective top tube is the horizontal distance from the point where the top tube and headtube meet and an extended line from the seat tube. The term has become widely used due to the popularity of sloping top tubes.