Blog

Ultra-condensed Answer:

The most commonly found seat tube angle among lightweight climbing bikes is 73.5°.

What Is a Seat Tube Angle?

The seat tube angle (STA) is the angle between the seat tube and a horizontal line (parallel to the ground) running through the bottom bracket.

What Is The Effect of the Seat Tube Angle On Climbing?

The seat tube angle is one of the main factors that determine the position of the rider in regard to the bottom bracket.

• A slacker (smaller) seat tube angle places the rider closer to the rear wheel.

• A steeper (larger) seat tube angle pushes the rider closer to the front wheel.

If the seat tube angle is very slack, a lot of weight will be placed over the rear wheel. This geometry is detrimental to climbing for the following reasons:

• The rear wheel becomes harder to spin. (Hence people often get out of the saddle when climbing to “free” the rear wheel and increase the power transfer to the pedals.)

• The front end loses traction because there’s less weight on the front wheel.

• The front wheel can be lifted accidentally; in extreme cases, the rider may “loop out” (The rear wheel would spin under the rider and get in front of him as it often happens during a failed wheelie.)

• Power transfer loss due to the position of the rider significantly behind the bottom bracket. The further the pedals are in front of you, the harder it is to generate maximum torque.)

To avoid the issues above and to balance out the current slack head tube angles, modern bicycles come with steeper seat tube angles.

A steeper seat tube angle offers the exact opposite, namely:

• More front-wheel traction
• Less weight on the rear wheel (the rear wheel is easier to spin)
• Lower chances of looping out
• More torque generation via the cranks thanks to the more vertical leg push.

Analyzing the Seat Tube Angles Of Modern Road Bikes

Road bikes are designed for both efficient descents and hard climbing. The table below contains the seat tube angles of popular models.

Note: STAs vary according to frame size. For this data block, I’m using the middle-size frames as they’re the most common.

Road Bikes

Gravel Bikes

In the case of road and gravel bikes, the average seat tube angle is about 73-74°. This angle provides sufficient front traction and pedaling power when going uphill.

If the angle was to be any steeper, the rider’s weight would shift forward too much. The position will be more difficult to maintain and some power transfer losses will be experienced.

The next table contains the seat tube angles of modern XC bikes. I chose to examine this MTB segment because it’s the one that comes with technical climbs.

At 74.9°, the average seat tube angle of XC bikes is ever so slightly steeper than what we have in the road and gravel segment, but the difference isn’t massive.

Meanwhile, trail bikes tend to have even steeper average seat tube angles of about 76°. However, trail bikes are not optimal climbers and their geometry isn’t the main focus in this case.

Analyzing The Seat Tube Angles Of Lightweight Climbing Bicycles

The next table contains the seat tube angles of light road bikes that top specialists consider “climbing monsters”.

The seat tube angles of lightweight climbing bikes are in the 73-74° range with 73.5° being the most common number.

Summary: What You Need To Know

• The ideal seat tube angle for climbing is modestly steep.

• A steeper head tube angle helps by improving front wheel traction, unweighing the rear wheel, and providing a more vertical leg push during pedaling.

• The seat tube angle of most road bikes is 73-74°. XC bikes have a 74-75° seat tube angle.

• The most commonly found seat tube angle on climbing specialist bikes is 73.5°

Do Not Obsess Over Seat Tube Angels

Even though geometry is important for climbing, a few degrees are not going to make or break a bike if the rest of the climbing factors are satisfied.

What are those?

• The bike has to be the correct size for the rider for comfort and maximum power output.

• The bike has to be of good quality so that the rider doesn’t experience annoying technical difficulties.

• The bike needs to have sufficiently low gears so that the rider can cover long hills. If the gearing is too high, seat tube angles matter as much as the color of the bike when you have to conquer a climb.

• Desire + Training (No amount of technical stuff can compensate for the lack of motivation, discipline, and training.)

Go ride whatever you have and don’t dream of perfect bikes as they don’t exist.

The perfect bike is the one you can get on today.