A seat tube angle between 73° and 75° is the norm for a hardtail today.
The most common number seems to be 73.5°. Those values preserve both the climbing capabilities of the bike as well as its aggressiveness.
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.
Note: The seat tube angle isn’t the angle between the seat tube and the chainstays.
The Relationship Between The Head Tube Angle and The Seat Tube Angle
The head tube angle (HTA) is the angle formed by the bike’s headtube and the ground.
Modern MTBs have slack (smaller) head tube angles for the following reasons:
- A slack HTA pushes the front wheel further in front of the rider and makes it easier to overcome massive obstacles.
- The position of the rider is safer during descents as the chances of flipping over the handlebars are lower.
- The frame can be combined with aggressive forks with very long travel.
- It’s easier to lift the front wheel to overcome an obstacle, jump, or perform a trick such as the bunny hop or rear wheel manual.
If a head tube angle is made slacker, and the seat tube angle isn’t modified accordingly, the rider will be stretched too much and the front wheel traction will be diminished to aggravating levels. Climbing will become very difficult and pedaling efficiency will be lost.
For that reason, slacker head tube angles come with steeper seat tube angles.
In short, the modern steep STAs are the result of the slacker HTAs rather than an independent goal.
The STA Differences Between Full Suspension MTBs and Hardtails
To compensate for the dynamic movement of the rear end and the STA ups and downs, full-suspension MTBs tend to have slacker seat tube angles than hardtails.
A hardtail can get away with some very slack STAs (e.g., 71°) precisely because the angle remains the same and there’s no need for compensation.
Analyzing The Seat Tube Angle Of Popular Hardtails
The table below contains the head tube and seat tube angles of many popular hardtails.
|Model||Head Tube Angle||Seat Tube Angle|
|Santa Cruz Chameleon 8||65°||74°|
|Vitus Sentier 29 VRX||66.5°||73°|
|Cannondale Scalpel HT HI-MOD 1||65.5°||74.5°|
|Nukeproof Scout Elite||64.5°||74°|
|Mondraker Podium Carbon RR SL||68.5°||73°|
|Santa Cruz Highball||69.5°||73°|
|Kona Big Honzo DL||67.5°||75°|
|Orange P7 R 29||65°||74°|
|Banshee Paradox V3||65°||76.25°|
|Rocky Mountain Growler 20||64°||75°|
|Ragley Marley 2.0||65.5°||73°|
|Vitus Rapide 29||68.5°||72.5°|
|Giant Fathom 2||66°||75°|
|Trek X-Caliber 8||68°||73°|
|Boardman MHT 8.9||68°||73.5°|
The average seat tube angle of modern hardtails is about 73-74° with 73.5° being the most common number.
This is a fairly conservative number that offers good climbing abilities without sacrificing the aggressiveness of the bike.
An angle smaller than 73° would be considered slightly slacker than expected whereas an angle larger than 74° is getting on the steeper side.
That said, one angle should not be the deciding factor when choosing a bicycle. One should take into consideration the entire geometry (head tube angle, bottom bracket height, chainstay length…etc.) as well as the built quality when making a choice.
Also, don’t forget to factor in frame size and wheelbase (distance between the axles.)
A hardtail with a small frame and short wheelbase can feel very agile and aggressive during cornering while having non-modern angles (e.g., a slack seat tube angle such as 71°).
At what cost?
Stability. Smaller bikes are fun, but they aren’t the most stable on descents.