Did you see the blog post on yesterday's Chita Peninsula exploration ride? The distance was short, but I’ve published the route, so please do take a look. There are still plenty of fascinating roads on the Chita Peninsula that seem well worth digging into. It might be a while before the next one, but I’ll be sure to let you know if I find more good roads.
Now, speaking of the Chita Peninsula, there’s a common route known as the "Chita-ichi," which is a loop around the entire peninsula. You just ride along the coastline, but that’s not really my style.
I definitely want to find and connect more routes like the one from yesterday. Dealing with the elevation is tough, but I love the way it adds variety to both the scenery and how you move your body.
So, today’s topic is about seat tube angles. You might be wondering how this connects to what I’ve been saying, but it boils down to the fact that I personally prefer riding routes with repetitive ups and downs in the mountains over riding on flat terrain.
Let’s break down how the seat tube angle relates to that.
What is seat tube angle?
The seat tube angle is the angle between the "seat tube" that supports the saddle and the ground (or a horizontal plane). This angle is a very important element of geometry that changes pedaling efficiency, the degree of forward leaning, the fore-aft position of the saddle, and what we call the center of gravity. Generally, a steeper angle (larger number) results in a more aggressive forward lean, prioritizing acceleration, while a slacker angle (smaller number) offers more comfort.
Geometry Comparison of My Bikes
| CIELO Road Racer Disc |
SEVEN CYCLES A-Frame Gravel 743 |
WILDE BIKES Rambler |
|
| Top Tube Length, Horizontal (mm) | 535 | 530 | 538 |
| Frame Stack (mm) | 522.2 | 583 | 565 |
| Frame Reach (mm) | 379.2 | 372 | 376 |
| Head Tube Length (mm) | 112.2 | 122 | 130 |
| Head Tube Angle (degrees) | 73° | 70.5° | 70.5° |
| Seat Tube Length (mm) | 455 | 440 | 450 |
| Seat Tube Angle (degrees) | 73.5° | 75° | 74° |
| BB Drop (mm) | 68 | 78 | 68 |
| Trail (mm) | 58 | 68 | 76 |
| Fork Length, Full (mm) | 366 | 395 | 407 |
| Fork Rake/Offset (mm) | 43 | 55 | 49 |
| Chain Stay Length (mm) | 415 | 438 | 438 |
| Bike Standover Height (mm) | 749 | 772 | 772 |
The CIELO is 73.5°, the SEVEN is 75°, and the WILDE is 74°. The CIELO’s 73.5° is what you could call a standard figure for a road bike. Likewise, 74° is typical for a gravel bike like the WILDE.
However, the SEVEN’s 75° is quite steep compared to the seat tube angles of most gravel bikes.
Let's look at the pros and cons of the seat tube angle.
| Pros | Cons | |
| Steep seat tube (Large number / e.g., 74°~76°) |
・Improved pedaling efficiency: When seated, the rider’s center of gravity is more easily positioned directly over or slightly ahead of the bottom bracket. This makes it easier to apply force directly downward, which is advantageous during climbs and acceleration. ・Nimble handling: Because the rider’s weight is kept over the center of the bike, it allows for agile maneuvering, which is beneficial on tight corners and complex trails. ・High cadence capability: The forward-leaning position and easier pelvic rotation make it easier to maintain a high cadence. ・Forward-leaning position: Naturally induces a forward-leaning posture, making it well-suited for road bikes or enduro bikes where efficient power transfer is required. |
・Reduced cruising efficiency/comfort: A more aggressive forward lean makes it harder for upper body weight to be distributed away from the handlebars, which can lead to fatigue in the arms and shoulders. ・Uncomfortable on flat roads: Since the hips are shifted forward, the pedals may feel like they are "behind" you, which can feel unnatural until you get used to it. Reduced straight-line stability: At higher speeds or on descents, the shifted center of gravity may make the bike feel unstable. |
| Slack seat tube (Small number / e.g., 71°~73°) |
・Comfortable cruising: Since the saddle is positioned closer to the rear wheel, upper body weight is better distributed toward the back, leading to less fatigue over long rides. It also makes it easier to maintain an upright posture. ・Pedaling stability: Makes it easier to tilt the pelvis backward, which is well-suited for long-distance rides where you sit and press down on heavy gears using your body weight. ・Easier reach to the ground: Even with the same seat tube length, a slacker angle often makes it easier to reach the ground when getting off the saddle. ・Improved straight-line stability: Because the rider’s center of gravity moves backward, the wheelbase tends to be longer, which reduces wobbling and increases stability at high speeds. ・Downhill maneuverability: The rear-biased center of gravity allows you to put your weight into the bike with confidence on steep descents. |
・Reduced climbing ability: On steep climbs, your weight is shifted too far toward the rear wheel, making it easier for the front wheel to lift and harder to keep the front end planted. ・Delayed power transfer: Especially when trying to adopt a forward-leaning position, it can feel as though power is not being transmitted directly. |
While there are various pros and cons, this is strictly judging based on the seat tube angle alone. Please keep in mind that the character of a frame is determined by all its geometry factors, including the head tube angle.
Moving on, let’s compare what types of bikes tend to have steep versus slack seat tubes.
| Steep seat tube (Large number / e.g., 74°~) |
Trail/Enduro MTBs / TT bikes / Keirin bikes |
| Slack seat tube (Small number / e.g., ~73°) |
Long-distance road bikes/Endurance road bikes / Cruisers/City bikes |
When you imagine these specific bike types, it’s clear that those pros and cons are accurately reflected in their designs.
The CIELO’s 73.5° is a standard road bike angle that is neither steep nor slack. It makes perfect sense when you consider that it’s intended for covering distances, tackling flat stretches, and occasionally handling some climbs. It’s what you might call an all-around road bike.
The WILDE’s 74° seat tube angle is also very common among other gravel bikes.
However, thinking in terms of gravel bikes, the SEVEN’s 75° angle is not something you see very often. If anything, it’s closer to the steeper angles found on modern enduro MTBs.
This design is meant to improve performance on rough terrain, especially during climbs. Given this point, it’s a perfect fit for me, as I prefer routes with a lot of climbing sections.
Admittedly, when I’m climbing mountain passes, I feel like I can pedal more efficiently and smoothly in the seated position on the SEVEN compared to the CIELO.
I suppose that’s the effect of this seat tube angle.
And when you combine that with the stability and comfort gained from the deep 78mm BB drop, it all fits perfectly with my preferred riding style.
Man, it’s a deep subject.
This time, I focused on the seat tube angle, but please remember that a bike's true character is always derived from the sum of all its measured geometry.
What should we talk about next? I haven’t actually decided yet, but please look forward to the next post.
