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This post compares and explains the differences between the terms reach and effective top tube.
Definitions
Reach – the horizontal distance from the center of the bottom bracket to the middle of the head tube. (image below)
Effective Top Tube (ETT) – the horizontal distance from the center of the head tube to a line extending out of the seat tube.
Reach vs. Effective Top Tube – What Are The Differences?
- Effective Top Tube = Important When Pedaling In a Seated Position
The effective top tube is dependent on the seat tube angle. (The seat tube angle is the angle between the seat tube and a horizontal line passing through the bottom bracket).
If we make the seat tube angle slacker, the effective top tube will have to become longer to reach the seat tube.
If we make the seat tube angle steeper (closer to the front wheel), the top tube will have to be shorter, provided there are no other changes to the frame.
The reverse is also true. If we make the top tube longer, the seat tube will have to get slacker; if we make the top tube shorter, the seat tube will have to be steeper.
Any changes to the actual top tube will inevitably result in the same changes to the effective top tube.
Ultimately, the effective top tube indicates the distance between the seat tube/saddle and the head tube.
It’s important to note that this measurement matters only when the rider pedals in a seated position.
If the rider stands up, the distance between the head tube and the seat tube is no longer as impactful.
In short:
Longer ETT = the bike feels longer/larger when pedaling
Shorter ETT = the bike feels shorter/smaller when pedaling
- The Reach Isn’t Affected By The Position of the Saddle
The position of the saddle affects the effective seat tube angle and therefore influences the effective top tube as well.
Moving the saddle forward steepens the effective seat tube angle and decreases the effective top tube. Moving the saddle backward slackens the effective seat tube angle and increases the effective top tube.
However, the saddle position has zero effect on the reach.
- Reach = Important When Pedaling Outside of the Saddle
The reach is dependent on the distance between the bottom bracket and the head tube. That measurement is not always affected by the top tube and the seat tube.
For example, if you slacken the seat tube angle and make the top tube longer to reach the new position of the seat tube, the reach will not change even though the effective top tube is longer.
In the graph above, you see that the reach does not change when we slacken the seat tube angle, but the effective top tube increases in length.
This “seat tube independence” of the reach makes it a good indicator of how the bike will feel when pedaling outside of the saddle.
A longer reach makes the bike feel larger when pedaling outside of the saddle whereas a shorter reach results makes the bike feel smaller.
- The Reach and the ETT Influence Each Other
If we increase the reach, the effective top tube will become longer too unless we steepen the seat tube angle to compensate.
If we increase the effective top tube, the reach will not necessarily increase because the extra length can be compensated by slackening the seat tube angle.
However, if we increase the top tube length without changing the seat tube angle, the downtube will have to get longer too. A longer downtube will result in a longer reach.
This effect is explained in greater detail in the post revealing how the seat tube angle affects the reach.
- The Reach Changes The WheelBase
(Wheelbase = the distance between the front and rear axle. Long wheelbase = stability; Short wheelbase = agility.)
It’s possible to increase or decrease the top tube without changing the wheelbase of the bike if we play with the seat tube angle.
However, changing the reach will result in a longer or shorter wheelbase regardless of the seat tube angle because the head tube will get closer or farther away from the bottom bracket.
The Current Trend
At the moment, the world of MTB is focused on slack head tube angles and steep seat tube angles.
The steep seat tube angle immediately results in a shorter effective top tube. To counteract this effect and make the bike feel larger when pedaling outside of the saddle manufacturers make the reach longer.
That said, the reach can compensate for the steep seat tube angle only to a degree. Sometimes the rider could feel a bit too “compressed”. In that case, the frame could be the wrong size entirely.
Which Number Is More Important – The Reach Or The Effective Top Tube?
Honestly, both the reach and the effective top tube should be taken into consideration.
If you only care about the reach, the bike will feel fine when you pedal outside of the saddle, but if the seat tube angle is “wrong” and thus the top tube is too short or long, you will feel “cramped” or “stretched” when pedaling.
The Same Fit Does Not Equal The Same Handling
It’s important to note that it’s possible to achieve an identical fit on two bikes with slightly different reaches and effective top tubes by playing with the stem, handlebars, and the position of the saddle.
The similar fit will not result in identical handling because the bike with the shorter reach could have a shorter wheelbase (it depends on the chainstays too). The value of the head tube angle will be very important too.
Thus, two bikes with a similar fit could perform differently.
Summary: What You Need To Know
- The effective top tube is the distance between the middle of the head tube and a line extending out of the seat tube.
- The effective top tube is highly dependent on the seat tube angle.
- The seat tube angle is the angle between a horizontal line passing through the bottom bracket and the seat tube.
- A slacker seat tube angle = longer top tube; a steeper seat tube angle = shorter top tube.
- The effective top tube indicates the distance between the seat post/saddle and the head tube when pedaling. If you want maximum pedaling comfort, the value of the ETT should be taken into consideration.
- The effective top tube is also dependent on the effective seat tube angle.
- The reach is the horizontal distance between the middle of the bottom bracket and the middle of the head tube.
- The reach is not dependent on the seat tube angle (unless we want to preserve the top tube a very specific length).
- If the top tube changes along with the seat tube angle, the reach remains the same.
- The reach comes into play when pedaling outside of the saddle.
- It’s entirely possible to get a bike with the right reach and the wrong effective top tube length.
- Both the reach and the effective top tube should be analyzed when making a decision.
- Of course, the effective top tube is slightly less important for bikes that aren’t meant for seated pedaling (e.g., BMX, dirt jumpers).
