The reach and the effective top tube should be both taken into consideration when sizing a new bike.
Special attention should be paid to the reach as it isn’t affected by the position of the saddle and it’s difficult to make up for poor reach.
The Effect of the Effective Top Tube On a Bike’s Size
The effective top tube (ETT) connects the middle of the head tube and a line that extends out of the seat tube (image below).
The effective top tube indicates the distance between the head tube and the seat tube. It is therefore valuable when determining how the bike will feel when pedaling in a seated position.
But even if the bike isn’t designed for seated pedaling (e.g., BMX, dirt jumpers), the ETT is still important because it can make the bike feel longer or shorter even when pedaling outside of the saddle.
Sizing a Bike According To The Effective Top Tube
In general, the taller a rider is, the longer the effective top tube has to be.
However, it’s important to note that two riders can be of the same height and need bicycles with different ETTs.
It comes down to bodily proportions (limb and torso length).
The two most common combinations are short torso + long limbs and long torso + short limbs. But there are other possibilities as well. (e.g., short torso + long legs + short arms..etc.)
If the rider has a short torso + long arms, he/she may still find a fairly long top tube comfortable because the longer arms will allow him/her to find an acceptable position that doesn’t stress the back.
If the rider has a short torso and short arms, however, the effective top tube will have to be shorter too.
For that reason, most charts based on the effective top tube should only serve as a guideline as they cannot account for a rider’s specific anthropometry.
(If you need an ETT to height chart for a road bike, I recommend the one in this article.)
The Positions Of The Saddle and the Stem’s Length Influence The ETT
The effective top tube length that could work for a rider is not a single number but a range because the position of the saddle and the stem’s length can make a bike shorter or longer.
Sliding the saddle forward steepens the effective seat tube angle and reduces the ETT. Moving the saddle backward does the opposite, namely increasing the ETT and slackening the effective seat tube angle.
The stem can also contribute in either direction by a few cm. That said, it’s recommended to stay away from massive stem changes because the length of the stem depends on the bike type.
A road bike needs a longer stem because the additional length makes the steering less sensitive and thus safer during high-speed descents.
An MTB needs a shorter stem for technical terrain. The longer bars on modern MTBs offer a lot of leverage and make up for the twitchiness that a short stem would otherwise introduce.
The Effect of Reach On a Bike’s Size
The reach is the horizontal distance between the middle of the head tube and the bottom bracket.
The reach is not always dependent on the seat tube angle and the length of the effective top tube.
Notice that I say “not always” because bike geometry is all interconnected, and thus the seat tube angle still affects the reach when certain conditions are met.
The reach comes into play when the riders stands on the pedals. If the reach is too long, the rider would feel stretched out when pedaling outside of the saddle; if the reach is too short, the rider will feel restricted and sometimes his knees may come in contact with the handlebars.
The needed reach is also dependent on the rider’s anthropometry. Someone with long arms and legs will need much greater reach than someone with short legs and arms.
You can use the following method to determine whether the reach is sufficient for you:
Step 1: Put the pedals in mid-position. (Or in other words, both pedals should be at the same level.)
Step 2: Place wooden blocks or books you don’t care about under the pedals to stabilize them and the bike.
Step 3: Step on the pedals, grab the handlebars, and try to stand up all the way. Ideally, you will be able to stand up with your arms straight. If you have to let go of the handlebars or have to keep your arms bent, the reach is too long.
The table below contains general reach guidelines.
|157cm to 167cm||5’2 to 5’6||410mm to 450mm|
|167cm to 178cm||5’6 to 5’10||430mm to 470mm|
|178cm to 188cm||5’10 to 6’2||450mm to 490mm|
|182cm+||6’2 or above||470mm to 510mm|
Note: Similar charts are just a guideline as there are many factors that influence how a bicycle will feel in the real world.
Stem Length Can Partially Compesante For Poor Reach
The only way to somewhat affect a bike’s reach is to get a longer or a shorter stem. (The saddle position affects the effective top tube but has no impact on a bike’s reach.)
A shorter stem will decrease the reach whereas a longer one will increase it. As mentioned previously, the new stem shouldn’t be radically shorter or longer (e.g., replacing a 120mm stem with a 30mm stem).
If the discrepancy between the old and new stem is very large, the bike’s handling will suffer and it may be wiser to simply get a new frame with the right reach.
Modern MTBs Are Focusing More On Reach
Modern MTBs are focused more on reach rather than the effective top tube. Many riders first choose the reach of their bike and then play with the position of the saddle to get the needed effective top tube.
The main reason for this is the modern slack geometry. Currently, MTBs come with a slack head tube angle providing stability when overcoming obstacles downhill and a steep seat tube angle compensating for some of the negatives that a slack head tube angle produces.
The steeper seat tube angle results in a shorter ETT. To counteract that effect, manufacturers make the reach slightly longer.
Summary: What You Need To Know
- The effective top tube data is valuable because it indicates how the bike will feel when pedaling in a seated position.
- The reach is also valuable data because it shows how the bike will feel when pedaling outside of the saddle.
- Ideally, both numbers are within a range that fits the rider’s individual anthropometry.
- The effective top tube can be affected by the position of the saddle and the stem’s length.
- The stem’s length can compensate for poor reach to a degree.
- The effect of the saddle position and the stem’s length is small and cannot compensate for a frame that’s significantly smaller or larger than needed.