How To Measure A Bike Frame? ( 8 Measures )
Jane Tu - November 18, 2022A properly sized bike will be faster and more effective in addition to being more comfortable and simple to ride. You’ll be on the right track to buying the right size bike the first time and measuring a bike frame. How to measure a bike frame? Continue reading, and you will learn it.
What do You need to Measure a Bike Frame?
- A tape measure
- A clinometer to measure angles (there are free smartphone apps you can download)
- A long spirit level (or you can use the clinometer app and a straight piece of wood)
- A plumb line (or you can improvise with string and a couple of blobs of Blu Tack)
Although the majority of manufacturers now size both road and mountain bikes in metric measurements, you may still come across some that do so. In fact, some companies combine the two, like Moots.
We strongly advise you to stick with metric measurements to maintain consistency. If you really must, you can convert centimeters to inches by multiplying by 2.54.
On a maker’s website, you can typically find geometry charts for every size of a current frameset. If your bike is still in production, it is worthwhile to make a copy of this since it will be more accurate than your measurements and probably come in useful in the future.
How to Measure a Bike Frame?
Here are six measures you need to learn.
Top Tube Length
The top tubes on bicycles used to be horizontal are the first to measure a bike frame. Now, the top tubes of many bicycles will be slanted.
The actual top-tube length will typically be shown in a bike geometry table. The horizontal top tube length, also known as the effective top tube length or virtual top tube in many geo charts, must be measured for an accurate measurement, regardless of the top tube angle.
That is the horizontal separation between the Seatpost centerline and the head tube centerline. To ensure that your measurement is truly horizontal, use your spirit level or the clinometer app when taking it.
Road bikes are frequently sized by top tube length by manufacturers. Mountain bikes, however, have frames marked S, M, L, etc., indicating the size of the bike. Some road bikes also use that system; Merida’s road bikes pass through S, S/M, M/L, and L.
The interpretation of this measurement will vary depending on the brand; however, Ridley’s size S frames have top tubes that are roughly 54 cm in length, which is comparable to the size medium frames of many other brands.
It’s important to remember that not all brands determine virtual top tube length in the same way.
For instance, Colnago measures the distance horizontally from the head tube to a vertically projected up from the top of the seat tube rather than accounting for the seatpost’s additional rearward projection, so its measurements are less accurate than those of other manufacturers. 54cm top tubes are comparable to 1950s Colnagos.
Seat Tube Length
The length of the seat tube is the distance in a straight line that exists between the bottom bracket’s center and its top. It is another to measure a bike frame.
It’s challenging to compare the dimensions of one bike to those of an alternative because some bikes, like the Trek Madone, have a significant extension of the seat tube above the top tube junction while others use a seat mast.
Additionally, the seat tube on mountain bikes in particular frequently has a kink, so you don’t want to follow that line because it will be longer.
If you’re unsure whether you’re measuring along the correct line, align your straight edge with the center of the bottom bracket and the top of the seat tube.
Wheelbase
The distance between the front and rear axles of your frame is its wheelbase. It is a significant factor in determining how well a frame rides and varies with frame size.
It’s not too difficult to measure, but you must set the fork straight ahead for an accurate reading.
Similar to reach and stack, it is important to perform the measurement several times to ensure that you get the same result. The accuracy will also be improved if you measure the wheelbase on both sides of the bike and average them, as this will account for any fork slant.
Front Centre
The front center is the other element of the wheelbase. Since it is measured from the axle to the front dropout, it is the same as the chainstay length.
In addition to toe overlap with the front wheel, it again has an impact on handling. Although bike manufacturers don’t frequently quote it, BMC, for instance, displays it on its geometry charts.
Because neither of these measurements is taken horizontally, the chainstay length and front center are not added to determine the wheelbase.
Reach and Stack
As a result, it is clear that comparing frame lengths for the top tube and seat tube can be challenging. Most manufacturers now display reach and stack values for their bikes to improve consistency.
These measure the angles between two crucial contact points, the bottom bracket and the top of the head tube, and have the benefit of being independent of the frame design.
We’ve published a more detailed explanation of why reach and stack are important here.
The reach, simply put, is the separation between the two on the horizontal plane. You’ll need your spirit level once more to measure it.
Affix a plumb line to the level’s end. If you are using Blue Tack, make sure the blob at the end of the string is fairly symmetrical and that your string hangs down straight; otherwise, your measurement might be off.
Align the level’s top edge with the top of the head tube’s centerline. Once the plumb line and the center of the bottom bracket spindle are intersected, advance and advance the level until they do. Simply calculate your reach by measuring the distance between the head tube and the top of the plumb line.
A different approach is to lean your bike against a wall, measure the distances from the bottom bracket and the top of the head tube, then subtract the two measurements. You must nevertheless ensure that your measurement is horizontal.
The stack is the vertical distance between the top of the head tube and the bottom bracket of the bicycle. Following the plumb line, you should be able to measure your stack once you’re ready to record your reach.
A different approach is to gauge the vertical distance from the floor to the top of your head tube, then gauge the bottom bracket’s height above the ground, and finally subtract these two measurements.
The capture of both reach and stack requires quite a bit of finesse; if you use the plumb line method, you’ll probably need a second set of hands, and it’s worth practicing to make sure you get it right.
Bottom Bracket Drop
The distance between the crank axle’s centerline and the height of the wheel axles is known as the bottom bracket drop.
You can measure it by determining the heights of the bottom bracket and the rear axle, then dividing the results. It’s yet another significant metric that bike manufacturers use in their geo charts.
Bottom Bracket Height
The distance from the ground to the center of the bottom bracket shell is the bottom bracket height, to sum things up. In order to get an accurate reading, keep your bike straight up in the air.
Contrary to bottom bracket drop, your tires will also have an (insignificant) impact on them, so make sure they are inflated to your normal running pressure.
Chainstay Length
The length of your chain stays, one of the two parts that make up your wheelbase, also significantly affects how your frame handles. Usually, a frame with shorter chain stays will feel more vivacious than one with longer stays.
A ruler can be used to measure the chainstay length, which is the straight line distance between the center of the bottom bracket axle and the center of the rear dropout.
Seat Tube and Head Tube Angles
The seat tube and head tube angles are two of the most crucial components that affect the handling, with more upright tube angles typically resulting in more responsive handling. It will be helpful to use your clinometer app at this point.
By aligning your smartphone and reading the value from the clinometer app, you can determine the seat tube angle if your seat tube is straight. For an accurate reading, make sure your bike is upright and resting on a flat surface.
If your seat tube has a kink, you must align the phone with this kink by using a straight edge to trace the line connecting the top of the seat tube and the bottom bracket shell.
The majority of more recent bicycles have tapered head tubes, which means that the angle of the head tube’s front and centerlines aren’t the same.
A straight edge can be used to align with the top and bottom centers of the head tube, or you can hold your phone at an angle relative to the centerline.
You can measure the angle of the head tube instead if your fork legs are straight and do not have an angle at the crown of the leg. Once more, it’s crucial that the bike be standing upright.
By aligning the clinometer with the steerer extension above the head tube, you can also gauge the head tube angle.
Do you know how to measure a bike frame? Measure the top tube length, seat tube length, wheelbase, front center, reach and stack, bottom bracket drop, bottom bracket height, chainstay, length, and seat tube and head tube angles, you will have comfortable riding.
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