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You don't choose your road bike frame like you choose your socks in the morning, or like you buy a loaf of bread... Pedaling a bike in your size is imperative to find the right compromise between comfort and performance. Frame length and height, measurements to take, size charts: we tell you everything you need to know in our guide to road bike frame sizes. Saddle up!
The postural study for an ergonomic bike
A good way to define the ideal dimensions of your future road bike frame is to perform a postural study at a cycling specialist.
The goal of the postural study is to find the optimal position on the bike for comfortable, pain-free rides. The geometry of the frame is to be taken into account, as well as the morphology of the cyclist and the intensity of the practice.
Thanks to this ergonomic analysis, you get valuable information on the dimensions of the frame that will suit you best.
Note that this study still has a certain cost and is not essential to find a bike frame in his size.
The road bike frame size charts
You should know that not all bike manufacturers offer the same frame size standards. And yes, there is no one universal guide to choosing the perfect frame, regardless of brand. Each manufacturer offers a table with the different sizes that can be expressed in cm, inches or in classic sizes (XS, S, M, L, XL, XXL). Be sure to consult these data when choosing your road bike frame.
The inseam for bike frame height
Thankfully, there is a baseline measurement for finding the right bike size: inseam height.
Since we don't all have the same body proportions, this crucial information will determine which bike frame height to choose, rather than your height.
To measure your inseam height, you'll need a fairly thick book, a tape measure and a pencil. Proceed as follows:
Stand barefoot and stand up straight against a wall. Place the book between your legs, in contact with the perineal area, applying gentle pressure.
Once the book is correctly positioned, carefully pull yourself away from the wall while holding it tightly against it.
Mark with a pencil line where the edge meets the wall, then use the tape measure to measure the distance from the floor to the marking.
Then multiply this result by 0.66 and you have the road bike frame size to choose.
Arm span for bike frame length
Fall between sizes? Don't panic, just take one more measurement to help you select the best option.
While the height of the bike frame is paramount, the distance between the handlebars and seat tube also plays a key role. This frame length depends on the size of your trunk and arms.
This is where the ape index comes into play to establish the ratio of arm span to rider height. This "monkey index" simply lets you know if you have long or short upper limbs!
To calculate your APE Index:
measure the distance of your arms apart, from one end to the other (a little outside help will be welcome);
apply the following mathematical formula: your height in cm - the span of your arms in cm
Is the result greater than zero? Then you should go for the larger size between the two options.
The result is less than zero? Then the smaller frame is what you need!
Choosing the right bike frame size for a child
Are you looking for a bike for your child?
Be aware that inseam measurement is also used. However, it is not the frame that will determine the proper size of the bike, but the wheel size.
The geometry of the bicycle frame
Height and length are key to defining road bike frame size, but there are other dimensions that also vary the parameters. Seasoned cyclists will look to play around with these settings to combine performance, comfort and efficiency.
Bike dimensions overview:
seat tube height (frame height);
top tube (or horizontal) length;
seat tube angle;
head tube angle;
head tube height;
wheelbase;
chainstay length;
bottom bracket drop;
fork height.
Stack and reach: interesting indicators
Popular with triathletes for years, stack and reach measurements are now being extended to all types of bikes.
These new elements provide, in effect, a more accurate estimate of the position on the bike:
The stack is a vertical measurement that extends from the bottom bracket axle to the highest virtual point on the head tube. A high stack translates into better comfort, but more resistance in the air.
The reach is a horizontal measurement that extends from the top of the steering column to the virtual point at the center of the bottom bracket. A high reach induces a reclined position on the bike that will delight riders looking for aerodynamics.
The stack and reach form a virtual right angle. Practical information to choose a position adapted to his practice.
Peripherals settings
Finally, adjusting the peripherals of the bike frame is not to be overlooked. The saddle and cockpit can dramatically vary the position on the bike and improve comfort or performance.
Stem, seatpost, saddle tilt and setback, handlebar width...all of these should be considered to get the most enjoyment out of your bike.
In any case, remember this: the secret to finding the right road bike frame size is to try it on!
