Updated on 9 November 2026. Recommended products are available at the time of this update.
To choose the right road bike size, start with your height and inside leg measurement, consult the model's size chart and compare stack and reach to understand how high and stretched out your riding position will be. With a second-hand bike, you also need to check that the saddle and handlebar can be adjusted to suit you: a letter or number in the listing is not enough.
How to choose
The frame size should allow you to pedal and reach the controls without forcing your position. Two people of the same height can have different leg, torso and arm lengths, so height alone narrows down the choice but does not settle it.
- Measure your height: barefoot, with your back against a wall and looking straight ahead. Place a book on your head to mark the point to measure.
- Measure your inside leg: barefoot, with your feet slightly apart, bring a book up between your legs until it rests firmly against you, similar to a saddle. Measure the vertical distance from the floor to the top edge of the book and repeat the measurement.
- Find the correct chart: it must be for that model and generation. The guidance for another bike from the same brand may differ.
- Consider how you ride: ride duration, flexibility and familiarity with a road riding position matter as much as your body measurements.
Your inside leg measurement helps you assess saddle height and clearance above the top tube when standing over the bike. However, it does not tell you the distance to the handlebar: that also requires geometry, torso proportions and trying out the position.
Formulas based on inside leg measurement can provide an initial guide, but they do not automatically turn a body measurement into the correct size for every frame.
Stack and reach: what they really mean
Stack and reach are two frame measurements, normally expressed in millimetres. Both start at the centre of the bottom bracket, the point around which the cranks rotate, and end at the centre of the top edge of the head tube.
- Stack: the vertical distance between these points. All other things being equal, a higher stack makes it easier to achieve a higher handlebar position.
- Reach: the horizontal distance. All other things being equal, a longer reach lengthens the front part of the frame.
These are not the final coordinates of your hands. The stem, spacers, handlebar shape and lever position alter where you hold the controls; saddle position also affects how far away they feel.
If you already have a bike you ride comfortably, find its stack and reach measurements and compare them with those of the model you are considering. Check the current adjustments too: frames with similar figures can have different cockpit setups.
If you want a less tucked position, consider geometry with a higher stack and shorter reach than racing alternatives, without choosing a larger size simply to raise the handlebar. To learn more about saddle support, read how to choose a saddle by shape, width and size.
Why S, M, L and numerical sizes vary between brands
Letter sizes do not follow a universal standard: one M can have different geometry from another M. Numbers such as 43, 56 or 59 may also refer to a seat tube measurement or a designation chosen by the brand.
On frames with a sloping top tube, seat tube length describes only part of the geometry. This is why there is no consistently valid conversion between L and 56, or between S and a particular numerical size.
- If you are looking for a second-hand bike in S, M or L: use the letter to shortlist listings, then check the model, year and geometry.
- If you are looking for a second-hand bike in size 56 or 59: ask what that number identifies and compare the stack and reach of the exact version.
- If you are looking for a budget road bike in size 43: check that the geometry suits you. A 44 or a XXS is not automatically equivalent.
If you are between sizes, compare the position you can achieve on each. Always choosing the smaller one may force you to raise the cockpit too far; choosing the larger one may make it difficult to shorten your riding position.
How to check the size of a second-hand road bike
Before buying, ask for a photo of the size marking and the exact model details. The previous owner's height can provide additional information, but it does not prove that the bike will fit you too.
- Find the original geometry: check stack, reach and the height of the top tube above the ground, if specified.
- Check the seatpost: it must allow the required height while respecting the minimum insertion depth and any other specified limits. Check whether it has been shortened.
- Check the fork steerer tube: if it has been cut very short, there may be no room to raise the handlebar. Spacers must stay within the manufacturer's limits.
- Check the cockpit: ask about stem length, handlebar width and replacement options. An integrated handlebar may require the entire component to be replaced.
- Try it with a correct initial setup: you should be able to reach the levers and brakes with relaxed shoulders and slightly bent elbows, without constantly seeking another hand position.
- Have its condition checked: the frame, fork, headset, wheels, brakes and drivetrain need to be checked separately from the size.
Do not move the saddle all the way forwards just to reach the handlebar: its position should be set for pedalling. Adjustments fine-tune a suitable frame, but cannot compensate for every difference in size.
A short test ride can reveal a position that is too stretched out or too low, without guaranteeing comfort after many hours. For other checks before buying, see the guide Used road bikes: how to buy without surprises.
Our recommendations, available now
These models from our selection show different sizing systems and geometries. Your choice should be confirmed against the specific geometry: they are not equivalent simply because their size letters or numbers are similar.
Megamo START 105 12s
An option for starting road cycling or continuing your rides, available in sizes XS, S, M, L and XL. It combines an 6061 aluminium frame, carbon fork, Shimano 105 12-speed drivetrain and hydraulic disc brakes.
Corratec CCT Team Elite Disc Road Bike Shimano 105 12-speed
Worth considering if you are looking for a road bike with a carbon frame and fork, a Shimano 105 12-speed groupset and Mavic Ksyrium wheels. The listed sizes are 48, 51, 54 and 57: an example of a numbering system that needs to be read alongside the model's size chart.
Fondriest Daga Road Bike Shimano 105 12-speed
This new bike is available in sizes 45 and 48, in Black or Orange, for road rides. The build includes a monocoque carbon frame, Shimano 105 12-speed, disc brakes and Fulcrum RS900 wheels.
Berria Belador Pro 105 Road Bike with Disc Brakes
This new bike is available in size S/53 and Dark Grey, suitable for road rides on climbs and flat terrain. It combines a HM2X carbon frame, Shimano 105 2x12-speed drivetrain and Vision Team 30 aluminium wheels.
Scott Addict 50 Disc Road Bike
Worth considering if you prefer a position with a higher stack and shorter reach than race bikes. The frame is made from HMF carbon, and the build includes a Shimano 105 drivetrain and Schwalbe ONE tyres in 700x34C.
You can compare other options in the Road Bikes collection. For shipping information, see the shipping policy.
Let's find the right riding position together in Casapulla
Evolution Bikes has been a family shop in Casapulla, in the province of Caserta, since 1974. Now in its third generation, it offers a workshop, bike fitting and e-bike servicing. Come and try the bike or have its adjustments checked: you can also ask us for advice, providing your height, inside leg measurement and the model you are considering.
Frequently asked questions
I am 175 cm tall: which road bike size should I choose?
Height alone is not enough to identify a precise size. Measure your inside leg too and consult the model's size chart, then compare stack and reach and check your riding position.
Does a size 56 road bike correspond to a M or a L?
There is no universal equivalent. Numbers and letters vary between brands and models: you need the size chart and geometry for the specific bike.
If I am between sizes, is the smaller or larger one better?
It depends on your body proportions and the position you can achieve within the components' limits. Compare stack, reach and adjustment ranges, ideally with a test ride or a bike fit assessment.
Can I make a used road bike that is too large fit by changing the stem?
A different stem can partly correct the distance to the handlebar, but it does not change the frame dimensions. Before buying, also check the minimum saddle height, clearance above the top tube and overall riding position.
