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How to choose the right road bike size, including second-hand bikes

Updated on 5 November 2026. The recommended products are available at the time of the update.

To choose your 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, also check the year, actual size and scope for adjustment: a letter or number in the listing is not enough.

How to choose

The right size should allow you to pedal, reach the controls and brake without forcing yourself into an awkward position. Two people of the same height can have different leg, torso and arm lengths, so they will not always choose the same frame.

  • Measure your height and inside leg: these help identify the initial sizes to consider.
  • Identify the model and year: use the relevant geometry chart, including when buying second-hand.
  • Compare stack and reach: these help you understand the position offered by the frame.
  • Check the available adjustments: the saddle and handlebar must be able to reach the required position within the components’ limits.
  • Try the bike: assess your position while pedalling with your hands on the controls.

Height and inside leg: how to take your measurements

Measure your height without shoes, standing against a wall and looking straight ahead. To measure your inside leg, you need a rigid book and a tape measure; having someone help makes the measurement easier to read.

  • Stand barefoot against a wall with your feet slightly apart.
  • Place the book between your legs with its spine horizontal, applying pressure similar to sitting on a saddle.
  • Measure the vertical distance from the floor to the top edge of the book.
  • Repeat the measurement to check the result.

Compare both measurements with the brand’s guidance. Your inside leg measurement helps assess saddle height and clearance above the top tube, but on its own it does not tell you how long the bike needs to be.

Formulas that multiply your inside leg measurement by a coefficient provide only a rough guide. They cannot automatically translate your measurements into a size for every modern frame.

Stack and reach: what they really mean

Stack and reach describe the position of the top of the head tube relative to the centre of the bottom bracket, the point around which the cranks rotate. They are normally expressed in millimetres.

  • Stack: the vertical distance between these two reference points. All other things being equal, a higher stack makes it easier to achieve a higher handlebar position.
  • Reach: the horizontal distance between the same reference points. All other things being equal, a longer reach places the steering area further forward.

These do not measure the final position of your hands: the stem, handlebar shape, levers, spacers and saddle position also matter. This is why two frames with similar stack and reach may require different adjustments.

If you already have a bike you feel comfortable riding, note its model, year, size and cockpit setup. Its geometry provides a useful reference for comparing another frame, even from a different brand.

For example, two bikes both labelled M may have stack measurements of 560 and 585 mm: the second has a front reference point that is 25 mm higher. This illustrates how to read the measurements, rather than prescribing the right position for you.

Why S, M, L and numerical sizes vary between brands

There is no universal correspondence between letters and numbers. A S does not always equal a 52, just as a L does not necessarily match a 56 or a 59.

Numerical sizes may refer to seat tube length, using different measurement methods, or they may be nominal designations. With a sloping top tube, the actual seat tube length tells you only part of the geometry.

  • Compare the exact model: geometry can vary even within the same brand.
  • Check the year: a frame update may change measurements and size designations.
  • Read the full geometry chart: alongside stack and reach, consider effective top tube length and standover height, where provided.

If you are looking for a second-hand road bike in size L, or second-hand road bikes in size S or M, use the letter to shortlist listings. The model’s measurements must confirm the size.

The same applies to a second-hand road bike in size 59 or 56: the number alone does not identify a height range that applies to everyone. Even when looking for a budget road bike in size 43, check the geometry and scope for adjustment before deciding.

If you are between sizes

Automatically choosing the smaller or larger size can cause problems. The smaller frame may leave the handlebar too low; the larger one may be too long or limit how far the saddle can be lowered.

  • Compare the stack and reach of the two sizes.
  • Check that the required saddle height can be achieved within the seatpost’s limits.
  • Check whether the handlebar can reach a height and distance that suit you.
  • Consider your flexibility, experience and ride duration, without choosing a position simply because it looks sportier.

The saddle should be adjusted to support your pedalling: moving it a long way forwards to get closer to the handlebar does not necessarily solve the problem of a frame that is too long. The stem and spacers allow adjustments, but have limits and can affect handling.

How to check the size of a second-hand road bike

Before arranging a test ride, ask for photos of the complete bike and its size marking. Ask for the exact model, year and any components that have been replaced: the current riding position may differ from that provided by the original build.

  • Check the frame’s identity: compare the stated size with the markings and the correct geometry chart.
  • Check the seatpost: it must be possible to raise or lower it as needed while respecting the minimum insertion depth and any other specified limits.
  • Look at the fork steerer: if it has been cut down, there may be no room to raise the stem with additional spacers.
  • Examine the cockpit: a handlebar with an integrated stem may require the entire component to be replaced to change the stem length.
  • Check any components cut to size: an integrated seatpost may limit the available adjustments.
  • Assess the condition too: damage, play and wear require a separate check from the size assessment.

Do not choose based on the previous owner’s height: their proportions and preferences may differ from yours. For more detail on the checks, read the guide to used road bikes: how to buy without surprises.

What to look for during a test ride

A short test ride can reveal obvious fit issues, but it does not guarantee comfort after many hours. Start with a sensible saddle adjustment and wear the shoes you intend to cycle in.

  • With your hands on the controls, you should be able to brake without overstretching.
  • Your shoulders and arms should not have to stay rigid to support you.
  • Your pelvis should not rock noticeably as you reach for the pedals.
  • Check that you can also ride in the drops with control.

Pain or tingling alone does not prove that the size is wrong: it can also be caused by the adjustments. If doubts remain, a bike fit assessment can help distinguish between the two issues.

Our recommendations, available now

These models from our selection show different size designations and riding positions. These are not used bikes: compare your chosen variant with your measurements and check size availability on the product page.

Megamo START 105 12s

This is a new road bike for anyone looking to start road cycling or continue their cycling journey, offered in sizes XS, S, M, L and XL. It combines a 6061 aluminium frame, a carbon fork and a Shimano 105 12-speed drivetrain with hydraulic disc brakes.

Fondriest Daga Road Bike Shimano 105 12-speed

This is a new bike to consider if you are comparing numerical sizes 45 and 48 for your road rides. It has a monocoque carbon frame, a Shimano 105 12-speed groupset and Fulcrum RS900 Disc Brake wheels.

Corratec CCT Team Elite Disc Road Bike Shimano 105 12-speed

For anyone looking for a road bike with a carbon frame and fork, this option uses numerical sizes 48, 51, 54 and 57. The build includes Shimano 105 12-speed components, disc brakes and Mavic Ksyrium wheels.

Berria Belador Pro 105 Road Bike with Disc Brakes

This is a new bike for road rides over climbs and flat terrain, available in size S/53 and Dark Grey. It combines a Belador 6 DISC frame in HM2X carbon, a Shimano 105 2x12-speed drivetrain and Vision Team 30 aluminium wheels.

Scott Addict 50 Disc Road Bike

Consider this if you prefer a more comfortable position than on a race bike: its geometry has a higher stack and shorter reach than competition models. The frame is made from HMF carbon, with a Shimano 105 drivetrain and Schwalbe ONE tyres in 700x34C.

You can compare other models in the Road Bikes collection. For shipping information, see the shipping policy.

Let’s find the right size 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 a bike or have your bike’s adjustments checked, or ask us for advice, giving 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: you need at least your inside leg measurement and the chart for the exact model. Then compare stack and reach and check your riding position, especially if you fall between two sizes.

Does size 56 always correspond to size L?

No, the correspondence varies between brands and models. A size 56 and a size L can have different geometries: check the chart for the correct model and year.

How can I tell whether a used road bike is my size?

Check the size on the frame, find the model’s geometry and check that the saddle and handlebar can be adjusted to the required position. Examine the fork steerer and seatpost too, as any cuts may limit adjustment.

If I am between two sizes, is the smaller or larger one better?

There is no single correct choice: it depends on your proportions, desired position and scope for adjustment. Compare the stack and reach of both sizes and, where possible, try them with adjustments suited to you.