Bicycle sizing: How to get the correct size bike and why it matters

There’s a little more to a bike fit than the right frame size. Here are some tips for making sure you buy the right size bike, and get it correctly setup.

Side note: We’ve also covered professional bike fitting if that’s of interest.

Before buying a bike

Bike frame size

There are two main ways bicycles are sized, in inches for mountain or hybrid bikes and centimetres for road bikes (and some of the sportier hybrids). The number denotes the length of the seat tube from the centre of the bottom bracket (where the cranks are inserted) to the top of the tube. It is ultimately a fairly meaningless number on its own and simply used to give a rough guide as to bike size.

Hybrid bike

No two bikes will be exactly the same, even if they have the same length seat tube. Depending on the intended style of riding the manufacturer has made the bike for, the various parts of the frame will all be different lengths and angles. Therefore, knowing what size you need in a bike is a good start, but not guaranteed to get you the right bike. This is where trying a bike out is your best option.

Most bike shops will let you test ride a bike before you commit to it. Be critical of the bike while you are trying it. Ask yourself questions like:

  • Do you feel like you are reaching too far or are you too scrunched up?
  • Do you have to raise the saddle almost the whole way up to get it big enough, or is the saddle slammed into the top tube?
  • Do you want to be upright or riding in low position and does the bike allow for that?
  • Does the bike feel as stable or as responsive as you would like?

Geometry charts

Once you have had one or two bikes, you will start to get an idea of what kind of riding position you do and do not like. When looking at bikes now, I look at the geometry charts and compare them to the dimensions I know about with my current bike. Generally the most important measurements to pay attention to are numbers 11 and 13 on the diagram below. 11 is the standover height – how long your legs need to be minimum to fit, although ideally you want at least a few cm’s extra clearance. 13 is the reach, which is a basic measure of, well, reach to the bar, which will only mean something if you compare it to your current bike.

geometry chart for size

As someone who is generally a big geek, I really like geometry charts and trying to figure out what bike frame might be best. I think it is a useful exercise in understanding more about positioning and bike behaviour if you are trying to get more into cycling as a sport, regardless of how amateur your interest may be (incredibly so in my case).

After buying a bike

Saddle height

Knowing how to set your saddle height is an important skill for being a regular cyclist and bike purchaser. If you make any changes to your saddle, shoes or bars, then you will need to readjust your saddle. It may also get changed when you take your bike for servicing.

Post adjustment angles

To get the correct saddle height is fairly easy. With the shoes that you will be riding in most sit on the saddle with a friend holding the bike for you – or stick one knee out against a wall, whatever feels comfortable. Place your heel on the pedal and put it all the way down to the bottom or 6 o’clock position. Like this your knee should be straight.

Saddle position

The saddle can move forwards a backwards on the rails, and therefore you can tweak your reach to the bars. This will not fix a bike that is too big for you, but can make your position on the pedals more comfortable and mean that your sit bones hit the correct part of the saddle overtime you sit down.

Saddle selection

You can also change the angle of your saddle. Ideally you want it to be pretty flat, but it is ultimately a personal decision as to whether you point the nose down or up, and it will vary by saddle and riding position on the bike. Similarly saddle shape can make a big difference to how a bike feels, even if it is not exactly related to fit – check out our post about finding the right saddle.

Stem

You can be on the right size frame but find the reach just a little too long or short. If this is the case you can change the length of the stem attaching the bars to the steering column. Again, this is something you don’t want to change drastically, and is best to get advice from your local bike shop, but it can make a good bike fit great.

Along the same lines, you can change the angle of your stem. All of them are reversible so can point up or down. When I got the Genesis Flyer, it was inverted and my reach was a tiny bit too long. I found flipping the stem around so it pointed up 7° rather than down made all the difference.

Handlebars

The width and shape of your handlebars can make a big difference to comfort, especially if they are drop bars. Width, reach and drop can all vary and make a huge difference to your comfort on a bike.

Parameters of handlebar measurements and size

A handy graphic from bicycling.com

The width is supposed to be roughly the same as the width of your shoulders so your arms are in a straight line and not compressing or over extending your chest. Reach to the levers can vary and make a bike a bit too big, much like the stem. The depth of the drop can be too great, meaning you never use that part of the bar, or too shallow meaning it’s pointless. If you struggle with any of these things, you can ask a bike shop to recommend a new set of bars and have them instal and set them up for you, or you can do it yourself.

I think the most important piece of advice is find a good bike shop that understands your need and has a range of bikes for you to try out. This is what I did when I got my first proper bike and it worked very well.

What are your tips for getting the right bike size and setting it up to fit you?

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8 Responses to Bicycle sizing: How to get the correct size bike and why it matters

  1. Ravi Roshan Jaiswal 09/09/2016 at 8:24 am #

    Hi Emily,

    Informative post indeed. I’m so excited to know the basic tips to get the correct size bike. I got amazed to know that why it matters to get perfect size bike. Honestly saying, I was unknown about the cycling tip and also, had no idea to get the bike and how to drive this.

    Looking very carefully the geometry charts was helpful for me to know the things before buying a bike. Also after buying a bike is wonderful.

    I was confused before about Handlebars. But finally, I got it. Hope these advice will help me ride a bike perfectly. Thanks for the great tutorial bike tutorial.

    Keep sharing.
    With regards. 🙂
    – Ravi.

  2. David Knowles 09/09/2016 at 1:54 pm #

    I ride an Electra Cruiser and don’t have to think or worry about those rules.I have ridden many bikes in my life and the Electra is by far the most comfortable.Electra Cruisers fit anyone and they can put their feet firmly on the ground,whilst having full extension of their legs.No wonder more people are giving up uncomfortable road bikes and buying Cruisers!

  3. Andy 10/09/2016 at 12:02 pm #

    The idea of a certain angle of hip and knee is good, but will depend on the position of the ankle joint. IMHO its easier to start with a simple measure of inside leg, and then multiply by 109% to give the distance from midpoint of saddle to top of axle of pedal.

    The crank must be near bottom, in a straight line with the seat tube.

    This is a great place to start, with small adjustments up or down, just 2 mm at a time to take account of things like length of foot, and amount of ankle movement your own pedalling style uses.

    Saddle position fore and aft is a bit more difficult to explain in just words.. needs a diagram and a tiny bit of knowledge of anatomy, but means getting the pedals horizontal and the back of the kneecap vertically over the pedal axle, using a plumb line.

    Might sound a bit complex, but can all be done with things found in an average house. Tape measure and string/ small weight.

  4. TOM 11/09/2016 at 4:18 pm #

    Good article. I took nearly 3 months to get my touring bikes fine tuned. Carried tools with me and made roadside adjustments. Then since no one else rides them, I tightened all bolts much as I could so adjustments would stay.

    >> Place your heel on the pedal and put it all the way down to the bottom or 6 o’clock position. Like this your knee should be straight.

    Is the one thing from the text that I disagree with. The knee should be slightly bent at the bottom of the pedal cycle (the picture of the girl above text .. with measurement 136.6) is the correct setup.
    One sure way of double checking is to have a friend ride behind you and watch your hips. If they are rocking, then the saddle is too high (legs having to reach too much) . If the knees are bowing out, the saddle is too low.

    Since I park sometimes in public places, saddle theft worries me. When absolutely sure that I had the saddle position dialed-in as I wanted it , then melted a little solder into the adjusting bolts tops so that a thief cannot get an Allen wrench in there to swipe saddle.

  5. Phil 14/09/2016 at 10:34 am #

    The type of bars, length of stem and hand position can make an enormous difference to riding position and comfort. I personally have never got on with drops, and dislike being stretched forwards and downwards by over-long stems in combination with either drops or straight bars. I fitted an Aheadset extender with several spacers, an adjustable short stem set at about 30 degrees upwards and a set of Velo Orange Tourist ( North Road type ) bars, angled slightly downwards. This allows me to sit mostly upright, with a neutral hand position and minimal pressure on my wrists. The result? No lower back, wrist or neck discomfort, I can ride all day without needing to change position, and I can see everything going on around me. Speed merchants will probably scoff at my non ‘aero’ position and lack of interest in cycling fast; I could not care less, as long as I’m going reasonably faster than walking or running I’m happy.

  6. Dan 14/09/2016 at 12:40 pm #

    For the past two years I’ve been riding a Boardman bike from Halfords which I thought was fine, until I bought myself an Electra Cruiser I. What a difference it makes! I thought that aches and pains were just part of regular cycling but since riding the Cruiser I don’t get any. Wish I’d found out about these sort of bikes sooner!

  7. david 26/09/2016 at 4:24 pm #

    I’ve been riding a bike for years and years and I’m still adjusting my position, no such thing as ‘correct’ A lot depends on the type of riding you’re doing

  8. Micheal 12/10/2016 at 10:18 am #

    I always understood from my father In law,who ran a cycle shop,that the height of the saddle is determined by sitting on the bike with the legs straight and the toes touching the ground. The toes should just be bent. The reason for this is when you stop you just put your feet down and don’t have to get off the saddle.

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