Choosing the correct size road bike – Geometry Explained

Shopping for a new bike can be exciting and confusing in equal measure, with an abundance of bikes all available in an array of sizes. So how do you go about ensuring that you find the right size for you? In ‘Choosing the correct size road bike – geometry explained’ we help you to work out what size is right for you.

Women-specific bikes

We like to think of all riders as being individuals and our priority is in making sure that the bike is right for your body shape, size and personal preference. All of our bikes are of a unisex design and are fully customisable to achieve the perfect fit for you. The crucial element to obtaining the right fit is to ensure that the sizing of key components is correct. These include the handlebars, handlebar stem and cranks. Specifying a ladies specific saddle is always highly recommended too.

Back to basics

Firstly we should address the elephant in the room that is ‘geometry’. This is to say that whenever you are searching for a bike you will often see the word geometry mentioned. So, what is ‘geometry’ and how does it affect how a bike performs? In short, it is simply this; geometry encompasses the shape, length, and angles of the tubes that come together to form the frameset.

Firstly we should address the elephant in the room that is ‘geometry’. This is to say that whenever you are searching for a bike you will often see the word geometry mentioned. So, what is ‘geometry’ and how does it affect how a bike performs? In short, it is simply this; geometry encompasses the shape, length, and angles of the tubes that come together to form the frameset.

The geometry of a bike affects the position you will find yourself sitting in, how the bike handles and its aerodynamic performance. A racing cyclist, for instance, seeks a more stretched out position for better aerodynamics. A mountain biker, on the other hand, needs a more comfortable, upright riding position. One that offers a head-up riding position to enable them to pick their lines as well as enhance stability and control.

Measuring your height and inside leg

Step one is height and inside leg, do you know these measurements? If you don’t we have some simple tips to help you determine these.

Height

  • Simply stand upright in bare feet, with your back against a wall/doorframe.
  • Place a pen or pencil atop your head and parallel to the floor.
  • Make a small mark on the surface and measure.

Inside Leg

  • In bare feet; stand upright with your back against a wall.
  • Place a book/ruler between your legs and level with your crotch.
  • Have someone measure the distance from the top of the book/ruler to the floor.

Frame Size

OK, now that you have your height and inside leg measurements, it’s time to apply them to your bike of choice. The good news is that we have done the hard part for you. Each bike on our website has a recommended height range for each individual frame size (see image above). This height range isn’t just based upon default factory measurements. We have collated data gained through numerous real-world measurements taken in-store and through test rides.

If you find that you fall between 2 sizes, the general rule is to opt for the smaller size. Because it’s considered easier to make a smaller bike fit. The stem and crank lengths can be lengthened and the seat post height can be extended. It is much more difficult to make a bike that is too large fit. After all, a seat post can only drop down so far!

Alternatively, you can pop into one of our showrooms and speak to our friendly team of experts. If this option is not available to you, we can also bring the showroom experience to you via a live one-way video call with one of our Live Instore Experts Team. All from the comfort of your own home.

Key Components

As we alluded to earlier, there are several key components that are customisable and which are essential to ensure that the bike you receive is right for you. Male or female, the rules to obtaining the correct measurements apply to both equally.

Handlebar width

Have someone measure the distance between the ac joints of your shoulders (the 2 knobbly bits to the front of your shoulder, where the collarbone and shoulder blade meet).

With the odd exception, most handlebar manufacturers will quote handlebars widths as a centre to centre measurement. This dimension is normally obtained by measuring the bars from the centres of each drop. When a bar has flared drops, the measurement is taken across the top, close to the brake levers. If they are a centre to centre model (like our LEVEL brand) you simply add 2cms to your shoulder measurement to obtain the correct width. If they are measured from outside to outside of the drops add 4cms.

Handlebar stem

Unlike handlebars, there is no magic formula to help you ascertain the correct length of the handlebar stem. Short of getting a professional bike fit that is. Given the general trend of female riders being shorter of torso and longer of leg, we find that a shorter stem length works better. The average male rider will normally opt for a stem length of between 90 and 110mm so we find a stem length in the region of 70-90mm is better suited to the female rider.

Generally the smaller the size of frame the shorter the stem should become. You may note that when you select frame sizes on our website the default sizes of the handlebar and handlebar stem decrease or increase correspondingly.

Crank Length

The length of the crank arms (the bit that your pedals screw into) can have a significant impact on comfort. Choosing the correct length cranks can help prevent sports-related injuries, increase power transfer or make climbing easier. Too long and you could find your knees clattering into your chest on the upstroke. Too short and you could find yourself losing out on the valuable power output from your long levers.

The most common choices offered are 165, 170mm, 172.5 and 175mm. It’s a commonly held belief that the size of a bike dictates how long the cranks should be. However, this is not strictly the case. Riders who require smaller bikes in the XS/Small range should certainly opt for the shortest option available. But in practice, it all comes down to personal preference as much as it does the size of the bike. There are a couple of formulas for determining which length of cranks are your ideal size.

Firstly, this formula calculates crank length based off 9.5% of your total height in cms. If we take a rider of 185cms height, for instance, 185×9.5= 17.575. So a 175 crank would be the ideal option for them. To muddy the waters slightly, this does not mean that this rider must absolutely use 175 cranks. They may prefer a faster-pedalling rhythm (cadence) so a slightly shorter crank would be more to their liking. A faster cadence is less impactful on the muscles but can be less efficient at cranking out the power.

Secondly, there is the inseam method. Take your inseam measurement in cms and multiply by 1.25 then add 65. If your inseam is 83cms then it works out as 83x 1.25=103.75+65 =168.75, so using this method you would probably round up to the nearest crank length of 170mm.

Saddle

We are all individuals and that means our anatomies all differ. This makes it very difficult to pinpoint exactly what saddle your body will be comfortable with. What is essential though is that it offers support for your sit bones (pelvic bones). Thankfully, there is a very simple method for measuring how far apart your pelvic bones are. All you need is

  • A flat bench or chair to sit on
  • A flat object that sits lower than the seat, that you can rest your feet on.
  • Piece of corrugated cardboard.
  • Tape measure.
  • Chalk (optional)

Take the cardboard and lay it on the seat.

Lower yourself onto the cardboard so it is aligned under your buttocks.

Raise your feet and place them on the lower footrest.

Try to simulate the position you would normally adopt when riding a bike. If you like a relaxed position sit more upright. If you prefer a more aggressive race position lean forward.

Hold this position for approximately 30 seconds.

Stand up and retrieve the piece of cardboard.

You should be able to make out 2 clear indentations imprinted upon the cardboard. These are produced by the sit bones and can be used to calculate your ideal saddle width. If you can’t make out the indentations clearly take a piece of chalk and rub it across the cardboard to bring out the indentations.

Next, take the tape measure and measure the distance between the indents. Using the centre of each as your start/finish points.

You can now apply this information to choose an appropriate saddle for your preferred style of riding. All saddles have a defined width so just find the one that best suits you.

Hybrid/MTB/Gravel – Add 20mm to the measurement, this will add more stability and comfort when assuming a more upright saddle position.

Endurance Road/Gravel – Add 10mm to the measurement, this saddle offers a good compromise of comfort and performance.

Further assistance

We hope this guide has been of assistance to you and helps you to work out what you need. This being said, there’s no better way to obtain the perfect size and fit than coming in to see us, whenever possible. For this reason, we now have 3 full-time showrooms located across England. Here, you can visit and be sized for our bikes and also receive some excellent buying advice from our team of friendly, professional and experienced experts.

We are also contactable through the usual channels;

By Video call

By far one of the best options is to use the Ribble Live In-Store Expert function brings the instore experience direct to the comfort of your own home. Simply click on the icon that appears at the bottom right corner of the website to be connected to one of our Instore Experts who will be delighted to assist you via a one-way video call. You see us but we cannot see you. They can take you through everything from sizing to build options and even offer close-ups of the bikes and equipment on their hand-held cameras.

Customer Service

You can contact our customer service team directly for friendly advice and assistance.

Social channels

You can also contact us through the usual social channels, by direct message through Twitter, or private message us through Facebook or Instagram.


How good is the HT Ti? Well one lucky owner sure loves his, read Jamie’s story here.


Katie Kookaburra took on the 1 climb – 26 times challenge, see how she got on here.


Introducing Murray Brindle, full-time bike mechanic, part-time enduro athlete and lover of all things cycling. Read it here.

13 Comments
  1. Hi, I’m interested in buying the Ribble Sportive Racing from the Ribble site. However, I’m quite confused about sizing.

    The chart size recommendation on this post conflicts with the information given on your frame size help page http://www.ribblecycles.co.uk/text/framesize.html

    I’m 5’11 and have a 33″ inseam ( 83.82cm ). According to the SLOPING GEOMETRY formula on this page ( 83.82 x 0 .64 = 53.6448cm ), I should be getting a 53cm sized frame. While the chart on this page suggests I go with a 56cm.

    The 53cm sized frame’s top tube is 558mm, matches more closely my current 56cm sized frame with a 560mm top tube. But now I’m not sure which to get.

    So which is right? and which do you reccommend?

    Thanks!

    ——————————————————————–

    “SLOPING GEOMETRY (Sloping Top Tube)
    Use the formula: Inside leg measurement (cm) x 0.64. The resultant size and round up or down to the nearest frame size option. If you are in between sizes we recommend you go for the smaller size.”

  2. Hi
    I am looking to buy my wife your clearance 2016 Evo pro carbon ultegra. What is the top tube length of the XS and S sizes? She is 5’4″ tall and presently rides a frame with top tube 54cm with 8cm stem and she is too stretched out.

  3. Hi, I am a sportive rider. I am 6ft with a 33 inch inside leg. I have a medium genesis zero 2015 frame currently. I felt the large was too big with a long top tube. The medium tt is 565mm with the large being 585.
    Felt like I was reaching on the large frame.

    So am looking at buying an upgrade. Will buy the sloping frame and that would put me at just over 53 cm based on your sportive chart. I note the toptube length would also seem consistent with my current bike.

    Can you confirm this is right? Whenever you look at height measurements on other sites it suggests 58 + so just eanted to be clear before I buy, thanks shaun

  4. My size is 171 height and 80 cm inseam leg, The ST of my Ribble Sportive Racing Green Carbon 2017 is 48 cm and the horizontal top tub 52 cm.

    Is that Bike too small for Me?

    Please Advise

  5. I currently have a volt pulse. It basically has 4 power settings, put simply:-
    Setting 1 gives assistance up to 5 mph
    Setting 2 up to 8 mph
    Setting 3 up to 12 mph
    Setting 4 up 15.5 mph
    This system wastes battery power as I don’t really need assistance to get up to 8 mph. For example, I would prefer the motor to kick-in after I get to 8 mph.
    Can you tell me how your e-bikes deliver their power?

  6. Hello I have a gran fondo size M.
    Please can you tell me how many cm this is as I’m looking to sell it
    Thanks!

  7. Hi, I have just very kindly been given a Ribble, it looks awesome but is going to take a lot of TLC to get back on the road. I pretty certain its a road bike but please how do I identify what type it is?
    Cheers
    Paul

  8. I am looking to buy an ebike for my wife, but she is only 5’1″. Would an XS for the CGR work? What us the stand-over height on that?

  9. I want to buy the CGR AL, I have a question on advertised bike weights which is a bit confusing. The CGR 725 medium with Tiagra is advertised weighing 10.65 pounds, whereas the CGR AL Tiagra medium, and a lighter frame is shown to be 11.5 pounds? Is this correct and if so what is it that constitutes the extra weight please?

  10. Good Morning,

    I am considering ordering a CGR 725 and I’d like to confirm which size bike might be best for me. I measure 68.5” tall with a 30“ in seam. What size bike would you recommend? What length of handle bar stem and length of crank arm might be most appropriate? Thank you.

  11. I am looking for an Endurance set up – however, the Stack / Reach for the Endurance frames for a Medium build are S 541 and R 390. That does feel like an Endurance set up – I currently have a BMC with a 559 / 383 and that feels a bit of reach.

    Am I mis-reading something in your geometry charts ?

Leave a Reply

Your email address will not be published.