Choosing the correct size road bike – Geometry Explained

In this ‘Choosing the correct size road bike – geometry explained’ guide we look to assist you in determining what size of bike 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 such as the handlebars, handlebar stem and cranks are correct and that an appropriate ladies saddle is fitted.

Back to basics

Whenever you are searching through websites for information on sizing you will see the word geometry feature heavily. What is the geometry and how does it affect how the bike performs? If we strip it back to the bare bones it is simply this; the term geometry encompasses the shape, length and angles of the tubes that 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 position for better aerodynamics. A mountain biker, on the other hand, needs a more comfortable, upright riding position that promotes more control and stability when riding off-road.

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 and 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. Simply have someone measure the distance from the top of the book/ruler to the floor.

Frame Size

This graphic is used on every bike in our range and displays the height range for each frame size.

Now 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 as each bike listed on our website has a specific height range listed for each individual frame size (see image above). The height range quoted for each bike is not simply based upon default factory measurements. We have also included information that has been collected from numerous real-world measurements of visitors to our stores as well as from staff who regularly test ride our machines.

If you find that you fall between 2 sizes the general rule is to go for the smaller size. Its easier to make a smaller bike fit by adjusting handlebar stem length and saddle height than it is to try and make a bike that’s too large fit. Alternatively, if you can make it into one of our showrooms one of our friendly team of experts can help you through the whole buying experience.

Key Components

As we alluded to earlier there are key components that are customisable and are essential to ensuring 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

Simply 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).

The handlebars widths that the manufacturers quote tend to be most commonly measured either from centre to centre or outside to outside of the drops. 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 outside to outside add 4cms.

Handlebar stem

Unlike handlebars, there is no magic formula to help you ascertain the correct length of handlebar stem. 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 if you select different frame sizes on our website the default sizes of the handlebar and handlebar stem decrease or increase depending upon whether you size up or size down.

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 and 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 choice offered when ordering a bike are 165, 170mm, 172.5 and 175mm. Its a commonly held belief that the size of a bike dictates how long the cranks should be, but 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 bike size. There are a couple of methods for determining which length of cranks are your ideal size.

The first is to base it off 9.5% of your total height in cms. If we take a rider of 185cms height for instance 9.5% of the total height equates to 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.

Or, you can use your inseam to determine the ideal length; inseam in cms x 1.25cms + 65. If your inseam is 83cms x 1.25+65 =168.75, so using this method you should select 170mm cranks.

Saddle

We are all individuals and we all have individual anatomies and this makes it very difficult to pinpoint exactly whats saddle your body will be comfortable with. What is absolutely essential though is that provides you with the correct amount of 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.

Now you have this you can apply it 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 is 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 which 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.

8 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!

Leave a Reply

Your email address will not be published.