Choosing the correct size road bike – Geometry Explained

Thursday, April 23, 2020

Shopping for a new bike is an exciting time, right? But, when faced with such a wealth of bikes to choose from, how do you ensure that you get the right size? Choosing the correct size road bike couldn’t be easier. As long as you are armed with the right information, of course. Check out our guide to find out what works best 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. Consequently, all of our bikes are of a unisex design and are fully customisable to achieve a fit that’s perfect for you. The crucial element to getting this right is to ensure that the sizing of key components is correct. Most notable of which are the handlebars, handlebar stem and cranks. Specifying a ladies specific saddle is always highly recommended too, of course.

Back to basics

Firstly we should address what exactly is meant when we refer to ‘geometry’. In short, it is simply this; geometry encompasses the shape, length, and angles of the tubes that come together to form the frameset.

For example, the image to the right shows each section of the frame and links it to the dimension in the chart below. For instance, an XS frame has a top tube (B) measurement of 52cms whereas the S has one that is 53.5cm.

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, will prefer a more stretched out position for improved aerodynamics. A mountain biker, on the other hand, needs a more comfortable, upright riding position. One that offers a head-up riding position that enables them to pick their lines and enhances the stability and control of the bike.

1. Measuring your height and inside leg

The first step is to determine your height and inside leg measurement. Do you know these? If not, we have you covered. Here are some simple tips to help you measure these. The methods described below are easier with the aid of a helpful assistant. However, you can also obtain the measurements yourself in the absence of a willing volunteer.

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.

2. 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). 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 via test rides.

If you find that you fall between 2 sizes, the general rule of thumb is to opt for the smaller size. Why you may ask? Well, it’s because it’s generally considered easier to make a bike that’s a little small fit than one that’s too large. There are certain alterations that you can make to a smaller bike to correct the sizing.

These include: lengthening the stem length, crank length and raising the saddle height. It is much more difficult to adjust a bike that is too large to fit the rider. After all, a seat post can only drop down so far. Whereas fitting too short a stem can result in overly responsive (twitchy) steering.

Alternatively, if you live or work in close proximity to one of our showrooms, we would thoroughly recommend visiting one. In-store, our friendly and knowledgeable experts can help you with everything from picking suitable components to measuring you up on one of our sizing jigs. Using these jigs we can simulate the specific dimensions of frame size and adjust the fit to get it just right for you.

However, if visiting a showroom is not possible, we can also deliver the showroom experience direct to you. Simply connect to one of our Live Instore Experts via a live one-way video call. Our experts can answer any queries you may have, offer advice on sizing and component choices or even provide a product demo of each bike. All from the comfort of your own home, and remember it’s completely anonymous. You can see us, but we cannot see you.

To connect with a Live Expert simply visit our website and click on the image in the bottom right corner of the screen.

3. Key Components

As we alluded to earlier, there are several key components that are customisable and which ensure that the bike you receive is right for you. Whether you’re male or female, the rules to obtaining the correct measurements apply to both equally. In direct contrast to an ‘off-the-peg’ bike where the components choices are preset, we offer an almost unlimited choice of customisation options.

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 handlebar widths as a centre to centre measurement. This dimension is normally obtained by measuring the bars from the centres of each drop. However some manufacturers such as Zipp will measure them from centre to centre across the tops.

If they are a centre to centre model, (like our own LEVEL brand) 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.

The 2 most common ways that manufacturers denote bar width is centre to centre or outside to outside

Handlebar stem

Unlike handlebars, there is no magic formula to help you ascertain the correct length of the handlebar stem. The only way to accurately determine this is to book a professional bike fitting or visit one of our showrooms. Given the general trend of female riders being shorter in the torso and long in the 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 120mm. Whereas a stem length in the region of 70-90mm is better suited to the female rider. Broadly speaking, the smaller the size of the frame, the shorter the stem should become.

When you select a frame size on our website the handlebar and stem lengths will default to our recommended size for that particular size. However, should you then change the size, these will decrease or increase correspondingly. You then have the option to amend these manually by clicking on ‘customise bike’.

Crank Length

The length of the crank arms (the bit that your pedals screw into) can have a significant impact on both comfort and performance. Choosing the correct length of 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 generated by your long levers.

Most components manufacturers will offer chainsets with a crank length of 165, 170mm, 172.5 and 175mm (this measurement is taken from the centre of the pedal axle to the centre of the cranks, as per the image above). The commonly held belief that the size of the bike should dictate how long the cranks are is a bit of a myth.

Riders who require smaller bikes in the XS/Small range will definitely benefit from shorter cranks. The smaller the bike the less gap there is for the front wheel to clear the frame’s downtube. But in practice, it all comes down to personal preference as much as it does the size of the bike. There are, however, a couple of formulas for determining what length of cranks would work best for you.

Firstly, this formula calculates crank length based on 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 that rider. To muddy the waters slightly, this does not mean that this rider must only ever use 175 cranks.

They may prefer a faster-pedalling rhythm (cadence) and in this instance, a slightly shorter crank may be more to their liking. A faster cadence is less impactful on the muscles but it could 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 83 x 1.25=103.75+65 =168.75. So, using this method you would round up to the nearest crank length of 170mm.

Saddle

As individuals, our anatomies are all very different. What may be comfortable for one person may cause discomfort for another. This makes it very difficult to pinpoint exactly what saddle will be comfortable for you. What is essential though is to ensure that it offers the right 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. A stool, box, or bench for instance.
  • Piece of corrugated cardboard.
  • Tape measure.
  • Chalk (optional)
  1. Take the cardboard and lay it on the seat.
  2. Lower yourself onto the cardboard so it is aligned under your buttocks.
  3. Raise your feet and place them on the lower footrest.
  4. 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.
  5. Hold this position for approximately 30 seconds.
  6. Stand up and retrieve the piece of cardboard.
  7. 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.
  8. Next, take the tape measure and measure the distance between the indents. Use 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/Gravel/MTB

Add 20mm to the measurement, this will add more stability and comfort when assuming a more upright riding posture

Endurance Road/Gravel

Add 10mm to the measurement, this saddle offers a good compromise between comfort and performance.

Further assistance

We hope that this guide has been of assistance to you, and helps you to work out what sizes you need.

Visit us

However, there’s no better way to perfect the sizing and fit than to come in and see us. That’s why we now have multiple showrooms located across England. Visit us for personal sizing guidance and to receive excellent buying advice from our team of friendly, professional and knowledgeable experts. Not to mention that you also get to see our range of bikes in the flesh of course.

Situated in the heart of the Ribble Valley, our flagship Clitheroe showroom offers you a bike shop experience like no other.

Additional contact methods

By Video Call

By far one of the best ways to get in touch is to use the Ribble Live In-Store Expert function. This service brings the in-store experience directly 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. It’s a one-way video call so you will be able to 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

Our customer service team is available to take your call 7 days a week and until late in the evenings on weekdays. Contact the 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 by private message through Facebook, Whatapp or Instagram.


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


New to cycling? Find the answers to the most common first-year questions here.


Looking at ordering a new bike but aren’t sure what gears you need? Our gearing explained guide is here to help you decide what suits your needs best.

5 Comments

Chase says:

Hi there!

Hope all is well.

I’m 180cm with a 86cm inseam. Looking to buy a Ribble HT Ti Enthusiast. Looking at the geo charts, i think the medium will suit better with the 630mm top tube and 455 reach with my short upper body.

Although i am seeing in some reviews that some of the measurements on the chart aren’t correct like wheelbase and reach for a Large are actually 1229 and 453 according to MTB -https://www.mbr.co.uk/reviews/hardtail/ribble-ht-725. I assume the steel – alu – and titanium versions of the bikes have same sized geometry

Let me know what you think is best. Want the bike to be a bit more playfull. Shipping to Canada so i definitely don’t want to mess up the sizing.

Cheers,
Chase

Thursday, June 2, 2022

Alan Gray says:

Hi Chase,
Apologies for the delayed response, I had to seek the thoughts of my MTB brethren before replying. To give you a comprehensive answer it has been suggested that we should find out of you already own an MTB and, if so, what make/model/size you run and what reach and stem length you prefer? A medium will certainly feel more playful on the tight, twisty bits and a large will offer more straight-line stability. We are double-checking the wheelbase dimensions as the ones we quote on our site are what appear on the frame drawings. This won’t really affect our recommendations to you, however.
We hope this helps
[email protected]

Thursday, June 9, 2022


Albert Serra says:

Hola, ya tenemos decidida la talla y elijo la M. Quiero montar el manillar LEVEL 5 con potencia integrada de 42 cm de ancho. Qué longitud de potencia elijo? 110 ó 125 cm. Mi longitud de brazo és 76 cm. Esdtoy hablando de la endurance sl electric
Gracias
Albert

Sunday, May 15, 2022

Alan Gray says:

Hola Albert,
Gracias por ponerse en contacto,
La longitud de la potencia está determinada tanto por la forma del cuerpo del ciclista como por su estilo de conducción. Por lo tanto, es casi imposible para nosotros recomendar a alguien la longitud de potencia ideal sin un ajuste completo de la bicicleta. Con su declaración de que había seleccionado un cuadro de tamaño mediano, creemos que una potencia de 125 mm puede ser demasiado larga. Una potencia tan larga proporcionará una posición de conducción muy estirada, similar a la de una carrera, que muchos encontrarán incómoda en viajes más largos. Por lo tanto, el 110 mm puede ser más adecuado para ti.
Saludos
Team Ribble

Monday, May 16, 2022


Albert Serra says:

Hi [email protected]

81 cm. Just let me know if you need further info

Best Regards

Albert

Thursday, April 28, 2022

Alan Gray says:

Hi Albert,
You are in between two sizes the, medium and the large. The best advice we can offer is that it will depend upon how you prefer your bikes to fit. Choosing the larger size will give you a taller front end for a slightly more relaxed riding position. Choosing the medium frame will give you a more aggressive riding position that results in a bike that is lighter and more nimble.
I hope this helps
[email protected]

Friday, April 29, 2022


Albert Serra says:

Buenas tardes. Estoy interesado en el.modelo Endurance SL e – Enthusiast o Pro, pero tengo la duda en la talla.
Mido 178 cm.
Cuál me recomiendan?
Y a nivel de manillar y potencial, con cual debería quedarme?
Necesitan más datos para poder valorar la talla?
Gracias

Wednesday, April 27, 2022

Alan Gray says:

Hi Albert,
Thanks for getting in touch. When someone is in between sizes the usual advice is to opt for the smaller of the two however we would need to know what your inside leg measurement is to offer a recommendation.
Best Regards
[email protected]

Wednesday, April 27, 2022


Adrian Fawcett says:

Hi there. Hoping you can give me a steer. I’m a 56 yr old mamil who has been coerced into cycling Lands End to John O Groats in August. I thought I should treat myself to an upgrade road bike for this event. I currently ride a Trek Domane 4 54 cm frame which like myself is starting to show wear and tear and I think is a little small – I bought off the shelf as it were when I got the cycling bug a few years ago – as I am 6 ft 1″.

My wish list would include as much carbon as can be squeezed in, disc brakes and a proper bike fit to ensure the most comfortable endurance ride possible. My budget would be a max of £2500, and I’d need possession by July to give me a month to get to know my new bike.

Does this sound like something you could help with?

Adrian

Wednesday, March 9, 2022

Alan Gray says:

Hi Adrian,
Thanks for getting in touch, as you may already be aware we do offer a range of bikes that provide an unprecedented level of customisation. Why do I mention this? Well, its because each individual model that you see advertised on our website is liable to offer an estimated delivery date based on the specific components listed for that bike. This date is displayed only when you select the frame size that you require. To make the process simpler, we have listed all of the bikes that offer the best despatch dates here. We have 5 showrooms across England that offer a bike sizing service, with a friendly team of knowledgeable bike experts to take you through the whole buying process. I would also thoroughly recommend our one-way video call service if you would like to chat with us before visiting one of our showrooms.
I hope this information helps
Best Regards
[email protected]

Thursday, March 10, 2022


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