You shouldn’t underestimate the importance of choosing the right road bike size.
An ill-fitting bike can not only negatively affect your comfort during a ride, it can reduce your efficiency and put you at risk of developing an injury.
It is possible to find a bike that fits well (for efficient power transfer and handling) and is also comfortable to ride.
So how do you get the right size bike for you?
This guide explains everything you need to know about sizing up a road bike, ensuring that you have the most enjoyable experience possible every time you get in the saddle.
photo: 2019 Merlin Inferno
How to ensure you get the right road bike frame size
This is your most important consideration.
Frame size is related to the seat tube length – so, a 56cm frame will have a seat tube that is 56cm long, for example.
Sizing recommendations have changed in the past few years. This is because manufacturers now produce compact (sloping) frame designs with lower top tubes, which means somebody who fitted a 56cm frame in the 1990s will probably need a different size now.
This handy bike frame sizing chart explains the approximate dimensions you need based on your height. Buying a bike is a bit like buying a suit, if you have any doubt with regards to sizing, it is wise to physically try sitting on/riding the bike first. Merlin staff are all experienced cyclists and can help, either in our Chorley showroom, over the phone, or via email.
Height (inches) Height (cm) Frame Size (cm)
4’10”- 5’3″ 148 – 160 46 – 50 (Extra Small)
5’3″ – 5’5″ 160 – 165 50 – 52 (Small)
5’5″ – 5’7″ 160 – 165 52 – 54 (Small – Medium)
5’7″ – 5’9″ 170 – 175 54 – 56 (Medium)
5’9″ – 5’11” 175 – 180 56 – 58 (Medium – Large)
5’11” – 6’2″ 180 – 188 58 – 60 (Large)
6’2″ – 6’5″ 188 – 196 60 – 62 (Extra Large)
The above size table is a very approximate guide. Some riders prefer to ride a smaller bike. Some manufacturers produce bikes which they label ‘Small’ which other manufacturers would label a medium. Checking a manufacturers geometry table for Seat Tube length and Top Tube length is a reliable way of confirming sizing.
Still unsure? Check out our guide to those who fall between bike sizes.
Measuring your stand-over height
Simply put, this is how far the top tube is from the ground. This can have a major bearing on your overall comfort levels and your performance.
If you know your inside leg measurement, this can be a good indicator of how high you need the top tube to be.
For the optimum size, there should be a few inches between your crotch and the top tube when you are standing bare foot with your legs straight and feet slightly apart. If you have too much of a gap, the bike is too small, if you have no room to manoeuvre, it’s too big.
*Important note* – You need to take the style of the frame into account, as a compact frame will have a lower stand-over height than a traditional horizontal geometry frame. This is because the top tube has a very clear slope.
Tip – If you have a compact or semi-compact geometry frame, make sure you have enough clearance along the entire length of the top tube, especially near the head tube, as this is the highest point.
Getting your saddle in the right position
An adult cyclist should be able to touch the floor with their tip-toes while sat in the saddle. If you can’t reach the floor, your saddle is too high; if you can put the entire base of your foot on the ground, you’re too low.
Here are a few tips to help you get your saddle in the perfect position…
1) Sit in the saddle and put the ball of your foot on the pedal. Have a slight bend in the leg and let the leg hang naturally. Your leg should not be perfectly straight.
2) You should find that there are a few inches difference between the saddle height and the size of your frame, and you will have seat post showing. Compact frames are smaller so more seat post will be showing and vice versa with traditional horizontal geometry frames.
3) Make sure the saddle is level and not sloping forwards or backwards. This can be extremely uncomfortable (especially when cycling longer distances).
4) Tweak the position of the saddle in the rails, moving it fore and aft until you’ve got it exactly how you want it. Imagine a plumb line running straight down from the centre of the knee cap through the ball of the foot (which is over the pedal axle) in the 3 O’clock position.
This is shown in the image below.
If you’re too far forward or back, it will not only be uncomfortable but you’ll also impact on your pedalling efficiency.
How to measure your reach on a road bike
Known as the ‘reach’, the distance between the saddle and handlebars depends on your own measurements and the length of your torso and arms. When determining your road bike sizing, understanding your reach distance is vital.
Here’s how you do it…
You can determine reach by sitting in the saddle in a normal riding position and placing your hands on the tops of the handlebars. If you look down the bars, the front axle should be hidden. If the axle is in front of the bars, however, then the reach is too short. If the axle is behind, the reach is too long.
It may seem simple, but this is actually a tried-and-tested method and popular within the cycling community.
Measuring your ‘Ape Index’
Tip – If you do want a more precise reach distance, a handy tool that we use is the Ape Index. This allows you to measure the ratio of your arm span relative to your height.
Reach distance can be changed by two factors on your bike – saddle position and stem length. If you have the saddle in a comfortable fore and aft position, then changing the stem length can give you the correct reach.
Be careful when adjusting your reach, however. Go too long and the bike’s handling will feel slow and sluggish, but if it’s too short then the steering will be twitchy and uncomfortable.
A good thing to go by is your arm span. If your arm span is shorter than your height by 5cm or more, then you’ll most likely need a smaller frame size.
However, if your arm span is bigger than your height by 5cm or more, then you should think about moving up to a bigger frame size.
What is stack height and how do I measure it?
Stack height is the space between the bottom of the lower headset cup and the top of the upper headset cup. This is the part of the frame that the top of the fork goes into.
The stack height of the bike depends largely upon the kind of bike it is. For example, sportive bikes tend to have a bigger stack height, while race bikes will usually have a shorter stack height for a lower front end.
Bikes with slightly longer reach and a lower stack height are generally more aggressive bikes, riding harder and with more of an elongated, ‘stretched out’ geometry.
Getting the correct road bike tyre sizes
Looking for the right tyre size can feel a little like navigating a minefield at times, and understanding the particulars can help you get things spot on.
On a road bike, tyre sizes are described using dimensions. For example, a road bike could measure as 700 x 25c. 700 is the standard rim size diameter, whilst 25c is the width of the tyre as you look down from a riding position.
Generally speaking, wider tyres provide more comfort as the volume of air in each tyre is larger. Tyre manufacturers now make lighter, faster tyres that are wider, to meet the needs of today’s riders and bikes. Several wheel manufacturers make wider 23mm or 25mm wide rims; these offer a high level of strength, performance and comfort when matched with wider 23mm/25mm tyres.
Most road bikes will have enough clearance to fit 25mm-wide tyres, which can offer a good amount of comfort for the rider. Newer disc-brake road/gravel/cyclocross bikes often have enough clearance for 35mm/38mm off-road tyres to cope with more challenging surfaces such as mud and gravel.
You can see our tyre section here.
photo: 2019 Merlin Ignite
Get on the road today!
This guide will stand you in good stead, but if in doubt, feel free to give us a call on 01772 432431, or email firstname.lastname@example.org, and we’ll help you out.