Are you in the market for a new bike, but not sure what size to get? Don’t worry, you’re not alone! Bike sizes are complicated and many people find the process of choosing a bike size to be confusing.
In this blog post, we will walk you through the process of choosing the perfect bike size for your height and inseam. We’ll also provide some tips on how to adjust your seat and handlebars so that you can ride in comfort.
Let’s get started!
Why You Shouldn’t Use The Recommended Size from Bike Manufacturers
Size charts provided by bike manufacturers are not always the best way to decide the right bike size for you. They might be good for the “average” people, but almost no one is perfectly average.
Everyone’s body is different and what may work for one person may not work for another.
Let’s first look at the Specialized bike size chart:
According to this chart, a 5’7″-5’9″ or 170-175 cm person should ride a size 54 Tarmac. This is likely one size too big. In the real world, a size 54 Specialized Tarmac bike would be too big for a person with a height of 170 cm.
So what will happen if you buy a size 54 Tarmac anyway? You will get various problems like shoulder pain, neck pain, and saddle sores, among many other things. In short, you won’t enjoy it.
Let’s see another examples from Trek. If you use their Size Finder tool to find out your size, they will likely recommend you a bike that is one or two sizes too big. They are worse than Specialized in this case.
So why do such big brands like Specialized and Trek do this?
No idea. But one reason I keep hearing is that a bike one size too big is “safer” for beginners because it has a higher stack and is easier to control with a wider handlebar. This is true to an extent, but for people who ride their bikes for more than an hour per session, you should get the correct bike size.
Use Geometry Charts to Compare Bike Sizes Between Brands
Some bike brands use numbers like 48, 52, 54, 56, 58, and so on to indicate their size. Others use letters like XS, S, M, L, and XL.
These two different styles can’t be compared to each other. And, even if two brands use the same format, you should never compare two bikes from different brands using only their size charts.
For example, a Colnago V3Rs size 52s is way bigger than a Trek Emonda size 52 because they use different measurements to decide that number. And a size S Canyon Ultimate is actually more comparable to a size M of Giant TCR.
See how annoying that is?
Okay, so how can you tell which bike is the right size for you?
Use geometry charts.
Geometry charts are like the blueprint of a bike frame. They show all the key dimensions and tube angles of a particular model, including things like the head angle, seat tube angle, stack, and reach, among many others.
Geometry charts are the only reliable way to tell how two bikes of different brands and models compare in size.
So, disregard all predetermined sizing options from every brand, and just use the geometry chart when you’re looking for a new bike.
The Correct Step to Choose The Right Bike Size
This is how to find the correct bike size for you:
1. Measure Your Height and Inseam
You can’t find a bike size based on height alone or inseam alone, both should be used together.
“Height” is pretty straightforward and most people already know their own height. “Inseam” in cycling is basically your leg length measured from the crotch. If inseam or inside leg measurement is new to you, here’s the easy way to measure yours. All you need is a hardcover book, or something of similar thickness, a pencil, and a tape measure.
To find your inseam, simply hold the book between your legs with the spine facing up. Make sure the book is pushed against your crotch but don’t push too hard. While barefooted, measure from the floor to the top of the spine.
If you can’t find someone to help you measure, face a wall and hold the book against the wall. Make sure the book is straight and all the wall-facing side is in contact with the wall. Make a mark at the top part of your book on your wall using a pencil. Finally, measure the pencil mark from the floor.
Repeat this process three times (or more if needed) and average out the results to get the most accurate measurement.
Now that you know your inseam, calculate your inseam-to-height ratio by dividing your inseam by your height. If your number is below 0.45, then you have short legs than average people, and if your number is above 0.47, then you have long legs.
Keep these measurements for now as they will be useful later.
2. Find Your Starting Point Using This Bike Frame Geometry Chart
Below you will find not the predefined size chart that is commonly found in other guides or bike brand websites. Those are arbitrary numbers that have no standards in any way. Instead, this is a geometry recommendation.
As said earlier, all bike brands use different systems and inconsistent numbering between brands, using a bike size chart might mislead you. That’s why instead of telling you the predefined size (S, M, L, 52, 54, 56, etc.) we’ll use the three bike measurements that matter the most when choosing a bike size:
- Effective top tube length: The horizontal distance from the head tube to the seat tube. Some bikes use this measurement as their size in centimeters.
- Stack: The vertical distance from the center of the bottom bracket to the top of the head tube.
- Reach: The horizontal distance from the center of the bottom bracket to the top of the head tube.
The three measurements dictate how large a bike is – there are others measurements like head tube and seat tube angle, but these do not vary much between bikes. Unlike a size chart, a geometry chart is consistent between brands so once you know the right geometry for you, you can easily choose any bike from any brand.
Keep in mind that the following table is a general guideline only to find your starting point.
| Height | Size (mm) | |||
|---|---|---|---|---|
| Centimeters | Inches | Effective Top Tube Length | Minimum Stack Height | Maximum Reach Length |
| 157 – 163 | 5’0″ – 5’4″ | 495 – 510 | 490 | 373 |
| 163 – 170 | 5’4″ – 5’7″ | 505 – 520 | 500 | 380 |
| 168 – 175 | 5’6″ – 5’9″ | 515 – 535 | 510 | 385 |
| 173 – 180 | 5’8″ – 5’11” | 530 – 547 | 530 | 390 |
| 178 – 185 | 5’10” – 6’1″ | 545 – 565 | 547 | 400 |
| 183 – 190 | 6′ – 6’3″ | 560 – 580 | 580 | 405 |
| 188 – 195 | 6’2″ – 6’5″ | 580 – 600 | 600 | 415 |
A few things to keep in mind based on the table above:
- This table is just a starting point of guidance. In reality, there is a chance that you might fit better with a frame one size smaller or bigger.
- If you have short legs (lower than 0.45 inseam-to-height ratio) you might need to size down
- If you have long legs (higher than 0.47 inseam-to-height ratio) you might need to size up or choose a different bike with a higher stack number
- The stack and reach value is most important for performance-oriented or aero road bikes. This type of bike usually has the longest and lowest front-end, making it hard to find the right fit. For endurance road bikes or gravel bikes, you can usually get away with only using the effective top tube length because these types of bikes are made to be more relaxed and upright.
- If you are in-between two sizes, always go with the lower size. Your body can tolerate a lower stack more than a longer reach. Also, you can use a longer stem (and maybe a longer seat post) on a smaller frame to increase the total size of your bike so that it fits you.
- Some bikes have sloping top tubes, some are more horizontal. On different bikes of a similar size, top tubes can have a big difference in length depending on the slope. So, when you compare different bike brands’ geometry charts, make sure to look for the effective or horizontal top tube length. If they use a different term, look at the frame geometry diagram which is usually included on the chart.
Here’s an example of how to find your bike size using the geometry chart:
If you are 183 cm or 6 feet tall, the chart above says you need a bike with a 545–565 mm effective top tube length, >547 mm stack, and <400mm reach. Now look at the Specialized Tarmac geometry chart below:
Based on our recommendation above, a 56 Tarmac might be your size. However, since the reach is too close to the limit, you might want to try a different bike with a shorter reach and higher stack instead if you have proportionally long legs – based on your inseam-to-height ratio.
3. Go to Some Bike Brands’ Websites and Compare the Geometry Charts
Now, hopefully, you have several options you have in mind and are not fixated on one bike brand only because they might not have the right fit for you.
For example, some bikes like the Specialized Tarmac are known for being very low and long on the front end. It is a great-looking bike, but not too beginner-friendly.
If your legs are proportionally longer than the average person’s (inseam-to-height ratio > 0.47), that means your reach is proportionally shorter. So, it might be worth looking for a different bike brand that has a shorter reach and higher stack. Or choose an endurance-oriented road bike instead.
Even if you plan to buy at a local bike shop, always check the geometry charts on your own first.
Local bike shop doesn’t usually have a professional bike fitter, and it’s not uncommon that they recommend you a bike that’s one or two sizes too big because they don’t know any better or they don’t have the right size in stock and still want to close a sale.
It’s a good idea to try the bike first if you have the chance. But a bike that’s only one size too big won’t probably be noticeable on a five-minute ride (even though it can make you miserable on a one-hour ride or more) especially if it’s your first bike.
Tip #1: Get a bike fit first
If you have a body functionality problem, are less flexible, or are very unfit, you should think about getting a professional bike fit first before buying an expensive bike. The less “average” you are compared to other people, the more problems you will have on the bike over a long period of riding.
Don’t worry, it is normal to get a bike fit even if you don’t yet have a bike. In fact, some bike fitters recommend doing so because buying the wrong bike size is a costly mistake.
Tip #2: What if you already have a bike and it feels too big or too small
Fortunately, apart from the bike frame itself, the rest of your bicycle is adjustable (to a point). It might cost you money to buy the new part, but you might not need a new bicycle frame.
So, first, assess how you feel on the bike.
Is the seat post too high or not high enough? This is the easiest one to fix because most bikes have a decent amount of seat post adjustment. You can also usually purchase a shorter or longer seat post if your current one doesn’t fit you.
Do you feel too low on the front end and it’s causing neck pain? Then you need to raise your handlebar. If you still have spacers on top of your stem, then raise the stem by moving the spacer below the stem. If not, then flip your stem upside down.
What if your bike feels too long for you? You can try using a shorter stem. The minimum recommended length for a road bike is 80 mm and most road bikes come with a 90 or 100 mm stem, so you have 1-2 cm room for adjustment.
Alternatively, get a new handlebar with a shorter reach. Depending on your current handlebar, you might be able to find another model with a 5-10 mm shorter reach. They are more expensive than a stem, though.
As a last resort, you can also tilt the handlebar backward so that the shifter hoods are closer to you.
What you should NOT do if you feel your bike feels too long is to push the saddle forward too much. Sure, by pushing the saddle forward you sit closer to the handlebar – effectively shortening the reach. However, doing that will cause arm, neck, and shoulder pain because you’re shifting your weight forward.
Finally, if the standover is too high, meaning you need to lean your bike sideways when you put both of your feet down because the top tube is hitting your crotch, then the frame is just simply too big for you and you need a new frame.
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