When I took up cycling again after a lengthy hiatus—I was bewildered when it came to bike sizing.
A friend informed me, if I could straddle the cycle’s top tube without doing myself a mischief—then it was ideal.
I said nothing, but to me, that sounded somewhat naive. I knew unless the bike fitted me properly, I wouldn’t enjoy the ride and could place myself in danger.
Hence, I took it upon myself to learn the truth behind bike sizing—revealed here.
Choosing the correct bike size for you involves:
- Considering your bike frame type.
- Measuring your inseam.
- Taking the bike out for a test ride.
- Making small adjustments.
- Listening to your body.
How to Find the Right Size Bike—The 2 Methods
Before I get down to the details of how to size a bike, let me share something with you.
About six months ago, I had a new back door to my house installed. The old one had definitely seen better days—years of use, boisterous children, and a rather large dog keen to get outside had all taken their toll.
So, me and my husband measured up the old door—and headed down to the local DIY store. We purchased a new one to fit—and took it home.
It was close—but it wasn’t exactly the right size.
For the rest of the day, my husband and I, with the aid of chisels and planes, had to gently mold the door to ensure a snug fit.
And it’s the same with bike fitting—it’s a two-step method.
Firstly, you need to select a cycle frame that’s the correct size for you—then you must make small adjustments to ensure it fits perfectly.
Method One—The Frame Size
The frame is the core in every cycle—a solid structure from which all the other components emanate. Without it, you’d just have a pile of useless wheels, cogs, cables and derailleurs.
And, unlike many parts of the cycle—it’s not adjustable.
Knowing how to fit a bike frame at the outset is vital. Choose incorrectly—and your cycling will be inefficient, lead to pulls and strains—and most worryingly, reduce your control, which could mean accidents.
When people speak of the frame size, what they’re actually referring to is the distance between the length of the seat tube from the crank to the top tube. Here are the steps to take to select the correct dimensions.
1. Consider Your Bike Frame Type
There are a plethora of bike frames on the market—ranging both in material construction and style.
Most often, manufacturers build them from four main compounds—steel renowned for its durability, aluminum to reduce weight, and the seriously top-end carbon fiber and titanium for both strength and lightness.
Additionally, the frame shape will often depend upon the bike’s function. Generally speaking, here are the key differences:
Cycles for Men or Women
It’s a fact—on average, women are shorter than men.
Hence, some manufacturers make cycles marketed as ‘women’s bike’s—typically characterized by having a shorter stack (the length between the frame bottom and the midpoint of the seat post) than the male varieties.
Traditionally, these ladies’ cycles also include a down-angled top-tube—allowing women to step-through onto the bike. Manufacturers originally included this feature to enable skirt-wearing women to mount their cycles with ease and without ruining their honor.
However, increasingly cycles are now available labeled as unisex. These are often indistinguishable between male and female models—but instead, have an immense range of frame sizes to cover all heights.
Furthermore, as more women now wear pants or jeans—the tell-tale step-through bikes are becoming rarer.
These cycles—utilized by fitness enthusiasts and speed lovers, have a large triangular frame, often with two sides of the same length. The top-tube is parallel to the ground.
While you can purchase these frames in small (S), medium (M) and large (L) sizes—these aren’t standardized across all brands. Hence, always check the actual measurements—which are traditionally in centimeters.
As these bikes are primarily for rough and uneven terrain, they tend to have a more compact triangular frame—lowering the rider’s center of gravity and thus increasing stability.
Typically the S, M, and L sizes are more industry standardized than road bikes—although always check the official dimensions of the manufacturer, usually declared in inches.
An amalgam of the best features of mountain and road bikes—popular amongst commuters and weekend riders.
Their frames can vary—angling either towards the off-road or racing style—and generally have centimeter measurements.
These cycles are easy to spot with their novel curved or S-shaped frames.
Giving an almost upright riding position—they’re popular with leisure riders and are associated with extensive comfort.
While the frame size (measured in centimeters) is valuable—many users consider it’s the overall riding position, handlebar location and seat comfort that are worth the most consideration.
These cycles are an anomaly—and you shouldn’t choose one through the same method as other bikes.
As they’re primarily for freestyle riding—having a lower top-tube in the frame to enable the rider to swing the bike beneath them if doing airborne tricks. Virtually always, these frames have their dimensions in centimeters.
For example, for sufficient clearance, a 5-foot 10-inch rider requires a 20-inch framed bike. If you compare the same frame size on a mountain bike—it would be the correct dimensions for someone 5-feet 5-inches.
Many children’s cycles follow the mountain bike-style, with a more ‘squat’ frame. This similarly promotes a lower center of gravity—making it easier for tiny-tots to remain upright.
Unlike other bikes, their dimensions relate to wheel size, not the frame.
2. Take Your Inseam Measurement
This bike sizing method is usually most accurate when completed with a (close) friend or partner. You need a book, tape measure and calculator.
Stand barefoot with your back against a wall and with your feet around six inches apart. Your friend should place the spine of the book horizontally between your legs and slide up deep into your groin.
Measure the distance from the top of the book to the floor in both centimeters and inches. This is your inseam measurement and essential for sizing your bike frame.
3. Calculating the Seat Tube Length for Road Bikes
With your inseam measurement in hand, multiply this figure by 0.67.
This gives you the frame size (in relation to the height of the seat tube) you need for a road bike. If the bike’s dimensions are in inches, multiply the seat tube height by 0.39 to convert.
4. Calculating the Top Tube Length for Mountain Bikes
Take your inseam length in inches, multiply by 0.67 and then deduct four inches.
That’s the length of the top tube you need.
For example, if you have a 34-inch inseam:
- 30 x 0.67 = 22.78 inches.
- 22.78 – 4 = 18.78 inches.
Hence, you would need a cycle with an 18.5-inch top tube—as unless you’re lucky enough have the funds to get a handmade cycle—this is the closest industry standard.
Where possible, when selecting your ideal mountain bike, look for the manufacturer’s ETT (effective top tube) length. This measurement is the horizontal distance between the head tube to the seat tube.
This provides more accurate bike sizing—as many top tubes on mountain bikes slope downwards—which will slightly skew your choice.
5. On Children’s Bikes Use the Wheel Diameter
The majority of children’s cycles have a fair deal of handlebar and seat adaptability. Thus, enabling you to adjust the bike as the little ones grow and not having to purchase a new model every Christmas.
That said, for safety and stability, the cycle should allow your kids to touch the floor with flat feet while in the saddle.
As a guide:
2 to 4 years 12 to 16-inch inseam 12-inch wheels
4 to 6 years 16 to 20-inch inseam 14-inch wheels
5 to 8 years 18 to 22-inch inseam 16-inch wheels
6 to 9 years 20 to 24-inch inseam 18-inch wheels
7 to 10 years 22 to 25-inch inseam 20-inch wheels
6. Before You Test the Bike Frame—Adjust the Height
If the bike seat isn’t in the correct position, your ride will be uncomfortable, require excessive effort and could be dangerous.
Stand astride the cycle and ideally get a friend to loosen the seat’s quick-release or untighten the restraining bolt—dependent on the style.
Reverse pedal until one foot is at the bottom of the pedal stroke (as close as possible to the ground). Then, either raise or lower the saddle so that your corresponding knee has a slight bend. Retighten the seat bolt.
Just a quick word of warning.
Always ensure that you don’t elevate the seat post beyond the ‘minimum insertion point’ marked on its side. If you need to go past this level, or are seriously close to the mark, then you need a larger frame.
7. Check the ‘Reach’ That’s the Most Comfortable
There are numerous algorithms, formulas and equations to determine the correct reach from the saddle to the handlebars. But, generally speaking, it's like buying new shoes.
If it feels right, then it’s right.
However, just a few pointers to keep in mind:
- Your elbows should be able to bend slightly—allowing for shock-absorption.
- Shifters and lever brakes can be controlled easily without stretching or changing position.
- Your back angle is ideal for your style—around 45 degrees for road bikes, 30-35 degrees for mountain cycles, and virtually upright for leisurely cruiser-type riding.
8. The Stand-Over Test
You should be able to stand over your bike comfortably—without having to put the cycle at a slight angle.
Hence, straddle the bike, feet shoulder-width apart, with your groin over the top tube. Measure the distance between the uppermost side of this tube and your pelvic bone.
Ideally, there should be around two to four inches of clearance—although some extreme road riders will allow for just one inch.
9. Take the Bike for a Test Ride
After you know your bicycle frame size and have made all the above checks and adjustments—it’s time to put that cycle to the test.
Getting your bike onto the road is the ultimate way to ensure you feel safe and comfortable on the cycle—and it’s going to provide years of riding pleasure.
What worked for me was trying out the cycle that my measurements indicated was ideal—then comparing to a size larger and smaller size. As we are all happily differently proportioned, and ride in different ways, it provides a ‘double-check’ that you’re selecting the ideal machine.
10. If You Can’t Test—Use an Online Guide
In many cases, purchasing a bike online means you can make some serious savings. The downside is—you can’t test beforehand.
Many manufacturers provide a bike size chart—illustrating what frame size you require dependent on your height. Admittedly, this isn’t as accurate as physically trying and adjusting a prospective purchase—however, it’s better than taking a pot-luck choice.
Additionally, there are some excellent and accurate online calculators—which take into account height, riding style (mountain, road, etc.) and inseam and indicate the ideal frame dimensions for your needs.
Simply Google ‘frame sizing guide for X bike’—where X indicates your preferred model—for one of these helpful tools.
11. See the Professionals
If you’re not keen on using a bicycle frame size chart—visit a professional bike store.
These guys and girls are experts.
They don’t just take your measurements, adjust the cycles and then allow you to try them out—but they also offer some valuable bike-selection advice relating to your physical capabilities, build and riding style.
12. Comfort, Comfort and Comfort
You can have all the advice in the world relating to seat angles, frame sizes, top tube lengths and reach. But, if the bike you’re considering purchasing isn’t comfortable—it’s not right for you.
In most cases, it will mean a little ‘playing’ with the cycle’s adjustable features to enable the ideal fit.
Furthermore, where possible, try to be flexible in your bike choices.
You may have your heart set on a mountain bike—yet a hybrid or cruiser may suit your particular riding style and physical dimensions more accurately.
Method Two—Making Small Adjustments
After following the above tips—you have the ideal frame. But, that’s only the first step in accurate bike sizing.
To ensure that you and your cycle become ‘one’ on the road—you make some small, yet vital, adjustments.
1. If There’s Knee Pain—Make a Change
Research, published in the International Journal of Sports Physical Therapy, indicates that saddle position is a major contributing factor to cyclists’ knee pain.
While you have already moved the seat to the ‘correct’ height—small changes can have a dramatic effect on reducing any patella discomfort.
Typically, if you’re noticing pain in the back of your knee, or feel your hamstring (back of the thigh) ‘pulling’—your seat is too high. Conversely, if the pain is on the front of your patella, or upper thigh, the saddle is too low.
In both circumstances, make a one-centimeter alteration in the required direction—and try again. You may need to make a couple of changes before you find the ideal saddle location.
2. Adjust Seat Fore/Aft Position
Ideally, with your pedals in the three o’clock position on the downward push—your knee should be directly above the balls of your forefoot.
If not, your seat needs adjusting.
Loosen the binder-bolt underneath the saddle and slide either forward or backward as required. Only make small changes, as each adjustment amplifies by the time it translates to your knee.
3. Change the Seat Tilt
Cyclists generally accept that the perfect angle for the cycle seat is parallel to the ground. While you can do this by eye—a more accurate method is to use a spirit level. And, this is the position you should always utilize when using a new bike.
However, remember the key to correct bike sizing—comfort.
Hence, if you find your saddle is causing pain, soreness or aches—it’s time to make a change.
Often, men find that a slight upward angle releases pressure on their nether regions, while women often discover that a downward sloping saddle is more comfortable.
To change the seat incline, loosen the angle bolts beneath the saddle—adjust and retighten. Some cycles have just one restrainer located on the side—others have two bolts—one in front and one behind the seat post.
4. Configure the Handlebars
Selecting the ideal handlebar position is a combination of riding style, safety and comfort.
While many people suggest that the bars should be level with the saddle, this isn’t suitable for everyone. For example, mountain bikers and racers typically have the bars lower than the seat—creating a more aerodynamic riding position and placing more weight on the front tire—increasing traction.
Conversely, hybrid and cruiser cyclists may have the handlebars higher than the saddle, giving a more upright body configuration that’s easier on the lower back.
Whatever your preferred position, always ensure that your elbows can bend slightly while seated and that you can operate shifters and brakes easily.
The simplest way to change the height is by altering the handlebar angle—with the stem unmoved. Typically, there are four bolts and a bracket where the bars meet the stem. Just loosen, maneuver the bar, and retighten.
A more complicated technique is to raise the handlebars by adding spacers between the stem and the frame—although often there are only a few millimeters of adjustment you can make.
Other Bike Sizing Considerations
To really obtain the perfect cycle for your needs, style and size, there are three final considerations I’d like to mention.
Invest in a Bike Fit
Ok, I’m not talking about the five to ten minutes that a bike shop technician will give you. Instead, take the approach of the pro-cyclists.
A professional bike fit is more than just checking the frame size and adjusting the saddle. Instead, it’s a holistic approach that aims to cover every aspect of your needs—and the bike size that will deliver.
Usually, this includes the bike fitter checking your:
- Physical measurements.
- Strength levels.
- Intended use for the cycle.
- Riding style.
- Experience on two wheels.
From this information, they can then advise on the ideal type and size of cycle you require. Furthermore, it doesn’t usually end here. Most commonly, there’s a follow-up—checking how you are finding your new bike, discussing any problems or discomfort you’re experiencing—and then making recommendations.
Listen to Your Body
Look, if you’re new to cycling, you’re going to get aches and pains. It’s the same with any exercise. Even the most exact bike sizing preparation will not change that.
However, if you experience discomfort from the moment you get in the saddle—or muscle-related aches don’t alleviate—then your bike needs adjustment.
Follow the tips above to make the necessary changes. And, if that doesn’t help, then consult a bike professional.
Amazon Offers Professional Fitting Services
If you’re looking for a professional bike fitting service—and you have no idea where to start—use Amazon.
In the same way as you order a bike online—you can also arrange for a complete bike sizing experience—ensuring your new cycle is going to provide years of comfortable and pleasurable riding.
How to Choose the Correct Bike Size Summary
Out on the road, your cycle is an extension of your body—and correct bike sizing is the key to ensuring they work together in harmony.
Use the above guide to select the correct frame, and then make those all-important micro-adjustments for the most comfortable experience.
In doing so, you'll have a cycle that’s safe, fun to use and effortless to ride.
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