Have you ever taken a new bike for a test ride only to find it just didn't feel right? There is actually more to sizing up these simple machines than one might think; a well-fitted bike goes far beyond adjusting the seat. When you're in the market for a bicycle, whether new or used; in-person or online, there are essential sizing characteristics of which to be aware.
Luckily, despite evolving terminology and endless options, these charts condense the information so you can shop around armed with knowledge and easily find your dream ride.
Why Is Sizing so Important?
Not only are there fundamental frame differences between mountain bikes and road bikes, but there are also correct and incorrect ways to measure yourself. Getting the appropriate sized bicycle maximizes power, speed, and efficiency and reduces fatigue and soreness. The differences lie primarily in the frame.
It's All in the Frame
The parts of a bike frame are as follows (see diagram for a visual):
- Top tube - The highest part of the frame, connecting the seat tube to the head tube
- Down tube - Connects the head tube to the bottom bracket and seat tube
- Seat tube - This part of the frame is where the seat goes in. It connects the bottom bracket and down tube to the top tube. The seat tube is the most important, as its length (usually given in centimeters) is synonymous with frame height and is sometimes the only measurement referred to as a frame's size (usually given in centimeters). This is especially true of terminology used to describe older models, so it's important when you're shopping for used bikes.
Mountain Bikes Versus Road Bikes
Because the intended purpose and terrian is different for road bikes and mountain bikes, they're designed very differently. While road bikes are built for speed and intended for smooth pavement, mountain bikes are meant for rough terrain and maximum shock absorption. This warrants a number of different components, from tires to frame geometry.
Differing frame shapes means mountain and road bike seat tubes will be different lengths. Because of this, your perfect frame height on a road bike won't be the correct fit on a mountain bike, so it's important to be aware of this when switching from one to the other.
Determining Bike Size
Now that you have the basics down, here are two ways to determine your ideal bike size. Be sure to take both into consideration for the most accurate frame size estimate.
Inseam
Measuring your inseam (the length of your leg from heel to crotch) is the first step to zeroing in on the proper frame size. Inseam measurement is not the sole method for determining size; however, for those with specialized needs, like triathlon cyclists, where torso length plays an integral role in fit, height and other measurements are also needed. In these cases, it's best to get professionally fitted at a trusted bike shop.
For an accurate at-home inseam measurement, you'll need:
- A tape measure
- A large hard-cover book (textbooks work well)
- A friend
To measure:
- Remove your shoes and stand straight and tall against a flat, empty wall.
- Place the book snugly between your legs with the binding facing up at the very top of your inseam.
- Have a friend measure from the floor to the book's binding. That number is your inseam.
Height
Another way to determine your frame size is by knowing your height.
Road Bikes
The following table indicates sizing for road bikes, based on both inseam and height in both inches and centimeters.
| Rider's Height | Inseam | Frame Size Range |
|---|---|---|
| 4'10" to 5'0" / 148cm to 152cm | 25.5 inches to 27 inches / 65cm to 69cm | 47cm to 48cm (XXS) |
| 5'0" to 5'3" / 152cm to 160cm | 27 inches to 28 inches / 69cm to 71cm | 49cm to 50cm (XS) |
| 5'3" to 5'6" / 160cm to 168cm | 28 inches to 29.5 inches / 71cm to 75cm | 51cm to 53cm (Small) |
| 5'6" to 5'9" / 168cm to 175cm | 29.5 inches to 31 inches / 75cm to 79cm | 54cm to 55cm (Medium) |
| 5'9" to 6'0" / 175cm to 183cm | 31 inches to 32.5 inches / 79cm to 83cm | 56cm to 58cm (Large) |
| 6'0" to 6'3" / 183cm to 190.5 cm | 32.5 inches to 34 inches / 83cm to 86cm | 59cm to 62cm (Large to XL) |
| 6'3" to 6'5" / 190.5 cm to 196cm | 34 inches to 36 inches / 86cm to 91cm | 62cm to 64cm (XL) |
Mountain Bikes
This table indicates mountain bike sizes based on both inseam and height in both inches and centimeters.
| Rider's Height | Inseam | Frame Size Range |
|---|---|---|
| 4'11" to 5'3″ / 150cm to 160cm | 26 inches to 28 inches / 66cm to 71cm | 13 to 15 inches |
| 5'3″ to 5'7″ / 160cm to 170cm | 28 inches to 29 inches / 71cm to 74cm | 15 to 17 inches |
| 5'7″ to 5'11" / 170cm to 180cm | 29 inches to 32 inches / 74cm to 81cm | 17 to 19 inches |
| 6'0″ to 6'2" / 183cm to 188cm | 32.5 inches to 33.5 inches / 83cm to 85cm | 19 to 21 inches |
| 6'2″ to 6'4″ / 188cm to 193cm | 33.5 inches to 35.5 inches / 85cm to 90cm | 21 to 23 inches |
Biking Safely
Now that you have a firm understanding of the importance of bike frame size, the differences between road and mountain bikes, and how to take accurate measurements to determine the ideal fit, you can confidently navigate both online and offline prospects. Once you have your dream bicycle, it's important to brush up on general bike safety tips. Then, be sure to look into local and state cycling laws to understand your rights and responsibilities as a cyclist. Happy riding!
