The Bicycle
Fit Guide

 

If you're having reservations about buying a bicycle over the Internet, you're not alone. One of the main reasons people hesitate to buy a bike online - instead of at their local bike shop – is that they can't actually sit on it or ride it first. After all, actually mounting a bike may be the best way to determine if it will fit you right.

Bike fit wins hands-down as the most important consideration when buying a bicycle, weighing in above such considerations as materials used, overall weight and brand. That's because a poor fit means discomfort, inefficient energy transfer and slower riding times – not to mention poor handling. Should you sacrifice a good fit for a good deal? Certainly not.

But unless you're a competitive cyclist, you don't need a bike shop specialist to fit you for a bicycle. This comprehensive guide will steer you through the process of sizing a bike, so you can be confident the bicycle you buy online will be just the right one for you. And don't forget – when you shop at Sierra Trading Post, you will find a much better deal than in any bike shop.

Measuring Up

Before you shop for a bike, you'll need to take several measurements of your own body. Bicycle sizes are based on a person's height and body frame dimensions – not on their weight. No matter how much you weigh, you'll need a smaller frame size if you're a person of shorter stature with short legs and arms… and vice-versa.

You'll want to know your overall height, your inseam length, and your torso and arm lengths. Be sure to remove your shoes prior to taking these measurements. Also be sure to have a helper. It makes taking these measurements much easier.

Measuring Your Height

If you don't already know your height, measure yourself while standing on a flat surface with your back against a wall. Feet should be spaced just less than shoulder width apart.

Measuring Your Inseam

The most important measurement when sizing a bicycle is your inseam length – essentially the inside length of your pant leg from crotch to floor. Since this is the primary measure used to calculate your best bike size, don't base your inseam simply on your jeans size. You need to be more precise. Here's how to do it:

• Stand with your back against a wall.
• Spread your feet 6-8” apart on a hard, smooth surface.
• Place a book between your legs and up against the wall, spine up; raise it until snug against your crotch (this mimics your bike seat).
• Have another person measure from the top of the book (spine) down to the floor.

Measuring Your Torso and Arms

You need your torso and arm lengths to help determine your ideal top-tube length. Here are a few steps to determine each measure.

Torso Length

• Repeat the first three steps for measuring your inseam.
• Measure from the spine of the book (the top) to the small “V” in your throat just above your sternum, in inches.

Arm Length

• Find the end of your collarbone, on the tip nearest your shoulder.
• Hold a pen or pencil in your fist (on the same side as the collarbone you've chosen).
• Have your helper measure from the end of your collarbone to the object in your fist, with your arm outstretched.

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Defining a Bike's “Size”

While many bikes offer a size you're familiar with, such as S, M, L or XL, others don't. Many bikes instead provide a “size” listed in inches or centimeters as one number (i.e., 18”). This size or “frame size” of a bike refers to the length of its seat tube. This measure is given in one of two ways: from the center of the bottom bracket to the top of the top tube (C-T) or from the center of the bottom bracket to the center of the top tube (C-C). Sometimes the specific size measure will actually be listed (“bottom bracket to top of top tube”) instead of simply calling a measure the bike's “size.”

A red arrow will highlight each component in the
diagram below when you click on the corresponding link.

There is no industry standard for gathering bicycle measurements or fitting cycle to rider, and different brands may measure their bikes in slightly different ways. Every brand of bicycle should offer some specifications based on their own measurement standards, though, so you can check out your bicycle brand's website for their preferred standards. For this guide, we'll focus on a C-T measurement standard. The C-C measure is usually only about 1 to 1.5 cm shorter than the C-T size for a bike, so you can make rough comparisons.

Comfort or cruiser bike size listings are usually an exception to the norm, with size actually being given simply as S-XL instead of listed as the seat tube length.

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Road Bike Fit

Road bikes are more difficult to accurately fit than other bike types, and require a few more measures to hone the fit. Besides the seat tube length, you need to have just enough horizontal length on a road bike to let you comfortably stretch forward into your pedaling stance.

To obtain your ideal seat tube height (or “size”) for a road bike, multiply your inseam (in cm) by .67 to get C-T length (or by .65 to get the C-C size for your seat tube). If you measured your height and inseam in inches, convert inches to centimeters by multiplying inches by 2.54 (Example: 30 inches x 2.54 = 76 cm).

For the best fit on a road bike, you also need to know your ideal “total reach'” which is the combined length of the top tube and stem. Unfortunately, there are many different ways to convert upper-body measures into the total reach for a road bike.

Here is a general formula you can use from the Lemond System to get an idea of your total reach (use inches for units of measure):

Total Reach = [(Torso Length + Arm Length) / 2] + 4 inches = (Top Tube + Stem)

Saddle height, which is measured from the center of the bottom bracket to the top of the bike seat, is another measure that helps you custom fit your bike.Since saddle height is adjustable on road bikes, this measure is not as important at the time of purchase as seat tube length and is not included with bike specifications. However, we have included an approximate saddle height in the table below (based on inseam) so you can use it as a starting point with your new bike.

Road Bike Sizing Table Ideal Frame Size (C-T Measure)
Inseam (in.)	Inseam (cm)	Seat Tube (cm)	Seat Tube (in.)	Saddle Height (cm)
27	69	46	18	61
28	71	48	19	63
29	74	49	19	65
30	76	51	20	67
31	79	53	21	70
32	81	54	21	72
33	84	56	22	74
34	86	58	23	76
34	89	60	23	78
36	91	61	24	81
37	94	63	25	83

Note: Taller riders (over 6'1”) may want to lean toward a slightly larger frame size (approx. 1-4 cm extra seat tube length) when selecting a size based on this table. For example, a tall person with a 36-inch inseam would require a 61 cm seat tube (size 61) based on the table, but might actually prefer a 63 cm seat tube.

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Mountain Bike/ Commuter Bike Fit

When sizing a mountain bike (MTB) or commuter bike, the most important thing to look at is the “stand-over height.” The stand-over height of a bike frame, or the distance from the center of the top tube to the ground, should be 2-5 inches less than your inseam. Aggressive mountain bikers will need 4-5 inches difference between stand-over height and inseam length, while commuters only need about 2 inches of clearance.

Another way to find your MTB size is to simply subtract about 10 cm (4 inches) from your ideal road bike frame size to find your MTB frame size. Thus a rider with a 33-inch inseam would need a 22-inch road frame and an MTB/ commuter frame around 18 inches.

Note: Most mountain bike measures are given in inches, while the majority of road bike specifications are only offered in metric units.

Since MTB seats are easily raised and lowered and the rider almost always stays in an upright position, the length of an MTB's top tube is as important as the frame size. This is important because if the top tube is too long, it will be difficult to keep your weight over the front wheel when riding uphill. You'll want to calculate your best top-tube length (measure in inches) and be sure the bike you're interested in offers a similar length. If you're looking at a bike's specifications on this website or any individual brand's website, this specification may be listed as the “effective top tube.” This term describes the imaginary horizontal top tube length for any bike with a top tube that is not perfectly horizontal.

Approximate top-tube length = [(Torso Length + Arm Length) / 2] – 6 inches

MTB/ Commuter Bike Sizing Table
Inseam (in.)	Stand-over Height (in.)	Seat Tube (in.)
27	22-25	14
28	23-26	14
29	24-27	15
30	25-28	16
31	26-29	17
32	27-30	17
33	28-31	18
34	29-32	19
35	30-33	19
36	31-34	20
37	32-35	21+

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Fitting a Comfort/ Cruiser Bike

Comfort bikes don't require a custom fit, but the closer the frame is to the perfect size, the more you'll enjoy your rides. Sizes are general, usually listed simply as S, M, L or XL. Base the size on your approximate height and inseam measures.

A Typical Comfort Bike Sizing Table
Height	Inseam	Approximate Size
5'3" to 5'6"	27-29"	S
5'6" to 5'10"	29-32"	M
5'10" to 6'1"	32-34"	L
6'1" to 6'4"	34-37"	XL

Women & Children’s Sizing

Compared to men, women and children (especially young girls) have shorter arms and longer legs. This means that they will have a slightly different fit on a bike, particularly on road bikes.

An easy rule of thumb for women and children is as follows: If you fall somewhere on the border between two bike sizes, go with the smaller size. It’s easier to control a smaller bike, and the saddle height can be increased easily. Also, realize that stand-over height will be more important for female and younger riders than will top-tube length.

If necessary, women and younger riders can change out the stem on their bike to a shorter stem, which will bring the handlebars closer to the rider, and can change out the handlebar for a narrower bar that better matches their shoulder width.

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Once the Bike Arrives: Minor Adjustments

Once your new bike arrives, you may need to fine-tune a few dimensions to account for your degree of flexibility and personal riding style. (Of course, we'd like to believe you’ve chosen the right frame after reading this guide!) Here are a few examples of minor alterations you can do at home or have done at a shop.

Note: We recommend that you always have a professional from a bicycle shop make all adjustments to any bicycle.

Adjust saddle height

Adjust your saddle height so you reach a near-full leg extension with every pedal, and experience a slight bend in the knee at the bottom of a pedal stroke. The correct saddle height will keep rides easier on your knees and allow for powerful downstrokes.

Adjust saddle tilt

There is no universally correct saddle tilt angle. This adjustment is simply based on comfort preference. Adjust the saddle tilt so that a.) you are comfortable, and b.) you don’t slide off the front of the saddle. Men tend to prefer the saddle nose tilted slightly up, while women tend to prefer it tilted slightly down.

Adjust stem length for a custom fit

Stems are often sold in 1 cm length increments, so that you can outfit your bike with the perfect stem for comfortable posture. Stem rise can also be increased for a rider with a shorter reach. Most bike shops will carry a variety of stem sizes.

Find your optimal handlebar size

The handlebars for road bikes come in multiple widths and configurations. If you want to custoimize your handlebars, select handlebars that are the same width as your shoulder joints. Go narrower for a more aerodynamic ride, or wider to have more room for your chest to experience easier breathing and added leverage.

Adjust handlebar height

If your back is getting sore or cramped after riding, you may need to raise the handlebars an inch or so. Bear in mind, though, that you’ll want the handlebars as low as possible if you’re going for aerodynamics on a road bike.

Other Adjustments

For any custom fits, such as adjusting your seat tube angle or crank length (i.e., bigger cranks for slow pedaling in higher gears), head to a bike shop and get help from a pro.

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