Bike Sizing and Parts

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How To Size A Bike

The type of riding you plan to do will determine the style of bike you choose, which in turn will dictate the frame size and components you will need. The most important part of buying a bike is finding one that fits you.


Determining your proper frame size

Frame size is not dependent on your overall height. Rather, it is more a matter of leg length. Here are some starting points to help you determine if a particular bike is within your size range.



Frame height

  • Generally speaking, when sizing a diamond frame bike, sometimes called a men’s or unisex frame, you need to measure how it will fit when you straddle the cross bar while flat-footed in the shoes you’ll be riding in. So measure your inseam from the bottom of your feet to your crotch.
    • For a road or hybrid bike, you should have an inch or two of clearance between your crotch and the top tube
    • For a mountain bike, clearance should be about four inches–especially if you’ll be riding in rugged terrain where an unplanned dismount is likely
    • BMX and freestyle bikes all have 20-inch wheels, so frame size isn’t really an issue. A rider’s physique and riding style is accommodated by choosing the appropriate seatpost, stem, handlebar and crankarm lengths.
    • When considering a women’s frame, or frame with no cross bar, clearance isn’t an issue. In this case, the best fit is usually determined by reach.
  • Frame sizes come in inches or centimeters, depending on the manufacturer
    • Not all manufacturers measure from the same points on the frame. Some measure from the bottom of the crankset to the top of the seat tube. Others may measure from center to center, bottom to center, or some other angle.
    • Also, not all frames have the same geometry. All of this means that a 21-inch frame from one company may fit very differently than the same size from another manufacturer.


  • Finding the right reach (the distance from the seat to the handlebars) is important for both comfort and control
  • As a rule of thumb, when you sit on the seat with your feet on the pedals and your hands on the handlebars, the handlebars should block your view of the front hub. You shouldn’t be stretched out like Superman or sitting upright.
  • Be sure you have at least a slight bend in your elbows no matter what style of bike you choose
  • Locked elbows (caused by too-long reach) are a frequent cause of shoulder, neck and back pain
  • If you feel scrunched up and your elbows are in your ribs, the reach is too short
  • If the top tube is slightly too long or short, reach can usually be adjusted by changing the stem length – the stem being the part that connects the handlebars to the steering tube


Determining your proper rim size

The rim is the outer part of a wheel that, along with the hub and spokes, supports the tire.

  • Rim size
    • Rims come in various sizes and materials
    • Rim sizes for road and hybrid bikes are usually 27-inch or 700 centimeters
    • Most mountain bikes have 26-inch rims
    • BMX and freestyle bikes have 20-inch rims
  • Rim width
    • Rim width will vary depending on intended use
    • Some rims are designed to accept a few different tire widths
    • Road and hybrid bike rims are narrower than mountain, BMX or freestyle bike rims
    • Narrow rims are lighter and offer less rolling resistance, whereas wide rims are heavier but offer greater durability
    • Rims can be made of steel, aluminum alloy, heat-treated alloy, carbon fiber or, at the extreme high-end, can consist of other expensive, space-age materials
    • For most types of riding, aluminum alloy rims offer the best value because they are light and absorb road shock
  • Quick-release wheels
    • Quick-release wheels are wheels that do not require tools to detach from the bike
    • They are particularly handy if you have to change a flat tire or transport the bike in a car


Choosing the proper tires

Tires greatly influence a bike’s riding characteristics, since they directly affect traction, steering and braking. There are two basic types of tires clincher and tubular.

  • Clincher
    • Refers to a conventional bike tire with a separate inner tube
    • When inflated, the tire clinches the rim as its inner edges, called the bead, become captured against the rim walls
    • Most road and all mountain, BMX and freestyle tires are clincher
  • Tubular (or sew-up)
    • Refer to a tube that is sewn into the tire, and then the tire is glued onto a special edgeless rim
    • These are only used for high-end road racing bikes

Tires for road and hybrid bikes

  • High-performance tires
    • High-performance tires are lightweight, narrow and can be inflated to high pressures (90 to 100 pounds or more)
    • They usually have a dual tread consisting of a firm center for low rolling resistance, flanked by a softer compound for good traction in turns
  • Recreational tires
    • Recreational tires are designed for durability and comfort
    • They’re heavier than performance tires, but usually last longer
  • Mountain bikes
    • Knobby treads
      • Knobby treads are aggressive, designed to dig into loose soil. They are usually designed specifically for front and back wheels.
    • Widely spaced
      • Widely spaced knobs are best in wet terrain because they limit mud accumulation
    • Tightly spaced
      • Tightly spaced knobs are better in drier conditions. Neither is ideal for riding on pavement.
    • Semi-slick or bald tires
      • Semi-slick or bald tires have knobs on both edges for gripping in turns, but the center section has very little tread to allow for faster straight-on riding. They are good on dry, packed dirt trails and roads.
    • Hybrid treads
      • Hybrid treads are cut into the tire rather than protruding like knobs. They are good for pavement, dirt roads and hard-packed trails.
    • Slick tires
      • Slick tires have no tread, and are designed to be ridden only on pavement
  • Kevlar tires
    • If you will be riding on city streets or in places where you may encounter debris, consider investing in kevlar tires
    • They are a bit more expensive than traditional tires, but could save you money and aggravation in the long run if you suffer from frequent flats and punctures


Bike components


  • Derailleurs are the mechanisms that lead the chain from one sprocket to another while the chain is moving forward
  • They are the components (one in front and one in back) that allow you to shift gears
  • BMX and freestyle bikes do not have multiple gears, and so will not have derailleurs


  • Handlebars help steer the bike, and are the place where brake levers and shifters are mounted
  • Most road bikes have drop style or racing handlebars that encourage an aerodynamic riding position
  • Mountain and hybrid bikes have upright or straight handlebars that encourage a more upright riding position for comfort and control


  • A comfortable saddle is key to enjoying your bike
  • Saddles are available in a wide variety of styles, and are easy to switch
  • Some padding is good, but more is not always better. Excess padding can add pressure and discomfort
  • Padding usually consists of gel or foam
  • Some saddles have cut-out sections, gel-padded areas, or holes cut through the top that are designed to combat male numbness and other anatomical concerns
  • If you are female, consider a women’s saddle. These models are wider in back to better accommodate women’s generally wider pelvic structure, and they have a shorter nose to better suit female anatomy.


  • A braking system is actually comprised of a few different components:
    • Brake levers are located on the handlebars and are used by the rider to slow or stop the bike
    • Brake calipers squeeze against the rims to control the bike’s speed
    • V-Brakes are a type of caliper brake in which the brake arms reach around the side of the wheel to press brake pads against the wheel rim. They are used primarily on mountain and BMX bikes.
    • Side-pull brakes have both cable arms on the same side of the caliper. They are best suited to road and recreational bikes.
    • Brake pads are blocks of rubber-like material that press against the wheel rim when the brakes are applied