Clincher Tires

Bike Tire Sizes

• Diameter (the A part of A x B)
  
  • The size of a tire can be found on the sidewall. This measurement is written as two numbers, separated by an X. For ex: 700 x 23 or 26 x 2.10. The first number is the diameter of the bead of the tire, in mm or in. Most adult bikes come in either the 700mm size or the 26in size. You'll find 700 tires on road bikes and 26 tires on mountain bikes.
    
• Width (the B part of A x B)
  
  • The second number on the tire's sidewall. On a 700 x 23 tire, the width of the tire is 23mm. As the width increases, the tire will have more surface contact with the ground. More surface contact gives you a more stable and comfortable ride. Less, however, means less friction and a faster ride.
• Width Fractions and Decimals
  
  • If you ride a bike with a 26in tire, the tire width will be denoted with either a decimal or a fraction--for ex: 26 x 1/75 or 26 x 1 3/4. Take note that even though the two tires appear to have the same width, if one is marked with a decimal and the other a fraction, they are actually two different sizes. If you're looking for an exact size match, make sure you don't choose one fraction tire and one decimal tire.
    
• Measurement Discrepancies and the ISO
  
  • If you measure the diameter and width of your tire, you'll find that they don't exactly match what's written on the tire. The numerous sizing systems -- and companies that try to cheat on their sizes -- make it hard to know what the numbers on a tire really mean. Fortunately, the International Organization for Standardization, or ISO, has created a system for tire sizing to regulate tire measurement and take the guesswork out of choosing the proper tire. Most new tires and rims will show the ISO measurement. The measurement marks width first, followed by diameter. If you want an exact match when you replace an old tire, match the ISO number.
• Compatibility
  
  • When it's time to buy new tires, always get tires with the same diameter as your old ones but you can choose a different width. Your bike's rims will hold a range of tire widths, although not all widths are recommended for every tire. See a tire width chart that shows proper compatibility.

Four most common tire sizes (for adult bikes):

Each group is roughly defined by the diameter of the tire with varying widths available within the same diameter.

1. 700C: the most common tire size. Found on most road and hybrid bikes. Widths range from 20-23mm for fast road bikes and from 38-42mm for hybrids/touring bikes. It has an inner diameter measure (a.k.a. "bead seat diameter" [BSD]) of 622mm. A tire labeled 25-622mm == 700 x 25. There is, however, a huge variation of the "true" outer diameter among 700C tires. For ex: a 700 x 20 road bike tire may be as small as about 660mm in diameter. There is no foolproof way to know if it'll fit your wheel other than trial and error.
2. 27 inch: 2nd most common tire size. Very popular on 10-speeds common from the '60s to '80s, but not many (or none) bikes are being made today based on this tire size. However, replacement 27-inch wheels are still available for these bikes, and the tires will probably continue to be produced for years to come. Though 27-inch and 700C tires use the same inner tubes, the tires themselves are not the same and should not be used interchangeably.
3. 26 inch: prevalent on mountain and comfort bikes. Became the de facto standard of the mountain bike since the '70s. Commonly available in widths from 1.25 inches up to 2.5 inches. Standard BSD is 559mm. As with 700C tires, the true outer diameter of the 26 inch will vary from one brand and model of tires to the next.
4. 650C: used on some triathlon/time trial bikes and smaller-framed women-specific bikes. Typically 1 inch in width. Not the same as 26-inch tires. 650C uses a BSD of 571mm. Similar to 700C and 27-inch, however, 650C and 26-inch inner tubes are interchangeable, given a close enough width.

Types of Bicycle Tires

1. Road
   
   • smooth and narrow; no tread
   • typical size: 700 x 23c
   • heavier riders can ride up to 25-28mm widths
   • racers will use a narrower (18-20mm) width
2. Hybrid
   
   • similar to road tires, but usually wider
   • typically at least 28mm and wider
   • may have tread pattern, but more for wet-weather street riding than for off-road
3. Mountain
   
   • comes in a variety of width and tread patterns
   • width and tread are best determined by terrain
   • be sure to check rim width and frame and brake clearance when buying new MTB tires

29 (MTB) = 28 (Vintage) = 700C (modern designation) = 622 ISO. And 27 is bigger than them all at 630.

How to pick the right replacement tube

1. Identify the valve type (Presta vs. Schraeder)
2. Find the tire size written on the tire sidewall and find the closest tube match
3. Diameter: It is always best to buy a tube that matches your tire in diameter. A 24" tube for a 24" tire, but close metric equivalent will also do the job as long as it's not too big of a difference
4. Width: It's not as important to purchase the exact width of tire as the typical tube has a fair amount of elasticity to conform to your existing bicycle tire. However, it is the best approach to get in the habit of purchasing tubes that closely match your tire size. If you buy a slightly wider tube, say 1/2" more, it will not cause any harm or remain under-inflated, however it will be much heavier with the extra rubber. If you h