The following is an excerpt from Cyclepath Mississauga's employee handbook. It is a detailed how-to on tire changes for entry level mechanics. Tire changes are the bread and butter of any good bike shop so a proper tire change is the first thing any bicycle mechanic should learn. Outside of the shop, any BMX rider reading this blog can use this guide to make sure they're doing their own tire changes properly, and can also make sure they handle tire changes on their friend's and family's non-BMX bikes the way the manufacture intended.
Peter’s Tire Change 101
Types of tires
There are two common designs for how tires are mounted to rims. The first and most common is the clincher tire. These tires use an innertube (or sealant in the case of tubeless tires) to hold the air inside the tire while the tire itself is mounted to the rim by a wire or kevlar bead. This hooks into a lip inside the rim as the tire inflates. A tubeless tire functions the same way but it uses sealant instead of an innertube to hold the air. The other design you may see is the tubular tire. These tires essentially have their innertube built in and are mounted to the rim with glue instead of a hooked bead. Tubular tires are almost exclusive to vintage or high end road bikes.
99% of the bikes you see will use clincher tires with innertubes. In the case of both tubular tires and tubeless tires which use sealant, the job should be performed by a senior mechanic. Both of these tire setups must be installed in a unique way.
Tires sizes
Tires can be broken down into three basic types to keep the sizes straight; Kids, Mountain, and Road. Each tire has three numbers designating its size. For example, 26” x 1.95 (559) is one of the most common sizes for department store mountain bikes. The first is the diameter (26’), the second is the width of the tire (1.95”), and the third is the BSD or Bead Seat Diameter. This is the precise diameter of the hooked bead’s interface with the rim. In most cases, the BSD can be ignored if the regular diameter and width match. If a tire looks like it should match a rim but doesn’t, check that the BSD’s match.
Road tires generally use metric measurements, with the exception of the old 27”x1 ¼” tires, which appear on old steel framed road bikes. You may see some other unusual sizes such as 650c, but in general you will see 700c x _____ (622) on road and hybrid bikes. Road bikes usually have a width between 20mm and 28mm. Hybrid and cyclocross bikes can use tires as wide as 45mm if the have the clearance.
Mountain tires come in three common imperial diameters: 26”, 27.5” (also known as 650b), and 29”. The widths vary from around 1.5” for street use, 2” for XC use, 3.5” for DH use, and 5” for fat bikes.. 26” and 27.5” tires are largely only compatible with their own sizes but 29” rims have the same BSD (622) as 700c wheels, meaning that wider hybrid tires will fit on a 29er wheel for street riding.
Kids tires come in a wide variety of diameters, but they all have a width around 2”, give or take. Bike shops tend to sell 12”, 16”, 20”, and 24” kids bikes, along with 20” BMX and some 18” BMX. 14” and 18” sizes are usually sold as childrens sizes at department stores so the options for replacement parts are not as plentiful.
You may see some older standards on older bikes. Pre-1970 cruiser bikes sometimes use 26” x 1 ⅜” tires. These are not compatible with normal 26” tires. A similar standard is used for wheelchairs, which use 24" x 1 ⅜” tires. Again, these are not compatible with regular 24” tires due to a the Bead Seat Diameter being measured from a different point.
As a general rule, equivalent conversions between decimals and fractions does not mean two tires are identical. A tire with an indicated size of 26" x 1.25" is NOT compatible with a tire with an indicated size of 26" x 1 ¼" because the change in units indicates a change in where the measurements are taken from.
Valves
There are three types of valves, two of which you must know how to use. The standard Schraeder valve is identical to a car and can be use with a regular air compressor head. Higher end bikes use a Presta valve, which is skinnier, must be opened and closed manually, and holds air longer at high pressures than a Schraeder valve. Dunlop (also known as Woods) valves are outdated and must be changed to the appropriate Schraeder valve tube.
Changing the tires
A tire change takes the average person half an hour from start to finish. Ideally this job should be fast and simple, taking around 10 minutes for a shop mechanic. The finished product should be perfectly seated so the tire runs round with no lumps and pumped to an ideal pressure roughly in the middle of the tire’s recommended range.
step 1
Remove the wheel(s) that need repair from the bike. Remove any remaining air from the tires by pushing on the valve cores. Most tires can be both removed and installed by hand, using force from the thumbs and palms. Tires that are too tight to remove by hand should be removed with tire levers. NEVER USE A SCREWDRIVER. Insert the lever under the bead and push down, forcing the bead off and out of the rim. Repeat for the inner bead.
step 2
With the old tire removed, separate the tube and tire and carefully inspect any parts that will be re-used. If the tire is be re-used, carefully run your hands inside the tire to check for foreign objects embedded in the tread. Tires that still show tread depth and are not dry or cracking can usually be re-used. Check the rimstrip for damage, and replace if knicks or wear are found. If the wheel needs to be trued, this is the best opportunity.
step 3
When installing the tire, install the first bead by hand. Make sure the logo on the tire is lined up directly across from or directly at the valve hole. This makes it easier to locate later punctures and looks professional. Put some air in the new tube just so it hold shape. Insert the valve first, then carefully push the tube into the tire all the way around. Some talcum powder applied to the tube may make it easier to push into the tire.
step 4
Most tires should be installed entirely by hand. Starting at the valve, use your palms to push the bead onto the rim, being careful not to pinch the tube between the rim and bead. If the tire is too tight (usually occurs with tubeless or high pressure tires), carefully use tire levers to install the tire by turning the lever around and reversing the process used to remove the tire. Remember to check that the tube is out of the way before each use of the lever and that you don’t scratch the surfaces on tubeless rims.
step 5
Check over and reinstall the wheel(s). Inflate the tire in small increments, to a firm pressure, ensuring the bead is properly hooked onto the rim. Reinstall the wheel and make sure the valve has a cap.
Check that the wheel is properly aligned in the frame and that quick release skewers are closed properly. Rear wheels cost more in labour because mechanics have to work around the gears and brake. Make sure the brakes and gears are working as well as possible and advise customer if any parts should be replaced or any additional service is needed. Finally, if the chain is dry, give it a light helping of lube.
