This page explains the merits of different wheel sizes, innertube valve types and spoke materials. It also explains the difference between single speed rear wheels, hub gear rear wheels and the two types of hub for derailleur gears.
During the last 20 years, there have been two common wheel sizes for adult bikes in the UK: 700c (622mm) and 26 inch (559mm). Wheel size is usually printed on the rim label or embossed on the rim.
This is the size I usually recommend for riding on roads and paths, unless I’m talking to someone who needs a particularly small frame. With a diameter of 622mm, it is large and that makes for a comfortable ride. There is a very wide range of tyres available available for 700c wheels, from thin to fat, smooth to knobbly. 700c is standard for road bikes and touring bikes. Mountain wheels are also available in this size, though the mountain bike industry refers to them as 29″ or 29er. 29ers are becoming more popular among mountain bikers precisely because they give a smoother ride.
This is the size found on most adult mountain bikes. Although slim tyres are available, they may give a harsh ride on a mountain bike because these wheels are less compliant than 700c, when compared like with like.
A wheel size that was commonly found on chromed-steel-rimmed roadsters (e.g. Raleigh 3-speeds) until the early 1990s was 26″ 1 3/8 (metric equivalent: 590mm BSD). These generally gave poor braking, particluarly in the wet and this size has more or less been phased out by manufacturers.
A wheel size that is being adopted by some mountain bike manufacturers is 27.5″, also known as 650B (metric equivalent: 584mm BSD). It remains to be seen whether this will eventually replace 26″ (559) on new mountain bikes.
Other wheel sizes are available, especially on older bikes or bikes for children, but tyres and innertubes are less widely available in the UK. A table showing all of the wheel sizes and their equivalent diameters in millimetres appears a third of the way down Sheldon Brown’s page on tyre sizing.
When replacing a rim or rebuilding a wheel using the same spokes, be sure to get the same model rim or a rim designed for the same spoke count and spoke length. The latter will mean at least checking the depth of the rim and whether it is single wall or double wall. Deep rims need shorter spokes.
Tyre valve hole
There are two types of innertube valve: Presta and Schrader. Schrader is a bit fatter and needs bigger hole in the wheel rim. So wheels are made for one type of valve and you need to buy innertubes with the correct type. Some older bike wheels have the Woods valve (known in the USA as the Dunlop valve). Woods innertubes can be replaced with Schrader ones, since the valves are the same diameter.
Many of the cheap wheels I’ve owned have suffered from broken or corroded spokes. When a spoke breaks, the wheel loses tension in that area and the rim may start rubbing against one of the brake pads. Stainless steel spokes are far more resistant to corrosion.
Single speed wheels are undished, with a screw thread to take a (BMX type) freewheel sprocket. Read more about single speed.
If you are replacing a wheel on a bike you need to replace it with one of the same type. If it is a derailleur wheel, it needs to have the same number of sprockets. There are two basic types of multi-speed rear wheel: a derailleur rear wheel has cluster of sprockets at the hub; a hub gear wheel has a fatter hub and usually only one sprocket.
Two types of derailleur wheel: freewheel and freehub
There are two basic designs of derailleur rear wheel, the freewheel type and the freehub type. The freewheel type has a threaded hub for the freewheel to screw on to. The freehub type has a small, splined cylinder that accepts a cassette of sprockets. Parts are not cross-compatible. So, if you’re replacing sprockets or you’re replacing your rear wheel and want to reuse your sprockets, you will need to know which type you have. Read more about freewheel vs freehub.