Derailer bikes can work fairly well even with the chain running at a considerable angle, but this should not be done with a derailerless setup. It is quite important to get the chainline just right.
You can check the chainline by installing the hub in the bike, with no chain installed. By placing your head just in front of the chainwheel, you can sight along the chainwheel and see back to the rear hub, to see if the chainwheel lines up exactly with the rear sprocket. If it doesn't, re-arrange spacers or change the bottom bracket axle as necessary. You might also hold a yardstick or other straightedge against the side of the chainwheel, reaching back to the sprockets.
Usually, on a bike that came with double chainwheels, the inner chainwheel will be more in line with the rear sprocket. For a neat appearance with a single chainwheel, you can buy a set of shorter "stack bolts" ( the 5 bolts that hold the chainwheel(s) to the crank spider). You may find it easier to locate these in a shop that deals in BMX bikes.
Most older one- speed hubs, such as BMX, fixed-gear and coaster-brake hubs have a chainline of about 40-42 mm (centerline of the frame/hub to center of the sprocket. )
The wider chainstays on mountain bikes often don't let you place a medium-sized chainwheel that close to the centerline of the bike, so there is a secondary de-facto standard chainline of about 52 mm for singlespeed mountain bikes. Stock MTB triple cranks usually have the outer chainring at around 52-57 mm; the middle is normally 47.5-50 mm.
If you convert a cassette Freehub ® to singlespeed, you can put the rear chainline anywhere you want to match that of the desired chainring.
There is more detailed information on chainline and chainline adjustment in our Bicycle Glossary's Chainline Entry and even more in our Chainline Articles.
===Montage des Hinterrads===