Correct Chain Tensioning

19/07/2017 3:43pm

All chains need to be correctly tensioned at all times. Why? A chain that is too tight wears the chain, sprockets and gearbox components very quickly and is in danger of snapping. A chain that is too loose also wears out the chain and sprockets and is in danger of jumping the sprockets and snapping from the whipping action created.

But what is correct? Approximately 20mm of sag with the chain at its tightest spot.

Correct Chain Tensioning

To ascertain this, first get a suitable lever and lift the chain run in the middle of it’s bottom run between the front and rear sprocket. The amount of lift you can detect with a sensible amount of pressure is its sag. Now move the rear wheel round several times and continue to test the sag. With a new chain it should be almost the same. With a used chain you will see that it is tighter in some positions than others. So first find its tightest position and then adjust the chain to have 20mm (3/4") of sag at this point. Do everything back up again and you are done. This is the sag you need to maintain at all times.


Tags: chainssprockets