This site has a lot of good information, and also for those of you who have CAD programs it includes comprehensive instructions on how to draft a sprocket of literally any
number of teeth. I've used it often, and it works great.
From a table on that site:
Motorcycle Chain Dimensions
Chain No. Pitch Roller Diameter Roller Width Sprocket thickness
520------ 5/8"----- 0.400"------ 1/4"-------- 0.227"
525------ 5/8"----- 0.400"------ 5/16"------- 0.284"
530------ 5/8"----- 0.400"------ 3/8"-------- 0.343"
Breaking it down, the 5
30 is the pitch in 1/8" increments, and the 30
is the inside width of the chain in 1/8" increments, with a decimal point between the two digits (525
From this it should be obvious that a 525 chain could not possibly fit on a 530 sprocket unless the sprocket was thinned substantially. It was, however, common to fit a 525 chain on 520 sprockets back in the flexi flyer days to give the chain some room to find true alignment when the frame and swingarm were merrily flexing in corners. Yup, they were that bad.
There are good reasons to run a 520 chain and aluminum sprockets on the track, where small advantages such as lower weight are important, especially where unsprung weight is kept to a minimum to help suspension compliance and the lower inertial mass of the components soaks up less power to get them moving. The difference in performance when not racing is vanishingly small, and has to be balanced with increased wear: basically the narrower the chain the greater the average load on the sprocket teeth for a given throttle application, and since most of these kits come with an alloy rear sprocket they won't last nearly as long as steel, depending, of course, on use and maintenance. Suspension compliance on the street will improve since an alloy sprocket weighs on average 1/3 that of a steel one, so the best compromise presently available are the Tri Metal sprockets,
with a radially thin steel chain wheel held by a lightweight alloy carrier, combining lighter weight and long wear. They are, however, quite expensive.