EDIT: I trust Ckau opinion over something I googled on the internet, but, It appears it's just a width difference between the chains.
http://answers.yahoo.com/question/in...4074926AAiXoxX
So I guess you could run a 530 cahin and a 520 sprocket?
If you change your rear tire size, you have also changed your gearing. Not alot, but a little bit.
Also keep in mind as you alter gearing engine RPM will change too. If you gear the kart for more TQ, you have raised the engine RPM at WOT. And if you installed a perfromance CDI that eliminated the rev limiter, you can actually over rev the engine and lead to engine failure.
And if you gear it for top speed, you ultimately lower the engine RPM at top speed because you have placed a higher load on the engine amking it work harder. So it increases heat, and may require a carb rejet to help prevent engine failure.
So it's not just a simple sprocket swap per say.....
Hope i didn't confuse you too much.