My bike came with a sprocket setup of -1/+3, and I don't know what length chain to buy to replace it. I ride a 2002 CBR F4i, the sprocket pitch is 520. Can anyone give me a clue?

 

You should replace the chain and sprockets as a set, and the set will come with the correct length.

 

Since your bike didn't come with a 520 set up, it would be interesting to know some of the statistics. Most 520 conversions involve a steel front sprocket, an aluminum alloy rear sprocket and the lighter weight 520 chain. Along with these changes, the gearing ratio is often changed as well to give more low end excelleration. We're often told that if you go that route, they won't last as long as staying with the same gearing and steel front and rear sprockets. I'm curious as to how old your current setup is and how many miles did you get on them.

The easiest way to answer your question is, if you're staying with the current gearing, then just count the number of links on your current chain and get one the same length.

 

I bought my bike used, so yes it did come with the 520 conversion setup. The previous owner claimed the chain was new when I bought it. I put a good 5,000 miles on it since feburary of 2010 (7 months). The sprockets are still fine, no excessive wear, no warping. Front sprocket is a vortex(15t), and the rear is a driven (49t). I have ordered a kit that has the same gearing and comes with a chain. Thanks for the help though guys.