Hello gtec, sorry can you explain a bit more in details what you intend to do?

Am I right to assume you want to increase your sprocket pitch by a couple of teeth?

Standard pitch for the rear sprocket is 45 teeth and 15 for the front one, you can see the reaction in revs/power when increasing number of teeth using the attached spreadsheet.

If you need details of a good suppliers please check out B & C Express here:
http://www.bandcexpress.co.uk/cgi-bi...l?cat=SPR-ROAD