You should listen to me. No, seriously, listen to me.
Join Date: Oct 2008
Location: Santa Barbara
Motorcycle: Blue 2006 GSX-R1000
Re: OEM vs Aftermarket Chain/Sprocket set and pitch
If the rear is aluminum, it's aftermarket. Not certain about yours, but OEM front sprockets are normally cushioned while most aftermarket are not. Again not sure about yours, but rear sprockets are commonly made by Sunstar and so marked - including the tooth count, though that's easy for you to count. Compare the cutouts in the rear with those in the service manual. OEM chains are commonly made by DID. This may be mentioned in the service manual.