sorry but i miss typed the mesurments for the front disc it is actually 180mm so im guessing the rear is a 160 ?
Don't guess, go and get a tape measure or a ruler. Take your existing rotor off the wheel, and literally measure the diameter of it.
Make sure the tape measure goes through the centre so you know you're getting the widest point. And if it's wavy, then measure at the widest point of the wavy bits.
When you've measured it, you should find that your measurement is the same as one of the standard sizes you can get.
There are disks that are brake specific. But most aftermarket disks can be used on a few different brakes. Easiest option is to get disks that are advertised for your particular brakes.
Posts
Parktools :?:SheldonBrown
http://www.pinkbike.com/photo/1327938/
Parktools :?:SheldonBrown
http://www.pinkbike.com/photo/1327938/
http://www.pinkbike.com/photo/1327938/
2006 Specialized Enduro Expert
http://www.pinkbike.com/photo/3192886/
2008 Custom Merlin Malt 4
http://www.pinkbike.com/photo/2962222/
2008 GT Avalanche Expert
http://www.pinkbike.com/photo/3453980/
http://www.pinkbike.com/photo/1327938/
140mm? measure it
http://www.pinkbike.com/photo/1327938/
2006 Specialized Enduro Expert
http://www.pinkbike.com/photo/3192886/
2008 Custom Merlin Malt 4
http://www.pinkbike.com/photo/2962222/
2008 GT Avalanche Expert
http://www.pinkbike.com/photo/3453980/
http://www.pinkbike.com/photo/1327938/
http://www.pinkbike.com/photo/1327938/
http://www.pinkbike.com/photo/1327938/
Make sure the tape measure goes through the centre so you know you're getting the widest point. And if it's wavy, then measure at the widest point of the wavy bits.
When you've measured it, you should find that your measurement is the same as one of the standard sizes you can get.
http://www.pinkbike.com/photo/1327938/