Hi,

I am new to this. At the moment, I am trying to upgrade my bike's disc brake (since the one comes along with the bike is rubbish) I did brought it to the bike shop but they told me that the rear disc is having a size that they don't have.

Here are my few questions:
1. What's the typical BCD (or PCD) of a disc brake rotor?
2. If the disc brake rotor' BCD of my bike doesn't match the mount, can I change the mount?
3. Since it is really hard to find a 140mm rotor, is it possible to change the size? (like the more popular 160mm)

Thanks for your help!!

If I understand you right and your wheel has the std. 6 bolt hookup and your bike will accomodate the 160mm then your fine. Can your lbs not look at it and make that determination? They should be able to.

If you change your rotor to the larger 160mm you have to relocate the caliper on the frame which the bracket for such is welded in place. I would search Ebay for a replacement rotor of the same size.

All you should need to change rotor sizes is an adapter. Your lbs should be able to easily order such an adapter if they do not have one in stock. Or, you could do it yourself: https://www.jensonusa.com/store/produ...+6+Rotors.aspx

It's not really a bcd standard like cranks. There are a few different standards but the 6 bolt is the most common. Shimano's centerlock style is another. There are some odd ones out there but without you specifying what brakes/rotors/hubs you have now, hard to say what your choices are. You can adapt a centerlock to a 6 bolt but not the other way around. Do you have an old 4 bolt type? Details help...

It seems that of mount for the rotor (it is a 6 bolt mount) doesn't match my new rotor set with caliper. Therefore, is it possible for just changing the caliper but not the rotor? Since the old rotor is still in good shape? Any advice?

Thanks!

Depends on the rotor diameter, adapter and braking track width, somewhat the type of caliper....details! If your new rotor is centerlock type then there is no adapting a 6-bolt hub mount to the centerlock rotor (just the other way around, i.e. you can have a centerlock type hub with adapter for a 6-bolt rotor).