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Discussion Starter · #1 ·
Hi guys.
I recently purchased a good used bike for a price I couldn't let up on.

It's a Giant XTC 1 29er from 2011 and has some shamino brakes on it which I really like. The other day I noticed something though. On the rear brake it has the wording for 180 rotors only. I'm pretty sure the stock brakes are for 160 in the back. I measured it and it seems to be the case.

What is going on with this? Do I need to replace my rear rotor to make it 180? Please see the picture and help me out.
Thanks!
 

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That piece is actually an adapter mount for the brake caliper. They come in different sizes to fit different size rotors and different brake manufacturers. If the rotor really is a 160, I'd get a smaller adapter. They're generally cheaper than rotors.
 

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I wouldn't think your brakes would work at all if the rotor and adaptor didn't match. Check with a Giant dealer, that frame is probably designed to work with that adaptor. I'll bet if you got a 160 adaptor you could run a 140 rotor and take about 5 grams off your bike(not worth it).
 

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I can't tell from your picture which adapter it is but a 180 front adapter will usually work as a 160 rear... When you look how the rotor sits in the caliper are the brake pads completely contacting the rotor? If the adapter is wrong your pads will sit high above the rotor and only about half of each pad will contact the rotor.
 

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I can't tell from your picture which adapter it is but a 180 front adapter will usually work as a 160 rear...
Huh. I didn't know that. Today I learned.
 

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Discussion Starter · #6 ·
I can't tell from your picture which adapter it is but a 180 front adapter will usually work as a 160 rear... When you look how the rotor sits in the caliper are the brake pads completely contacting the rotor? If the adapter is wrong your pads will sit high above the rotor and only about half of each pad will contact the rotor.
Thanks for that advice, It's hard to tell because from any angle it appears blocked but from the top down it appears that a good 90% of the rotor is make solid contact with the brake pads.
It's hard to tell what is pad and what is caliper and where the rotor sits but from my best guess its a good 90% - Would that be acceptable or should I look into a different adapter?
Thanks again!
 

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I can't really see in your photo as the lettering is a bit blurred but it looks like I can see a "F" indicating a front rotor adaptor. Is the part number:

Shimano F180P/S Disc Brake Adaptor

BR8913.jpg

This is a rear mount for 160mm:

BR8916.jpg

Basically the same thing.
 

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That is an IS (International Standard) frame mount for your caliper. I have also found that a 203mm IS adaptor will work as a 203 IS up front, and will work as a 180 IS rear. 180 IS front works as a 160 IS rear. So on and so forth.

203 PM (Post Mount) adaptors work for the same size (203/180/160 or whatever) front AND rear.
 

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Discussion Starter · #9 ·
Pardon my ignorance,
so what you are saying DethWshBrk is that I'm good to go with what is on there?
Appreciate the help everyone!
 

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Yeah yer good ...it wouldn't line up if it was wrong. ^^What was said up there is correct..the 180 is if mounted on the front.
My bike has the same "if you use it in the rear it's a 160 mount" =
IMG-20140308-00609.jpg
See the label^^^
 

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Yes, you are good to go!

Honestly, to make it simpler, if the wrong size caliper adapter was on, the caliper would not even fit.
 
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