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Downgrading from 200mm rotor to 180mm

12K views 23 replies 16 participants last post by  keckros 
#1 ·
Thinking of downgrading front rotor from 200mm to 180mm (Guide R, Rockshox Pike RC3 MY2018).

Current setup looks like this:


Am I right thinking that I can just remove that adapter between the fork and caliber and the new rotor will fit fine?
 

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#4 ·
Pikes with no adapter are 180. If you check your adapter it'll say something like "180 to 203 PM" and it'll be about 11mm thick.

You'll never in a million years notice that weight savings, but you'll definitely notice a lack of braking power! I wouldnt do it unless you're specifically having a problem with the front end locking up.
 
#5 ·
Pikes with no adapter are 180. If you check your adapter it'll say something like "180 to 203 PM" and it'll be about 11mm thick.

You'll never in a million years notice that weight savings, but you'll definitely notice a lack of braking power! I wouldnt do it unless you're specifically having a problem with the front end locking up.
Agreed. Wouldn't recommend dropping to 180mm. However, if you do please send me your rotor and adapter. (seriously)
 
#9 ·
I could understand doing this with shimano brakes, but with guides...? Tweaking the lever reach and/or pad compound is plenty to adjust the feel, without crippling performance. I'm curious about OP's reasoning.


You may or may not need new bolts. It's easy to check (remove the adapter and see if you bottom out), and every shop i've worked at would be happy to give you the correct size if necessary. They accumulate them because nobody downgrades rotors.
 
#11 ·
So my current situation with the front brake is like here: https://forums.mtbr.com/brake-time/...en-piston-advancement-retraction-1044785.html

Took the bike to LBS where they changed the caliper. Still looked the same so took it back for a re-check but was told that it's fine as it is. So I am able to align the caliper so that it does not rub (pain in the ass tho because pistons are so uneven) when driving straight, but on uphills or tight curves it still rubs a bit. LBS also told that switching to smaller rotor would probably fix the mentioned rub as smaller rotor would warp less under stress.

Current rotor is almost dead straight - would probably bend it more if tried to fix :)

To me, that caliper does not look 100% OK and in the other thread OP got new one from SRAM under warranty.

Have already resetted the pistons multiple times and still the inner side pistons move out much more while not retracting much. Outer side pistons barely move.
 
#12 ·
A different sized rotor wont change any of this behavior. How do you align your caliper with your rotor?

Pistons sticking is quite common. Most of the time I find cleaning them up and exercising them works pretty well.

  1. Remove wheel and pads
  2. Do a full brake bleed so you know your not fighting an air bubble in the Caliper.

    Once the brake bleed is completed
  3. Squeeze brake lever so Pistons start to come out,
  4. If one side is coming out faster put pressure on those pistons, the slower pistons should start coming out.
  5. Once the pistons are out pretty far clean them up with a Qtip with a little ISO alcohol on them
  6. Once cleaned I lubricate the pistons with whatever brake fluid is designed for the system
  7. Press the pistons back in fully and start working the lever.
  8. You may need to repeat step 7 multiple times, but as long as nothing is terribly wrong the pistons will start coming more equally.
 
#18 ·
Yep. Done it myself a few times. It's an annoyance but no biggie. Usually you can just push it back it but if it does fall out completely it gives you an opportunity to really clean the piston and wipe out the bore with a lint-free wiper. Stick it back in and bleed.
 
#21 ·
My Guide T's did the same damn thing on 180mm rotors. One side of the calipers pistons would advance further out then the other side. No matter what I did, they always wound up like that. Got rid of those POS's and got a set of Magura Sport Trails. Best $250 I've spent on the bike.
 
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