Downgrading from 200mm rotor to 180mm- Mtbr.com
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  1. #1
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    Downgrading from 200mm rotor to 180mm

    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?
    Attached Thumbnails Attached Thumbnails Downgrading from 200mm rotor to 180mm-1165761d1509876789-sram-guide-caliper-bolt-holes-bolts-bcre_140826-1788.jpg  


  2. #2
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    The smart money would be to call the manufacturer and ask them what is the standard they set that fork up for. But I'm sure some one on here owns or has owned that fork.

  3. #3
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    Per the 2018 Pike Manual below (pg 18-19), if you fork is *Boost it's min rotor is 180mm if it's not boost it's 160mm and you'd need an adapter to go to 180.


    https://www.servicearchive.sram.com/...lish_rev_d.pdf
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  4. #4
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    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. #5
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    Quote Originally Posted by One Pivot View Post
    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)

  6. #6
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    I would have no qualms going to 180. But I really haven't ever lacked braking power as long as everything was working properly. If anything, I had brakes that were too grabby, and bigger rotors could exacerbate that.
    Do the math.

  7. #7
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    Yeah you could just remove the spacer. I'd leave it.

    Waiting on my 246mm rotor to arrive any day now
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  8. #8
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    I'll need shorter bolts too after removing the adapter, right?

  9. #9
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    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.
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  10. #10
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    Iím curious as well as to the rationale for the downgrade. Having 180s front and rear on all my bikes, I have been suffering from acute rotor envy for some time now.
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  11. #11
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    So my current situation with the front brake is like here: https://forums.mtbr.com/brake-time/g...n-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. #12
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    Quote Originally Posted by keckros View Post
    So my current situation with the front brake is like here: https://forums.mtbr.com/brake-time/g...n-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.
    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.

  13. #13
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    Quote Originally Posted by Magsrgod View Post
    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.
    I align the caliper with the rotor first by eye so rotor sits in the middle and then spin the wheel to make sure it does not rub anywhere, then tighten up at the correct spot.

    I would have thought that LBS did bleed the brakes while changing the caliper but I guess I'll try that next.

    Exercising the pistons is a bit tricky since I have to put pressure on 2 pistons on the other side Would need some kind of custom bleed block that would hold those 2 in place while allowing other side to move.

    Thanks everyone!

  14. #14
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    Quote Originally Posted by keckros View Post
    I align the caliper with the rotor first by eye so rotor sits in the middle and then spin the wheel to make sure it does not rub anywhere, then tighten up at the correct spot.

    I would have thought that LBS did bleed the brakes while changing the caliper but I guess I'll try that next.

    Exercising the pistons is a bit tricky since I have to put pressure on 2 pistons on the other side Would need some kind of custom bleed block that would hold those 2 in place while allowing other side to move.

    Thanks everyone!
    To align the rotor you should back the caliper bolts out just enough so the caliper can move around freely on the bolts. Spin the wheel, grab and hold the brake. With the brake held tighten the caliper bolts, if your rotor is true you caliper will be perfectly aligned.

    You also don't need a custom bleed block for 4 pots, a 17mm box end wrench will work perfectly for holding both pistons.

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  15. #15
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    Quote Originally Posted by keckros View Post

    Exercising the pistons is a bit tricky since I have to put pressure on 2 pistons on the other side Would need some kind of custom bleed block that would hold those 2 in place while allowing other side to move.

    Thanks everyone!
    I find a plastic tire lever is effective. You really only want to hold back the "fast" pistons to get the "slow" ones out, cleaned, and moving freely again. This can be a time consuming process the first few times, but definitely worth it for dialed brakes.

  16. #16
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    As far as step 5, tread carefully. There's a fine line between piston out enough to clean thoroughly and piston on the floor, and it's about one lever squeeze.

    I imagine there's a few folks around here that can vouch for that.

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  17. #17
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    Quote Originally Posted by clintj View Post
    As far as step 5, tread carefully. There's a fine line between piston out enough to clean thoroughly and piston on the floor, and it's about one lever squeeze.

    I imagine there's a few folks around here that can vouch for that.

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    Including myself! I should have mentioned that, when they look like their pretty far out, then there out far enough!

  18. #18
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    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.
    Do the math.

  19. #19
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    Quote Originally Posted by keckros View Post
    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.
    I think your LBS is grasping at straws. Typically 200mm rotors are 2mm thick, and smaller ones are 1.8mm. There are exceptions, but 200 rotors are usually the most resistant to warp.


    But i agree with them; intermittent rub isn't worth stressing over.


    Other stuff to check- PMs are faced correctly, decent torque on through axle, no slop in hub bearings. Also aligning by eye can introduce problems, ironically.
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  20. #20
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    Quote Originally Posted by jeremy3220 View Post
    Agreed. Wouldn't recommend dropping to 180mm. However, if you do please send me your rotor and adapter. (seriously)
    I'll take them, too. I'll even send him a 180 in response if these two pieces show up in my mailbox.

  21. #21
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    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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  22. #22
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    Going from 200 to 180 was not a logical solution from the shop...you are getting better advice on this forum

    Sent from my XT1585 using Tapatalk

  23. #23
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    Quote Originally Posted by chadbrochills View Post
    Got rid of those POS's
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  24. #24
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    Quote Originally Posted by wytemike21 View Post
    Going from 200 to 180 was not a logical solution from the shop...you are getting better advice on this forum

    Sent from my XT1585 using Tapatalk
    Yeah, figured that out too. Actually got the sticky side pistons moving more now - my Topeak powerlink pliers were just the "right" tool to hold other side in place while pumping the lever Much better situation now based on this days ride.

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