140mm rotor on the rear

Mrtennis
Mrtennis Posts: 153
edited February 2013 in MTB workshop & tech
I am sure this has been brought up plenty of time so sorry!
My frame has IS mounts but I've just bought some disc brakes which are post mount. I know that I need the adapter. But I would also like to run 140mm rotor on the rear. I asked in a bike shop and he said that it's rare to do that and it would be hard to find an adapter that would do it.
I haven't found much on the internet but from what I've read, am I right in think that a front adapter which is for a 160mm rotor, if used on the the rear will then be suitable for a 140mm rotor?

Comments

  • nicklouse
    nicklouse Posts: 50,673
    correct.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Mrtennis
    Mrtennis Posts: 153
    nicklouse wrote:
    correct.
    Maybe I was a bit too quick in posting on here because I've found a couple of other people mention it on the web now so I'm not so nervous about trying it. I suppose it was probably the fact that the guy in the shop didn't tell me that shocked me. Is there any reason he wouldn't tell or did he just not know his stuff?
    I think I made a mistake here but I actually ordered 2 140mm, one for front and one for rear. I know everyone will say that's just not powerfull enough, as did the guy in the shop, but I don't care :) . He did actually say though that it's just not possible to run a 140mm in the front, no adapter available. Is that right, or has he got it wrong again? Is there something I can find to run that setup?
  • nicklouse
    nicklouse Posts: 50,673
    there are no 140mm front adapters.

    but there may be an odd caliper that might do.

    but I cant think of one at the moment.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Mrtennis
    Mrtennis Posts: 153
    nicklouse wrote:
    there are no 140mm front adapters.

    but there may be an odd caliper that might do.

    but I cant think of one at the moment.
    Ah ok, never mind then. You may remember from one of my previuos threads I have bought some juicy ultimates. Time to change my order then.
    Thanks for moving the thread too, wasn't sure where it belonged :)
  • Mrtennis
    Mrtennis Posts: 153
    http://www.cyclingnews.com/features/pho ... -10/165644

    Seems like it is possible to use a 140mm up front after all!

    While weight saving clearly isn't going to be a a reason to do it, my 140mm rotor was cheaper than a 160, it will look fairly unique, and I won't have to mess about changing my order! Since it seems to be so rare to have 140mm up front though I am now wondering whether it's out right dangerous!?!? I have been using v's until now so surely a 140mm rotor up front isn't going to be less powerfull? The main advantage for discs for me is that they will still be good in mud and wet. I was perfectly happy with my v's in the dry, so as long as I still have that performance than it should be fine?
  • The Rookie
    The Rookie Posts: 27,812
    140mm with modern brakes will be fine up front...clearly that fix only works with IS forks not PM!
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • nicklouse
    nicklouse Posts: 50,673
    Mrtennis wrote:
    http://www.cyclingnews.com/features/photos/on-show-north-american-handmade-bicycle-show-part-10/165644

    Seems like it is possible to use a 140mm up front after all!

    While weight saving clearly isn't going to be a a reason to do it, my 140mm rotor was cheaper than a 160, it will look fairly unique, and I won't have to mess about changing my order! Since it seems to be so rare to have 140mm up front though I am now wondering whether it's out right dangerous!?!? I have been using v's until now so surely a 140mm rotor up front isn't going to be less powerfull? The main advantage for discs for me is that they will still be good in mud and wet. I was perfectly happy with my v's in the dry, so as long as I still have that performance than it should be fine?
    Mmm not sure that the mounts are in the IS position.

    so if you try it please report back. I dont have any 140 to check.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Mrtennis
    Mrtennis Posts: 153
    The Beginner wrote:
    140mm with modern brakes will be fine up front...clearly that fix only works with IS forks not PM!
    Yes mine is IS so I need to buy an adapter anyway.
    I've read in another forum that it's not possible, but reasons I don't quite understand. I'll copy and paste to here and see if you know what he's on about
    Current front disc mount standards are for a 160mm minimum rotor size. On a suspension fork it is likely not possible to even use an adaptor to use a smaller rotor because of the size of the fork slider. Even tougher with post mount vs IS. Same would apply for a rotor smaller than 140mm on the rear. Yet to see a bicycle rotor smaller than 140, either.

    I do have a custom bike with 140mm rotors front and rear. Uses a rigid fork and rear spec IS disc mounts.
    Unfortunately no one that I know of makes a 140mm front adapter. This is due to what you have already noted, clearance on an IS mount fork. I could possibly be done on a post mount fork as long as the diameter of the lowers wasn't too great. But most modern post mount forks with stanchions larger than 28mm would have a lower leg diameter that would interfere with the caliper.
    Unfortunately no one that I know of makes a 140mm front adapter. This is due to what you have already noted, clearance on an IS mount fork. I could possibly be done on a post mount fork as long as the diameter of the lowers wasn't too great. But most modern post mount forks with stanchions larger than 28mm would have a lower leg diameter that would interfere with the caliper.
  • The Rookie
    The Rookie Posts: 27,812
    Read what you linked to, it's a 'bodge' in that he's using a 203mm adaptor but mounted upside down, hence the other comments you found. With Nick though, the original mounts on that fork look 'funny'.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • nicklouse
    nicklouse Posts: 50,673
    The Beginner wrote:
    Read what you linked to, it's a 'bodge' in that he's using a 203mm adaptor but mounted upside down, hence the other comments you found. With Nick though, the original mounts on that fork look 'funny'.
    look like mine on the fixed.

    mosaic_white_disc_600.jpghow do it look?


    but mine is the wrong way around
    img0184s.jpg

    and the spec


    My main issue with the one with the 140mm disc is the caliper is in the best posible place to exert the max ejection force on the hub.

    will have to look into this more.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Mrtennis
    Mrtennis Posts: 153
    well i decided to cancel the order in the end for one of the 140's and order a 160. Was a bit more expensive and will take longer to get here (had already decided I was getting the ashima airator so couldn't be bothered to start looking again for something else) as there don't seem to be any 160mm airators left in the UK - merlincycles had great offers on the 140, 180, 2.. (only £10 posted!) but had sold out of the 160, as had everywhere else. I have another spare 160mm knocking around that I can use until that one arrives anyway....now just waiting for the brakes to arrive in the next day or two!
  • cobba
    cobba Posts: 282
    The Beginner wrote:
    140mm with modern brakes will be fine up front...clearly that fix only works with IS forks not PM!
    140mm would be ok for certain types of riding but definitely not all, some CX riders use 140mm rotors on the front and rear but the smaller the rotor is the quicker it will fade and loose power.

    140mm post mount forks are possible and are available, the following document shows the measurements for the different post mount sizes.

    http://www.hayesdiscbrake.com/wp-content/uploads/2010/04/e-10722-1_RA.pdf

    The size of suspension fork lowers, the positioning of the fork dropouts and the positioning of the post mounts are the limiting factor in what size post mounts can be used.

    140mm post mount forks.
    http://www.bikeradar.com/road/gear/article/pro-bike-ryan-trebons-cannondale-superx-hi-mod-disc-35994/
    http://www.bikerumor.com/2013/02/05/pro-bike-yannick-eckmanns-specialized-s-works-crux/
    http://www.cxmagazine.com/ryan-trebons-solid-disc-brake-rotors-spy-photos
    http://www.cyclingnews.com/features/photos/race-tech-colorado-cross-classic-and-boulder-cup/195885
    http://www.cyclingnews.com/features/photos/eurobike-2012-tech-colnago-expands-electric-hydraulic-range/237301

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