Two wheel sets, rotor/pads question

JW599
JW599 Posts: 30
edited June 2017 in MTB workshop & tech
Upgraded my wheels a few months back.

Wanting to keep the old set with slicks so I can quickly swap for winter commutes/long road riding.

The rotors fitted to the new wheels have a smaller braking surface and completely different pattern (Shimano RT-66 6 bolt). The old wheel set has RT-20 centre locks.

Is it best to have matching rotors on both wheels to save swapping the pads each time I change wheels? I'm just concered the wear with a small braking surface could cause an issue when going to a larger braking surface.

I'll get a cheap cassette with lower tooth count and chain, so if all is well I only need to swap wheels and chain for a quick change.

After bedding in the new rotors with fresh pads (+ a brake bleed) it still doesn't feel as though there is as much bite as before.

Maybe just get the 6 bolt version of my old rotors the new wheels? Seems a shame to disgard the new rotors that cost more. Brakes are basic M355's, resin only.

Comments

  • The Rookie
    The Rookie Posts: 27,812
    Not sure what you mean by small braking surface? I presume you mean minimalist with lots of cutouts? Won't be an issue as long as they are the same diameter and near enough the same width.
    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.
  • JW599
    JW599 Posts: 30
    The Rookie wrote:
    Not sure what you mean by small braking surface? I presume you mean minimalist with lots of cutouts? Won't be an issue as long as they are the same diameter and near enough the same width.

    Yeah, here are the two patterns. Both 160mm, newer rotors have a smaller area that contact the pads.

    http://chainreactioncycles.scene7.com/i ... 00&hei=505

    http://chainreactioncycles.scene7.com/i ... 00&hei=505
  • The Rookie
    The Rookie Posts: 27,812
    No issue at all, neither is exactly radical like an Ashima or Alligator! which would be fine anyway.
    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.
  • cobba
    cobba Posts: 282
    The Rookie wrote:
    Not sure what you mean by small braking surface?

    Shimano makes 'wide' rotors and 'narrow' rotors to suit the 'wide' pads and 'narrow' pads that are used in different caliper models.

    http://productinfo.shimano.com/images/ti/1.8/en/C-461-03-00_EN.png

    http://productinfo.shimano.com/#/com/2.3?types=mtb&acid=C-460&cid=C-460

    Wide pads on a narrow rotor means that some of the pads braking surface will be overhanging the inner edge of the rotor's braking area and will be wearing down the rotor 'arms'.
  • The Rookie
    The Rookie Posts: 27,812
    Indeed, but narrow isnt small, hence wanting clarification.....
    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.
  • JW599
    JW599 Posts: 30
    The image linked by cobba shows exacly what I described as a smaller braking surface.

    The caliper uses B type pads and the linked Shimano site sugguests using the wide rotor type for my brake (I currently have a narrow fitted).

    The wide rotor can be bought for under a tenner so I will try it out and see if there is an improvement.

    The current rotors seem usable, but since upgrading the wheels the brakes havn't felt "right" since. Have tried everyting (clean pistons with cotton bud, caliper & rotor with isopropyl, fitted new pads, full brake bleed, re-aligned, lots of time to bed in).

    The feel is like braking when the rotors get wet in a downpour of rain. It bites, but more pressure is needed. Before upgrading the wheels I could lock the front wheel or get the back end up. Doesn't happen now.

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