Shimano M395 / disc rotor compatability

Mister_gMister_g Posts: 55
edited September 2014 in MTB workshop & tech
Hello all,

I have a Giant Talon 1 fitted with Shimano M395 calipers and 160mm SM-RT56 rotors marked 'Resin Pad Only'.

I have put ~130 miles on it over the last few months (almost all off road) and noticed that the original pads were wearing quite quickly. When looking for replacement pads, I saw that I could get a pair of RT66 disc rotors from CRC, for the price of a set of pads, that would let me run sintered pads (for better life, & maybe less fade). One of the questions on the CRC page was whether the rotors were compatible with 395 calipers, and the answer (from CRC Staff) was "Running this rotor with the M395 caliper and Sintered pads will not be a problem."

Having ordered them, and fitted the front, I'm concerned that the RT66 aren't compatible with the M395 calipers:

Here they are side by side (RT56 on left, RT66 on right):

DSC00845_zps649075ab.jpg

Here they are with the RT66 on top of the RT56 - the outer part where the pad contacts is substantially narrower on the RT66 than the RT56.

DSC00846_zps576701dd.jpg

I fitted the disc and rode around the block to bed the pads in a bit and you can see that the pad is running against the disc spider arms by several mm:

DSC00850_zpsaa02fe03.jpg

This doesn't look acceptable to me, but would welcome 2nd opinions.

After some further research, I believe that the disc rotors I would need to take the full width (depth?) of the M395 calipers, that are compatible with metal/sintered pades would be the SM-RT61. Can anyone confirm that, or offer an alternative? (They look like they have been discontinued, but are still available on ebay.)

At the moment, I'm inclined to take the RT66 off again and return the un-used one, at least to CRC.

Thoughts & advice appreciated.

Posts

  • Chunkers1980Chunkers1980 Posts: 8,035
    You're worried about nothing and in the first place
  • cooldadcooldad Posts: 32,904
    Agreed. Will work fine, but the best thing to do with the 'resin only' tag is ignore it.
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  • Mister_gMister_g Posts: 55
    Thanks for the comments.
    cooldad wrote:
    ... the best thing to do with the 'resin only' tag is ignore it.

    I've seen arguments both ways from previous discussions here (& elsewhere), and it was what I was tempted to do until I saw some cheap discs that were *definitely* metal pad compatible... :?

    I've taken the new disc off again for now, as I can't reconcile my engineering sensibiliies to losing 15-20% of the pad contact area (and I'm supposed to be doing the Marin trail tomorrow and want to have confidence in the bike).

    I'll have to give it some more thought...
  • The RookieThe Rookie Posts: 27,575
    And what do your engineering sensibilities tell you would be the effect of losing pad area? (Ignoring any change due to the different hole patterns)
  • Mister_gMister_g Posts: 55
    The Rookie wrote:
    And what do your engineering sensibilities tell you would be the effect of losing pad area? (Ignoring any change due to the different hole patterns)

    I don't know - possibly reduction of braking force or increased pad wear for the same braking force. I'm also nervous about the contact with the inner part of the pad being intermittent - it just doesn't seem *right*.
  • The RookieThe Rookie Posts: 27,575
    Mister_g wrote:
    The Rookie wrote:
    And what do your engineering sensibilities tell you would be the effect of losing pad area? (Ignoring any change due to the different hole patterns)

    I don't know - possibly reduction of braking force or increased pad wear for the same braking force. I'm also nervous about the contact with the inner part of the pad being intermittent - it just doesn't seem *right*.
    No, no loss of braking force, area doesn't affect it, the pad may wear very slightly faster, but not significantly. Many bike braking systems have pads overlapping the inner edge of the main part of the disc, it's common and truly I wouldnt worry about it.
  • OK, I hear what you're saying! :)

    I think even Shimano agree - this table (from a 2008 document - I couldn't find newer) shows which disc rotors are narrow or wide (the only 'wide' discs that are compatible with metal pads *are* the RT61s), and in a foot note says that if you use the wide type pads (the B and E types) with a narrow disc it's life will be shorter ("durability ... become shorter"), which implicitly suggests that the combination is acceptable.

    brakes2_zps69eaea17.jpg

    (Pads from the same document for reference:)

    brakes1_zps61467928.jpg

    For the sake of a tenner, or so, I think I'll still swap to RT61s, though (it just makes me feel better, ok? :wink: ).

    Thanks for the replies.
  • swod1swod1 Posts: 1,592
    Put your old rotors on if they aren't bent to see how the braking is with those ?

    i use the rt 66 rotor on the rear and and even thinner rt64 slx rotor on the front without any issues.
  • swod1 wrote:
    Put your old rotors on if they aren't bent to see how the braking is with those ?

    Yeah, that's what I've done for now (I only changed the front).

    With Nukeproof Enduro semi metallic pads and the RT56 rotor, the actual braking is fine - I feel they are substantially more powerful than the OE pads. (They seem to be really chewing up the rotor, though, so if that continues, I still think I will change to RT61s at some point.)

    I should also add that it has been suggested that if I were to re-fit the RT-66 rotors that I could shim out the caliper by a few mm so that the pads are centred on the available disc rotor surface, which seems sensible, too.

    Thanks folks.
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