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When I bought my fun bike, the standard pads were B01S. Then a bit later, Shimano released B03S, that was touted as "40% more durable than B01S, with the same braking performance", and deprecated B01S. And recently they released B05S, that are also presented as "40% more durable than B03S", and they deprecated B03S. Magura/SwissStop also has different compounds, were one can chose between "initial bite" and "durable".

But what about the rotor? With a very simplistic view, if pads are more durable by being harder (or staying harder as they heat - maybe more sensible for resin pads than metallic ones), isn't there a risk that the rotor wears faster? Or are there other factors to be taken into account?

(Given pads are trivial to replace, and rotors may not be (especially if one wants to apply the correct torque setting), it may be more sensitive to prioritise the rotor's lifespan over the pads' one)

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  • Not an answer, but I don't think rotors wear fast enough to be an important point of concern, regardless of what pads you use. Even with full metallic pads, you're likely to get many thousand km out of a rotor. Of course, this is before considering the cost savings of more infrequent pad replacements as well.
    – MaplePanda
    Commented Mar 26, 2023 at 1:55
  • @MaplePanda I actually reached 1.5mm with the fun bike, after 3 or 4 pads replacements. The stock rotors were the most basic Shimano ones (SM-RT26), only used with B01S. I replaced them with RT54 - along with the wheels, wear seems to be limited now, so the quality of the steel may have a role too.
    – Rеnаud
    Commented Mar 26, 2023 at 6:54
  • @MaplePanda I had some ceramic pads once. I estimate that they wore the (sintered-compatible) front rotor several times faster than my previous sintered pads
    – Chris H
    Commented Mar 27, 2023 at 14:52
  • Don't forget how soft can wear hard. Imagine some really hard grit, and getting that embedded in some soft pads. Compare that to harder pads (still softer than the rotors) that the grit wouldn't embed in. If there's a steady supply of abrasive slurry, the grit doesn't even have to embed to cause accelerated wear, and both pads and rotors will wear faster, This all means it's not a simple relationship between wear and hardness.
    – Chris H
    Commented Mar 27, 2023 at 14:55
  • But I run sintered pads on my tourer and my rotors have lasted many sets of pads
    – Chris H
    Commented Mar 27, 2023 at 14:56

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I would say the phrase, "more durable," is squarely in the realm of marketing jargon and is of little use in determining whether the pads are of the two general categories of disc brake pads, "resin" and "metal", which DO carry connotations related to rotor wear with them. These terms, while helpful in determining pad and rotor compatibility and for a few overall expectations of performance characteristics, are a little misleading from the reality of what disc pads are. Both classes of pads have resin bound fibers of metal (copper alloy)to a more or less degree.

BO3S & BO5S sit within the "resin" category of pad. The characteristic ratings are identical between the two models, as are the compatible hydraulic calipers. Being "resin" class pads they can be used with all rotors compatible with the calipers. Apparently even official Shimano product documents are not free from a marketing opportunity, as one can see Shimano notes how the BO5S is "40% more durable" by means of an asterisk and footnote.

While I would guess the "more durable" claim here refers to resistance to wear and increased lifespan, and/or resistance to performance fade during usage instances that generate a lot of heat. The fact they are classed as "resin" pads, mean we can then only expect a characteristic of generally lower wear to a rotor. Lower wear compared only to the general characteristic of the "metal" class of pads.

Rotors can have compatibility concerns in regard to the type of pad that can be used with them. Some rotors--generally those at the lower tier of the hierarchy, and lower price points--are designed such that only "resin" pads should be used with them. There is no further pad material limitations (like "use only with 40% more durable" resin pads) given other than they be in the "resin" class.. That, then, is the practical information required to equip disc brakes. Your question is a good one, and I wonder too, about the details surrounding the durability statements. The fact is that both resin models may be used for any given compatible rotor. The inference is that a difference in the degree of wear to that rotor is negligible. Certainly not 40 or any significant percentage more or worse wear to a rotor going from a B03 to a BO5.

Obviously, there is a significant degree of difference in rotor wear between a given "resin" class pad and it's "metal" counterpart. Hence, the "resin only" designation of some rotors. And useful rotor life is diminished when metal pads are used exclusively.

Rotor life typically ends when the thickness reaches 1.5 to 1.55mm, depending on manufacturer. You'll get to that mark sooner using metal pads on a given rotor than you would if it's resin counterpart is used. Any anecdotal evidence of a higher degree of wear between pads of the same class (resin or metal) is something I've not seen discussed. It may or may not exist, but there hasn't been a significance tied to it other than one can expect "resin pad" qualities from both resin models. In terms of wear, that would be less than with a metal pad choice.

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