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These calipers aren't supplied with rotors, so the answer to the very similarly titled What features make a disc brake caliper unsuitable for use with other than resin pads can't possibly apply.

Shimano MT200 brakes are listed by several dealers as compatible only with resin pads. I have some spare semi-metallic pads, and Shimano make metal pads that fit the form factor - so why aren't they compatible?

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  • Heat tolerance can be the only answer. Can we find figures on heat generated by resin vs metallic?
    – Noise
    Mar 22 at 13:06
  • @JoeK I've been discussing this with some engineering cycling friends and we're thinking along similar lines. But heat generation is likely to be pretty much the same: consider stopping on a flat road - the brakes have to turn the kinetic energy into heat. There may be a tiny amount going into wear (breaking bonds in the pad material) but this must be tiny as wear is slow. So it would seem to have far more to do with heat distribution...
    – Chris H
    Mar 22 at 13:09
  • ...(since writing the Q) I've been looking at figures for thermal conductivity (TC) of various materials, but can't even pin down the materials some say sintered copper some say bronze and there's a factor of 5-6 in the thermal conductivity. Then we could do with knowing the porosity, but we could guess at about 60% of the bulk thermal conductivity. Resins vary hugely in TC, and we don't know much about the ones used in brakes. The best approach the TC of bronze, while the worst are an order of magnitude lower
    – Chris H
    Mar 22 at 13:12
  • As a heavy rider and nervous descender I'm still considering mechanical brakes, but that's also got a lot to do with the generally poor promax ones I've got at the moment
    – Chris H
    Mar 22 at 13:14
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    @Criggie that's good to know, thanks. They seem like astonishingly good value - a full setup, pre-bled costs about as much as just the caliper for the mechanical brakes I was considering, and Shimano stuff tends to be reliable and well thought out. The Promax ones I have are neither - practically impossible to bleed even with one of the mounting bolts removed (which it has to be as it blocks the bleed screw)
    – Chris H
    Mar 23 at 8:51

3 Answers 3

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Since the question is phrased in the abstract and not with regard to one model, here is the abstract answer: While in general calipers offer a choice of pad compounds, calipers do differ in how well they manage heat, and there are various expense- and weight-adding design elements some calipers have that help them manage it much better than others. Metal pads in particular tend to go along with riding styles that involve sustained heavy braking. The kind of riding where the pros of metal pads outweigh the cons is also the kind of riding where hypothetically a manufacturer could see fit to say that recreational-level caliper model X is outside of its intended usage, and will be overly prone to fade, need frequent bleeding, and so on. In practice, manufacturers issue intended use guidelines for their brake models based on riding type and loads carried. I haven't seen any explicitly do it by saying a certain pad compound is incompatible.

Shimano likes to stick to a tech support and liability management strategy of saying "this caliper takes this model pad and can be used with these three rotors" and the like, even though there are other pads and rotors in their lineup that may be physically compatible in terms of form factor. For example:

BR-MT200 specs

There are many other rotors, pads, and levers in the lineup that are physically compatible in practice, but these are the ones that are warranted and that they stand behind. It is easy as a consumer to criticize this practice and see cynical aspects to it, and it can be frustrating at times to deal with the world of bike parts compatibility as presented by Shimano because it often leads to a need to read between the lines just to make things work or do the right thing, especially when working with old parts, but one must also understand they've chosen to be in the business of selling bike parts systems that are designed to work together. That's simply their prerogative, and note also that while it may result in a lot of nuisances for people dealing with their parts out in the real world, they make almost all their money selling to bike brands who are speccing out bikes and need systems of parts that will just work, which is part of where the "X works with Y and Z and that's it" ethos comes from. Yes they have to counterbalance that against the risk of reputational damage from their prissiness about these issues, but it's self-evident that the balance they strike works for them.

In this case, Shimano doesn't scream out loud in their own literature that BR-MT200 must only be used with resin, but the rotors they spec for it are resin-only (cheap, not as hard) and the pads they spec for it are resin. They're trying to guide people away from pushing the brake beyond what it's really made for.

BR-MT200 is a good example of a brake that hotrods pretty well but was still only developed and marketed as an entry-level, recreational product. If it does better than they may have expected under demanding conditions and people are pushing it hard with some success, that's not necessarily Shimano's "fault" and it still doesn't oblige them to recommend it as anything more than an entry level product. Some manufacturers have taken to speccing it on cargo ebikes, which I think is unwise and pushing everyone's luck too much, even though it mostly works out okay. In my opinion one of the things we're all just going to have to see about is how well they and other plastic-piston brakes hold up over time on such bikes, but the result will be interesting either way.

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    That's a nice summary of the big picture - thanks. I come at this as very much a recreational rider on MTB (XC style and general exploring) but one who descends quite slowly - like many recreational riders when we venture onto the (easier) red trails. I'm also pretty heavy and thinking about bikepacking, while I like metal pads from big rides on my tourer in hilly areas. I'm probably OK with resin on the MTB anyway
    – Chris H
    Mar 23 at 8:54
  • BTW my first experience of disc brakes was mechanical ones on heavy but non-cargo e-bike (Tektro) and I was thoroughly unimpressed, but I can see how basic disc brakes might fit in to the model of a rider who doesn't ride hard, and the maintenance is to take it into the shop a couple of times a year. If the pistons are plastic, that will limit the heat transfer to the fluid compared to metal - so long as the plastic doesn't cook, but I'd expect the resin o the braking surface to smoke before that
    – Chris H
    Mar 23 at 8:57
  • @ChrisH I believe the pistons on even the MT200 are a fancy high-temp phenolic resin. It would be a huge safety liability to have polyethylene pistons or something haha.
    – MaplePanda
    Mar 23 at 17:55
  • @MaplePanda that's what I expect too. Such resins have fairly low thermal conductivity so won't transfer too much heat into the oil - but quite a bit could still get there in the end
    – Chris H
    Mar 23 at 18:09
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    @ NathanKnutson I have a little bit of experience with engineering plastics (and also oven-proof phenolic resin handles on cooking pots). Assuming @MaplePanda is right with the material, thermal and wear properties can be very good, with wear in particular being better than aluminium. Tolerance to plausible contaminants should be good too, and they should be less likely to bind to the mating parts (e.g. the fixed pad adjusters in BB5s can get very stiff) . I'd be a little reluctant to be a very early adopter on any radically new brakes but the basic design has been around for long enough.
    – Chris H
    Mar 24 at 10:06
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I've done exactly that - I've used metal pads in the BR-MT400 brake calipers. As a pretty heavy rider (93kgs) that rides lots of pretty steep descents (1000 meters vertical descend at 10km) I've had lots of problems with brakes that didn't work as good at the end of the descends as in the beginning.

So I've changed the pads to metal pads and first of all everything was better. But after a one of my most intense descends the caliper lost lots of oil. I am happy that this just happened after the descend when it was standing in my garage. The next time I drove the levers were mushy and I had to fill and bleed the brake.

After that everything worked fine again.

I've changed to semi-metallic pads (Jagwire Sport Semi-Metallic) and everything was fine again.

Still not happy with the perfomance of the brakes I've changed to 4 pod brakes and hope that this solved my brake problems.

tl;dr I've used metal pads with the BR-MT400 caliper and it looked like it overheated. After switching back to semi-metallic pads and bleeding the brake everything worked fine again. So I'd say that these calipers are not able to handle the increased heat that can occur if you're using metal brake pads

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While "heat generation is likely to be pretty much the same", heat distribution is likely quite different. The thermal energy is far from equally divided between a resin brake pad (and ultimately the caliper) and the rotor.

With a resin pad, the rotor likely takes most of the heat, sparing the caliper from overheating. Nicer calipers have what looks like a built-in heatsink, even if they are not declared as such. The rotor is already a natural heatsink. The surface that was most recently heated has moved on and is now in contact with air to cool down. Since it will be cooler when it comes around to the pad, and since the low thermal coefficient of a resin pad would not have enabled it to move the heat away too quickly, the rotor will be the one to absorb most of the generated heat. Some rotors have (what is declared to be) a heatsink. They would be a better bet for use with metal pads, if perhaps only marginally because they cease to be a heatsink for the calipers once the brake lever is released. (The only trouble perhaps is that on long descents you wouldn't be able to choose between quick-and-hard braking and long-and-mild braking.)

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  • Of course some pads have a heatsink too (not ones that would fit the brakes I'm getting)
    – Chris H
    Mar 23 at 17:21

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