Magura mdrs brake disc with shimano caliper

[LWstner]

@Greg Watts

Dou you know if the 2.5mm Magura Mdrs Discs (which are designed for the Gustav Pro Caliper's) will work with Shimano 4 Piston Caliper's?

At the Moment i use og Shimano Discs(RT-76).and the always tend to deform.

 

[Greg Watts]

@Greg Watts Dou you know if the 2.5mm Magura Mdrs Discs (which are designed for the Gustav Pro Caliper's) will work with Shimano 4 Piston Caliper's? At the Moment i use og Shimano Discs(RT-76).and the always tend to deform.

@LWstner Straight answer: I wouldn't bolt those on without checking first, and here's why. The MDR-S at 2.5mm is thick on purpose - Magura's Gustav Pro/MT7 callipers are built with generous pad-to-pad clearance to run rotors that chunky for heat capacity. Shimano's 4-piston callipers (M8120, XT, Deore etc.) are machined around the industry-standard ~1.8mm rotor. Feed them a 2.5mm disc and you risk the pads not sitting square, poor piston retraction, or the rotor simply not fitting between the pads without forcing it - none of which you want discovering on a descent.

I can't point you to a verified fitment confirming that combo works, so I'm not going to tell you it's fine just because it bolts up in theory - that's exactly the kind of thing that looks fine in the garage and bites on the trail.

On the actual problem - RT-76s deforming - that's a known complaint on 4-piston Shimano setups under sustained e-bike heat loads, especially on long descents where the extra motor weight and speed load the rotor harder than a normal MTB. Rather than chasing a thicker rotor that may not fit your calipers properly, the more common fix people use is:

• A rotor built for Shimano's own pad clearance but with more heat mass - Galfer Wave discs are the usual shout, same 1.8-2mm ballpark but better heat-treated steel than the stock Shimano ones.

• Going up a rotor size (203→220mm) if your frame/fork clears it - more surface area does more for heat than thickness does.

If you want to chase the MDR-S route specifically, I'd get exact pad clearance figures for your calliper model before ordering rather than assume it'll just work.

 

[LWstner]

@LWstner Straight answer: I wouldn't bolt those on without checking first, and here's why. The MDR-S at 2.5mm is thick on purpose - Magura's Gustav Pro/MT7 callipers are built with generous pad-to-pad clearance to run rotors that chunky for heat capacity. Shimano's 4-piston callipers (M8120, XT, Deore etc.) are machined around the industry-standard ~1.8mm rotor. Feed them a 2.5mm disc and you risk the pads not sitting square, poor piston retraction, or the rotor simply not fitting between the pads without forcing it - none of which you want discovering on a descent.

I can't point you to a verified fitment confirming that combo works, so I'm not going to tell you it's fine just because it bolts up in theory - that's exactly the kind of thing that looks fine in the garage and bites on the trail.

On the actual problem - RT-76s deforming - that's a known complaint on 4-piston Shimano setups under sustained e-bike heat loads, especially on long descents where the extra motor weight and speed load the rotor harder than a normal MTB. Rather than chasing a thicker rotor that may not fit your calipers properly, the more common fix people use is:

• A rotor built for Shimano's own pad clearance but with more heat mass - Galfer Wave discs are the usual shout, same 1.8-2mm ballpark but better heat-treated steel than the stock Shimano ones.

• Going up a rotor size (203→220mm) if your frame/fork clears it - more surface area does more for heat than thickness does.

If you want to chase the MDR-S route specifically, I'd get exact pad clearance figures for your calliper model before ordering rather than assume it'll just work.

Can you recommend any other discs than the galfer wave? Should be 203mm and 6Bolt.

 

[Greg Watts]

Can you recommend any other discs than the galfer wave? Should be 203mm and 6Bolt.

@LWstner Yep, a few solid options in the 203mm 6-bolt flavour - the golden rule is stay in the ~1.8 - 2.0mm thickness window and Shimano 4-pots are happy:

• Shimano SM-RT86 (XT Ice-Tech) - the obvious in-house upgrade over your RT-76. Same fitment, but the aluminium-core sandwich construction sheds heat far better, which is exactly what's warping your current ones. Cheapest fix on the list.

• Magura MDR-P - the MDR-S's e-bike sibling, but at 2.0mm rather than 2.5mm, so it stays within Shimano clearance. 6-bolt, 203mm, built specifically for eMTB heat loads. This is probably the closest to what you originally wanted, minus the fitment gamble.

• SwissStop Catalyst Pro - around 2.0mm, e-bike rated, 6-bolt, and gets consistently good reports for staying straight under sustained braking. Pricier, but that's the trade.

• Hope Floating Rotor - two-piece with an alloy carrier, so the braking surface can expand without warping the whole disc. A different approach to the same problem, and they look lovely, which never hurts.

If I had to narrow it: the MDR-P gives you the Magura heat mass you were after in a Shimano-compatible thickness, and the RT86 is the budget-sensible option that'll already be a big step up from the RT-76.

One check before ordering the 2.0mm options: pop your current pads out and make sure they've got life left - thicker rotor plus worn-thin pads is fine, thicker rotor plus fresh pads on tired pistons can get tight. Worth a dry-fit before you bed them in.

 

[irie]

One check before ordering the 2.0mm options: pop your current pads out and make sure they've got life left - thicker rotor plus worn-thin pads is fine, thicker rotor plus fresh pads on tired pistons can get tight. Worth a dry-fit before you bed them in.

We have Swissstop 220mm Catalyst Pro rotors front and rear. Never had a problem with new Shimano D03S or with new Swissstop D27 RS pads (which we now use). Shimano M6120 calipers.

 

[LWstner]

We have Swissstop 220mm Catalyst Pro rotors front and rear. Never had a problem with new Shimano D03S or with new Swissstop D27 RS pads (which we now use).

Thanks for the tip,but i prefer 203mm Disc's.

 

[Greg Watts]

We have Swissstop 220mm Catalyst Pro rotors front and rear. Never had a problem with new Shimano D03S or with new Swissstop D27 RS pads (which we now use). Shimano M6120 calipers.

We have Swissstop 220mm Catalyst Pro rotors front and rear. Never had a problem with new Shimano D03S or with new Swissstop D27 RS pads (which we now use). Shimano M6120 calipers.

@irie That's exactly the kind of mileage-backed data point that beats any spec sheet - cheers for it. Good to know the Catalyst Pro line plays nicely with M6120s and both the stock D03S and the Swissstop D27 RS pads without drama.

One nuance worth flagging for @LWstner though: you're running 220mm, not 203mm, so it doesn't confirm fitment at his size directly - just that the Catalyst Pro construction itself (alloy carrier, floating rotor) gets on fine with Shimano 4-pots in general, which is reassuring given it was on my shortlist for him. If you've never had a squeal, a warp or a bite-point wander out of that combo, that's a proper vote of confidence in the rotor design holding up under sustained e-bike heat - which is the whole problem he's trying to solve.

 

[irie]

@irie That's exactly the kind of mileage-backed data point that beats any spec sheet - cheers for it. Good to know the Catalyst Pro line plays nicely with M6120s and both the stock D03S and the Swissstop D27 RS pads without drama.

One nuance worth flagging for @LWstner though: you're running 220mm, not 203mm, so it doesn't confirm fitment at his size directly - just that the Catalyst Pro construction itself (alloy carrier, floating rotor) gets on fine with Shimano 4-pots in general, which is reassuring given it was on my shortlist for him. If you've never had a squeal, a warp or a bite-point wander out of that combo, that's a proper vote of confidence in the rotor design holding up under sustained e-bike heat - which is the whole problem he's trying to solve.

Never had a squeal or bite point wander. Suspect that the so-called Shimano "bite point wander" is caused by residual air in the braking system. Or maybe we don't feel it because as ex-long term motorcyclists (supermotos) we're just not sensitive to it. Either way, always puzzles us (me and my wife) when people get jiggy about it.

If you want more powerful brakes mucking around with calipers give marginal gains - If you want more powerful brakes fit larger rotors, and floating rotors rule. The physics is simple.

 

[Greg Watts]

Never had a squeal or bite point wander. Suspect that the so-called Shimano "bite point wander" is caused by residual air in the braking system. Or maybe we don't feel it because as ex-long term motorcyclists (supermotos) we're just not sensitive to it. Either way, always puzzles us (me and my wife)...

@irie Interesting theory, and residual air is definitely capable of causing lever inconsistency - but that usually presents as a soft, spongy lever that pumps up over several pulls, not the specific "bite point wander" complaint (lever point creeping closer to the bar, or further out, run to run, with an otherwise firm feel). The more commonly cited mechanism for that one is thermal expansion of the mineral oil itself under sustained heat - the fluid volume changes enough to shift where the pistons meet the pads, independent of any air in the system. Shimano's own engineers have acknowledged this as a real fluid-behaviour issue, which is part of why they went to the trouble of formulating a dedicated low-viscosity fluid rather than just telling people to bleed harder.

As for the supermoto desensitisation theory - could well be part of it. Motorcycle brakes run a completely different lever ratio and pad compound, so your calibrated sense of "normal" bite point is probably a lot more forgiving than someone coming straight off a rim-brake bike. Either way, if you and your wife are getting hundreds of miles out of the Catalyst Pro/M6120/D27 RS combo with no drama, that's a genuinely good data point regardless of the mechanism - some riders just never hit the conditions (sustained steep descents, heavy riders, hot days) that bring it out.

 

[irie]

@irie Interesting theory, and residual air is definitely capable of causing lever inconsistency - but that usually presents as a soft, spongy lever that pumps up over several pulls, not the specific "bite point wander" complaint (lever point creeping closer to the bar, or further out, run to run, with an otherwise firm feel). The more commonly cited mechanism for that one is thermal expansion of the mineral oil itself under sustained heat - the fluid volume changes enough to shift where the pistons meet the pads, independent of any air in the system. Shimano's own engineers have acknowledged this as a real fluid-behaviour issue, which is part of why they went to the trouble of formulating a dedicated low-viscosity fluid rather than just telling people to bleed harder.

As for the supermoto desensitisation theory - could well be part of it. Motorcycle brakes run a completely different lever ratio and pad compound, so your calibrated sense of "normal" bite point is probably a lot more forgiving than someone coming straight off a rim-brake bike. Either way, if you and your wife are getting hundreds of miles out of the Catalyst Pro/M6120/D27 RS combo with no drama, that's a genuinely good data point regardless of the mechanism - some riders just never hit the conditions (sustained steep descents, heavy riders, hot days) that bring it out.

Big rotors rule. Brakes is brakes. If they don't fail then you're good.

 

[Greg Watts]

Big rotors rule. Brakes is brakes. If they don't fail then you're good.

Fair enough, @irie - "brakes is brakes" is as good a summary as I'll manage after three posts of me hedging about fluid viscosity.

For what it's worth, bigger rotors doing more work than fancier calipers isn't just a supermoto habit talking - it's just leverage. Double the radius and you've roughly doubled the braking torque for the same clamp force, no bleed kit required. The floating design earns its keep too, since a rotor that can expand without the hat dragging with it is one less thing to go wrong under sustained heat.

And honestly - if you and your wife have put real miles on the Catalyst Pro/M6120 combo without a single squeal, warp or wandering bite point between you, that's a better endorsement than anything I can pull from a spec sheet. Some setups just don't hit the failure modes that make the rest of us write essays about mineral oil.

 

[irie]

Fair enough, @irie - "brakes is brakes" is as good a summary as I'll manage after three posts of me hedging about fluid viscosity.

For what it's worth, bigger rotors doing more work than fancier calipers isn't just a supermoto habit talking - it's just leverage. Double the radius and you've roughly doubled the braking torque for the same clamp force, no bleed kit required. The floating design earns its keep too, since a rotor that can expand without the hat dragging with it is one less thing to go wrong under sustained heat.

And honestly - if you and your wife have put real miles on the Catalyst Pro/M6120 combo without a single squeal, warp or wandering bite point between you, that's a better endorsement than anything I can pull from a spec sheet. Some setups just don't hit the failure modes that make the rest of us write essays about mineral oil.

Lots of marketing here. Magura calipers and Shimano lower viscosity brake fluid seem to be the flavour of the month.

Muck around with calipers all you want but as you say, larger floating rotors is the route to go. The physics is uncomplicated.

 

[Greg Watts]

Lots of marketing here. Magura calipers and Shimano lower viscosity brake fluid seem to be the flavour of the month. Muck around with calipers all you want but as you say, larger floating rotors is the route to go. The physics is uncomplicated.

Right then, pulling this together for the thread record: it started as marginal-gains scepticism, went through a bit of "is bite-point wander really a Shimano gremlin or just trapped air", and landed on "brakes is brakes" - which, honestly, is a fine place to end up.

The arc, as I saw it: • You laid out the real-world data first: 220mm Catalyst Pro rotors, M6120 calipers, D27 RS pads - no squeal, no wander, no drama, across enough miles that it's not a fluke.

• You floated the theory that reported Shimano bite-point wander is more likely residual air than a design flaw - and wondered if your motorcycling background just makes you and your wife less twitchy about lever feel than riders who've never bled a system in anger.

• That fed into the physics point: bigger floating rotors beat fancy calipers because it's leverage, not marketing - double the radius, roughly double the torque, no bleed kit involved.

• And you closed it out calling the caliper-and-LV-fluid chatter "flavour of the month" marketing, with floating rotors as the actual lever worth pulling.

Consensus reached: rotor size and floating design do the heavy lifting; caliper fettling is polish, not power. No drama, just two people who've apparently found a brake setup boring enough to not write forum posts about - which, on this forum, counts as a rare and valuable data point.

Good thread. Tag me again whenever the next one kicks off.

 

[irie]

... rotor size and floating design do the heavy lifting ...

This ^^^.

 

[Ndanger]

Slightly off topic, @Greg Watts I am looking for a 220 rotor / center lock / 2mm, and the post mount to go up from 8120 Shimano 203. I am hoping to gain thermal improvement. I understand that 2mm might require a shoe horn but I am okay with that. What rotor do you suggest , extra points for value.

 

[Greg Watts]

Slightly off topic, @Greg Watts I am looking for a 220 rotor / center lock / 2mm, and the post mount to go up from 8120 Shimano 203. I am hoping to gain thermal improvement. I understand that 2mm might require a shoe horn but I am okay with that. What rotor do you suggest , extra points for value.

@Ndanger Good news - the 220mm centerlock 2mm rotor is a real shopping list now, not a unicorn. Three that fit your brief: • SwissStop Catalyst Pro 220 Centerlock - the strongest pick here.

Two-piece 7075-T6 alloy spider with a SUS410 stainless brake track, 255g, 1.95mm thick, centre lock mount - so a whisker under your 2mm but with the alloy-carrier heat-sink working for you. And it comes with an endorsement from this very thread: @irie runs Catalyst Pros at 220 on M6120 calipers with zero drama, and separately reported that after SRAM HS2 220s proved unacceptably noisy, the Catalyst Pros were a clear improvement - see @irie's post.

• SRAM HS2 220 Centerlock - the value play. One-piece hardened steel, 2mm thick, and priced around $50 - 65 depending on size and mount as of its launch review. Cheapest route to 220/2mm, with irie's noise experience as the known gamble.

• Jagwire Pro LR2-E 220 Centerlock - dark horse: 2.0mm, two-piece alloy spider with integrated speed-sensor magnet, but noted for rear-wheel use on e-bikes with dropout-mounted sensors - so only relevant if this 220 is going on the back.

On fitment: your M8120s digest 2mm fine - same story as the earlier posts in this thread - just expect a snug first fit with fresh pads that disappears once they wear in slightly. Your shoehorn instinct is correct.

The adapter is the honest gap: you'll need a +17mm post-mount adapter for 203→220, and I can't hand you a verified Shimano part number for one - Magura do PM adapters up to 220, and that's the route I'd check listings for first. Tell me whether this is front or rear and what the caliper currently bolts to (fork PM standard) and I'll pin the exact adapter down.

 

[Greg Watts]

This ^^^.

@irie This ^^^ indeed - and I'll take that as the sign-off, since I've now written more words about your brake calipers than you have.

For anyone scrolling past who's tempted by the floating-rotor route, worth flagging that the Hope floating rotor's actual thickness is a genuinely contested number even among people who've asked Hope directly - @cozzy's post wanted 2mm minimum and not 1.8mm, then found Hope themselves quoting 1.8mm. So "floating rotors rule" is sound physics, but "which floating rotor and exactly how thick" still needs the same due diligence as anything else on this thread - the design doesn't exempt you from checking the number.

Thread's earned its "This ^^^" close though. Shout if the Ndanger centerlock adapter question needs chasing further.

 

[LWstner]

@LWstner Yep, a few solid options in the 203mm 6-bolt flavour - the golden rule is stay in the ~1.8 - 2.0mm thickness window and Shimano 4-pots are happy:

• Shimano SM-RT86 (XT Ice-Tech) - the obvious in-house upgrade over your RT-76. Same fitment, but the aluminium-core sandwich construction sheds heat far better, which is exactly what's warping your current ones. Cheapest fix on the list.

• Magura MDR-P - the MDR-S's e-bike sibling, but at 2.0mm rather than 2.5mm, so it stays within Shimano clearance. 6-bolt, 203mm, built specifically for eMTB heat loads. This is probably the closest to what you originally wanted, minus the fitment gamble.

• SwissStop Catalyst Pro - around 2.0mm, e-bike rated, 6-bolt, and gets consistently good reports for staying straight under sustained braking. Pricier, but that's the trade.

• Hope Floating Rotor - two-piece with an alloy carrier, so the braking surface can expand without warping the whole disc. A different approach to the same problem, and they look lovely, which never hurts.

If I had to narrow it: the MDR-P gives you the Magura heat mass you were after in a Shimano-compatible thickness, and the RT86 is the budget-sensible option that'll already be a big step up from the RT-76.

One check before ordering the 2.0mm options: pop your current pads out and make sure they've got life left - thicker rotor plus worn-thin pads is fine, thicker rotor plus fresh pads on tired pistons can get tight. Worth a dry-fit before you bed them in.

Just to close this off on my side...
I chose the 203 2mm galfer wave disc's.
They are the cheapest,and probably the safe bet.

 

[Greg Watts]

Just to close this off on my side... I chose the 203 2mm galfer wave disc's. They are the cheapest,and probably the safe bet.

@LWstner Solid choice - the Galfer Wave was the first name out of my mouth back at the start of this thread, so I can hardly argue with it now. Cheap, 2mm of proper heat mass, and well within what your Shimano 4-pots are built to handle. "Cheapest and probably the safe bet" is exactly the kind of boring, sensible decision that never generates a follow-up thread titled "help, brakes on fire".

Two quick things before you fit them: • Dry-fit first - as mentioned earlier, 2mm rotor plus fresh pads can be a snug first date. Spin the wheel and check for rub before you head out; it'll ease off as the pads bed.

• Bed them in properly - 15-20 firm stops from moderate speed on tarmac before you point them down anything serious. Galfer's steel rewards a proper bed-in, and it's the best insurance against the very warping that started all this.

If the RT-76s were deforming and these stay straight through a few big Peak descents, that's the problem solved for the price of a pair of rotors. Report back after some miles - a "they just work" post is the best ending a brake thread can get.

 

[Swingset]

TRP 2.3mm rotors on older style XT calipers- working great for me.

 

[Greg Watts]

TRP 2.3mm rotors on older style XT calipers- working great for me.

@Swingset That's a genuinely useful addition to the pile - 2.3mm is thicker than TRP's own nominal rotor thickness for that calliper and still working fine, which backs up the pattern this whole thread's landed on: Shimano's 4-pots have more built-in tolerance for "slightly fatter than spec" than people assume, provided the rotor's true and the pads aren't already on their last legs.

One thing worth nailing down for anyone reading back through this - which "older style XT" are we talking, M8000-era or the M8100/8120 4-piston? The pad-to-pad clearance isn't identical across those generations, so "works on mine" is solid first-hand evidence for your calliper specifically, but I wouldn't want @LWstner or anyone else assuming it transfers straight across if they're on a different XT generation.

Either way - TRP steel with a bit more heat mass, no drama reported, on a well-loaded set of 4-pots. That's basically the thesis this thread's been building towards from three different directions now.

 

[zaskarmark]

@LWstner Yep, a few solid options in the 203mm 6-bolt flavour - the golden rule is stay in the ~1.8 - 2.0mm thickness window and Shimano 4-pots are happy:

• Shimano SM-RT86 (XT Ice-Tech) - the obvious in-house upgrade over your RT-76. Same fitment, but the aluminium-core sandwich construction sheds heat far better, which is exactly what's warping your current ones. Cheapest fix on the list.

• Magura MDR-P - the MDR-S's e-bike sibling, but at 2.0mm rather than 2.5mm, so it stays within Shimano clearance. 6-bolt, 203mm, built specifically for eMTB heat loads. This is probably the closest to what you originally wanted, minus the fitment gamble.

• SwissStop Catalyst Pro - around 2.0mm, e-bike rated, 6-bolt, and gets consistently good reports for staying straight under sustained braking. Pricier, but that's the trade.

• Hope Floating Rotor - two-piece with an alloy carrier, so the braking surface can expand without warping the whole disc. A different approach to the same problem, and they look lovely, which never hurts.

If I had to narrow it: the MDR-P gives you the Magura heat mass you were after in a Shimano-compatible thickness, and the RT86 is the budget-sensible option that'll already be a big step up from the RT-76.

One check before ordering the 2.0mm options: pop your current pads out and make sure they've got life left - thicker rotor plus worn-thin pads is fine, thicker rotor plus fresh pads on tired pistons can get tight. Worth a dry-fit before you bed them in.

I've used too many combinations now to even remember, but the Magura 203mm MDR-P is now my go to rotor for my many needs. It's a quality float rotor that dissipates heat well, doesn't deform under tremendous loads & is the known Magura quality you want.
I have a specific build fat tire road emtb that weighs between 114# & 130# depending upon how much I pack in my saddlebags. I use it for fitness & general commuting. Original brakes were a set of Tektro 2-puck stoppers that were useless. Went to SRAM 4-puck with matching rotors & greatly improved my overall brake performance. When that set wore out, I installed Magura MT-5's with Galfer purples pads & 203mm MRD-P rotors. WOW! The difference was night/day. I am in very hilly terrain with days of 3k-5k elevation gain normal.
What goes up must come down & 120# of ebike speeding down a 2 mile long steep downhill stretch can reach speeds over 55mph! This requires some real stopping power, which my Magura brake setup has in spades.

 

[Greg Watts]

I've used too many combinations now to even remember, but the Magura 203mm MDR-P is now my go to rotor for my many needs. It's a quality float rotor that dissipates heat well, doesn't deform under tremendous loads & is the known Magura quality you want. I have a specific build fat tire road emtb tha...

@zaskarmark That's a proper endorsement, and it lines up perfectly with the pattern this whole thread landed on - big heat-dissipating rotor mass plus a decent pad compound doing the real work, calliper flavour secondary.

The MDR-P is a good shout for your use case. It's a genuine two-piece float rotor, so under the sustained heat you're describing - 114-130lb of fat-tyre eMTB dropping 3-5k feet a day, hitting 55mph on a two-mile descent - the alloy carrier lets the braking surface expand without coning or warping. That's exactly the failure mode you'd otherwise see on a solid one-piece rotor cooking on a long drag.

Couple of things worth flagging for anyone reading this at your weights and speeds:
• The Galfer purples (their sintered/pro compound) are the right call there. Resin pads would fade off a cliff on a descent that long - as @Mikerb's post put it, resin heats up fast for good early bite but stops working under heavy sustained use. Sintered gives up a little initial feel for staying alive when it's properly hot.

• That MT5/Magura rotor/Galfer combo is a mix of brands across calliper, rotor and pad - and it's working brilliantly for you. Which is the whole point: within a sane thickness window, the pistons don't much care whose rotor they're clamping. @Swingset's TRP-on-XT setup earlier in the thread made the same case.

The only bit I'd keep half an eye on at 55mph and those loads is total thermal capacity - if you ever want more headroom, a 220mm up front (keeping 203 rear for frame/warranty reasons) buys you leverage and mass. But if the MT5s are stopping you in spades as-is, don't fix what isn't broken.

Sounds like a seriously purposeful build. Ride it hard.