RT-MT900 vs RT-CL900

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cleanneon98
Posts: 513
Joined: Sun Aug 06, 2023 2:26 pm

by cleanneon98

Currently using 160mm front and rear MT900 rotors (XTR line). I've been debating on getting the CL900 (Dura Ace line) same size just for looks but wondering if there is any performance difference. The XTR is a few grams lighter and has larger looking cooling vents.

MT900
IMG_6650.jpeg
CL900
IMG_6649.jpeg
IMG_6649.jpeg (103.09 KiB) Viewed 947 times
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OtterSpace
Posts: 392
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Location: California Silicon Valley

by OtterSpace

The first question I'd ask is what kind of riding you do. For sub 20% and non-technical descent road riding in the dry you will likely be fine with something like a 160f/140r galifer 1 part rotor which is much lighter and a good price.

Answering the direct question the new rotors are heavier but perform better for the same heat load. Does this matter for your use case? Only you can decide. Shimano rotors are near if not best per rotor size thermally with each version getting better but the latest version being heavier than the previous option.

In general Shimano's high end rotors perform very well thermally but are comparatively heavy, tick from different rates of metal deformation in their sandwitch construction, and fall off a cliff when near the wear mark as the outer steel layers flake off. Also generally speaking there are three types of rotors, 1 part, floating 2 part which isolate the rotor from the carrier (central spider), and semi 2 part pinned construction like Shimano which semi isolate the rotor from the carrier but still transfer some heat.
  • 1 part is best for weight but is often over optimized for weight over performance, can deform laterally more than other options, and transfers heat to the hub.
  • floating rotor removes the specific heat issues listed for 1 part rotors but offers thermal mass only in the floating surface which at smaller sizes can be fairly low.
  • semi 2 part is a compromise but in smaller (road) rotor sizes often offers more thermal mass than the above two types.
Shimano unified their mountain and road rotors starting with MT900 so I just refer to them by level (XTR/Dura-Ace, Ultegra/XT, etc).

At a high level comparing between the Dura-Ace level rotors:

The older Dura-Ace SM-RT900 (140 & 160 size only). This rotor is heavy and aero and prone to ticking which shows that is is more thermally limited compared to future versions. I'd avoid these unless you are super marginal gaining a TT or long event bike. It's ticking was at least partially exacerbated by the pad clearance from previous gen Shimano Hydro calipers.

The older Dura-Ace level RT-MT900 (is available in all road & mtb sizes). This rotor is the lightest shimano option with less reported ticking than the previous gen but worse than other options from personal experience.

The current Dura-Ace level RT-CL900 (is available in all road & mtb sizes). This rotor is heavier than the previous version with less reported ticking than all older option but still worse ticking than other options from personal experience.
  • Shimano's marketing says the following:
  • Quieter than ever, but with superb, consistent braking performance on any long, steep descents thanks to excellent heat dissipation
  • The new arm shape is more robust, leading to quieter operation
Personally I would only sidegrade between the latest two gens if you are running into severe thermal braking issues like fade & squeal but I wouldnt bother due to ticking which likely gets better but is inherent to the Shimano approach. Also I'd start with a front only swap where heat loads are higher.

Lastly this wasnt asked but Dura-Ace level and Ultegra level rotors weigh the same. Dura-Ace level adds a thermal paint for slightly better thermal performance according to Shimano's marketing. This is the same for all iterations of Shimano rotors. Also the thermal coating is easier to clean but likely doesnt make much of a performance difference unless you are doing steep 20%+ and technical descents
paint.PNG
Last edited by OtterSpace on Mon Jun 10, 2024 4:21 am, edited 1 time in total.

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satanas
Posts: 370
Joined: Sat Jul 04, 2020 5:45 pm

by satanas

FWIW, I had terrible howling in any wet weather with the RT-900 rotors (160f/140r with DA 9170 calipers), and both newer generations have been said to be better in this regard. The latest (CL-900) are supposed to be the quietest. The noise from the older rotors was extemely unnerving to me, but YMMV.

cleanneon98
Posts: 513
Joined: Sun Aug 06, 2023 2:26 pm

by cleanneon98

Thanks for the detailed response. I'm looking to stick to Shimano rotors so I guess I'll stick to XTR unless the styling really compels me it seems like there's no real benefit to DA over XTR for me
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Greeners
Posts: 31
Joined: Fri Apr 26, 2024 10:13 am

by Greeners

Surely the pad compound being used makes a difference? Std organic pads are awful & tend to overheat easily, not to be confused with the disc not withstanding the heating from prolonged use. (but not mentioned)

cleanneon98
Posts: 513
Joined: Sun Aug 06, 2023 2:26 pm

by cleanneon98

Greeners wrote:
Mon Jun 10, 2024 11:56 am
Surely the pad compound being used makes a difference? Std organic pads are awful & tend to overheat easily, not to be confused with the disc not withstanding the heating from prolonged use. (but not mentioned)
I'm using the L04c pads here
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parajba
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Location: London, United Kingdom

by parajba

I am building a new bike with 9250. I do technical mountain descends. On my old bike I have the MT900.
What' do people buy in these days? CL or MT? I am not interested in lighter brands and I would stick with Shimano rotors. Thanks!
I think the MT still look better.

BernieMoves
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by BernieMoves

CL, they warp less.

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cleanneon98
Posts: 513
Joined: Sun Aug 06, 2023 2:26 pm

by cleanneon98

So I ended up making the switch just for a styling standpoint. They do seem a little quieter under normal operation, I can't say much yet because I just bedded the pads to them and did a little local thing but tried a few hard stops and they felt good. I'll see how they do as far as performance and the ting ting ting thing after some longer descents and update again.

One thing the stock photos don't show well, the XTR rotor has a gloss black but the Dura Ace black is a matte finish.
TREK Madone Gen 7 SLR - 7.43kg
TREK Fuel EX Gen 5 - overbuilt and overweight

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