MTB rotors to replace Ultegra 8000?

Discuss light weight issues concerning road bikes & parts.
jeepntrek
Posts: 21
Joined: Wed Jul 25, 2018 11:23 pm

by jeepntrek

I’m sitting here confused about 1 component choice on my new Emonda ALR build and unsure if i should make an objection to the builders at my local shop.
On the build list i chose ultegra disc. I go in yesterday as the bike is getting partly built (waiting on groupset) but they already have rotors on? I was confused. They explain.
My LBS boys decided i needed heavier duty braking than the Ultegra discs so they’ve opted for Shimano XT rt-81 rotors AKA MtB rotors??? does this sound right?
These guys have serviced my mtb’s for years and my gravel/commuter for the last year, and have been out riding with me here and there over the years. Needless to say, they definitely know my riding style. So, I want to believe them but I was looking very forward to the style of those Ultegra disc brake rotors AND everything I read says the Ultegra has better heat dissipation.

Basically, am I right to want what I had agreed (especially b/c they are so pretty :wink: ) on or are the MtB discs actually offering superior stopping power?
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by Weenie


TurboKoo
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by TurboKoo

No, most of the times it’s about availability.
Same with pros. They demanded so much discs before Dura Ace disc production was running that they got Mtb discs.
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Hexsense
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by Hexsense

No, MTB rotor is not better at breaking for the same size.
Their Ice tech XTR rotor weight a tiny bit less than Dura-ace rotor (both still weight more than Sram CenterlineX) . So you could be able to run bigger rotor size for less of extra weight. And bigger rotor= better breaking.
Basically, A solid road 140mm maybe able to shred heat like mtb 160mm rotor because of their more efficient heat sink design, and being more aero since it is a smaller disc. But in term of breaking performance, 160mm rotor still win a 140mm. Nothing except few grams of weight stop you from running road 160mm rotor though.
Another note is road rotor size stop at 160mm as the biggest size. If you really need 180mm or larger on road (i doubt it) then yeah, you need MTB rotor.

Also, if front rotor and rear rotor are the same size, it's either front is too small or rear is too big. They don't face the same force or heat, which dictate rotor size.

If anything else is better on MTB, it maybe default brake pad. Road disc likes to use organic pad because it is quieter. But many MTB shipped with Metalic pads which brake better but noisier. Again, nothing stop you from changing disc brake pad.

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kdawg
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Joined: Wed Nov 20, 2013 9:10 pm

by kdawg

Are metallic pads really better? I thought they were harder sonlast better in mucky conditions but the softer material of organic pads was grippier - and that is my experience.
I'm left handed, if that matters.

TobinHatesYou
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by TobinHatesYou

Resin pads will have more initial bite and better modulation, but sintered pads are going to have more overall stopping power, are less likely to fade and will last a lot longer for people who do a lot of elevation.
Last edited by TobinHatesYou on Tue Aug 07, 2018 9:34 pm, edited 1 time in total.

FIJIGabe
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by FIJIGabe

TobinHatesYou wrote:
Tue Aug 07, 2018 9:20 pm
Resin pads will have more initial bite and better modulation, but sintered pads are going to have more stopping overall stopping power, are less likely to fade and will last a lot longer for people who do a lot of elevation.
I was about to post this. I've been running metallic pads for several seasons on my CX bike, and the pads still have quite a bit of life left in them. I use the same pads for gravel riding, too, so it gets a fair bit of use.
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jeepntrek
Posts: 21
Joined: Wed Jul 25, 2018 11:23 pm

by jeepntrek

my apologies, they are 160mm rotors on both front and back.

Valbrona
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by Valbrona

Never trust someone with tattoos like that to wash your car let alone build your bike.

shimmeD
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by shimmeD

LOL :lol: even though it can be construed as skin prejudice.
Less is more.

MichaelB
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Joined: Tue Apr 22, 2008 4:31 am

by MichaelB

Hexsense wrote:
Tue Aug 07, 2018 8:11 pm
No, MTB rotor is not better at breaking for the same size.
This. The new R8000 rotor would be better at heat shedding than the RT81.

I have used a variety of IceTech rotors, RT86, RT81, RT68, and RT70 (some 6 bolt & some CL), and they all work the same.

jeepntrek
Posts: 21
Joined: Wed Jul 25, 2018 11:23 pm

by jeepntrek

Welp, decided “*f##k* it” and ordered a cracking set of Dura-Ace 160mm (probably overkill for 150 pound me) rotors, that black is too damn sexy to pass up!

Hexsense
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by Hexsense

At that weight, instead of 160mm set. Do 160mm front and 140mm rear. 160mm in the back is way overkill for your weight and it will locked up easily.
Using bigger front than rear so you don't have to be very deliberate about pressing rear brake significantly more gently with less force than front brake. It is actually easier to use than using same size rotor.
Flat mount brake can use either size with different adapter configuration anyway.

TobinHatesYou
Posts: 1773
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Locking up disc brake rotors is pretty damn hard. If you do it frequently, the solution isn't smaller rotors...it's replacing your ham-fists with fingers and improving your braking technique.

jeepntrek
Posts: 21
Joined: Wed Jul 25, 2018 11:23 pm

by jeepntrek

thanks tobin! yeah i have been on equal-sized front and back disc rotors on my MtB and gravelcross commuter, and have never experienced this insanely easy locking up of the rear wheel I always read so much about. If i experience otherwise, I will definitely let you know you were right, Hexsense!

I appreciate everyone’s input!

TobinHatesYou
Posts: 1773
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

I wish I got along with the very sleek looking RT-900 rotors. I've have basically decided that SRAM Centerline X rotors are objectively better overall than the Shimano RT-900 or Campy H11. It's just that they are the ugliest of the three...

by Weenie


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