Help Disc Brake Questions

Conrad

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#1
Hi all

We we're having a discussion about disc brakes in another thread so I thought I'd start a disc brake thread and pick everyone's brains. I'm experimenting with disc brakes for the first time and I've got a few questions. I recently built up a gravel frankenbike and I've currently got 160mm rotors on the front and back. I changed the front pads to sintered and the rear are still the standard resin pads. A couple of weeks ago I went down Wada and it fried my front rotor and the resin pad. I have since replaced the front rotor and installed sintered pads.
Here is a picture of the worn rotor (notice how far down the rotor the wear extends - thanks for pointing this out @luka ). I'd like to upgrade to a 180mm rotor on the front wheel, what rotor should I use, which will better match the braking surface of the pads (wide rotor?) and will also work well with sintered pads? Thanks in advance for your insights.

screenshot_20180810-085728-png.16746


I'm leaning towards getting HS1 rotors. Here is a diagram of HS1 rotors showing the position of the pads and the "wear line":
 
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#2
It's your money, and I'm no expert, but everything I've read suggests 180 mm rotors are overkill for road/gravel use. The extra size is really just for dissipating heat, and - unless you're exceptionally heavy and very timid on descents - you won't generate more heat than a 160 mm rotor can safely radiate. You'd need an adapter to move the position of the caliper, and the different distribution of torque will alter the stresses in the fork/mounting system and could lead to early failure.
 

Conrad

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#3
It's your money, and I'm no expert, but everything I've read suggests 180 mm rotors are overkill for road/gravel use. The extra size is really just for dissipating heat, and - unless you're exceptionally heavy and very timid on descents - you won't generate more heat than a 160 mm rotor can safely radiate. You'd need an adapter to move the position of the caliper, and the different distribution of torque will alter the stresses in the fork/mounting system and could lead to early failure.
You made a lot of good points, and I agree that the adapter would change the stress that the mounting points would be under. I'm concerned more about rotor and pad wear than overall braking force. Wada and Kobu tunnel wore through my front rotor and pads so I want to find a way to get a longer service life out of my brakes. I don't know much about disc brakes but I was hoping to achieve this by reducing the force applied to the front rotor and if possible finding a rotor which is a better match for my sintered pads. Thanks for your input, you've given me some food for thought.
 

luka

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#4
my caliper arrived and the rotor should come tomorrow morning. be forewarned about my million questions on installation and bedding in haha
 
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kiwisimon

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#5
I'm concerned more about rotor and pad wear than overall braking force. Wada and Kobu tunnel wore through my front rotor and pads so I want to find a way to get a longer service life out of my brakes.
How many descents did it take to wear out the pads and rotors? And who set up the brakes on your current bike?
 

Conrad

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#6
How many descents did it take to wear out the pads and rotors? And who set up the brakes on your current bike?
The brakes only have about three or four decent rides on them (Wada, etc) plus commuting for about six weeks. They seemed to be holding up okay until that last Wada ride where I think they overheated and got chewed out. In answer to your second question, I usually build my own bikes, which yields mixed results, but I kind of enjoy learning as I go.
 

luka

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#7
BTW, here is the elaborate answer from TRP which puts my mind at rest about them being "narrow" or "wide":

Avoid confusion altogether and purchase TRP rotors, all of which are compatible with your HY/RD system.
 

luka

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#8
for your continued amusement, my reply:

Dear Dustin,

Thank you for your reply. My predicament is that TRP rotors are
not readily available where I live: Tokyo - Japan. On the other hand,
as you can imagine, Shimano products abound.

So if I've really reached customer service, and not sales dept,
please see if you or someone else can answer my query about
your product. There are at least 3 more riding buddies who
are now waiting for update on this from me (all on HY/RD),
and while not a statistically significant market share by any
means (even if we include our whole cycling circle we could
reach by word-of-mouth) surely you can see your interest
(if not your job duty) in addressing concerns we collectively
have and leaving a good impression of your company with
people already very interested in it and its products, rather
than avoiding our issue altogether for a cheap try at sales talk.

As customers who have bought a TRP product, do we mean
anything to the company except a potential market to sell more?

Hope you find time to put together (or point me to already
existing?) a detailed reply on dimensions and compatibility
of these calipers/pads so we can put them to good use
without unnecessary expenditure on try-and-fail rotors
soon.

More concretely, since we are talking about road bikes here,
people are looking into SM-RT800, SM-RT900 and SM-RT81
types, all of which say "narrow" and have those cooling wings
which could potentially interfere.

Regards,
Luka B
 
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Conrad

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#9
BTW, here is the elaborate answer from TRP which puts my mind at rest about them being "narrow" or "wide":

Avoid confusion altogether and purchase TRP rotors, all of which are compatible with your HY/RD system.
Did the narrow/wide rotors terminology turn out to be a Shimano only thing? I'm using Shimano compatible pads so I might go for Shimano rotors that can handle sintered pads.
 

luka

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#10
"narrow" and "wide" terminology is indeed Shimano-only, as far as I can tell. or to put it more precisely, only Shimano have goon through the work of getting this out to people, as I have a feeling others are simply avoiding the compatibility problem which is present. especially if you consider the growing overlap between road and MTB
 
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kiwisimon

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#11
Just say ShimaNO to funky standards unless you are looking at forced compliance. Many have learnt that Shimano does not play well with other brands.

OTOH if you burned through the disc pads and rotors in a few weeks I think there may have been operator error at either installation or application. There should be absolutely no need to use 180mm rotors on a gravel bike. Something was maybe not lined up. Do you have a picture of the old pads? Will probably tell us more than the scarred rotor.
Hope this gets sorted out for you.
There is also no shame in going to a professional shop when you are out of your area of expertise. It's actually how I learnt a lot.
 

luka

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#12
Just say ShimaNO to funky standards unless you are looking at forced compliance. Many have learnt that Shimano does not play well with other brands.
my problem is, I don't see any other rotors (except cheap non-brand Chinese stuff I'm not going near to) readily available for order here (amazon.jp, rakuten, yahoo.jp/shopping etc) and am forced into thinking and looking into how will these work or won't with my now non-Shimano calipers you see
 

Conrad

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#13
I think there could have been some alignment issues as @kiwisimon pointed out. Unfortunately I don't have the old pads anymore, but from memory as I was coming down Wada I was getting plenty of braking force, without any strange noises, but towards the bottom of the hill my front brakes started to squeal and fade. I'm pretty new to disc brakes but I'm guessing that's down to overheating (and also misalignment). When I got home I realised how much meat had been taken off the front rotor and pads.

Here is an interesting chart about narrow/wide resin/sintered rotor compatibility, I found it here, it's pretty old but there's some useful info:

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kiwisimon

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#15
do you have shimano centerlock hubs? If so get http://www.cb-asahi.co.jp/item/64/20/item100000032064.html or an adapter and open up a heap of choices. http://www.cb-asahi.co.jp/item/93/15/item100000011593.html

I get your frustration but your letter to TRP is perhaps better directed to the distributor who sold you the parts not the manufacturer? They are after all the people who took your money.
Dear Dustin,

Thank you for your reply. My predicament is that TRP rotors are
not readily available where I live: Tokyo - Japan. On the other hand,
as you can imagine, Shimano products abound.
didn't you get rotors with the units you bought? http://www.akiworld.co.jp/trp/d-HYRD-160.html
they should ship with mounting hardware, rotors and 6 bolts to attach the rotors to the six bolt hub.

https://item.rakuten.co.jp/qbei/pi-627839/ if you have Shimano centerlock hubs.
 
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luka

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thanks @kiwisimon , that last rakuten item just might be what I'll buy next. in short, I only got the caliper from some rakuten place which had the best offer (12,800 yen) but no rotors. I have centerlock and got the only "wide" rotor I could find on Amazon because I wanted a quick delivery (it's only about a 1,000 yen SH-RT54). now, finally I've set them up, outer cable shortened, inner cable 2 cm short so had to put a new one, 2x meishi on the right, nothing on the left to finally centre the bloody pads, but am now done. only have to bed them in tomorrow and hopefully conutinue commuting as normal from Monday. I've confirmed that these are also "wide" calipers, as the pads hit the braking surface to the last mm, but do not go over on the rotor arms. unsure if the pads I've got there are metallic or resin (or mix) so if the rotor goes butter on me soon I'll get that TRP-25 (proly gonna buy it anyway as a spare, or will move the new I got on the front now to the rear, as I've learned that in my current setup as well the rotors are too narrow for the pads, see the pic)

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the old spent rotor

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kiwisimon

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#17
Those discs are pretty entry level and can/should only take resin pads. Maybe you should slip the pads out and check if they are metal or resin. Not sure what the meishi cards are for? Won't the caliper self centre?
 
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luka

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#18
yeah the disk rotor is pretty entry level, just the 1st thing I could get my hands onto. will get those TRP-25 now that you have helpfully point them out. this is my 105 groupset commuter heavy bike, workhorse thing, so not a lot in the budget for it. I'm kinda scared to get the pads out. don't know much about the pistons behind them, and the whole oil setup? even if I could get them out, how do I know if it's resin, or mixed, or metal? the meishi were indeed needed to centre the caliper when newly installed. I don't have the proper alignment tool or anything else readily available. they're done their job now, and rest peacefully in the trash can
 

luka

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#19
got the TRP rotor ordered now. better to put that from the get go, and bed it properly from the start. the shimano one will go to the rear, with the cheaper, mechanical caliper anyway

 
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kiwisimon

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#20
so now when you pull the lever the pads both contact the disc at the same time right? You might want to check that after you bed them in. Take it slowly bedding them in. The new pads when you bought them the description should tell you if they are resin or metal. I think @bloaker has these on his bike (one of the bakers dozen) so I'll bow out and defer to his experience. good luck and remember if you aren't sure just ask. It can save a shit load of cash and even skin.
 
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