road disc brakes

hamishm
Posts: 763
Joined: Wed Oct 28, 2009 11:31 pm

road disc brakes

Postby hamishm » Tue Aug 30, 2016 7:48 pm

I'm planning to buy a frame and parts and build a bike myself, and it'll have disc brakes. But I'm a bit confused about what bits are required exactly for the brakes.

The frame specs says it needs post mount brakes and 160mm rotors. I gather there are post mount brakes and there are flat mount brakes? If I was going to order the Shimano R785 or RS785 brakes for example how would I know if it's the post mount?

I notice that the online shops have various adapters (eg at https://www.evanscycles.com/components/ ... ake_spares) - what are these for?

Then with regard to rotors there is centre-lock and 6-bolt mounting, and I just need to choose whichever matches the wheels?

thanks and excuse the ignorance...!

eeksll
Posts: 2631
Joined: Tue Oct 20, 2009 10:36 pm

Re: road disc brakes

Postby eeksll » Tue Aug 30, 2016 9:46 pm

don't know anything about the actual road disc brake.

The adapters are so you can use different sized disc rotors.

Yes regarding 6 bolt / centerlock, get the ones that match your wheels. You can get adapters, I use a centre lock to 6 bolt adapter myself.

User avatar
Duck!
Expert
Posts: 9857
Joined: Tue May 21, 2013 8:21 pm
Location: On The Tools

Re: road disc brakes

Postby Duck! » Tue Aug 30, 2016 10:29 pm

R/RS785 brakes are post-mount; they're not available in flat-mount (flat-mount calipers are RS405/505/805 and not-yet-available R9120 Dura-Ace).

If your frame and fork are post-mount, and you're not planning on using larger than 160mm rotors, you won't need any adaptors, but you also won't be able to use 140mm rotors, because you won't get the calipers low enough.

Although it has its detractors, Centrelock is a much simpler system, using a splined hub interface and a single cassette-style lockring (which uses the same tool). 6-bolt is more widely used, but has a tendency to strip skin off one's knuckles whenever the rotors need to be removed, and for destroying the necessary Torx tool.... Centrelock hubs can be adapted to take 6-bolt rotors, but it's not possible to go the other way.
I had a thought, but it got run over as it crossed my mind.

ironhanglider
Posts: 2842
Joined: Fri Apr 17, 2009 9:44 pm
Location: Middle East, Melbourne

Re: road disc brakes

Postby ironhanglider » Wed Aug 31, 2016 7:42 am

Why do disc rotors need a Torx tool anyway?

I mean why do they use Torx bolts?

Cheers,

Cameron

User avatar
Duck!
Expert
Posts: 9857
Joined: Tue May 21, 2013 8:21 pm
Location: On The Tools

Re: road disc brakes

Postby Duck! » Wed Aug 31, 2016 8:58 am

I dunno, ask the people who make them!
I had a thought, but it got run over as it crossed my mind.

Calvin27
Posts: 2435
Joined: Sat Feb 09, 2013 5:45 pm

Re: road disc brakes

Postby Calvin27 » Wed Aug 31, 2016 9:08 am

ironhanglider wrote: I mean why do they use Torx bolts?
Something about tamper proof. Well at least that was the story when torx first came out, kind of pointless now that everyone has torx tools!

The engineering answer is because torx bolts can take a greater torque for a given size than hex/phillips/flathead. Which is probably why people strip the threads a lot :P
Heavy road bike
Cushy dirt bike
Very cushy dirt bike
Bike crushed by car (RIP)
No brakes bike
Ebike

User avatar
find_bruce
Moderator
Moderator
Posts: 10579
Joined: Mon May 09, 2011 8:42 pm
Location: Sydney

Re: road disc brakes

Postby find_bruce » Wed Aug 31, 2016 9:09 am

My WAG is that torx are used because discs use small button head screws which would mean very small allen heads which would be unreliable in getting sufficient tension

User avatar
Duck!
Expert
Posts: 9857
Joined: Tue May 21, 2013 8:21 pm
Location: On The Tools

Re: road disc brakes

Postby Duck! » Wed Aug 31, 2016 10:22 am

Yet they smother so much threadlocker on them that you destroy the bolts and keys trying to undo the damn things!
I had a thought, but it got run over as it crossed my mind.

hamishm
Posts: 763
Joined: Wed Oct 28, 2009 11:31 pm

Re: road disc brakes

Postby hamishm » Wed Aug 31, 2016 11:01 am

ironhanglider wrote:I mean why do they use Torx bolts?
Instead of what?

Torx in general is so you don't over-tighten and destroy the heads of the screws. https://en.wikipedia.org/wiki/Torx

hamishm
Posts: 763
Joined: Wed Oct 28, 2009 11:31 pm

Re: road disc brakes

Postby hamishm » Wed Aug 31, 2016 11:09 am

Duck! wrote:R/RS785 brakes are post-mount; they're not available in flat-mount (flat-mount calipers are RS405/505/805 and not-yet-available R9120 Dura-Ace).

If your frame and fork are post-mount, and you're not planning on using larger than 160mm rotors, you won't need any adaptors, but you also won't be able to use 140mm rotors, because you won't get the calipers low enough.
Thanks Duck. So if I'm happy with 160mm rotors (and obviously that's a topic that needs more googling) then all I need is the calipers and rotors and no other bits?

User avatar
Duck!
Expert
Posts: 9857
Joined: Tue May 21, 2013 8:21 pm
Location: On The Tools

Re: road disc brakes

Postby Duck! » Wed Aug 31, 2016 11:29 am

Correct. Check the fine print of your frame & fork; they may specify only 160mm rotors.
I had a thought, but it got run over as it crossed my mind.

hamishm
Posts: 763
Joined: Wed Oct 28, 2009 11:31 pm

Re: road disc brakes

Postby hamishm » Wed Aug 31, 2016 11:38 am

By the way, I see there's R785 and RS785. Is the difference just the hose routing? How would I decide which to get / would I care?

hamishm
Posts: 763
Joined: Wed Oct 28, 2009 11:31 pm

Re: road disc brakes

Postby hamishm » Wed Aug 31, 2016 11:53 am

Duck! wrote:Correct. Check the fine print of your frame & fork; they may specify only 160mm rotors.
It does just say 160mm rotors. I tried to find out what's common on road bikes and could only find that Giant seems to have 140mm on the Defys. This project of mine is a gravel / touring bike so with a bit of luggage 160mm is probably a good idea anyway. It's just a weight penalty right?

User avatar
silentC
Posts: 2442
Joined: Mon May 05, 2014 5:24 pm
Location: Far South Coast NSW

Re: road disc brakes

Postby silentC » Wed Aug 31, 2016 12:21 pm

Weight difference is SFA I think. 160mm is generally recommended for road use. More so if you are carrying luggage I would think.
"If your next bike does not have disc brakes, the bike after that certainly will"
- Me

User avatar
biker jk
Posts: 7001
Joined: Tue Nov 17, 2009 6:18 pm
Location: Sydney

Re: road disc brakes

Postby biker jk » Wed Aug 31, 2016 12:46 pm

Not that you'll be racing but the UCI has recommended 160mm rotors for the pro peloton.

User avatar
Duck!
Expert
Posts: 9857
Joined: Tue May 21, 2013 8:21 pm
Location: On The Tools

Re: road disc brakes

Postby Duck! » Wed Aug 31, 2016 2:09 pm

hamishm wrote:By the way, I see there's R785 and RS785. Is the difference just the hose routing? How would I decide which to get / would I care?
The routing is the only difference. RS785 is a better design; its inboard hose entry suits a wider range of frame routing options, particularly internally through the chainstay. R785 can still be used, but this kind of hose routing tends to make the caliper more difficult to align, and is also more prone to being kicked on your upstroke.
hamishm wrote:
Duck! wrote:Correct. Check the fine print of your frame & fork; they may specify only 160mm rotors.
It does just say 160mm rotors. I tried to find out what's common on road bikes and could only find that Giant seems to have 140mm on the Defys. This project of mine is a gravel / touring bike so with a bit of luggage 160mm is probably a good idea anyway. It's just a weight penalty right?
As mentioned above, although it won't affect you, the UCI-specified standard is 160mm rotors. There are pros & cons to all rotor sizes; smaller ones can be a bit more prone to overheating because the smaller surface area doesn't radiate as effectively, plus due to lower leverage don't pack quite as much braking punch. Bigger rotors cool better and give more braking power, but impose greater stresses, particularly on the fork, which is why you need to find out what the maximum allowable size is. The weight difference is negligible. I'd just go with 160mm rotors.
I had a thought, but it got run over as it crossed my mind.

ironhanglider
Posts: 2842
Joined: Fri Apr 17, 2009 9:44 pm
Location: Middle East, Melbourne

Re: road disc brakes

Postby ironhanglider » Wed Aug 31, 2016 9:45 pm

hamishm wrote:
ironhanglider wrote:I mean why do they use Torx bolts?
Instead of what?

Torx in general is so you don't over-tighten and destroy the heads of the screws. https://en.wikipedia.org/wiki/Torx
The shaft of the bolt is just a standard M5 thread, the same as many other bolts on the bike which are all Allen bolts.

I understand that the torx design is intended to reduce the likelihood of the driver slipping out of the bolt and damaging one or the other, but actually makes over tightening more likely unless you use a torque wrench.

It simply makes one more tool to carry around.

I don't own a bike with disc brakes yet, but I'd be tempted to replace the rotor bolts with regular M5 Allen head bolts if the extra bulk didn't foul anything, just for simplicity sake.

Cheers,

Cameron

User avatar
silentC
Posts: 2442
Joined: Mon May 05, 2014 5:24 pm
Location: Far South Coast NSW

Re: road disc brakes

Postby silentC » Thu Sep 01, 2016 9:32 am

Just get centre lock! My disc bike hasn't any Torx bolts.
"If your next bike does not have disc brakes, the bike after that certainly will"
- Me

User avatar
MichaelB
Posts: 14775
Joined: Tue Feb 20, 2007 9:29 am
Location: Adelaide, South Australia

Re: road disc brakes

Postby MichaelB » Thu Sep 01, 2016 12:48 pm

silentC wrote:Just get centre lock! My disc bike hasn't any Torx bolts.
+1 to that. Just done that conversion myself.

slaw
Posts: 85
Joined: Tue Dec 03, 2013 1:14 pm

Re: road disc brakes

Postby slaw » Thu Sep 01, 2016 1:06 pm

I have a mixture of Torx bolt rotors and Centrelock. Initially I did buy some short allen bolts to replace the torx ones but since I've got a multi-tool with the correct driver, I never bothered swapping the bolts. Also my Rohloff and some chainring bolts require a few different sized torx tools, so I have a Y shaped tool with 3 different sizes.

Centrelock is fine too, but for one set of wheels I have, I needed to get a different lockring to fit around the bigger axle. This cost an extra $35 and it uses a bottom bracket tool which I already had.

User avatar
biker jk
Posts: 7001
Joined: Tue Nov 17, 2009 6:18 pm
Location: Sydney

Re: road disc brakes

Postby biker jk » Thu Sep 01, 2016 1:33 pm

silentC wrote:Just get centre lock! My disc bike hasn't any Torx bolts.
Apart from on the chainrings. :lol:

User avatar
Duck!
Expert
Posts: 9857
Joined: Tue May 21, 2013 8:21 pm
Location: On The Tools

Re: road disc brakes

Postby Duck! » Thu Sep 01, 2016 1:52 pm

slaw wrote: Centrelock is fine too, but for one set of wheels I have, I needed to get a different lockring to fit around the bigger axle. This cost an extra $35 and it uses a bottom bracket tool which I already had.
Centrelock OS (15 & 20mm through axle, not sure about 12mm*) hubs should include the necessary lockring. My M9010 XTR did.

EDIT: 12mm T/A Centrelock hubs use the standard lockring supplied with the rotors. Built a bike with them today. :-)
I had a thought, but it got run over as it crossed my mind.

slaw
Posts: 85
Joined: Tue Dec 03, 2013 1:14 pm

Re: road disc brakes

Postby slaw » Fri Sep 02, 2016 11:15 am

These wheels - no lockrings:

https://www.merlincycles.com/kinesis-cr ... 87507.html

A review there does mention the need for the OS lockring. Not sure if that review was there when I bought them. I only needed one for the front wheel. I've since seen that the Shimano centrelock to 6 bolt adaptor includes the OS lockring so I could have got one of those cheaper, but I wanted to get the wheels going just after they arrived, so I had to try a few LBSs before finding one that had one in stock which is why I ended paying top dollar for a Formula branded lockring.

hamishm
Posts: 763
Joined: Wed Oct 28, 2009 11:31 pm

Re: road disc brakes

Postby hamishm » Fri Sep 02, 2016 11:34 am

Do you have these slaw? I'm looking around for wheels for the gravel bike and these are a top contender. Only concern I've read is that they could be a bit stronger.

slaw
Posts: 85
Joined: Tue Dec 03, 2013 1:14 pm

Re: road disc brakes

Postby slaw » Mon Sep 05, 2016 11:07 am

Yes I do have them. Happy with them so far. Much lighter than the stock wheels on my Oppy and not too exy. I've done several hundred kms on them with either 42 Maxxis Rambler gravel tyres or 32 gatorskins for commuting. These are a b**ch to put on though. I do have a tubeless kit, but haven't set it up yet, which I'd do if I was to only leave on the gravel tyres.

I should probably check them over, but there are no obvious issues.

Who is online

Users browsing this forum: No registered users