road disc brakes
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road disc brakes
Postby hamishm » Tue Aug 30, 2016 7:48 pm
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...!
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Re: road disc brakes
Postby eeksll » Tue Aug 30, 2016 9:46 pm
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.
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Re: road disc brakes
Postby Duck! » Tue Aug 30, 2016 10:29 pm
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.
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Re: road disc brakes
Postby ironhanglider » Wed Aug 31, 2016 7:42 am
I mean why do they use Torx bolts?
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Re: road disc brakes
Postby Duck! » Wed Aug 31, 2016 8:58 am
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Re: road disc brakes
Postby Calvin27 » Wed Aug 31, 2016 9:08 am
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!ironhanglider wrote: I mean why do they use Torx bolts?
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
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Re: road disc brakes
Postby find_bruce » Wed Aug 31, 2016 9:09 am
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Re: road disc brakes
Postby Duck! » Wed Aug 31, 2016 10:22 am
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Re: road disc brakes
Postby hamishm » Wed Aug 31, 2016 11:01 am
Instead of what?ironhanglider wrote:I mean why do they use Torx bolts?
Torx in general is so you don't over-tighten and destroy the heads of the screws. https://en.wikipedia.org/wiki/Torx
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Re: road disc brakes
Postby hamishm » Wed Aug 31, 2016 11:09 am
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?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.
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Re: road disc brakes
Postby Duck! » Wed Aug 31, 2016 11:29 am
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Re: road disc brakes
Postby hamishm » Wed Aug 31, 2016 11:38 am
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Re: road disc brakes
Postby hamishm » Wed Aug 31, 2016 11:53 am
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?Duck! wrote:Correct. Check the fine print of your frame & fork; they may specify only 160mm rotors.
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Re: road disc brakes
Postby silentC » Wed Aug 31, 2016 12:21 pm
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Re: road disc brakes
Postby biker jk » Wed Aug 31, 2016 12:46 pm
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Re: road disc brakes
Postby Duck! » Wed Aug 31, 2016 2:09 pm
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: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?
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.hamishm wrote: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?Duck! wrote:Correct. Check the fine print of your frame & fork; they may specify only 160mm rotors.
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Re: road disc brakes
Postby ironhanglider » Wed Aug 31, 2016 9:45 pm
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.hamishm wrote:Instead of what?ironhanglider wrote:I mean why do they use Torx bolts?
Torx in general is so you don't over-tighten and destroy the heads of the screws. https://en.wikipedia.org/wiki/Torx
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
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Re: road disc brakes
Postby silentC » Thu Sep 01, 2016 9:32 am
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Re: road disc brakes
Postby MichaelB » Thu Sep 01, 2016 12:48 pm
+1 to that. Just done that conversion myself.silentC wrote:Just get centre lock! My disc bike hasn't any Torx bolts.
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Re: road disc brakes
Postby slaw » Thu Sep 01, 2016 1:06 pm
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.
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Re: road disc brakes
Postby biker jk » Thu Sep 01, 2016 1:33 pm
Apart from on the chainrings.silentC wrote:Just get centre lock! My disc bike hasn't any Torx bolts.
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Re: road disc brakes
Postby Duck! » Thu Sep 01, 2016 1:52 pm
Centrelock OS (15 & 20mm through axle, not sure about 12mm*) hubs should include the necessary lockring. My M9010 XTR did.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.
EDIT: 12mm T/A Centrelock hubs use the standard lockring supplied with the rotors. Built a bike with them today.
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Re: road disc brakes
Postby slaw » Fri Sep 02, 2016 11:15 am
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.
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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.
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Re: road disc brakes
Postby slaw » Mon Sep 05, 2016 11:07 am
I should probably check them over, but there are no obvious issues.
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