Disc brakes, adaptors to increase rotor diameter

[Joerg]

The adapters to increase rotor size in a post-post situation (which I
have front and back) look like this:

http://i.ebayimg.com/images/g/oK8AAOSwKZ5Z3IAu/s-l1600.jpg

My MTB has a factory one from 160 to 180mm up front but I am considering
203mm. That would make the thing even more extreme, like this where the
screws would look more cattywompus or out of line than they already do:

https://i.ebayimg.com/images/g/w4MAAOSwwN5ZfbTa/s-l500.jpg

Why are the spacings so different on both sides while for 160mm their
are not?

--
Regards, Joerg

http://www.analogconsultants.com/

[Joerg]

P.S.: Does anyone know whether these go from native 160mm to 203mm?

https://erpimgs.idealhere.com/ImageFormal/65/ff/df/65ffdf5a-b06b-4dc4-9c3f-8ca09b275658/descriptions/82ff732d-5124-422b-b0de-5c963c864243.jpg

F/R probably means for front and rear. There are also F203 versions but
they look the same. Ideally I'd want 203mm rotors on both wheels because
the rack on my MTB is often heavily loaded.

[Ralph Barone]

Probably because the axis along which the brake gets extended is not
perpendicular to the outer surface of the disk, so as you slide the caliber
outwards, you have to rotate it a bit to keep it tangential to the outer
surface of the disk.

[jbeattie]

The angle of the caliper changes as you get into the larger rotor sizes and thus the disparity. http://www.bikehugger.com/posts/road-disc-brake-tech-flat-mount-vs-post-mount/

The deal with adapters is that they usually assume the resident posts are sized for 160mm rotors. That is a correct assumption for your bike. My CAADX was, amazingly, sized for a 140mm front rotor, so my 180mm adapter was actually a 160mm adapter.

-- Jay Beattie.

[Tim McNamara]

On Wed, 11 Oct 2017 18:16:20 -0700 (PDT), jbeattie <jbeat...@msn.com>
wrote:

> On Wednesday, October 11, 2017 at 2:36:03 PM UTC-7, Joerg wrote:
>> The adapters to increase rotor size in a post-post situation (which I
>> have front and back) look like this:

If you keep following that logic, you'll have a disc diameter of 622 mm.

Oh, wait....

[James]

Haha. I thought that, but couldn't be bothered typing it.

--
JS

[cycl...@gmail.com]

On Wednesday, October 11, 2017 at 2:36:03 PM UTC-7, Joerg wrote:

Your first adapter is the normal one used on all rear brakes for cross bikes as far as I know. Putting larger disks on road bikes is sort of counter-productive since the problem with them already is excessive power.

[Joerg]

On 2017-10-11 18:16, jbeattie wrote:
> On Wednesday, October 11, 2017 at 2:36:03 PM UTC-7, Joerg wrote:
>> The adapters to increase rotor size in a post-post situation (which
>> I have front and back) look like this:
>>
>> http://i.ebayimg.com/images/g/oK8AAOSwKZ5Z3IAu/s-l1600.jpg
>>
>> My MTB has a factory one from 160 to 180mm up front but I am
>> considering 203mm. That would make the thing even more extreme,
>> like this where the screws would look more cattywompus or out of
>> line than they already do:
>>
>> https://i.ebayimg.com/images/g/w4MAAOSwwN5ZfbTa/s-l500.jpg
>>
>> Why are the spacings so different on both sides while for 160mm
>> their are not?
>
> The angle of the caliper changes as you get into the larger rotor
> sizes and thus the disparity.

Understood. This is also what Ralph wrote. However, many calipers such
as mine have round pads where it doesn't matter if the angle is slighlty
different.

> http://www.bikehugger.com/posts/road-disc-brake-tech-flat-mount-vs-post-mount/
>
> The deal with adapters is that they usually assume the resident
> posts are sized for 160mm rotors. That is a correct assumption for
> your bike. My CAADX was, amazingly, sized for a 140mm front rotor, so
> my 180mm adapter was actually a 160mm adapter.
>

My mounts are both native 160mm so ideally I'd like to go from there to
203mm without stacking two adapters. The front currently has a 160-180mm
adapter and for whatever reason that one also adds angle.

[Joerg]

I wonder if that's critical for round pads. The 160-180mm that was
factory installed up front is angled but the calipers look like it
wouldn't have mattered.

[Joerg]

On 2017-10-12 07:15, cycl...@gmail.com wrote:
> On Wednesday, October 11, 2017 at 2:36:03 PM UTC-7, Joerg wrote:
>> The adapters to increase rotor size in a post-post situation (which
>> I have front and back) look like this:
>>
>> http://i.ebayimg.com/images/g/oK8AAOSwKZ5Z3IAu/s-l1600.jpg
>>
>> My MTB has a factory one from 160 to 180mm up front but I am
>> considering 203mm. That would make the thing even more extreme,
>> like this where the screws would look more cattywompus or out of
>> line than they already do:
>>
>> https://i.ebayimg.com/images/g/w4MAAOSwwN5ZfbTa/s-l500.jpg
>>
>> Why are the spacings so different on both sides while for 160mm
>> their are not?
>
> Your first adapter is the normal one used on all rear brakes for
> cross bikes as far as I know.

My bike has that kind on the front. I'd much prefer the type below
because it would avoid the extremely long screws that are otherwise
needed for a 160mm-native to 203mm-rotor conversion:

https://erpimgs.idealhere.com/ImageFormal/65/ff/df/65ffdf5a-b06b-4dc4-9c3f-8ca09b275658/descriptions/82ff732d-5124-422b-b0de-5c963c864243.jpg

If they work for 160-203, which the sites that sell them don't really say.


> ... Putting larger disks on road bikes is

> sort of counter-productive since the problem with them already is
> excessive power.
>

It is for a often heavily loaded MTB where I sometimes get to the limits
of the current 180mm & 160mm setup. Where water contacting the front
rotor lets off some hissing.

[Andre Jute]

I already have a brake disc diameter of 622mm. You could too. First, buy a bike with standard 622mm rims. Next, fit Magura hydraulic rim brakes (several varieties available for touring, utility and road bikes). Result, powerful but very manageable 622mm disc brakes, economical on "pads" too. Hey presto, your brakes are powerful enough to ride with Joerg.

Andre Jute
Logic is good, but common sense is essential

[jbeattie]

On Thursday, October 12, 2017 at 7:36:15 AM UTC-7, Joerg wrote:
> On 2017-10-11 18:16, jbeattie wrote:
> > On Wednesday, October 11, 2017 at 2:36:03 PM UTC-7, Joerg wrote:
> >> The adapters to increase rotor size in a post-post situation (which
> >> I have front and back) look like this:
> >>
> >> http://i.ebayimg.com/images/g/oK8AAOSwKZ5Z3IAu/s-l1600.jpg
> >>
> >> My MTB has a factory one from 160 to 180mm up front but I am
> >> considering 203mm. That would make the thing even more extreme,
> >> like this where the screws would look more cattywompus or out of
> >> line than they already do:
> >>
> >> https://i.ebayimg.com/images/g/w4MAAOSwwN5ZfbTa/s-l500.jpg
> >>
> >> Why are the spacings so different on both sides while for 160mm
> >> their are not?
> >
> > The angle of the caliper changes as you get into the larger rotor
> > sizes and thus the disparity.
>
>
> Understood. This is also what Ralph wrote. However, many calipers such
> as mine have round pads where it doesn't matter if the angle is slighlty
> different.

I don't know your brakes, but the rotor might hit the internals if the caliper is not angled correctly. You want the mechanism following the arc of the rotor, which is what you will get with your spacer. You also want to engage as much of the rotor as possible. I don't think any of this is optional, is it? You just put in the spacer, and you're done.

-- Jay Beattie.

[Joerg]

On 2017-10-12 09:26, jbeattie wrote:
> On Thursday, October 12, 2017 at 7:36:15 AM UTC-7, Joerg wrote:
>> On 2017-10-11 18:16, jbeattie wrote:
>>> On Wednesday, October 11, 2017 at 2:36:03 PM UTC-7, Joerg wrote:
>>>> The adapters to increase rotor size in a post-post situation
>>>> (which I have front and back) look like this:
>>>>
>>>> http://i.ebayimg.com/images/g/oK8AAOSwKZ5Z3IAu/s-l1600.jpg
>>>>
>>>> My MTB has a factory one from 160 to 180mm up front but I am
>>>> considering 203mm. That would make the thing even more
>>>> extreme, like this where the screws would look more cattywompus
>>>> or out of line than they already do:
>>>>
>>>> https://i.ebayimg.com/images/g/w4MAAOSwwN5ZfbTa/s-l500.jpg
>>>>
>>>> Why are the spacings so different on both sides while for
>>>> 160mm their are not?
>>>
>>> The angle of the caliper changes as you get into the larger
>>> rotor sizes and thus the disparity.
>>
>>
>> Understood. This is also what Ralph wrote. However, many calipers
>> such as mine have round pads where it doesn't matter if the angle
>> is slighlty different.
>
> I don't know your brakes, but the rotor might hit the internals if
> the caliper is not angled correctly. You want the mechanism following
> the arc of the rotor, which is what you will get with your spacer.

It should also work with this spacer which avoids long screws:

https://erpimgs.idealhere.com/ImageFormal/65/ff/df/65ffdf5a-b06b-4dc4-9c3f-8ca09b275658/descriptions/82ff732d-5124-422b-b0de-5c963c864243.jpg

It moves the rotor out plus up so the angle should remain roughly
similar. Shimano has these as well but I just got an answer from Jenson
USA which carries them. They are flat and only 10mm (looks less though)
and my calipers need more "dive room" than that.

http://www.jensonusa.com/Shimano-F203PP-Disc-Brake-Adapter#brm-search?request_type=search&search_type=keyword&q=BR407Z47&l=BR407Z47

So I'd need the bellied ones like in the link.

> You also want to engage as much of the rotor as possible. I don't
> think any of this is optional, is it? You just put in the spacer, and
> you're done.
>

Just have to make sure it's the correct adapter. Adding a washer here or
there for fine tuning isn't a problem.

[cycl...@gmail.com]

I'm still having this problem with why you would want disk brakes on a road bike in California. Extra weight, extra rolling resistance, extra cost, far too much power the way it was and there is little rain in California to worry about the slight delay in action between a rim and disk brake.

[Joerg]

It is for my mountain bike. Currently it has 7" up front and 6" in back.
That is only borderline adequate for the loading and riding I do.
Yesterday I rode a trail where I taxed them a bit much again. I want to
upgrade both wheels to 8". Both are native 160mm and the front has an
adapter which I'd have to change out.

There is nothing that can replace brake power. Except more brake power.


> ... Extra weight, extra rolling resistance,

> extra cost, far too much power the way it was and there is little
> rain in California to worry about the slight delay in action between
> a rim and disk brake.
>

In the winter it rains a lot up here in the Sierra foothills. There is
also a lot of standing water and creek crossings after which I
experience that dreaded 1-2sec "free fall" with rim brakes. Plus dirt
where I reach in and while getting some tepid brake response there is a
goose bump generating sandpaper noise.

So yes, if I ever need a new road bike I have two non-negotiable
requirements. Number one is disk brakes and number two is that the frame
must accept cyclocross-width tires. And must tolerate a serious rack.

[cycl...@gmail.com]

Perhaps going balls-to-the-walls on an MTB with a heavy load you can detect a braking delay but as I said before - even coming out of creek crossings I never have problems with rim brakes. The ONLY difference is surface area of the brake shoes.

[Joerg]

On 2017-10-13 11:36, cycl...@gmail.com wrote:
> On Friday, October 13, 2017 at 10:15:10 AM UTC-7, Joerg wrote:
>> On 2017-10-13 08:50, cycl...@gmail.com wrote:

[...]

>>> ... Extra weight, extra rolling resistance, extra cost, far too
>>> much power the way it was and there is little rain in California
>>> to worry about the slight delay in action between a rim and disk
>>> brake.
>>>
>>
>> In the winter it rains a lot up here in the Sierra foothills. There
>> is also a lot of standing water and creek crossings after which I
>> experience that dreaded 1-2sec "free fall" with rim brakes. Plus
>> dirt where I reach in and while getting some tepid brake response
>> there is a goose bump generating sandpaper noise.
>>
>> So yes, if I ever need a new road bike I have two non-negotiable
>> requirements. Number one is disk brakes and number two is that the
>> frame must accept cyclocross-width tires. And must tolerate a
>> serious rack.
>
> Perhaps going balls-to-the-walls on an MTB with a heavy load you can
> detect a braking delay but as I said before - even coming out of
> creek crossings I never have problems with rim brakes. The ONLY
> difference is surface area of the brake shoes.
>

Getting older I don't ride aggressivley anymore. Maybe because the more
I ride the more I see and hear about nasty crashes and their aftermath.

Creek crossings usually mean uphill at the other end but they also mean
the rims can be muddy. My Wednesday ride was on a very typical
singletrack of that kind. Up and down all the time and with a creek at
the bottoms. On my old rim brake MTB that would have meant going down
the slopes after the uphill section with sandpapering brakes. There are
no bike wash stations on the trails. It's a horrid sound because our
soil contains a lot of decomposed granite. After about 1000mi the rims
of that old MTB look pretty much shot.

The white knuckle moment with the rim brakes on my old MTB happened
while up on the flat section of a hill. Curvy trail along the rim. Went
through a large puddle, towards a sharp turn, hit the brakes, no brakes!

Pad size doesn't matter much except that wider pads last longer. So if
my brake calipers are through I'll look for ones that have wider pads or
maybe even double pads. The pads will cost more but then I hopefully
don't have to replace them every 800-1000mi.