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 Post subject: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 11:57 am 
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Joined: Sat May 21, 2016 12:59 pm
Posts: 349
Anyone tried to use 140 rotor on front ?

hydro 140 vs hydro 160?
hydro 140 vs mechanical 160?
mechanical 140 vs mechanical 160?

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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 12:14 pm 
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Joined: Sat Dec 17, 2016 7:28 pm
Posts: 116
hydro 140 used to be stock on some Giant and Specializes road bikes. I tried just 160/140 combination and it was ok..


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 Post subject: Re: 140 front disc rotor
Posted: Sun Nov 05, 2017 12:14 pm 


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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 12:42 pm 
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Joined: Thu Dec 12, 2013 9:48 pm
Posts: 72
Road calipers are much weaker than those from mtb. 140 mm in front is acceptable only at low speeds (ex. CX course) due to lack of stopping power and heat management.


Last edited by uraz on Sun Nov 05, 2017 4:49 pm, edited 1 time in total.

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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 2:24 pm 
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Joined: Sat May 21, 2016 12:59 pm
Posts: 349
I live in flat windy area with low temperatures, mostly do solo riding, so the heat management is less of a problem
"Stopping power" and "weaker calipers" - this factors are more important,
I am trying to find any subjective or objective reviews about this factors

"Stopping power" - this is my main concern, I'd like to know how longer will be stopping distance
and how significantly more input required to perform the same maneuvers as with 160 rotors
my guess it is less significant difference on hydro, and more significant on mechanical (spyre)

"Weaker calipers" - this is first time I am hearing about it.
first gen road caliper BR-R785 was copy of mtb calipers BR-M785,
is someone made a comparison of BR-R785 vs new flat mount calipers + 160 adaptor?

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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 3:53 pm 
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Joined: Sun Jan 08, 2017 12:44 pm
Posts: 66
When I went from post mount bike with br-R785 to a br-rs505 calipers, I felt lowered breaking power. Brake pads are a little smaller on the flat mount calipers. Maybe 10-20% less power, but it's very subjective..
I think 140/140 on a bike is absolutely fine for a low weight drivers (~under 80kg) no matter where is the bike mostly used.
To be on the safe side it's better to use the metallic pads that won't fade, but they might squeal like a mother f*cker.


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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 4:15 pm 
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Joined: Tue Apr 18, 2006 3:03 am
Posts: 2673
Location: Islip, NY
uraz wrote:
Road calipers are much weaker than those from mtb. 140 mm in front is acceptable only at low speeds (ex. CX course) due to lack of stopping power and heat management.


I'd also add a time trial or tri bike to that list. Definitely 160mm front for road bike.

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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 5:06 pm 
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Joined: Thu Dec 12, 2013 9:48 pm
Posts: 72
I don't know if it is true for shimano but sram road caliper uses 18 mm pistons compared to 20 mm in mtb versions. I heard that sram red brakes are stronger than dura-ace but could not confirm this. In emergency situation I have to pull levers like a mad men to make them perform at 100% braking power. It supose to be a "good modulation" but I would rather call it mediocre stopping power. (160 mm front, 140 mm rear, sram red hydroR, sram organic brake pads, centerline rotors).


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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 5:18 pm 
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Joined: Sat Dec 17, 2016 7:28 pm
Posts: 116
strange, 160/140 mm should be fine. I used to have it and switched from 160mm rear because it made the bike going into skid too easily. Now on 160/160 because it was supplied with the bike, but I can see no real supremacy, both sizes works well.


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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 8:38 pm 
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Joined: Sat May 21, 2016 12:59 pm
Posts: 349
Interesting finds (thanks bikehugger):

1. Brake pads in shimano flatmount calipers are much smaller ~20% (calculated measuring next photo)
this explains all the difference in power
[08.11.2017 update: conclusion is wrong, link to youngs_modulus post with more info]

Attachment:
File comment: (Photo E) Shimano flat-mount vs post-mount brake pads. Note that for these models, the flat-mount pad is smaller than the post.
bikehugger-pads.jpg
bikehugger-pads.jpg [ 6.12 KiB | Viewed 772 times ]


2. It is possible to use 140mm front rotor with powerfull Shimano MTB calipers using this flat to post mount adaptor:
SM-MA-F140P/D (weight 25g @ bike24)

Attachment:
File comment: SM-MA-F140P/D
smmaf140pd.jpg
smmaf140pd.jpg [ 3.02 KiB | Viewed 772 times ]


two piston BR-RS785, BR-R785, BR-M785, BR-M9000 will give 20% extra power
four piston BR-M8020 will give 40% extra power (and cooking abilities on 140mm rotor)

Attachment:
File comment: (Photo set A) Post vs flat-mount. To the left, both calipers set up for front 140mm rotors. To the right, the same two calipers set up for 160mm front rotors. In each pairing, post-mount caliper is on the left, flat-mount right.
bikehugger-flatmount-postmount.jpg
bikehugger-flatmount-postmount.jpg [ 3.53 KiB | Viewed 772 times ]


3. There are some 140mm postmount forks, but they are hard find

4. Mechanical disc TRP Spyre Flat Mount version performs the same as Post Mount version according to review link
(uses Shimano M525 MTB brake pads, should be weaker vs road hydro calipers, but not that big difference as BR-R785)

5. TRP Hylex RS FLAT MOUNT road hydraulics caliper uses Shimano M525 MTB brake pads
there is a good chance that it is compatible with shimano hydro STI (and gives 20% extra braking surface)
(previous model non-RS TRP Hylex was compatible with Shimano STI)

Attachment:
File comment: TRP Hylex RS Flat Mount
trp-hylex.jpg
trp-hylex.jpg [ 4.44 KiB | Viewed 743 times ]

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Last edited by ooo on Wed Nov 08, 2017 9:01 am, edited 3 times in total.

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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 9:10 pm 
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Joined: Sun Jan 08, 2017 12:44 pm
Posts: 66
I don't see the point in increasing breaking power. On the road side we have much smaller tire contact path with the ground in comparison to mtb. Increasing power is just going to lock up the wheels and bring just troubles. Shimano went the right way with decreasing break pads size and calipers can be smaller and lighter with still enough of braking power. And with firmer breaker lever squeeze we can still all lock the wheels just fine.


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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 9:25 pm 
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Joined: Thu Dec 12, 2013 9:48 pm
Posts: 72
I can't get even close to locking front wheel with road hydraulic brakes which is a shame in my opinion. There is a ton of grip on soft, slick tires when road is dry and clean (most typical conditions), way more than on mtb (damp forest, sand, loose rocks, etc).

Only reason I see, why road brakes are so pathetic is that some guys (and girls) don't want or can't handle brakes that are able to throw them out of a bike. Also very strong brakes could be problematic in rain.


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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 10:15 pm 
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Joined: Sat May 24, 2014 12:09 pm
Posts: 821
Maybe slight OT, but would it be possible to fit a 140mm rotor at the back of a stock 160mm spec'ed bike like the those latest Scotts (Addict and Scott). There seems to be an adaptor that could be removed, but do the bolt hols of frame and caliper match? Similar to my Canyon, but haven't tried to remove the alu plate and see if I can bolt the caliper directly to the frame...

Image

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Retired:
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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 10:28 pm 
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Joined: Wed Feb 08, 2017 2:10 am
Posts: 223
No. Those flat mount brakes on your Scott require that mounting wedge to function. Can't mount them otherwise.


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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 11:13 pm 
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Joined: Thu Dec 12, 2013 9:48 pm
Posts: 72
On Focus Izalco you just drop aluminium adapter, use shorter bolts and 140mm rotor can be mounted.

Image


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 Post subject: Re: 140 front disc rotor
Posted: Sun Nov 05, 2017 11:13 pm 


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 Post subject: Re: 140 front disc rotor
PostPosted: Sun Nov 05, 2017 11:19 pm 
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Joined: Tue Jan 28, 2014 6:52 pm
Posts: 1532
I have 140s front and rear on my Crux and it seems to stop better than my Colnago with rim brakes.

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